Questions on Chemical Bonding

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Chapter 6 - Answer Key to Section Review 1-3

Section Review 1

1. What is the main distinction between ionic and covalent bonding?

Answer (A): Ionic bonding involves the electrical attraction between large numbers of anions and cations. Covalent bonding involves the sharing of electron pairs between two atoms.

Translation:

-Ionic bonding happens between a metal and a non-metal (east coast and west coast)

-One atom completely donates its valence electrons to another atom

-Metals become CATIONS (positive charge/oxidation state); Non-metals become ANIONS (negative charge/oxidation state)

Example: Na + Cl → Na+Cl- or Mg + O → Mg2+O2-

-In covalent bonding one atom completely shares its valence electrons with another atom (west coast and west coast)

Example: H2O, CO2

2. How is electronegativity used in determining the ionic or covalent character of the bonding between two elements?

A: A large difference in electronegativity between two atoms in a bond will result in ionic bonding. A small difference in electronegativity between two atoms will result in covalent bonding.

Translation: Electronegativity difference between 0-0.3 = Non-polar covalent bond

Electronegativity difference between 0.3-1.7 = Polar covalent bond

Electronegativity difference greater than 1.7 = Ionic bond

3. What type of bonding would be expected between the following atoms?

a) Li and F = ionic
b) Cu and S = polar-covalent
c) I and Br = polar-covalent
Translation:

Non-polar covalent bond – the electron pairs that make up the bond are “hanging out” right in the middle of the two atoms

Polar covalent bond – the electron pairs that make up the bond are “hanging out” closer to the more electronegative atom

4. List the three pairs of atoms referred to in the previous question in order of increasing ionic character of the bonding between them.

A: I and Br, Cu and S, Li and F

5. Compare the following pairs of atoms: Cu and Cl; I and Cl

a. Which pair would have a bond with a greater percent ionic character?

A: Electronegativities: Cu = 1.9, Cl = 3.0, I = 2.5

Differences in electronegativies: CuCl = 1.1, ICl = 0.5

*CuCl has the greater percent ionic character

b. In which pair would Cl have the greater negative charge?

A: The chlorine in CuCl has greater negative partial charge that the chlorine in ICl. There is a greater difference in electronegativities between Cu and Cl; therefore, there is a greater separation of charge between Cu and Cl than between I and Cl.

Section Review 2

1. Define the following: a. bond length, b. bond energy

A: a. the distance at which two covalently bonded atoms minimize their potential energy

b. the energy required to break a chemical bond and form neutral, isolated atoms (gas phase)

2. State the octet rule.

A: Chemical compounds tend to form so that each atom gains, loses, or shares electrons until an octet of electrons exists in its highest occupied energy level.

Translation: All atoms want a fully occupied valence shell (aka highest occupied energy level); generally that means 8 atoms – 2 electrons in an s orbital and 6 electrons in a p orbital. Atoms will bond with one another so that they can have these 8 electrons (octo is the prefix 8)

3. How many pairs of electrons are shared in the following types of covalent bonds?

a. a single bond – one (2 electrons)

b. a double bond – two (4 electrons)

c. a triple bond – three (6 electrons)

4. Draw the Lewis structures for the following molecules.

We answered this question in class. Here is a link to a website that can help you with Lewis Dot Structures. http://www.ausetute.com.au/lewisstr.html

This should also help you with Section 3 review…

Section Review 3

1. Give two examples of an ionic compound.

A: Magnesium chloride, MgCl2; CaF2

2. Use electron-dot notation to demonstrate the formation of ionic compounds involving...
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