Question

Draw the all Lewis Structures and assign formal charges for the following molecules or ions

a) Methane, CH4
b) Ammonia, NH
c) Phosphorus Pentafluoride
d) Nitrate ion

Answer 1

To draw the Lewis structures for CH4, NH3, PF5, and NO3-, we distribute valence electrons to satisfy the octet rule, and we calculate formal charges based on differences between valence electrons and the electrons in bonds and lone pairs. The resulting structures have carbon, phosphorus, and nitrogen as central atoms, with appropriate bonding to hydrogen, fluorine, and oxygen, which minimizes formal charges.

Step-by-step explanation:

Drawing Lewis Structures and Assigning Formal Charges

To draw the Lewis structures for the given molecules or ions and assign formal charges, we must consider the total number of valence electrons and arrange them to satisfy the octet rule while minimizing the formal charges on each atom.

1. Methane (CH4): Carbon has 4 valence electrons and each hydrogen has 1 valence electron, totaling 8 electrons to be distributed. In the Lewis structure, carbon is at the center with four single bonds to hydrogen atoms, using up all 8 electrons. The formal charges on all atoms are zero.
2. Ammonia (NH3): Nitrogen has 5 valence electrons and hydrogen has 1 valence electron each. The Lewis structure has nitrogen in the center with three single bonds to hydrogen atoms and one lone pair of electrons. The formal charge on nitrogen is zero and on each hydrogen is also zero.
3. Phosphorus Pentafluoride (PF5): Phosphorus has 5 valence electrons and each fluorine has 7 valence electrons, for a total of 40 valence electrons. Phosphorus forms five single bonds with fluorine atoms, using up all the electrons. The formal charges on all atoms are zero.
4. Nitrate ion (NO3-): Nitrogen has 5 valence electrons and each oxygen has 6 valence electrons, plus one extra electron for the negative charge, totaling 24 electrons. The most common structure is nitrogen in the center with two single-bonded oxygens and one double-bonded oxygen, with an overall -1 charge distributed across the oxygens in the different resonance structures. Formal charges will be assigned based on valence minus the number of bonds and dots.

Formal charges are calculated by taking the number of valence electrons for a neutral atom, subtracting the electrons in lone pairs, and subtracting half the number of bonding electrons. A formal charge of zero is generally more stable.