Atoms, Molecules, and Ions

Question 1

How is the atomic mass unit (amu) defined?

Answer 1

One amu is exactly ½ of the mass of one carbon-12 atom, which is equal to 1.66 ×10^-24 grams.

Question 2

What is the atomic number?

Answer 2

The atomic number is the number of protons in the nucleus of an atom.

Question 3

What is the mass number?

Answer 3

The mass number is the total number of protons and neutrons in an atom.

Question 4

What is an ion?

Answer 4

An ion is an atom that has an unequal amount of protons and electrons; in other words, it is electrically charged.

Question 5

What is a cation?

Answer 5

A cation is a positively charged atom.

Question 6

What is an anion?

Answer 6

An anion is a negatively charged atom.

Question 7

What do each of the numbers represent in this chemical symbol?

Answer 7

24 represents the mass number, 12 represents the atomic number, and 2+ represents the charge of the ion.

Question 8

What is an isomer?

Answer 8

Isomers are compounds with the same chemical formula but different molecular structures.

Question 9

What is a structural isomer?

Answer 9

A structural isomer is a compound in which the molecules differ in how the atoms are connected to each other.

Question 10

What is a spatial isomer?

Answer 10

A spatial isomer is a compound in which the relative orientations of the atoms in space can be different.

Question 11

What are metals?

Answer 11

Metals are elements that are shiny, malleable, good conductors of heat and electricity.

Question 12

What are nonmetals?

Answer 12

Nonmetals are elements that appear dull and are poor conductors of heat and electricity.

Question 13

What are metalloids?

Answer 13

Metalloids are elements that conduct heat and electricity moderately well, and possess some properties of metals and some properties of nonmetals.

Question 14

What are ionic bonds?

Answer 14

Ionic bonds are electrostatic forces of attraction that result from the transfer of electrons and the formation of ions.

Question 15

What are covalent bonds?

Answer 15

Covalent bonds are attractive forces between the positively charged nuclei of the bonded atoms and one or more pairs of electrons that are located between the atoms.

Question 16

What are some properties of ionic compounds?

Answer 16

• Ionic compounds are solids with typically high melting and boiling points, due to the strong attractions between the positive and negative ions.
• They are hard and brittle, also due to the strong attraction between the ions.
• They conduct electricity when dissolved in water, as the dissociated ions are able to move freely through the liquid; but in solid form, they are not electrically conductive because the ions are not free to move.

Question 17

What are some properties of molecular (covalent) molecules?

Answer 17

• Molecular compounds have relatively low bioling and melting points, as the attractive forces between the molecules are not as strong as in ionic compounds.
• They often exist as gases, low-boiling liquids, and low-melting solids.
• They tend to be soft and relatively flexible.
• They tend to be more flammable than ionic compounds, as many of them contain carbon and hydrogen.
• When dissolved in water, they do not conduct electricity because they do not consist of ions.

Question 18

Why are molecular compounds named differently than ionic compounds?

Answer 18

The charges of cations and anions dictate their ratios in ionic compounds, but covalent bonds can have significant variation in the combination ratios of the atoms in a molecule (for example, CO vs. CO₂). Therefore, the name must specify the number of atoms of each element.