MOLECULAR SHAPES MOLECULAR SHAPES

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1 Molecules with 2 electron pair groups around Linear molecules have polar bonds, but are the central atom form a linear shape. usually non-polar. is 180 linear 2 electron pairs around the central atom 1 Molecules with 3 electron pair groups around Trigonal planar molecules have polar bonds, the central atom form a trigonal planar shape. but are usually non-polar. 3 electron is 120 pairs around the central atom trigonal planar 2 1

2 Molecules with 2 bonding pairs and 1 nonbonding molecules pair have groups polar around bonds, the and central are polar. atom Bent form a bent shape. bent 1 Nonbonding pair 2 bonding pairs around Bond the angle central atom is Tetrahedral Molecules molecules with 4 electron have polar pairs bonds, groups and around are usually the central non-polar. atom form a tetrahedral shape. 4 bonding pairs around the central atom tetrahedral is

3 Molecules with 3 bonding pairs and 1 nonbonding molecules pair groups have around polar bonds, the central and are atom polar. Pyramidal form a pyramidal shape. pyramidal 1 Nonbonding pair 3 bonding pairs around the central is atom 5 Molecules with 2 bonding pairs and 2 nonbonding molecules pair have groups polar around bonds, the and central are polar. atom Bent form a bent shape. bent 2 Nonbonding pair 2 bonding pairs around the is central atom 6 3

4 SUMMARY OF Linear Trigonal planar Tetrahedral Bent Pyramidal Symmetrical shapes Polar bonds Non-polar molecules Unsymmetrical shapes Polar bonds Polar molecules 7 ATTRACTIVE FORCES IN MOLECULES Many differences in the properties of solids and liquids are associated with the attractive forces that keep their molecules together. These forces range from very strong to very weak and are responsible for the wide range of properties observed in these substances. 8 4

5 ATTRACTIVE FORCES IN MOLECULES Ionic solids have high melting points that are due to the strong nature of the ionic bond and the forces of attraction between the cation and the anion. Na + ionic bond Cl - 9 ATTRACTIVE FORCES IN MOLECULES Covalent molecules also contain attractive forces, but of a weaker nature than the ionic compounds. The forces between covalent molecules can be divided into three types: Dispersion forces Dipole-dipole attractions Hydrogen bonds 10 5

6 DISPERSION FORCES These forces exist between non-polar molecules, and are the weakest of the 3 types of covalent forces. These forces are caused by temporary shifts in distribution of electrons in a non-polar molecule that cause a temporary dipole. Temporary dipole δ+ δ- δ+ δ- F F F F 11 DIPOLE-DIPOLE ATTRACTIONS These forces exist in polar molecules and are moderate strength. The negative end of a polar molecule is attracted to the positive end of another such molecule by these forces. δ+ δ- δ+ δ- Br Cl Br Cl 12 6

7 HYDROGEN BONDS These are the strongest of the 3 types of forces and are formed between molecules that have a hydrogen attached to the very electronegative elements (F, O and N). δ+ δ- δ+ δ- H F H F 13 HYDROGEN BONDING IN WATER 14 7

8 15 THE END 16 8