2.4: ions and ionic compounds

ion: an atom or group of atoms with a charge
- charged atoms are monatomic ions whereas charged groups of atoms are polyatomic ions
cation: a positively charged ion
- formed when an atom loses an electron or electrons
anion: negatively charged ion
- formed when an atom gains an electron or electrons
ionic compounds are held together by the attraction between the oppositely-charged ions
ionic solids are often called salts
atoms gain or lose electrons to become more stable
elements seek to achieve the electron configuration of the closest noble gas to them on the periodic table
when they gain or lose electrons, atoms become charged (ions)

compound: a pure substance that contains two or more elements
the type of elements present dictate the type of compound and bonding of the substance
types of compounds
- ionic compounds
- formed between a metal and a nonmetal
- have ionic bonds (electrons are transferred from the metal atom to the nonmetal atom)
- electrostatic attraction holds ions together
- form formula units
- molecular compounds
- formed between two nonmetals
- have covalent bonds (electrons are shared by the nonmetal atoms)
- form molecules