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QUESTION 2 NOV 2013 2.1 Define the term covalent bond. A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons. 2.2 Draw Lewis structures for: 2.2.1 CH_4 The central carbon atom forms single bonds with four hydrogen atoms. There are no lone pairs on the central carbon atom. & H & \\ & | & \\ H & - & C & - & H \\ & | & \\ & H & 2.2.2 NH_3 The central nitrogen atom forms single bonds with three hydrogen atoms and has one lone pair of electrons. & H & \\ & | & \\ H & - & N & - & H (The lone pair on the nitrogen atom is represented by the two dots.) 2.3 Write down the number of lone pairs of electrons on the central atom in CH_4. 0 2.4 Which ONE of the molecules in QUESTION 2.2 can form a dative covalent bond? NH_3 can form a dative covalent bond by donating its lone pair of electrons from the nitrogen atom. NH_3 2.5 Write down the shape of the NH_3 molecule. Trigonal pyramidal 2.6 Explain why CH_4 is a non-polar molecule, while NH_3 is a polar molecule. Step 1: Analyze bond polarity and molecular shape for CH_4. In CH_4, the C-H bonds are slightly polar due to a small electronegativity difference. The molecule has a symmetrical tetrahedral shape. Step 2: Determine the overall polarity of CH_4. The four C-H bond dipoles are identical in magnitude and symmetrically arranged, causing them to cancel each other out. This results in a net dipole moment of zero, making CH_4 a non-polar molecule. Step 3: Analyze bond polarity and molecular shape for NH_3. In NH_3, the N-H bonds are polar due to the significant electronegativity difference between nitrogen and hydrogen. The molecule has a trigonal pyramidal shape, and the nitrogen atom has one lone pair of electrons. Step 4: Determine the overall polarity of NH_3. Due to the trigonal pyramidal shape and the presence of the lone pair, the N-H bond dipoles do not cancel each other out. This results in a net dipole moment, making NH_3 a polar molecule. Got more? Send 'em