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How To Determine The Base Element In A Covalent Bond When Drawing A Lewis Dot

Chapter seven. Chemic Bonding and Molecular Geometry

7.iii Lewis Symbols and Structures

Learning Objectives

Past the terminate of this department, y'all will be able to:

  • Write Lewis symbols for neutral atoms and ions
  • Draw Lewis structures depicting the bonding in simple molecules

Thus far in this chapter, we take discussed the various types of bonds that grade between atoms and/or ions. In all cases, these bonds involve the sharing or transfer of valence shell electrons between atoms. In this department, we will explore the typical method for depicting valence crush electrons and chemical bonds, namely Lewis symbols and Lewis structures.

Lewis Symbols

We apply Lewis symbols to describe valence electron configurations of atoms and monatomic ions. A Lewis symbol consists of an elemental symbol surrounded past one dot for each of its valence electrons:

A Lewis structure of calcium is shown. A lone pair of electrons are shown to the right of the symbol.

Figure 1 shows the Lewis symbols for the elements of the third menstruation of the periodic table.

A table is shown that has three columns and nine rows. The header row reads
Figure i. Lewis symbols illustrating the number of valence electrons for each element in the third catamenia of the periodic tabular array.

Lewis symbols tin can besides be used to illustrate the formation of cations from atoms, every bit shown here for sodium and calcium:

Two diagrams are shown. The left diagram shows a Lewis dot structure of sodium with one dot, then a right-facing arrow leading to a sodium symbol with a superscripted plus sign, a plus sign, and the letter

Likewise, they can be used to evidence the germination of anions from atoms, as shown here for chlorine and sulfur:

Two diagrams are shown. The left diagram shows a Lewis dot structure of chlorine with seven dots and the letter

Effigy 2 demonstrates the employ of Lewis symbols to show the transfer of electrons during the formation of ionic compounds.

A table is shown with four rows. The header row reads
Figure 2. Cations are formed when atoms lose electrons, represented by fewer Lewis dots, whereas anions are formed by atoms gaining electrons. The full number of electrons does not change.

Lewis Structures

We as well use Lewis symbols to indicate the germination of covalent bonds, which are shown in Lewis structures, drawings that describe the bonding in molecules and polyatomic ions. For example, when two chlorine atoms class a chlorine molecule, they share i pair of electrons:

A Lewis dot diagram shows a reaction. Two chlorine symbols, each surrounded by seven dots are separated by a plus sign. The dots on the first atom are all black and the dots on the second atom are all read. The phrase,

The Lewis structure indicates that each Cl cantlet has iii pairs of electrons that are not used in bonding (called lone pairs) and ane shared pair of electrons (written betwixt the atoms). A dash (or line) is sometimes used to point a shared pair of electrons:

Two Lewis structures are shown. The left-hand structure shows two H atoms connected by a single bond. The right-hand structure shows two C l atoms connected by a single bond and each surrounded by six dots.

A single shared pair of electrons is called a single bail. Each Cl atom interacts with eight valence electrons: the six in the lone pairs and the two in the single bail.

The Octet Dominion

The other halogen molecules (Fii, Brtwo, I2, and At2) form bonds similar those in the chlorine molecule: 1 single bail between atoms and three lone pairs of electrons per atom. This allows each halogen cantlet to have a noble gas electron configuration. The trend of master grouping atoms to grade plenty bonds to obtain eight valence electrons is known as the octet rule.

The number of bonds that an atom can class can often exist predicted from the number of electrons needed to reach an octet (viii valence electrons); this is especially true of the nonmetals of the 2d menstruum of the periodic table (C, N, O, and F). For case, each atom of a group 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach an octet. These four electrons tin can exist gained by forming four covalent bonds, as illustrated here for carbon in CCl4 (carbon tetrachloride) and silicon in SiHfour (silane). Considering hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule. The transition elements and inner transition elements also practice not follow the octet rule:

Two sets of Lewis dot structures are shown. The left structures depict five C l symbols in a cross shape with eight dots around each, the word

Grouping 15 elements such as nitrogen have five valence electrons in the atomic Lewis symbol: 1 lone pair and three unpaired electrons. To obtain an octet, these atoms class three covalent bonds, as in NHthree (ammonia). Oxygen and other atoms in group 16 obtain an octet by forming two covalent bonds:

Three Lewis structures labeled,

Double and Triple Bonds

As previously mentioned, when a pair of atoms shares one pair of electrons, we phone call this a unmarried bond. However, a pair of atoms may need to share more than ane pair of electrons in society to attain the requisite octet. A double bond forms when ii pairs of electrons are shared between a pair of atoms, as between the carbon and oxygen atoms in CH2O (formaldehyde) and between the 2 carbon atoms in C2H4 (ethylene):

Two pairs of Lewis structures are shown. The left pair of structures shows a carbon atom forming single bonds to two hydrogen atoms. There are four electrons between the C atom and an O atom. The O atom also has two pairs of dots. The word

A triple bond forms when three electron pairs are shared by a pair of atoms, equally in carbon monoxide (CO) and the cyanide ion (CN):

Two pairs of Lewis structures are shown and connected by a right-facing arrow. The left pair of structures show a C atom and an O atom with six dots in between them and a lone pair on each. The word

Writing Lewis Structures with the Octet Rule

For very unproblematic molecules and molecular ions, we can write the Lewis structures by simply pairing upwards the unpaired electrons on the elective atoms. Encounter these examples:

Three reactions are shown with Lewis dot diagrams. The first shows a hydrogen with one red dot, a plus sign and a bromine with seven dots, one of which is red, connected by a right-facing arrow to a hydrogen and bromine with a pair of red dots in between them. There are also three lone pairs on the bromine. The second reaction shows a hydrogen with a coefficient of two and one red dot, a plus sign, and a sulfur atom with six dots, two of which are red, connected by a right facing arrow to two hydrogen atoms and one sulfur atom. There are two red dots in between the two hydrogen atoms and the sulfur atom. Both pairs of these dots are red. The sulfur atom also has two lone pairs of dots. The third reaction shows two nitrogen atoms each with five dots, three of which are red, separated by a plus sign, and connected by a right-facing arrow to two nitrogen atoms with six red electron dots in between one another. Each nitrogen atom also has one lone pair of electrons.

For more complicated molecules and molecular ions, it is helpful to follow the stride-by-step procedure outlined hither:

  1. Make up one's mind the full number of valence (outer crush) electrons. For cations, decrease one electron for each positive charge. For anions, add one electron for each negative charge.
  2. Draw a skeleton structure of the molecule or ion, arranging the atoms around a central atom. (More often than not, the least electronegative element should be placed in the center.) Connect each atom to the cardinal atom with a unmarried bail (ane electron pair).
  3. Distribute the remaining electrons as lonely pairs on the terminal atoms (except hydrogen), completing an octet effectually each atom.
  4. Place all remaining electrons on the central cantlet.
  5. Rearrange the electrons of the outer atoms to brand multiple bonds with the primal atom in lodge to obtain octets wherever possible.

Let us determine the Lewis structures of SiH4, CHO2−, NO+, and OF2 equally examples in following this procedure:

  1. Determine the total number of valence (outer trounce) electrons in the molecule or ion.
    • For a molecule, we add together the number of valence electrons on each atom in the molecule:

      [latex]\begin{array}{r r l} \text{SiH}_4 & & \\[1em] & \text{Si: four valence electrons/atom} \times i \;\text{cantlet} & = 4 \\[1em] \rule[-0.5ex]{21em}{0.1ex}\hspace{-21em} + & \text{H: one valence electron/atom} \times 4 \;\text{atoms} & = four \\[1em] & & = 8 \;\text{valence electrons} \end{array}[/latex]

    • For a negative ion, such as CHOtwo , we add the number of valence electrons on the atoms to the number of negative charges on the ion (one electron is gained for each single negative accuse):

      [latex]\begin{assortment}{r r fifty} {\text{CHO}_2}^{-} & & \\[1em] & \text{C: 4 valence electrons/atom} \times i \;\text{atom} & = 4 \\[1em] & \text{H: 1 valence electron/cantlet} \times 1 \;\text{atom} & = i \\[1em] & \text{O: half dozen valence electrons/atom} \times 2 \;\text{atoms} & = 12 \\[1em] \rule[-0.5ex]{21.5em}{0.1ex}\hspace{-21.5em} + & 1\;\text{additional electron} & = 1 \\[1em] & & = 18 \;\text{valence electrons} \end{assortment}[/latex]

    • For a positive ion, such as NO+, nosotros add together the number of valence electrons on the atoms in the ion and so subtract the number of positive charges on the ion (i electron is lost for each single positive accuse) from the total number of valence electrons:

      [latex]\begin{array}{r r l} \text{NO}^{+} & & \\[1em] & \text{N: 5 valence electrons/cantlet} \times ane \;\text{atom} & = v \\[1em] & \text{O: six valence electrons/atom} \times i \;\text{cantlet} & = 6 \\[1em] \rule[-0.5ex]{21em}{0.1ex}\hspace{-21em} + & -1 \;\text{electron (positive charge)} & = -1 \\[1em] & & = 10 \;\text{valence electrons} \end{array}[/latex]

    • Since OFtwo is a neutral molecule, we simply add the number of valence electrons:

      [latex]\begin{array}{r r fifty} \text{OF}_{2} & & \\[1em] & \text{O: 6 valence electrons/atom} \times 1 \;\text{cantlet} & = half dozen \\[1em] \dominion[-0.5ex]{21em}{0.1ex}\hspace{-21em} + & \text{F: seven valence electrons/cantlet} \times 2 \;\text{atoms} & = 14 \\[1em] & & = 20 \;\text{valence electrons} \stop{array}[/latex]

  2. Describe a skeleton structure of the molecule or ion, arranging the atoms around a central atom and connecting each atom to the central atom with a single (one electron pair) bond. (Note that nosotros denote ions with brackets around the structure, indicating the charge outside the brackets:)Four Lewis diagrams are shown. The first shows one silicon single boned to four hydrogen atoms. The second shows a carbon which forms a single bond with an oxygen and a hydrogen and a double bond with a second oxygen. This structure is surrounded by brackets and has a superscripted negative sign near the upper right corner. The third structure shows a nitrogen single bonded to an oxygen and surrounded by brackets with a superscripted plus sign in the upper right corner. The last structure shows two fluorine atoms single bonded to a central oxygen.When several arrangements of atoms are possible, as for CHO2 , we must use experimental bear witness to choose the correct one. In general, the less electronegative elements are more likely to be primal atoms. In CHO2 , the less electronegative carbon atom occupies the central position with the oxygen and hydrogen atoms surrounding information technology. Other examples include P in POCliii, S in And so2, and Cl in ClO4 . An exception is that hydrogen is nearly never a primal atom. Equally the about electronegative element, fluorine too cannot be a central atom.
  3. Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen) to complete their valence shells with an octet of electrons.
    • There are no remaining electrons on SiH4, so it is unchanged:Four Lewis structures are shown. The first shows one silicon single boned to four hydrogen atoms. The second shows a carbon single bonded to two oxygen atoms that each have three lone pairs and single bonded to a hydrogen. This structure is surrounded by brackets and has a superscripted negative sign near the upper right corner. The third structure shows a nitrogen single bonded to an oxygen, each with three lone pairs of electrons. This structure is surrounded by brackets with a superscripted plus sign in the upper right corner. The last structure shows two fluorine atoms, each with three lone pairs of electrons, single bonded to a central oxygen.
  4. Identify all remaining electrons on the central atom.
    • For SiH4, CHOii , and NO+, in that location are no remaining electrons; we already placed all of the electrons determined in Footstep one.
    • For OFtwo, we had 16 electrons remaining in Step 3, and nosotros placed 12, leaving iv to be placed on the primal cantlet:A Lewis structure shows two fluorine atoms, each with three lone pairs of electrons, single bonded to a central oxygen which has two lone pairs of electrons.
  5. Rearrange the electrons of the outer atoms to make multiple bonds with the fundamental cantlet in guild to obtain octets wherever possible.

Example i

Writing Lewis Structures
NASA'south Cassini-Huygens mission detected a large cloud of toxic hydrogen cyanide (HCN) on Titan, i of Saturn's moons. Titan also contains ethane (H3CCH3), acetylene (HCCH), and ammonia (NH3). What are the Lewis structures of these molecules?

Solution

  1. Calculate the number of valence electrons.HCN: (1 × 1) + (4 × 1) + (v × one) = 10H3CCH3: (one × iii) + (2 × 4) + (1 × 3) = 14HCCH: (1 × ane) + (2 × four) + (1 × 1) = 10NHiii: (5 × 1) + (3 × 1) = 8
  2. Describe a skeleton and connect the atoms with single bonds. Remember that H is never a central atom:Four Lewis structures are shown. The first structure shows a carbon atom single bonded to a hydrogen atom and a nitrogen atom. The second structure shows two carbon atoms single bonded to one another. Each is single bonded to three hydrogen atoms. The third structure shows two carbon atoms single bonded to one another and each single bonded to one hydrogen atom. The fourth structure shows a nitrogen atom single bonded to three hydrogen atoms.
  3. Where needed, distribute electrons to the last atoms: Four Lewis structures are shown. The first structure shows a carbon atom single bonded to a hydrogen atom and a nitrogen atom, which has three lone pairs of electrons. The second structure shows two carbon atoms single bonded to one another. Each is single bonded to three hydrogen atoms. The third structure shows two carbon atoms single bonded to one another and each single bonded to one hydrogen atom. The fourth structure shows a nitrogen atom single bonded to three hydrogen atoms.HCN: six electrons placed on NH3CCHthree: no electrons remainHCCH: no terminal atoms capable of accepting electrons

    NH3: no final atoms capable of accepting electrons

  4. Where needed, place remaining electrons on the central cantlet: Four Lewis structures are shown. The first structure shows a carbon atom single bonded to a hydrogen atom and a nitrogen atom, which has three lone pairs of electrons. The second structure shows two carbon atoms single bonded to one another. Each is single bonded to three hydrogen atoms. The third structure shows two carbon atoms, each with a lone pair of electrons, single bonded to one another and each single bonded to one hydrogen atom. The fourth structure shows a nitrogen atom with a lone pair of electrons single bonded to three hydrogen atoms.HCN: no electrons remainH3CCHthree: no electrons remainHCCH: four electrons placed on carbon

    NH3: 2 electrons placed on nitrogen

  5. Where needed, rearrange electrons to course multiple bonds in order to obtain an octet on each atom:HCN: class two more than C–N bondsH3CCH3: all atoms have the correct number of electronsHCCH: form a triple bail between the two carbon atomsNH3: all atoms have the right number of electrons

    Four Lewis structures are shown. The first structure shows a carbon atom single bonded to a hydrogen atom and a nitrogen atom, which has three lone pairs of electrons. Two curved arrows point from the nitrogen to the carbon. Below this structure is the word

Bank check Your Learning
Both carbon monoxide, CO, and carbon dioxide, CO2, are products of the combustion of fossil fuels. Both of these gases too cause problems: CO is toxic and COii has been implicated in global climate change. What are the Lewis structures of these two molecules?

Respond:

Two Lewis structures are shown. The left shows a carbon triple bonded to an oxygen, each with a lone electron pair. The right structure shows a carbon double bonded to an oxygen on each side. Each oxygen has two lone pairs of electrons.

Fullerene Chemical science

Carbon soot has been known to human being since prehistoric times, merely it was not until fairly recently that the molecular structure of the main component of soot was discovered. In 1996, the Nobel Prize in Chemistry was awarded to Richard Smalley (Figure three), Robert Curl, and Harold Kroto for their work in discovering a new class of carbon, the Csixty buckminsterfullerene molecule (Figure 1 in Chapter 7 Introduction). An entire class of compounds, including spheres and tubes of various shapes, were discovered based on Csixty. This type of molecule, called a fullerene, shows promise in a variety of applications. Because of their size and shape, fullerenes tin encapsulate other molecules, so they have shown potential in various applications from hydrogen storage to targeted drug delivery systems. They also possess unique electronic and optical properties that take been put to good use in solar powered devices and chemic sensors.

A photo of Richard Smalley is shown.
Effigy 3. Richard Smalley (1943–2005), a professor of physics, chemistry, and astronomy at Rice Academy, was one of the leading advocates for fullerene chemistry. Upon his expiry in 2005, the U.s. Senate honored him as the "Father of Nanotechnology." (credit: The states Department of Energy)

Exceptions to the Octet Dominion

Many covalent molecules take central atoms that exercise not accept viii electrons in their Lewis structures. These molecules autumn into three categories:

  • Odd-electron molecules have an odd number of valence electrons, and therefore have an unpaired electron.
  • Electron-deficient molecules have a cardinal atom that has fewer electrons than needed for a noble gas configuration.
  • Hypervalent molecules have a central cantlet that has more electrons than needed for a noble gas configuration.

Odd-electron Molecules

Nosotros call molecules that contain an odd number of electrons free radicals. Nitric oxide, NO, is an case of an odd-electron molecule; it is produced in internal combustion engines when oxygen and nitrogen react at high temperatures.

To draw the Lewis structure for an odd-electron molecule similar NO, we follow the same five steps nosotros would for other molecules, but with a few small-scale changes:

  1. Make up one's mind the total number of valence (outer shell) electrons. The sum of the valence electrons is five (from N) + 6 (from O) = 11. The odd number immediately tells us that we have a free radical, so nosotros know that not every atom tin take 8 electrons in its valence crush.
  2. Draw a skeleton structure of the molecule. Nosotros can hands draw a skeleton with an Northward–O unmarried bond:N–O
  3. Distribute the remaining electrons as lone pairs on the terminal atoms. In this example, there is no primal atom, so we distribute the electrons around both atoms. We give eight electrons to the more than electronegative atom in these situations; thus oxygen has the filled valence shell:
    A Lewis structure shows a nitrogen atom, with one lone pair and one lone electron single bonded to an oxygen atom with three lone pairs of electrons.
  4. Place all remaining electrons on the central atom. Since in that location are no remaining electrons, this pace does not apply.
  5. Rearrange the electrons to brand multiple bonds with the primal atom in club to obtain octets wherever possible. We know that an odd-electron molecule cannot accept an octet for every cantlet, just we want to go each atom as close to an octet as possible. In this case, nitrogen has merely five electrons around it. To move closer to an octet for nitrogen, we have one of the lone pairs from oxygen and use information technology to class a NO double bond. (Nosotros cannot have another lone pair of electrons on oxygen and form a triple bail because nitrogen would and so accept nine electrons:)
    A Lewis structure shows a nitrogen atom, with one lone pair and one lone electron double bonded to an oxygen atom with two lone pairs of electrons.

Electron-deficient Molecules

We will also run into a few molecules that contain fundamental atoms that practise non have a filled valence shell. By and large, these are molecules with central atoms from groups 2 and 12, outer atoms that are hydrogen, or other atoms that do not form multiple bonds. For example, in the Lewis structures of beryllium dihydride, BeH2, and boron trifluoride, BF3, the beryllium and boron atoms each have only four and half-dozen electrons, respectively. It is possible to depict a structure with a double bond betwixt a boron cantlet and a fluorine atom in BFiii, satisfying the octet rule, but experimental evidence indicates the bail lengths are closer to that expected for B–F single bonds. This suggests the best Lewis structure has three B–F unmarried bonds and an electron scarce boron. The reactivity of the compound is also consequent with an electron deficient boron. All the same, the B–F bonds are slightly shorter than what is actually expected for B–F unmarried bonds, indicating that some double bond graphic symbol is constitute in the bodily molecule.

Two Lewis structures are shown. The left shows a beryllium atom single bonded to two hydrogen atoms. The right shows a boron atom single bonded to three fluorine atoms, each with three lone pairs of electrons.

An atom like the boron atom in BFiii, which does not take viii electrons, is very reactive. It readily combines with a molecule containing an atom with a lone pair of electrons. For case, NHiii reacts with BF3 because the lone pair on nitrogen can be shared with the boron atom:

A reaction is shown with three Lewis diagrams. The left diagram shows a boron atom single bonded to three fluorine atoms, each with three lone pairs of electrons. There is a plus sign. The next structure shows a nitrogen atom with one lone pair of electrons single bonded to three hydrogen atoms. A right-facing arrow leads to the final Lewis structure that shows a boron atom single bonded to a nitrogen atom and single bonded to three fluorine atoms, each with three lone pairs of electrons. The nitrogen atom is also single bonded to three hydrogen atoms. The bond between the boron atom and the nitrogen atom is colored red.

Hypervalent Molecules

Elements in the 2nd period of the periodic tabular array (n = 2) can accommodate only eight electrons in their valence shell orbitals because they have just four valence orbitals (one 2s and iii 2p orbitals). Elements in the 3rd and higher periods (n ≥ 3) take more than than four valence orbitals and tin share more than four pairs of electrons with other atoms considering they accept empty d orbitals in the same shell. Molecules formed from these elements are sometimes called hypervalent molecules. Figure 4 shows the Lewis structures for ii hypervalent molecules, PCl5 and SFsix.

Two Lewis structures are shown. The left shows a phosphorus atom single bonded to five chlorine atoms, each with three lone pairs of electrons. The right shows a sulfur atom single bonded to six fluorine atoms, each with three lone pairs of electrons.
Figure four. In PCl5, the central cantlet phosphorus shares five pairs of electrons. In SF6, sulfur shares six pairs of electrons.

In some hypervalent molecules, such as IF5 and XeF4, some of the electrons in the outer vanquish of the primal atom are lone pairs:

Two Lewis structures are shown. The left shows an iodine atom with one lone pair single bonded to five fluorine atoms, each with three lone pairs of electrons. The right diagram shows a xenon atom with two lone pairs of electrons single bonded to four fluorine atoms, each with three lone pairs of electrons.

When we write the Lewis structures for these molecules, nosotros find that we have electrons left over after filling the valence shells of the outer atoms with eight electrons. These additional electrons must exist assigned to the key atom.

Example 2

Writing Lewis Structures: Octet Rule Violations
Xenon is a element of group 0, but information technology forms a number of stable compounds. We examined XeFfour before. What are the Lewis structures of XeFii and XeF6?

Solution
We can draw the Lewis construction of any covalent molecule past following the six steps discussed earlier. In this case, we can condense the final few steps, since non all of them use.

  1. Calculate the number of valence electrons: XeF2: 8 + (2 × 7) = 22XeF6: 8 + (6 × vii) = 50
  2. Describe a skeleton joining the atoms by single bonds. Xenon will exist the central atom because fluorine cannot be a central atom:
    Two Lewis diagrams are shown. The left depicts a xenon atom single bonded to two fluorine atoms. The right shows a xenon atom single bonded to six fluorine atoms.
  3. Distribute the remaining electrons.XeFtwo: We place three lone pairs of electrons around each F atom, accounting for 12 electrons and giving each F atom 8 electrons. Thus, six electrons (three lone pairs) remain. These lone pairs must exist placed on the Xe cantlet. This is acceptable because Xe atoms have empty valence vanquish d orbitals and can adjust more than eight electrons. The Lewis structure of XeF2 shows 2 bonding pairs and three lone pairs of electrons around the Xe cantlet:
    A Lewis diagram shows a xenon atom with three lone pairs of electrons single bonded to two fluorine atoms, each with three lone pairs of electrons.XeFhalf-dozen: We place three lone pairs of electrons effectually each F atom, bookkeeping for 36 electrons. Two electrons remain, and this lone pair is placed on the Xe atom:This structure shows a xenon atom single bonded to six fluorine atoms. Each fluorine atom has three lone pairs of electrons.

Bank check Your Learning
The halogens form a class of compounds called the interhalogens, in which element of group vii atoms covalently bail to each other. Write the Lewis structures for the interhalogens BrCl3 and ICliv .

Answer:

Two Lewis structures are shown. The left depicts a bromine atom with two lone pairs of electrons single bonded to three chlorine atoms, each with three lone pairs of electrons. The right shows an iodine atom, with two lone pairs of electrons, single boned to four chlorine atoms, each with three lone pairs of electrons. This structure is surrounded by brackets and has a superscripted negative sign.

Key Concepts and Summary

Valence electronic structures tin can exist visualized past drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). Lone pairs, unpaired electrons, and single, double, or triple bonds are used to indicate where the valence electrons are located around each atom in a Lewis structure. Virtually structures—peculiarly those containing second row elements—obey the octet rule, in which every cantlet (except H) is surrounded by eight electrons. Exceptions to the octet dominion occur for odd-electron molecules (gratis radicals), electron-deficient molecules, and hypervalent molecules.

Chemistry End of Chapter Exercises

  1. Write the Lewis symbols for each of the following ions:

    (a) Every bitiii–

    (b) I

    (c) Be2+

    (d) O2–

    (e) Gathree+

    (f) Li+

    (grand) Due north3–

  2. Many monatomic ions are found in seawater, including the ions formed from the following listing of elements. Write the Lewis symbols for the monatomic ions formed from the following elements:

    (a) Cl

    (b) Na

    (c) Mg

    (d) Ca

    (e) K

    (f) Br

    (g) Sr

    (h) F

  3. Write the Lewis symbols of the ions in each of the following ionic compounds and the Lewis symbols of the atom from which they are formed:

    (a) MgS

    (b) Al2O3

    (c) GaCl3

    (d) Yard2O

    (eastward) Li3North

    (f) KF

  4. In the Lewis structures listed here, Grand and X correspond various elements in the third menstruation of the periodic tabular array. Write the formula of each compound using the chemical symbols of each element:

    (a)

    Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted two positive sign. The right shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign outside of the brackets.

    (b)

    Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted three positive sign. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted negative sign and a subscripted three both outside of the brackets.

    (c)

    Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted positive sign and a subscripted two outside of the brackets. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign outside of the brackets.

    (d)

    Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted three positive sign and a subscripted two outside of the brackets. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign and subscripted three both outside of the brackets.

  5. Write the Lewis structure for the diatomic molecule Ptwo, an unstable form of phosphorus found in high-temperature phosphorus vapor.
  6. Write Lewis structures for the post-obit:

    (a) Htwo

    (b) HBr

    (c) PCliii

    (d) SF2

    (east) H2CCHtwo

    (f) HNNH

    (grand) H2CNH

    (h) NO

    (i) N2

    (j) CO

    (one thousand) CN

  7. Write Lewis structures for the following:

    (a) Oii

    (b) H2CO

    (c) AsF3

    (d) ClNO

    (e) SiClfour

    (f) HiiiO+

    (g) NHfour +

    (h) BF4

    (i) HCCH

    (j) ClCN

    (k) Cii 2+

  8. Write Lewis structures for the following:

    (a) ClF3

    (b) PCl5

    (c) BFiii

    (d) PFvi

  9. Write Lewis structures for the following:

    (a) SeFhalf-dozen

    (b) XeF4

    (c) SeCl3 +

    (d) CltwoBBCltwo (contains a B–B bond)

  10. Write Lewis structures for:

    (a) PO4 3−

    (b) ICl4

    (c) SOiii 2−

    (d) HONO

  11. Correct the following statement: "The bonds in solid PbCltwo are ionic; the bond in a HCl molecule is covalent. Thus, all of the valence electrons in PbCl2 are located on the Cl ions, and all of the valence electrons in a HCl molecule are shared between the H and Cl atoms."
  12. Write Lewis structures for the following molecules or ions:

    (a) SbHiii

    (b) XeFii

    (c) Se8 (a cyclic molecule with a band of eight Se atoms)

  13. Methanol, H3COH, is used as the fuel in some race cars. Ethanol, C2H5OH, is used extensively equally motor fuel in Brazil. Both methanol and ethanol produce COtwo and H2O when they burn. Write the chemical equations for these combustion reactions using Lewis structures instead of chemical formulas.
  14. Many planets in our solar system incorporate organic chemicals including methyl hydride (CH4) and traces of ethylene (C2Hiv), ethane (CiiH6), propyne (HthreeCCCH), and diacetylene (HCCCCH). Write the Lewis structures for each of these molecules.
  15. Carbon tetrachloride was formerly used in fire extinguishers for electrical fires. Information technology is no longer used for this purpose because of the germination of the toxic gas phosgene, Cl2CO. Write the Lewis structures for carbon tetrachloride and phosgene.
  16. Identify the atoms that correspond to each of the following electron configurations. Then, write the Lewis symbol for the common ion formed from each atom:

    (a) is 2twosouthward iiiip 5

    (b) 1s iitwos 22p 6iiis two

    (c) 1southward twoiis iitwop 6threes 23p half-dozen4south ii3d x

    (d) 1due south 22south twoiip viiiis twothreep 64southward 23d 104p 4

    (eastward) 1due south 2twos ii2p 63s 23p 64s 23d 10fourp ane

  17. The system of atoms in several biologically important molecules is given here. Complete the Lewis structures of these molecules by calculation multiple bonds and lone pairs. Do non add whatever more atoms.

    (a) the amino acid serine:

    A Lewis structure is shown. A nitrogen atom is single bonded to two hydrogen atoms and a carbon atom. The carbon atom is single bonded to a hydrogen atom and two other carbon atoms. One of these carbon atoms is single bonded to two hydrogen atoms and an oxygen atom. The oxygen atom is bonded to a hydrogen atom. The other carbon atom is single bonded to two oxygen atoms, one of which is bonded to a hydrogen atom.

    (b) urea:

    A Lewis structure is shown. A nitrogen atom is single bonded to two hydrogen atoms and a carbon atom. The carbon atom is single bonded to an oxygen atom and another nitrogen atom. That nitrogen atom is then single bonded to two hydrogen atoms.

    (c) pyruvic acid:

    A Lewis structure is shown. A carbon atom is single bonded to three hydrogen atoms and another carbon atom. The second carbon atom is single bonded to an oxygen atom and a third carbon atom. This carbon is then single bonded to two oxygen atoms, one of which is single bonded to a hydrogen atom.

    (d) uracil:

    A Lewis hexagonal ring structure is shown. From the top of the ring (moving clockwise), three carbon atoms, one nitrogen atom, a carbon atom, and a nitrogen atom are single bonded to each another. The top carbon atom is single bonded to an oxygen atom. The second and third carbons and the nitrogen atom are each single bonded to a hydrogen atom. The next carbon atom is single bonded to an oxygen atom, and the last nitrogen atom is single bonded to a hydrogen atom.

    (east) carbonic acid:

    A Lewis structure is shown. A carbon atom is single bonded to three oxygen atoms. Two of those oxygen atoms are each single bonded to a hydrogen atom.

  18. A chemical compound with a molar mass of about 28 chiliad/mol contains 85.7% carbon and 14.3% hydrogen by mass. Write the Lewis structure for a molecule of the compound.
  19. A compound with a tooth mass of almost 42 thou/mol contains 85.7% carbon and xiv.3% hydrogen by mass. Write the Lewis structure for a molecule of the chemical compound.
  20. Two arrangements of atoms are possible for a compound with a molar mass of well-nigh 45 1000/mol that contains 52.two% C, 13.1% H, and 34.7% O by mass. Write the Lewis structures for the two molecules.
  21. How are unmarried, double, and triple bonds like? How practice they differ?

Glossary

double bond
covalent bond in which two pairs of electrons are shared between 2 atoms
gratis radical
molecule that contains an odd number of electrons
hypervalent molecule
molecule containing at to the lowest degree one main grouping element that has more than eight electrons in its valence trounce
Lewis construction
diagram showing lonely pairs and bonding pairs of electrons in a molecule or an ion
Lewis symbol
symbol for an element or monatomic ion that uses a dot to represent each valence electron in the element or ion
lone pair
two (a pair of) valence electrons that are not used to grade a covalent bond
octet rule
guideline that states main group atoms volition course structures in which eight valence electrons interact with each nucleus, counting bonding electrons as interacting with both atoms continued past the bond
single bail
bond in which a single pair of electrons is shared between two atoms
triple bail
bond in which three pairs of electrons are shared between two atoms

Solutions

Answers to Chemical science Stop of Chapter Exercises

one. (a) 8 electrons:
A Lewis dot diagram shows the symbol for arsenic, A s, surrounded by eight dots and a superscripted three negative sign.;

(b) eight electrons:

A Lewis dot diagram shows the symbol for iodine, I, surrounded by eight dots and a superscripted negative sign.;

(c) no electrons

Be2+;

(d) eight electrons:

A Lewis dot diagram shows the symbol for oxygen, O, surrounded by eight dots and a superscripted two negative sign.;

(e) no electrons

Gaiii+;

(f) no electrons

Li+;

(grand) eight electrons:

A Lewis dot diagram shows the symbol for nitrogen, N, surrounded by eight dots and a superscripted three negative sign.

3. (a)

Two Lewis structures are shown. The left shows the symbol M g with a superscripted two positive sign while the right shows the symbol S surrounded by eight dots and a superscripted two negative sign.;

(b)

Two Lewis structures are shown. The left shows the symbol A l with a superscripted three positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign.;

(c)

Two Lewis structures are shown. The left shows the symbol G a with a superscripted three positive sign while the right shows the symbol C l surrounded by eight dots and a superscripted negative sign.;

(d)

Two Lewis structures are shown. The left shows the symbol K with a superscripted positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign.>;

(due east)

Two Lewis structures are shown. The left shows the symbol L i with a superscripted positive sign while the right shows the symbol N surrounded by eight dots and a superscripted three negative sign.;

(f)

Two Lewis structures are shown. The left shows the symbol K with a superscripted positive sign while the right shows the symbol F surrounded by eight dots and a superscripted negative sign.

5.
A Lewis diagram shows two phosphorus atoms triple bonded together each with one lone electron pair.

7. (a)
A Lewis structure shows two oxygen atoms double bonded together, and each has two lone pairs of electrons.

In this case, the Lewis structure is inadequate to draw the fact that experimental studies take shown two unpaired electrons in each oxygen molecule.

(b)

A Lewis structure shows a carbon atom that is single bonded to two hydrogen atoms and double bonded to an oxygen atom. The oxygen atom has two lone pairs of electrons.;

(c)

A Lewis structure shows an arsenic atom single bonded to three fluorine atoms. Each fluorine atom has a lone pair of electrons.;

(d)

A Lewis structure shows a nitrogen atom with a lone pair of electrons single bonded to a chlorine atom that has three lone pairs of electrons. The nitrogen is also double bonded to an oxygen which has two lone pairs of electrons. ;

(e)

A Lewis structure shows a silicon atom that is single bonded to four chlorine atoms. Each chlorine atom has three lone pairs of electrons.;

(f)

A Lewis structure shows an oxygen atom with a lone pair of electrons single bonded to three hydrogen atoms. The structure is surrounded by brackets with a superscripted positive sign.;

(g)

A Lewis structure shows a nitrogen atom single bonded to four hydrogen atoms. The structure is surrounded by brackets with a superscripted positive sign.;

(h)

A Lewis structure shows a boron atom single bonded to four fluorine atoms. Each fluorine atom has three lone pairs of electrons. The structure is surrounded by brackets with a superscripted negative sign.;

(i)

A Lewis structure shows two carbon atoms that are triple bonded together. Each carbon is also single bonded to a hydrogen atom.;

(j)

A Lewis structure shows a carbon atom that is triple bonded to a nitrogen atom that has one lone pair of electrons. The carbon is also single bonded to a chlorine atom that has three lone pairs of electrons.;

(thou)

A Lewis structure shows two carbon atoms joined with a triple bond. A superscripted 2 positive sign lies to the right of the second carbon.

9. (a) SeF6:
A Lewis structure shows a selenium atom single bonded to six fluorine atoms, each with three lone pairs of electrons.;

(b) XeF4:

A Lewis structure shows a xenon atom with two lone pairs of electrons. It is single bonded to four fluorine atoms each with three lone pairs of electrons.;

(c) SeCl3 +:

A Lewis structure shows a selenium atom with one lone pair of electrons single bonded to three chlorine atoms each with three lone pairs of electrons. The whole structure is surrounded by brackets.;

(d) Cl2BBCl2:

A Lewis structure shows two boron atoms that are single bonded together. Each is also single bonded to two chlorine atoms that both have three lone pairs of electrons.

11. Two valence electrons per Pb cantlet are transferred to Cl atoms; the resulting Pbtwo+ ion has a 6southward 2 valence shell configuration. Two of the valence electrons in the HCl molecule are shared, and the other six are located on the Cl atom as lone pairs of electrons.

13.
Two reactions are shown using Lewis structures. The top reaction shows a carbon atom, single bonded to three hydrogen atoms and single bonded to an oxygen atom with two lone pairs of electrons. The oxygen atom is also bonded to a hydrogen atom. This is followed by a plus sign and the number one point five, followed by two oxygen atoms bonded together with a double bond and each with two lone pairs of electrons. A right-facing arrow leads to a carbon atom that is double bonded to two oxygen atoms, each of which has two lone pairs of electrons. This structure is followed by a plus sign, a number two, and a structure made up of an oxygen with two lone pairs of electrons single bonded to two hydrogen atoms. The bottom reaction shows a carbon atom, single bonded to three hydrogen atoms and single bonded to another carbon atom. The second carbon atom is single bonded to two hydrogen atoms and one oxygen atom with two lone pairs of electrons. The oxygen atom is also bonded to a hydrogen atom. This is followed by a plus sign and the number three, followed by two oxygen atoms bonded together with a double bond. Each oxygen atom has two lone pairs of electrons. A right-facing arrow leads to a number two and a carbon atom that is double bonded to two oxygen atoms, each of which has two lone pairs of electrons. This structure is followed by a plus sign, a number three, and a structure made up of an oxygen with two lone pairs of electrons single bonded to two hydrogen atoms.

fifteen.
Two Lewis structures are shown. The left depicts a carbon atom single bonded to four chlorine atoms, each with three lone pairs of electrons. The right shows a carbon atom double bonded to an oxygen atom that has two lone pairs of electrons. The carbon atom is also single bonded to two chlorine atoms, each of which has three lone pairs of electrons.

17. (a)
A Lewis structure is shown. A nitrogen atom is single bonded to two hydrogen atoms and a carbon atom. The carbon atom is single bonded to a hydrogen atom and two other carbon atoms. One of these carbon atoms is single bonded to two hydrogen atoms and an oxygen atom. The oxygen atom is bonded to a hydrogen atom. The other carbon is single bonded to two oxygen atoms, one of which is bonded to a hydrogen atom. The oxygen atoms have two lone pairs of electron dots, and the nitrogen atom has one lone pair of electron dots.;

(b)

A Lewis structure is shown. A nitrogen atom is single bonded to two hydrogen atoms and a carbon atom. The carbon atom is single bonded to an oxygen atom and one nitrogen atom. That nitrogen atom is then single bonded to two hydrogen atoms. The oxygen atom has two lone pairs of electron dots, and the nitrogen atoms have one lone pair of electron dots each.;

(c)

A Lewis structure is shown. A carbon atom is single bonded to three hydrogen atoms and a carbon atom. The carbon atom is single bonded to an oxygen atom and a third carbon atom. This carbon is then single bonded to two oxygen atoms, one of which is single bonded to a hydrogen atom. Each oxygen atom has two lone pairs of electron dots.;

(d)

A Lewis hexagonal ring structure is shown. From the top of the ring, three carbon atoms, one nitrogen atom, a carbon atom and a nitrogen atom are single bonded to one another. The top carbon is single bonded to an oxygen, the second and third carbons and the nitrogen atom are each single bonded to a hydrogen atom. The next carbon is single bonded to an oxygen atom and the last nitrogen is single bonded to a hydrogen atom. The oxygen atoms have two lone pairs of electron dots, and the nitrogen atoms have one lone pair of electron dots.;

(eastward)

A Lewis structure is shown. A carbon atom is single bonded to three oxygen atoms. Two of those oxygen atoms are each single bonded to a hydrogen atom. Each oxygen atom has two lone pairs of electron dots.

19.
A Lewis structure is shown. A carbon atom is single bonded to three hydrogen atoms and another carbon atom. The second carbon atom is double bonded to another carbon atom and single bonded to a hydrogen atom. The last carbon is single bonded to two hydrogen atoms.

21. Each bail includes a sharing of electrons between atoms. Two electrons are shared in a single bond; four electrons are shared in a double bond; and six electrons are shared in a triple bail.

How To Determine The Base Element In A Covalent Bond When Drawing A Lewis Dot,

Source: https://opentextbc.ca/chemistry/chapter/7-3-lewis-symbols-and-structures/

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