(3.1) Classifying Chemical Compounds
Atoms can combine to form compounds of two bond types: Intramolecular – within the molecule Ionic Covalent ◦ Polar Covalent ◦ Non-Polar Covalent Co-ordinate covalent ◦ Metallic Intermolecular – between molecules Hydrogen Bonding London Dispersion forces (LDF) Dipole- dipole mations/chang_7e_esp/bom1s2_11.swf mations/chang_7e_esp/bom1s2_11.swf Van der waals forces
Physical properties Ex: Solubility high solubilityvs.low solubility Chemical bonds form when the valence e - of atoms interact. Atoms can either exchange or share electrons
When 2 atoms exchange (or transfer) electrons 1 atom loses an e - 1 atom gains an e - metal non-metal lose gain
form crystals have high melting and boiling points very hard and very brittle conduct electricity when they dissolve in water or molten but not in the solid state
When 2 atoms share electrons Usually forms between two non-metals
have much lower melting and boiling points than ionic compounds soft and squishy (compared to ionic compounds, anyway) more flammable than ionic compounds don't conduct electricity in water. Covalent compounds aren't usually very soluble in water.
What type of bonding is present in the following? Draw Lewis diagrams to illustrate. CaCl 2 H2OH2O NH 3 AlCl 3 Ca 3 N 2 CO 2
Electronegativity is a periodic trend that can be useful. Defn: Electronegativity (EN) is a measure of an atom’s ability to attract electrons in a chemical bond. When 2 atoms form a bond, each atom attracts the other’s electrons in addition to its own.
As you go across a period, EN increases As you go down a group, EN decreases This trend can be summarized on your periodic table. radius metallic properties IE EA IE EA EN
The difference between EN values ( EN) for the 2 atoms in a bond can be used to predict bond type. Ex: CaF 2 EN = Chemical bonds range from mostly ionic to mostly covalent.
EN values mostly polar mostly ionic covalent covalent
Polar Bond: ◦ unequal sharing of electrons. One atom in the molecule draws electrons closer to itself. Example: HF has a polar bond because Fluorine atom is more electronegative and so it draws electrons CLOSER to itself, giving the bond polarity Non-polar bond: ◦ PERFECT SHARING OF ELECTRONS
If a molecule contains polar covalent bonds, the entire molecule may have a positive end and a negative end, in which case it would be classified as a polar molecule. Not all molecules containing polar covalent bonds are polar molecules, Carbon tetrachloride, CCl 4 (l), and HCl(g) Molecules with non polar bonds are all non polar molecules
i) calcium fluoride EN = CaF 2 ii) hydrogen chloride EN = HCl iii) oxygen EN = O2O2