Nitrogen generally forms three bonds and is considered: A) Tetravalent B) Divale

Question

Nitrogen generally forms three bonds and is considered: A) Tetravalent B) Divalent C) Trivalent D) Monovalent E) Qudravalent A polar covalent bond is found in which of these compounds? A) H_2 B) F_2 C)NaCI D)HF E)N_2 For the following molecule, indicate the correct formal charge on boron and oxygen respectively. A) B= +1; 0 = +1 B) B = -1; O = -1 C)B = +1; O = -1 D)B = -1; O = +1 E) None of the choices are correct. Which of the following molecules, with any formal charges omitted, would be considered the most likely Lew structure for nitric acid. HNO_3? A) I B) II C) III D) IV E) None of the structures represent a Lewis structure of HNO_3 Which atom is most electronegative in the compound below? A C B) H C)O D)N E)F Which element in the second row of the periodic table has six valence electrons and a valence of two? A) Boron B) Carbon C) Nitrogen D) Oxygen E) None have a valence of two Which of the structures below contain an sp hybridized carbon? A) I and II B) III and IV C) II and III D) II and IV E) none of the above

Explanation / Answer

Ques. 1. Atomic number of Nitrogen is 7. Therefore valence electrons 2,5 and electron configuration is 1s22s22p3

In dinitrogen molecule (N2), nitrogen forms a triple bond with itself to follow the octet rule.

                                                          :NN:

Thus the valency of nitrogen (N) is 3. Hence nitrogen is considered as trivalent. Option C is correct

Ques.2   HF has polar covalent bond because they are sharing electrons and therefore covalent. And it is polar because of the difference in electronegativity between H and F. In polar covalent molecules, one atom has a partial negative charge and other atom has a partial positive charge. Option D is correct.

Ques 3. Formula for calculating formal charge is:

                                 FC = GN - UE - 1/2BE

where FC = formal charge

GN = number of valence electrons in free, nonbonded atom

UE = number of unshared electrons

BE = number of electrons shared in covalent bonds.

In the given molecule, The formal charge on Boron is calculated as folloows. Boron has three valence electrons, GN = 3, no lone pair of electron, UE= 0, and eight shared electrons with F and O, BE = 8. Thus

FC = 3 - 0 -1/2(8) => 3- 4=> -1

Thus the calculated formal charge on boron is -1.

Now calculating the formal charge on oxygen as follows. Oxygen has six valence electrons, GN = 6, two unshared electrons in one lone pair, UE = 2, and six shared electrons in two oxygen-carbon and in one oxygen-boron covalent bonds , BE = 6.

FC = 6 - 2 - 1/2 (6) => 6 - 5 => +1

Thus the calculated formal charge on oxygen is +1. Option D is correct.

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