Question

1) Define Lewis structures (2) and present two examples (4 pts) for representations of two compounds or species where one has 4 carbon and a nitrogen and the other has 4 carbon, a chlorine and an oxygen with two pairs shared with one of the carbons. Complete the structure with the H that is required.

2) Define the electronic pair repulsion model (VSEPR) and apply it to an organic compound of 4 or more    carbons that have a double or triple covalent bond. Complete the structure with the H that are require. (5)

3) Explain why carbon and nitrogen combine chemically resulting in compounds sharing

1, 2 or 3 pairs of electrons. (3 pts). Present an example of each case. (1 pt. Each)

Answer 1

1. Lewis structure - The Lewis structure of a compound is a structural representation such that it shows atom to atom connectivity and also the position of non - bonded electron pairs i.e. lone pairs where bonding electron pairs are represented by dash and non - bonding electron pairs are shown in dots.

Examples -

Examples 1. T ICIC 4 2. 1 T

2. VSEPR theory which is also known as valance she'll electron pair repulsion theory, predicts the shape of a molecule or ion on the basis of minimum electrostatic between the negatively charged electrons in the valence shell of central atom.

This theory assumes that all the valance shell electron pairs (bonding or non - bonding) are oriented in space the central atom as far apart as possible to minimize repulsion. It is further assumed that lone pairs repel stronger than bond pairs. The spatial distribution of non pairs determine the gross shape of the molecule.

Examples -

H sp Carbon S13 Carboon -CH =2 carbon

3. Carbon and nitrogen can form single covalent bond, double bond and also triple bond. At first, we have to consider their electronic configurations. For carbon, the no. maximum covalency is 4 and for nitrogen is 3.

Hence , the electron sharing between these atoms can be one- one ,two -two or three - three each thus leads to the formation of single, double and triple bond respectively.

Examples -

Nitaile Imire Amine H2GCEN H2C-2c H2G-N2 three-three One-One electToM Hu o tawo elechon haring botween CeN leiton Sharing betuen Cand N betwean C &N CEN