Ionic & Covalent Bonds
Ionic bonds form when electrons TRANSFER from a metal to a nonmetal, creating attracted opposite ions (NaCl); covalent bonds form when two nonmetals SHARE electron pairs (H2O, CO2).
Atoms bond to reach a full outer shell (the octet rule). Hydrogen bonds — weak attractions between polar molecules, not true bonds within them — explain water’s surface tension and hold DNA’s two strands together.