an electron in the highest occupied energy level of an atom a notation that depicts valence electrons as dots around the atomic symbol of the element; the symbol represents the inner electrons and atomic nucleus; also called Lewis dot structure chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level a negative ion formed when a halogen atom gains an electron a compound that consists of positive and negative ions the electrostatic force that holds oppositely charged particles together in an ionic compound an expression that indicates the number and type of atoms present in the smallest representative unit of a substance

1. Valence electron

an electron in the highest occupied energy level of an atom

2. Electron dot structure

a notation that depicts valence electrons as dots around the atomic symbol of the element; the symbol represents the inner electrons and atomic nucleus; also called Lewis dot structure

3. Octet rule

chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level

4. Halide ion

a negative ion formed when a halogen atom gains an electron

5. Ionic compound

a compound that consists of positive and negative ions

6. Ionic bond

the electrostatic force that holds oppositely charged particles together in an ionic compound

7. Chemical formula

an expression that indicates the number and type of atoms present in the smallest representative unit of a substance.

8. Formula unit

the lowest whole-number ratio of ions in an ionic compound; in magnesium chloride, the ratio of magnesium ions to chloride ions is 1:2 and the formula unit is MgCl2

9. Coordination number

the number of ions of opposite charge that surround each ion in a crystal.

10. Metallic bond

the force of attraction that holds metals together; it consists of the attraction of free-floating valence electrons for positively charged metal ions

11. Alloy

a mixture composed of two or more elements, at least one of which is a metal.