What is a covalent bond? Why does carbon form covalent bonds? Draw the electron dot structures of methane and nitrogen.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define in one line. A covalent bond is formed when two atoms share a pair of electrons.
2 · Explain why carbon shares. Carbon (2, 4) cannot gain 4 electrons (its nucleus cannot hold 10) or lose 4 (that needs too much energy), so it shares 4 electrons.
3 · Draw methane. Draw C in the centre with four H around it and one shared pair between C and each H. Then draw the line structure with four single bonds. Label: shared pair, C, H.
4 · Draw nitrogen. Draw two N atoms with three shared pairs between them and one lone pair on each. Write N≡N.
5 · Add the properties. Covalent compounds have low melting and boiling points and are poor conductors of electricity.
6 · Link to real life.CNG used in autos and buses is mainly methane, a covalent compound.
7 · Close in one line. So sharing lets carbon reach a full outer shell of 8 electrons.
Scoring tip: Draw the shared pairs between the atoms and the lone pairs on the outside. Count to 8 around each atom before you finish.
