Snow Flakes

Naming Binary Covalent Compounds The first element in the formula is named first, followed by the second with the suffix -ide Prefixes are added to the elements name for both the first and the second mono- 1 di- 2 tri- 3 tetra- 4 penta- 5 hexa- 6 hepta- 7 octa- 8 nona- 9 deca- 10 Never use mono- for the first element

Polar and Non-polar Covalent Bonds Reminder: The ability of an atom within a molecule to draw electrons toward itself is called electronegativity. An electron pair shared between two atoms of the same element is called a non-polar covalent bond N2, H2, F2 all have non-polar covalent bonds Each element has the same electronegativity so both atoms attract electrons equally.

Polar and Non-polar Covalent Bonds What if two different atoms with different electronegativities? HF H = 2.2, F = 4.0 so F will attract electron better An electron pair is more likely to reside closer to the nucleus of the atom with the greater electronegativity and forms a polar covalent bond. The greater the difference between the electronegativites, the more polar the bond. H F

Polar and Nonpolar Covalent Bonds What if the difference between the electronegativities is really large? Na and F Na = 0.93, F = 4.0 Difference is 3.07! Called an ionic bond.

Polarity of Molecules Just as bonds can be polar (electronegativity of atoms) so can molecules If the atoms attract electrons around the central atom symmetrically, the molecule is non-polar C O B F O H If the atoms pull electrons around the central atom asymmetrically, the molecule is polar

Oil and Water Oil is non-polar Water is polar That is why oil and water don’t mix

VSEPR Theory Valence Shell Electron Pair Repulsion Theory Use VSEPR to predict the shape of molecules based on the Lewis structure Shape of the molecule is affected by each of the valence shell electron pairs surrounding a central atom The regions of electron space around the atom repel each other and strive to get as far away from each other a possible Region of electron space are: a non-bonding lone pair bonding electrons

Possible VSEPR Shapes 5 VSEPR shapes corresponding to number of regions of electron space 6 regions: Octahedron 5 regions: Trigonal bipyramid 4 regions: Tetrahedron - 109.5° apart 3 regions: Trigonal Planar - 120° apart 2 regions: Linear - 180° apart

Predicting Shape - CH4 C H 1. Draw Lewis Structure of Molecule 2. Count regions of electron space around central atom - Each bonding region (single, double or triple bond) counts as one - Each lone pair counts as one 3. Assign VSEPR shape 4 Regions 4. Place lone pairs (if applicable) on shape Tetrahedron No Lone Pairs 5. Assign structure by positions of the bonded atoms Tetrahedron

Predicting Shape - H2O O H 1. Draw Lewis Structure of Molecule 2. Count regions of electron space around central atom - Each bonding region (single, double or triple bond) counts as one - Each lone pair counts as one • O H 3. Assign VSEPR shape 4 Regions 4. Place lone pairs (if applicable) on shape Tetrahedron 2 Lone Pairs 5. Assign structure by positions of the bonded atoms Bent

Shapes of Molecules

Group Work Predict the shape and polarity (polar or non-polar) of the following molecules NH3 BCl3 HF

Interactions between molecules Three phases of matter Solid ordered structure fixed volume and shape independent of container Strong interaction between molecules Liquid loosely ordered fixed volume, but not fixed shape - dependent on container Moderate interaction between molecules Gas No order Volume dependent on container Always occupies all of its container Almost no interaction between molecules