Chapter 4: Molecules & Compounds

Question 1

What is the difference between a mixture and a compound?

Answer 1

In a compound, elements combine in fixed, definite proportions; in a mixture, elements can mix in any proportion whatsoever.

Question 2

Why do chemical bonds form?

Answer 2

Chemical bonds form because they lower the potential energy of the charged particles that compose atoms.

Question 3

Define an ionic bond.

Answer 3

A bond that forms between a metal and a nonmetal.

Question 4

Define a covalent bond.

Answer 4

A bond that forms between two or more nonmetals.

Question 5

Define empirical formula.

Answer 5

An empirical formula indicates the relative number of atoms of each element in a compound.

Question 6

Define molecular formula.

Answer 6

A molecular formula indicates the actual number of atoms of each element in a molecule of a compound. The molecular formula is always a whole-number multiple of the empirical formula.

Question 7

Define structural formula.

Answer 7

A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other.

Question 8

Name the elements that exist as diatomic molecules.

Answer 8

H, N, O, F, Cl, Br, I.

Question 9

Define formula unit.

Answer 9

The basic unit of an ionic compound is the formula unit. It is the smallest, electrically neutral collection of ions. It usually does not exist as a discrete entity but rather as a part of a larger lattice.

Question 10

Why is the formation of an ionic compound exothermic?

Answer 10

When anions and cations come together, they form a lattice. This lattice has energy associated with its formation. When the ions form this lattice, the potential energy decreases, as dictated by Coulomb’s Law. This energy is given off in the form of heat.

Question 11

Define oxyanions.

Answer 11

Anions containing oxygen and another element.

Question 12

What is the relationship between the number of carbon atoms in an alkane and its boiling point? Why?

Answer 12

As the number of carbon atoms increases in the n-alkanes, so does their boiling point. The increase is due to the increasing dispersion force with increasing molar mass.

Question 13

Define functional group.

Answer 13

A functional group is a characteristic atom or group of atoms inserted into a hydrocarbon. They can dramatically change the properties of the organic compound.

Question 14

Define formula mass.

Answer 14

Formula mass is the average mass of a molecule of a compound (also known as molecular mass or molecular weight). It is equal to the sum of the atomic masses of all the atoms in its chemical formula.

Question 15

Define mass percent composition.

Answer 15

The mass percent composition of an element (or mass percent) is that element’s percentage of the compound’s total mass.

Question 16

How does combustion analysis work, and what is its purpose?

Answer 16

Combustion analysis is a way to obtain empirical formulas for unknown compounds, especially those containing carbon and hydrogen. Using this technique, the unknown compound undergoes combustion (or burning) in the presence of pure oxygen. When the sample is burned, all of the carbon in the sample is converted to carbon dioxide, and all of the hydrogen is converted to water. Using those weights, the empirical formula of the compound can be determined.

Question 17

Name some metals (important ones from the chart) that form cations with different charges.

Answer 17

Cr, Fe, Co, Cu, Sn, Hg, and Pb.

Question 18

Name the metals (outside the group 1A and 2A metals) whose charge is invariant from one compound to another. Give their charge as well.

Answer 18

Sc (3+), Ag (1+), Zn (2+), and Al (3+).