How Atoms Combine

Compounds A compound is a molecule made up of two or more different atoms or elements Ex.) H2O = compound – molecule of water For most elements they are stable when the outer energy level is full A state of stability is achieved by most elements by chemical bonds Chemical bonds are forces that hold elements together in a compound

Covalent Bonds This is a bond when elements share electrons A molecule is composed of two or more atoms are held together by covalent bonds

Polar Molecules These are covalent that do not share electrons equally Water is the best example

Ions Not all atoms bond by sharing electrons Bonds can be created by an element gaining or losing valence electrons An atom that gains or loses an electron is a charged particle called an ion In general, an atom that has less then 4 valence electrons will lose their electrons When an atom loses its’ electrons it becomes positive (Ca+2) When an atom has more then 4 valence electrons it will gain their electrons When an atom gains electrons it becomes negative (O-2)

Ionic Bonds Positive and negative ions are attracted to one another (opposites attract) The attractive forces between two ions of opposite charge is called an ionic bond