A compound is a substance formed when two or more chemical elements are chemically bonded together. Which of the following is an example of a compound?

• Oxygen (O2)

• Water (H2O)

• Gold (Au)

• Iron (Fe)

A chemical formula is a representation of a substance using symbols for its constituent elements. What does it tell you?

• The number of atoms of each element in a molecule

• The physical state of the substance

• The color of the substance

• The taste of the substance

What is a formula mass?

• The sum of the atomic masses of all atoms in a molecule

• The weight of a single atom

• The number of atoms in a molecule

• The volume of a molecule

The unit of formula mass is:

• grams

• moles

• atomic mass units (amu)

• liters

Find the formula mass of the following compounds: NaCl, Ca(OH)₂, (NH₄)₃PO₄.

• The formula mass of NaCl is 58.44 g/mol, Ca(OH)₂ is 74.09 g/mol, and (NH₄)₃PO₄ is 149.09 g/mol.

• The formula mass of NaCl is 60.00 g/mol, Ca(OH)₂ is 70.00 g/mol, and (NH₄)₃PO₄ is 150.00 g/mol.

• The formula mass of NaCl is 55.00 g/mol, Ca(OH)₂ is 75.00 g/mol, and (NH₄)₃PO₄ is 148.00 g/mol.

• The formula mass of NaCl is 59.00 g/mol, Ca(OH)₂ is 73.00 g/mol, and (NH₄)₃PO₄ is 147.00 g/mol.

The octet rule is:

• A principle that atoms are most stable when they have eight electrons in their valence shell.

• A rule that states atoms are stable with six electrons in their valence shell.

• A guideline that suggests atoms are stable with ten electrons in their valence shell.

• A theory that atoms are stable with four electrons in their valence shell.

Which two elements are the exception to the octet rule, and how are they exempted?

• Hydrogen and Helium; they have fewer than 8 electrons in their outer shell

• Carbon and Nitrogen; they can form double bonds

• Oxygen and Sulfur; they can form triple bonds

• Fluorine and Neon; they have a full outer shell

Valence electrons are:

• the electrons in the outermost shell of an atom

• the electrons in the innermost shell of an atom

• the protons in the nucleus of an atom

• the neutrons in the nucleus of an atom

Ions are:

• neutral atoms

• charged particles

• molecules

• uncharged particles

Cations are formed when an atom loses electrons. What are cations?

• Positively charged ions

• Negatively charged ions

• Neutral atoms

• Molecules