Everything Science Grade 11

CHAPTER 1. ATOMICCOMBINATIONS 1.5

A dative covalent bond (also known as a coordinate covalent bond) is adescription of co-

valent bonding betweentwo atoms in which bothelectrons shared in the bond come from the

same atom. This happens when a Lewis base (anelectron donor) donatesa pair of electrons to

a Lewis acid (an electron acceptor). Lewis acidsand bases will be discussed in Section 8.1 in

Chapter 8.

One example of a molecule that contains a dative covalent bond is the ammonium ion

(NH+ 4 ) shown in the figure below. The hydrogen ionH+does not contain any electrons, and

therefore the electrons that are in the bond thatforms between this ion and the nitrogen atom,

come only from the nitrogen.

H N

ו××

××

ו

H

H + [H]+ H N

ו××

××

ו

H

H

H

Exercise 1 - 2

1. Represent each of thefollowing atoms using Lewis notation:

(a) beryllium

(b) calcium

(c) lithium

2. Represent each of thefollowing molecules using Lewis notation:

(a) bromine gas (Br 2 )

(b) carbon dioxide (CO 2 )

Which of these two molecules contains a double bond?

3. Two chemical reactions are described below.
   
   
   • nitrogen and hydrogenreact to form NH 3
   
   
   • carbon and hydrogen bond to form a moleculeof CH 4
   
   
   
   

For each reaction, give:

(a) the valency of eachof the atoms involved inthe reaction

(b) the Lewis structure of the product that is formed

(c) the chemical formula of the product

(d) the name of the product

4. A chemical compound has the following Lewis notation:

X Y

ו

××

××

ו

H

(a) How many valenceelectrons does elementY have?

(b) What is the valencyof element Y?