How Atoms Combine

Compounds A compound is a substance that is composed of atoms of two or more different elements that are chemically combined. Ex: water. An atom is chemically stable when its outermost energy level is full. Atoms fill their outermost level by making chemical bonds.

Bonds Covalent bond is the attraction of two atoms for a shared pair of electrons that holds the atoms together. A molecule is composed of two or more atoms held together by covalent bonds. An atom that gains or loses an electron is a charged particle called an ion. An ionic bond is the attractive force between two ions of opposite charges.

Chemical Reactions The change of one or more substances into other substances is called a chemical reaction. A solution is a homogeneous mixture whose components cannot be distinguished and can be classified as liquid, gaseous, solid or a combination. Ex: brewed coffee.

Mixtures vs. Solutions Heterogeneous mixture is when components are easily recognizable Ex: sand in water Homogeneous mixture is when components are NOT easily recognizable; another name is solution. Ex: Kool-Aid