Shape and polarity

1. Drawing dot-and-cross diagrams

1.1. 1. Arrange atoms such that least EN is the central atom while most EN are peripheral

1.2. 2. Count total no. valence e (take into acc e gained/lost if molecule is ion)

1.3. 3. Assign 1 bond pair to every 2 bonded atoms and lone pairs to peripheral atoms (complete octet)

1.4. 4. Remaining e assigned as lone pairs of central atom

1.5. 5. Ensure central atom has complete octet, if not reassign e from peripheral to form multiple bonds with central

1.6. 6. Allocate dots and crosses to represent e of diff atoms

2. New node

3. Polarity

3.1. 1.Existence of polar bonds: non-polar if polar bonds cancel each other, polar if polar bonds do not cancel each other out

3.2. 2. Shape: Polar molecules are not symmetrical in shape

3.3. 3.Lone pairs of e: lone pairs are -ve, form delta- end of dipole, so if central atom has lone pairs on one side, it is polar

4. Valence Shell Electron Pair Repulsion (VSEPR) Theory

4.1. Postulate 1: E pairs in valence shell experience least repulsion when far apart as possible, so they adopt positions that maximise separations to minimise repulsion

4.1.1. New node

4.2. New node

4.3. Postulate 2: lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion

4.3.1. because lone pair closer to nucleus as its attracted by 1 +ve nucleus (bond pair attracted by 2), causing distortion in expected shape so bond angle between bond-pair bond-pair e will be smaller

4.4. Postulate 3: Increase in EN of central atom causes greater displacement of electron density of bond pairs towards central atom, so greater repulsion btw bond pairs of e and larger bond angle