no simple, and yet complete, way to define this forces that hold groups of atoms together and make them function as a unit a bond will form if the energy of the bonded atoms is lower than that of the separated atoms 2 CCl 4 - Covalent C Cl HCl - Covalent H Cl MgF 2 - Ionic [ F ] 2 [Mg] 2+ H 2 O - Covalent H O H NH 3 - Covalent H N H H NaCl - Ionic [ Cl ] [Na] + OH - Covalent O H H 2 - Covalent HH HCl - Covalent H Cl H CO 2 - Covalent COO Na 2 O - Ionic [ O ] 2 [Na] 2 + H N H H H N H H OO OO O 2 - Covalent OO C II II I 2 - Covalent [ O ] 3 2 [Al] 2 3+ Al 2 O 3 - Ionic NH 3 - Covalent OO O OOO O 3 - Covalent H C H H H H C H H H bond strength from smallest to largest single double triple bond length from smallest to largest triple d o u b l e s i n g l e VSEPR Theory YouTube (4:52) VSEPR Theory YouTube (4:52) the structure around a given atom is determined mostly by minimizing electron pair repulsions electron pairs (IB calls negative charge centres) are lone pairs pairs of electrons around a central atom not in a bond with another atom bonding pairs pairs of electrons being shared found in the space between the atoms (can be single, double, or triple bonds) the repulsion between electron pairs (negative charge centres) causes molecular shapes to adjust electron pairs arrange themselves around the central atom so that they are as far apart from each other as possible explains the three dimensional shape of a molecule SL level HL level Copyright Cengage Learning. All rights reserved 2 bonding pairs 0 lone pairs linear Shapes for species with 2, 3, and 4 negative charge centres on the central atom 3 bonding pairs 0 lone pairs 2 bonding pairs 1 lone pairs trigonal planar bent 4 bonding pairs 0 lone pairs 3 bonding pairs 1 lone pair 2 bonding pairs 2 lone pairs tetrhedral trigonal pyramid bent shared bonding electrons pairs are pulled (as in a tug-of-war) between atoms results in an equal OR unequal sharing atoms in the bond pull shared pair of electrons equally always the case in diatomic molecules H 2 O 2 N 2 Cl 2 . atoms in the bond pull the shared pair of electrons unequally results in a dipole because it has two poles Ex: HCl, H 2 O BF 3 non-polar molecule more electronegative atoms have a greater attraction for electrons a number is assigned to each element to quantify how much is wants/likes electrons atoms with the higher electronegativity give that side of the molecule a slightly negative charge ( -) less electronegative atoms therefore have a slightly positive charge ( +) covalent, non-polar covalent, polar ionic 0.1 1.8 > covalent, nonpolar covalent, slightly polar covalent, very polar ionic electronegativty difference probable type of bond Arrange the following bonds from most to least polar: a) NFOFCF a) CF, NF, OF b)CFNOSiF b) SiF, CF, NO c)ClCl, BCl, SCl c) BCl, SCl, ClCl H2OH2O CO 2 CH 3 Cl CCl 4 non-polar polar Which of the following molecules have a dipole moment? H 2 O, CO 2, SO 2, and CH 4 O H H dipole moment polar molecule S O O CO O no dipole moment nonpolar molecule dipole moment polar molecule C H H HH no dipole moment nonpolar molecule