Everything Science Grade 10

4.4 CHAPTER 4. THE ATOM

Step 3:Find the number of electrons

Sodium is neutral, so it has the same number of electrons as protons.

The number of electrons is 11.

Step 4:Find A

From the periodic table we see thatA= 23.

Step 5:Work out the number of neutrons

We knowAandZso we can findN:N=A−Z= 23−11 = 12.

Step 6:Write the answer

In standard notation sodium is given by:^2311 Na. The number of protons

is 11, the number of neutrons is 12 and the number of electrons is 11.

Exercise 4 - 2

1. Explain the meaning of each of the following terms:

a. nucleus

b. electron

c. atomic mass

2. Complete the following table:

Element Atomic

mass

units

Atomic

number

Number of

protons

Number of

electrons

Number of

neutrons

Mg 24 12

O 8

17

Ni 28

40 20

Zn

0

C 12 6

Al3+ 13

O^2 − 18

74 Chemistry: Matter and Materials