Covalent radius: the distance between the nuclei of two atoms of an element when they are held together by a single bond. Metallic radius: distance between the nuclei of two atoms in a metallic crystal. The size of an atom is closely related to its electron configuration. Recall that the lower an orbital"s energy, the more tightly an electron in that orbital is held to the nucleus and the smaller the orbital. Ionization energy- the amount of energy required to remove an electron from a gaseous atom. X (g) x+ (g) + e- (g) When moving down a group, ionization energy decreases. When moving left to right across a period, ionization energy increases. **group 3a and 6a are exceptions to the trend, both are lower than predicted. Cations- when an atom loses one or more electrons. Anions- when an atom gains one or more electrons.
