1. Drawing Lewis diagrams

2. Lewis diagrams, also called electron-dot diagrams, are used to work out how electrons are shared in a molecule. Once we know the locations of electrons in a molecule we can work out its shape and polarity. All the valence (outer-shell) electrons must be shown. It is not necessary to distinguish between electrons from the different atoms.

3. 1.Work out the total number of valence electrons. 2.Position the symbols for the atoms. 3.Place one pair of electrons wherever there must be a bond. 4.Distribute the other electrons, starting with the outer atoms. 5.Put the remaining electrons on the central atom. Each of 5 Cls have 7 valence electrons, and the P has 5, so the total is 40 electrons. PCl : : : : : : : : : : : : : : : : : : : : Draw the Lewis diagram for PCl 5 All electrons distributed, all atoms satisfied. This is the final Lewis diagram.

4. PCl : : : : : : : : : : : : : : : : : : : : Elements beyond the second row of the periodic table (Na and beyond) are able to hold more than 8 electrons in their valence shell, due to the presence of d-orbitals. The maximum number of electrons any atom can have is double its original number (each electron may invite one ‘friend’). Thus S can have a maximum of 12 electrons around it, but B can only have 6.

5. Draw the Lewis diagram for NO 3 – Total number of electrons: 5 + 3(6) + 1 = 24. NOO O :::: :: : : : :: : All 24 electrons have been distributed. The O atoms have 8 electrons each, which satisfies them, but the N atom only has 6 electrons around it, which is unacceptable. Move one pair of electrons to make a double bond. : – All atoms now have an acceptable number of electrons. This is the final Lewis diagram.

6. Draw the Lewis diagram for I 3 – Each I atom has 7 valence electrons. Include one more electron for the minus charge, and the total is 22 electrons. III:: Count electrons Place atoms and charge. Electrons where there must be bonds. Make outer atoms happy. Rest of electrons on central atom. All atoms satisfied. :: : : : : : : : –