Why does salt shatter while copper bends? Why is water bent and carbon dioxide straight? This unit connects how atoms bond (ionic, covalent, metallic) to the structures they form, then uses Lewis diagrams and VSEPR to predict a molecule's shape, bond angles and polarity.
Electronegativity rises across a period and falls down a group. Atoms with similar electronegativity share electrons equally (nonpolar covalent); unequal sharing makes a polar covalent bond, and ionic and covalent bonding form a continuum. Metal–nonmetal bonds are usually ionic, nonmetal–nonmetal bonds covalent, and metals share a sea of electrons.
A potential energy vs. internuclear distance graph shows the bond length (the distance at the energy minimum) and the bond energy (the depth of the well). Higher bond order means shorter, stronger bonds. Coulomb's law ranks ionic attractions: bigger charges and smaller ions attract more strongly.
An ionic solid is a repeating 3-D array of cations and anions arranged to maximize attractions and minimize repulsions. That structure explains why ionic solids are hard, brittle and conduct only when melted or dissolved.
A metal is a lattice of positive ions in a sea of delocalized electrons, which explains conductivity and malleability. Interstitial alloys put small atoms in the gaps between large ones (steel); substitutional alloys swap in atoms of similar size (brass).
A Lewis diagram shows how valence electrons are arranged in a molecule: shared pairs as bonds and unshared pairs as lone pairs. Count valence electrons, connect the atoms, complete octets on outer atoms, and use multiple bonds when the central atom falls short.
When several equivalent Lewis diagrams can be drawn, the real molecule is a resonance hybrid of them, with bond orders and lengths in between. When the diagrams aren't equivalent, the one with formal charges closest to zero (and any negative charge on the most electronegative atom) is the best model.
Electron domains around a central atom repel each other and spread as far apart as possible. Counting domains and lone pairs gives the shape, bond angles and polarity. sp, sp² and sp³ atoms have ideal angles of 180°, 120° and 109.5°. Multiple bonds contain sigma and pi bonds, and pi bonds block rotation.