Chapter 9

Question 1

__________ __________ predict chemical bonding in nature.

Answer 1

Lewis structures

Question 2

Step 1 for writing a Lewis structure for a molecular compound:

Answer 2

1. Write the correct skeletal structure for the molecule

Question 3

Step 2 for writing a Lewis structure for a molecular compound:

Answer 3

2. Calculate the total # of electrons for the Lewis structure by summing the valence electrons of each atom in the molecule.

Question 4

Step 3 for writing a Lewis structure for a molecular compound:

Answer 4

Distribute the electrons among the atoms, giving octets to as many atoms as possible.

Question 5

Step 4 for writing a Lewis structure for a molecular compound:

Answer 5

If any atoms lack an octet, form double or triple bonds as necessary to give them octets.

Question 6

“At the ends”.

Answer 6

Terminal

Question 7

The only way to determine the skeletal structure of a molecule with absolute certainty is to __________ _____ _________ ________.

Answer 7

Examine it’s structure experimentally

Question 8

__________ atoms are always terminal.

Answer 8

Hydrogen

Question 9

__________ atoms must form at least two bonds.

Answer 9

Central

Question 10

Put the more __________ __________ in terminal positions.

Answer 10

Electronegative elements

Question 11

Put the __________ electronegative elements (other than hydrogen) in the central position.

Answer 11

Less

Question 12

If you are writing a Lewis structure for a __________ _____, the charge of the ion must be considered when calculating the total # of electrons.

Answer 12

Polyatomic ion

Question 13

_____ one electron for each negative charge.

Answer 13

Add

Question 14

__________ one electron for each positive charge.

Answer 14

Subtract

Question 15

The Lewis structure for a __________ _____ is usually written within brackets.

Answer 15

Polyatomic ion

Question 16

For the polyatomic ion NH(subscript 4)^+ , there are 9 electrons. Would you add an electron to make the total 10, or subtract and make it 8?

Answer 16

Subtract and make it 8

Question 17

This is used when two or more valid Lewis structures can be drawn for the same compound.

Answer 17

Resonance

Question 18

An electron book-keeping system that allows us to discriminate between alternative Lewis structures.

Answer 18

Formal charge

Question 19

Where there are two or more valid Lewis structures for the same molecule, we find that, in nature, the molecule exists as an _________ of the structures.

Answer 19

Average

Question 20

Two or more valid Lewis structures that are shown with double-headed arrows between them to indicate that the actual structure of the molecule is intermediate between them:

Answer 20

Resonance structures

Question 21

The actual structure of a molecule that is intermediate between two or more resonance structures:

Answer 21

Resonance hybrid

Question 22

The only structure that actually exists is the __________ structure-the individual resonance structures do not exist and are merely a convenient way to describe the actual structure.

Answer 22

Hybrid

Question 23

The concept of __________ is an adaptation of Lewis theory that helps account for the complexity of actual molecules.

Answer 23

Resonance

Question 24

In Lewis theory, electrons are ________ either on one atom or between atoms.

Answer 24

Localized

Question 25

The _________ of electrons lowers their energy; it stabilizes them.

Answer 25

Delocalization

Question 26

__________ __________ is a fictitious charge assigned to each atom in a Lewis structure that helps us to distinguish among competing Lewis structures.

Answer 26

Formal charge

Question 27

The charge that an atom would have if all bonding electrons were shared equally between the bonded atoms.

Answer 27

Formal charge

Question 28

The calculated charge for an atom if we completely ignore the effects of electronegativity.

Answer 28

Formal charge

Question 29

Formal charge =

Answer 29

(# of valence electrons) - [# of nonbonding electrons for element +1/2(number of bonding electrons)]

Question 30

The sum of all formal charges in a neutral molecule must be _____.

Answer 30

Zero

Question 31

The sum of all formal charges in an ion must equal _______.

Answer 31

The charge of the ion

Question 32

Small (or zero) formal charges on individual atoms are __________ than large ones.

Answer 32

Better

Question 33

When formal charge cannot be avoided, negative formal charge should reside on the __________ __________ atom.

Answer 33

Most electronegative

Question 34

A technique in which X-rays are scattered from crystals of the molecule of interest.

Answer 34

X-ray crystallography

Question 35

In 1989, researchers used X-ray crystallography to determine the structure of a molecule called what?

Answer 35

HIV-protease

Question 36

Without HIV-protease, HIV cannot spread in the human body because the virus cannot __________.

Answer 36

Replicate

Question 37

The working part of a molecule.

Answer 37

The active site

Question 38

Models that predict how atoms bond together to form molecules.

Answer 38

Bonding theories

Question 39

Many AIDS patients are still alive today because of:

Answer 39

Protease inhibitors

Question 40

Without chemical bonding, there would be only how many different kinds of substance?

Answer 40

91 (# of elements on the periodic table)

Question 41

Chemical bonds form because they lower the __________ __________ between the charged particles that compose atoms.

Answer 41

Potential energy

Question 42

If atomic/electron interactions result in an overall net reduction of energy between charged particles, what forms?

Answer 42

A chemical bond

Question 43

Metals tend to have low:

Answer 43

Ionization energies

Question 44

Nonmetals tend to have negative:

Answer 44

Electron affinities

Question 45

Nonmetals readily gain __________.

Answer 45

Electrons

Question 46

Nonmetals tend to have high:

Answer 46

Ionization energies

Question 47

Lowest potential energy = most __________.

Answer 47

Stable

Question 48

Since metals have low ionization energies, they tend to lose electrons __________.

Answer 48

Easily

Question 49

In the __________ __________ model, all of the atoms in a metallic lattice pool their valence electrons.

Answer 49

Electron sea model

Question 50

Lewis theory focuses on:

Answer 50

Valence electrons

Question 51

The easiest way to calculate lattice energy is with the:

Answer 51

Born-Haber cycle

Question 52

The magnitude of lattice energy __________ as we move down a column.

Answer 52

Decreases

Question 53

Lone pair electrons are also called:

Answer 53

Nonbonding electrons

Question 54

In general, double bonds are __________ and __________ than single bonds.

Answer 54

Shorter and stronger

Question 55

Triple bonds are even __________ and __________ than double bonds.

Answer 55

Shorter and stronger

Question 56

__________ bonds are directional.

Answer 56

Covalent

Question 57

The fundamental units of colvalently bonded compounds are __________ __________.

Answer 57

Individual molecules

Question 58

In covalently bonded molecular compounds, the interactions __________ molecules is much weaker than the bonding interactions __________ a molecule.

Answer 58

Between, within

Question 59

__________ compounds tend to have lower melting and boiling points than _________ compounds.

Answer 59

Molecular, ionic

Question 60

Intermediate in nature between a pure covalent bond and an ionic bond.

Answer 60

Polar covalent bond

Question 61

Having a positive pole and a negative pole.

Answer 61

Polar

Question 62

The ability of an atom to attract electrons to itself in a chemical bond (which results in polar and ionic bonds).

Answer 62

Electronegativity

Question 63

Elecgronegativity was quantified by American chemist:

Answer 63

Linus Pauling

Question 64

Energy required to break a bond.

Answer 64

Bond energy

Question 65

Electrons are shared equally and exactly.

Answer 65

Pure covalent bond

Question 66

Non-polar.

Answer 66

Purely covalent