Chapter 2, Problem 1P

Draw Lewis structures to describe the bonding in the following molecules: (a) ${\text{F}}_2$; (b) ${\text{BF}}_3$; (C) ${\text{NH}}_3$;(d) ${\text{H}}_2\text{Se}$;(e) ${\text{H}}_2{\text{O}}_2$;(f) ${\text{BeCl}}_2$;(g) ${\text{SiH}}_4$;(h) ${\text{PF}}_5$

Interpretation Introduction

Interpretation:

Lewis structures to describe the bonding in the following molecules: (a) ${\text{F}}_2$ (b) ${\text{BF}}_{\text{3}}$ (c) ${\text{NH}}_{\text{3}}$ (d) ${\text{H}}_{\text{2}}\text{Se}$ (e) ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ (f) ${\text{BeCl}}_{\text{2}}$ (g) ${\text{SiH}}_{\text{4}}$ (h) ${\text{PF}}_{\text{5}}$ are to be drawn.

Concept Introduction:

A chemical bond is a force of attraction which holds two atoms together.

Lewis presented a method of describing the arrangement of valence electrons in molecule. The basic rule of this theory is that electrons in a molecule should be in pair.

The single (odd) electron present in a molecule indicates that the species is a radical.

The electrons present in the outermost shell of an atom are called valence electrons.

Answer to Problem 1P

Solution:

(a)

(b)

(c)

(d)

$\text{H}··\text{Se}··\text{H}$

(e)

(f)

(g)

(h)

Explanation of Solution

Lewis structure is used to represent the valence electron present in an atom. In Lewis structures dots or crosses are used to represent number of valence electrons and the nuclei are indicated by appropriate elemental symbols.

1. For molecule ${\text{F}}_2$

   The atomic number of Fluorine atom = 9

   The ground state electron configuration of F atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

   Valence electron in F atom = ${\text{2s}}^{\text{2}}{\text{2p}}^5$ = 7

   So, it gains one electron to complete its octet and attain a stable noble gas electronic configuration.

   Hence, fluorine can form single covalent bond with another fluorine atom.

   Each fluorine atom carries three lone pair of electrons.

   The Lewis structure of ${\text{F}}_2$ molecule is drawn below:

   Or

2. For molecule ${\text{BF}}_{\text{3}}$

   The atomic number of Boron atom = 5

   The ground state electron configuration of B atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^1$

   Valence electron in B atom = ${\text{2s}}^{\text{2}}{\text{2p}}^1$ = 3

   The atomic number of Fluorine atom = 9

   The ground state electron configuration of F atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

   Valence electron in F atom = ${\text{2s}}^{\text{2}}{\text{2p}}^5$ = 7

   So, it gains one electron to complete its octet and attain a stable nearest noble gas electronic configuration.

   In ${\text{BF}}_{\text{3}}$ molecule, three single covalent bond are formed between one carbon atom and three fluorine atoms.

   The Lewis structure of ${\text{BF}}_{\text{3}}$ molecule is drawn below:

   Or

3. For molecule ${\text{NH}}_{\text{3}}$

   The atomic number of Nitrogen atom = 7

   The ground state electron configuration of N atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^3$

   Valence electron in N atom = ${\text{2s}}^{\text{2}}{\text{2p}}^3$ = 5

   So, it gains three electrons to complete its octet and attain stable nearest noble gas electronic configuration.

   Hence, N can form three covalent bonds.

   The atomic number of Hydrogen atom = 1

   The ground state electron configuration of H atom is ${\text{1s}}^1$

   Valence electron in H atom = ${\text{1s}}^1$ = 1

   In ${\text{NH}}_{\text{3}}$ molecule, three single covalent bond are formed between one nitrogen atom and three hydrogen atoms.

   The Lewis structure of ${\text{NH}}_{\text{3}}$ molecule is drawn below:

   Or

4. For molecule ${\text{H}}_{\text{2}}\text{Se}$

   The atomic number of Selenium atom = 34

   The ground state electron configuration of Se atom is $\left[\text{Ar}\right]{\text{3d}}^{\text{10}}{\text{4s}}^{\text{2}}{\text{4p}}^{\text{4}}$

   Valence electron in Se atom = ${\text{4s}}^{\text{2}}{\text{4p}}^{\text{4}}$ = 6

   So, it gains two electrons to complete its octet and attain stable nearest noble gas electronic configuration.

   Hence, selenium can form two covalent bonds.

   The atomic number of H atom = 1

   The ground state electron configuration of hydrogen atom is ${\text{1s}}^1$

   Valence electron in H atom = ${\text{1s}}^1$ = 1

   In ${\text{H}}_{\text{2}}\text{Se}$ molecule, two single covalent bond are formed between one selenium atom and two hydrogen atoms by two sharing pair of electrons.

   The Lewis structure of ${\text{H}}_{\text{2}}\text{Se}$ molecule is drawn below:

   $\text{H}··\text{Se}··\text{H}$ Or $\text{H}-\text{Se}-\text{H}$

5. For molecule ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$

   The atomic number of Oxygen atom = 8

   The ground state electron configuration of O atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^4$

   Valence electron in O atom = ${\text{2s}}^{\text{2}}{\text{2p}}^4$ = 6

   So, it gains two electrons to complete its octet and attain stable nearest noble gas electronic configuration.

   Hence, oxygen can form two covalent bonds.

   The atomic number of Hydrogen atom = 1

   The ground state electron configuration of H atom is ${\text{1s}}^1$

   Valence electron in H atom = ${\text{1s}}^1$ = 1

   In ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ molecule, two single covalent bond are formed between two oxygen atoms and two hydrogen atoms by two sharing pair of electrons.

   The Lewis structure of ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ molecule is drawn below:

   

   Or

   $\text{H}-\text{O}-\text{O}-\text{H}$

6. For molecule ${\text{BeCl}}_{\text{2}}$

   The atomic number of Beryllium atom = 4

   The ground state electron configuration of Be atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}$

   Valence electron in Be atom = ${\text{2s}}^{\text{2}}$ = 2

   The atomic number of Chlorine atom = 17

   The ground state electron configuration of Cl atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^{\text{5}}$

   Valence electron in Cl atom = ${\text{3s}}^{\text{2}}{\text{3p}}^{\text{5}}$ = 7

   So, it gains one electron to complete its octet and attain stable nearest noble gas electronic configuration.

   In ${\text{BeCl}}_{\text{2}}$ molecule, two single covalent bond are formed between one beryllium atoms and two chlorine atoms.

   The Lewis structure of ${\text{BeCl}}_{\text{2}}$ molecule is drawn below:

   

   Or

   $\text{Cl}-\text{Be}-\text{Cl}$

7. For molecule ${\text{SiH}}_{\text{4}}$

   The atomic number of Silicon atom = 14

   The ground state electron configuration of Si atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^2$

   Valence electron in Si atom = ${\text{3s}}^{\text{2}}{\text{3p}}^2$ = 4

   The atomic number of Hydrogen atom = 1

   The ground state electron configuration of H atom is ${\text{1s}}^1$

   Valence electron in H atom = ${\text{1s}}^1$ = 1

   In ${\text{SiH}}_{\text{4}}$ molecule, four single covalent bond are formed between one silicon atom and four hydrogen atoms.

   The Lewis structure of ${\text{SiH}}_{\text{4}}$ molecule is drawn below:

   Or

8. For molecule ${\text{PF}}_{\text{5}}$

   The atomic number of Phosphorous atom = 15

   The ground state electron configuration of P atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^3$

   Valence electron in P atom = ${\text{3s}}^{\text{2}}{\text{3p}}^3$ = 5

   So, it gains three electrons to complete its octet and attain stable nearest noble gas electronic configuration.

   The atomic number of F atom = 9

   The ground state electron configuration of fluorine atom is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

   Valence electron in F atom = ${\text{2s}}^{\text{2}}{\text{2p}}^5$ = 7

   In case of ${\text{PF}}_{\text{5}}$ molecule, five single covalent bond are formed between one phosphorous atom and five fluorine atoms.

   The Lewis structure of ${\text{PF}}_{\text{5}}$ molecule is drawn below:

   Or