Chapter 8: Bonding: General Concepts

Question 1

Bond energy

Answer 1

Energy required to break the bond

Question 2

Ionic bonding

Answer 2

The electrostatic attraction between oppositely charged ions

Question 3

Why are bonds formed?

Answer 3

So the system can achieve the lowest possible energy by behaving this way

Question 4

Ionic compound

Answer 4

A compound that results when a metal reacts with a nonmetal to form a cation and an anion (any compound that conducts an electric current when melted)

Question 5

Coulomb’s law

Answer 5

E = (2.31 x 10^-19 J • nm)(Q1Q2/r)
E = energy of interaction between a pair of ions
r = distance between the ion centers in nm
Q1 and Q2 = numerical ion charges

Question 6

Bond length

Answer 6

The distance between the nuclei of the two atoms connected by a bond; the distance where the total energy of a diatomic molecule is minimal

Question 7

Covalent bonding

Answer 7

A type of bonding in which electrons are shared by atoms

Question 8

Polar covalent bond

Answer 8

A covalent bond in which the electrons are not shared equally because one atom attracts them more strongly than the other

Question 9

Electronegativity

Answer 9

The ability of an atom in a molecule to attract shared electrons to itself

Question 10

On the periodic table, electronegativity increases…

Answer 10

Going left to right across a period

Question 11

On the periodic table, electronegativity decreases…

Answer 11

Going down a group for representative elements

Question 12

Dipole moment

Answer 12

A property of a molecule whose charge distribution can be represented by a center of positive charge and a center of negative charge

Question 13

Types of molecules with polar bonds but no resulting dipole moment

Answer 13

1. Linear molecules with two identical bonds
2. Planar molecules with three identical bonds 120 degrees apart
3. Tetrahedral molecules with four identical bonds 109.5 degrees apart

Question 14

When a positive ion is formed by removing one or more electrons from a neutral atom, the resulting cation is _____ than its parent atom.

Answer 14

Smaller

Question 15

When a negative ion is formed by add one or more electrons to a neutral atom, the resulting anion is _____ than its parent atom.

Answer 15

Larger

Question 16

On the periodic table, ion sizes increase…

Answer 16

Down a group

Question 17

Isoelectric ions

Answer 17

Ions containing the same number of electrons

Question 18

Lattice energy

Answer 18

The change in energy that takes place when separated gaseous ions are packed together to form an ionic solid

[k(Q1Q2)]/r

Question 19

Lattice energy processes become more exothermic when…

Answer 19

Ionic charges increase and distances between the ions in the solid decrease

Question 20

Percent ionic character of a bond

Answer 20

(measured dipole moment of X-Y/calculated dipole moment of X+Y-) x 100%

Question 21

Single bond

Answer 21

A bond in which one pair of electrons is shared by two atoms

Question 22

Double bond

Answer 22

A bond in which two pairs of electrons are shared by two atoms

Question 23

Triple bond

Answer 23

A bond in which three pairs of electrons are shared by two atoms

Question 24

For bonds to be broken, energy must be ______ to the system

Answer 24

Added

Question 25

The formation of a bond ________ energy

Answer 25

Releases

Question 26

∆H

Answer 26

∆H = ∑n x D(bonds broken) - ∑n x D(bonds formed)

Question 27

Localized electron model

Answer 27

A model that assumes that a molecule is composed of atoms that are bound together by sharing pairs of electrons using the atomic orbitals of the bound atoms

Question 28

Lone pair

Answer 28

An electron pair that is localized on a given atom; an electron pair not involved in bonding

Question 29

Bonding pair

Answer 29

An electron pair found in the space between two atoms

Question 30

Lewis structure

Answer 30

A diagram of a molecule showing how the valence electrons are arranged among the atoms in the molecule

Question 31

Duet rule

Answer 31

Hydrogen forms stable molecules when it shares two electrons

Question 32

Octet rule

Answer 32

The observation that atoms of nonmetals tend to form the most stable molecules when they are surrounded by eight electrons (to fill their valence orbitals)

Question 33

Steps for writing Lewis structures

Answer 33

1. Find the total number of valence electrons. Add an electron for every negative charge. Subtract an electron for every positive charge. 2. Decide the central atom (least electronegative, except for H) and draw bonds. Subtract the electrons used from the total in step 1. 3. Assign the leftover electrons to the terminal atoms. Subtract the electrons from the total in step 2. 4. If necessary, assign any leftover electrons to the central atom. If the central atom has an octet or exceeds an octet, you are usually done. If central does not have an octet, create multiple bonds.

Question 34

Which elements should always be assumed to obey the octet rule?

Answer 34

C, N, O, and F

Question 35

Which elements often have fewer than eight electrons around them in their compounds?

Answer 35

B and Be

Question 36

Which elements never exceed the octet rule?

Answer 36

Second row elements because their valence orbitals can only hold 8 electrons.

Question 37

Which elements can exceed the octet rule?

Answer 37

Third row and heavier elements because of their empty d orbitals

Question 38

Resonance

Answer 38

A condition when more than one valid Lewis structure can be written for a particular molecule. The actual electronic structure is not represented by any one of the Lewis structures but by the average of all of them

Question 39

Formal charge

Answer 39

The difference between the number of valence electrons on the free atom and the number of valence electrons assigned to the atom in the molecule (number of valence electrons on free atom) - (number of valence electrons assigned to the atom in the molecule) Assigned valence electrons = (number of lone pair electrons) + 1/2(number of shared electrons)

Question 40

Molecular structure

Answer 40

The three-dimensional arrangement of the atoms in a molecule