It forms strong bonds with c, h, o, n, p, s, the halogens, and some metals: organic compounds are everywhere around us. Structure of atoms: protons + neutrons = nucleus, electrons, electrons are confined to regions of space called principle energy levels (shells, shell = primary quantum number, each shell can hold 2n2 electrons (n = (cid:1005), (cid:1006), (cid:1007), (cid:1008) ) Shells are divided into subshells called orbitals, which are designated by the letters s, p, d, f s = one per shell: every shell has an s orbital. Lowest energy: p = set of three per shell 2 and higher, dumbbell shape. 1s22s22p2: 4 valence electrons, can form up to 4 bonds. Shared by the two atoms and fills the valence shell. Determine the number of valence electrons in the molecule or ion. Show a single bond (bonding pair) of electrons as a single line: begin to add remaining electrons so that each atom has a complete valence shell.