Chemical Bonding Topic 5 Chemical Bonding Metallic Metal atoms only Ionic Metal + nonmetal atoms Covalent Nonmetal + nonmetal atoms Polar covalent Nonpolar covalent Coordinate covalent

Metallic Bonding Occurs in metal samples –Copper and brass for example Atoms involved lose valence e- –Forming + ions immersed in a “sea of e-”

Metallic Solids Metallic solids have certain properties due to these free, mobile e- –Malleable (hammered into thin sheet) –Ductile (drawn into wire) –Good conductors of heat and electricity (s, l, g) –Lustrous (shiny) –Generally hard –Generally high mp & bp

Ionic Bonding Occurs between metal and nonmetal atoms due to transfer of e- –NaCl and MgO for example The metal loses e- forming a + ion The nonmetal gains e- forming a – ion The oppositely charged ions are attracted to each other forming the ionic bond

Ionic Solids Ionic solids have certain characteristics due to the crystal lattice formed by the + and - ions –Poor conductors as solids (good as l, g, aq) –Generally hard –Generally high mp

Covalent Bonding Occurs between nonmetal atoms –HCl and CO 2 for example Involves the sharing of e- between atoms Sharing may be –Equal (Nonpolar covalent, Cl 2 ) –Unequal (Polar covalent, HCl) –“Moocher” (Coordinate covalent, NH 4 + )

Covalent Solids *2 types* Molecular Solids –Poor conductors (s, l, g, aq) –Soft –Low mp –Examples: ice (H 2 O), sugar (C 12 H 22 O 11 ), dry ice (CO 2 ) Network Solids –Poor conductors (s, l, g, aq) –Hard –High mp –Examples: sand (SiO 2 ), graphite, diamond, asbestos, SiC

Polar and Nonpolar Molecules Polar Molecules Uneven distribution of charge Have a + end and a - end Asymmetrical shape Examples: H 2 O, HCl, NH 3 Nonpolar Molecules Even distribution of charge No opposite ends Symmetrical shape Examples: CO 2, H 2, CH 4

Forces of Attraction Between Molecules Dipole-Dipole attraction occurs between polar molecules, the + end of one molecule is attracted to the – end of another, throughout the sample. Hydrogen Bonding is a type of dipole- dipole attraction between molecules containing hydrogen such as H 2 O, NH 3, and HF. Accounts for properties of water.

Forces of Attraction continued… Weak Intermolecular Forces (van der Waals’ & London Dispersion) of attraction occur between nonpolar molecules due to momentary uneven distribution of charge as electrons move around. Molecule-Ion Forces of attraction occur between polar molecules and dissolved ions. NaCl(aq) for example.