How many electron pairs surround an atom of nitrogen (N, element 7) in the compund NF3?
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To determine the number of electron pairs surrounding an atom in a compound, you need to consider its Lewis structure.
1. Start by determining the total number of valence electrons for the nitrogen atom (N). Nitrogen is in Group 15, so it has 5 valence electrons.
2. The compound NF3 consists of one nitrogen atom surrounded by three fluorine atoms (F). Fluorine is in Group 17 and has 7 valence electrons per atom.
3. Calculate the total number of valence electrons by summing the valence electrons of each atom in the compound:
Nitrogen (N) = 5 valence electrons
Fluorine (F) = 7 valence electrons × 3 = 21 valence electrons
Total = 5 + 21 = 26 valence electrons
4. Place the nitrogen atom (N) in the center and the three fluorine atoms (F) around it. Connect each atom using a single bond (line) to represent the sharing of two electrons.
F - N - F
|
F
5. Subtract the number of electrons used for bonds from the total number of valence electrons (26 - 8 = 18). This accounts for the electrons in the chemical bonds.
6. The remaining electrons need to be placed on the outer atoms (fluorine) in pairs to satisfy the octet rule (except for hydrogen). Each pair is represented by a lone pair (two dots).
F - N - F
: :
F F
7. Distribute the remaining 18 electrons as lone pairs on the fluorine atoms (F):
F - N - F
: : :
F . F . F
8. Count the number of electron pairs around the nitrogen atom (N). In this case, there are 4 pairs, consisting of 1 bond pair (between N and each F atom) and 3 lone pairs (on the three F atoms).
Therefore, an atom of nitrogen (N) in the compound NF3 is surrounded by 4 electron pairs.