Sea of delocalised electrons holds lattice together
As you go across a period add one valence electron
As you go down a group add one valance shell - all elements in the same group will contain similar chemical properties
The 3D structure of molecules can be determined using electron pair repulsion (VSEPR). Lone pairs repel bonding pairs, this how trigonal pyramidal molecules are formed.
Structure of an atom
The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas.