next question number 4 to 9..

4.Write the isotopes notation for krypton-78. Given that the proton number of Kr is 36.

= Kr

5.What is the average atomic mass of element X if X consists of 78.7% of atom with a mass of 24.0 amu, 10.1% of atoms with a mass of 25.0 amu and 11.2% of atoms with a mass of 26.0 amu?

Average atomic mass =

=

=

=25.17 amu

6.Calculate average atomic mass of Neon.

Average atomic mass =

=
=20.19 amu

7. a)percentage =

b) Ar =

=

= 35.5

8. Ar =

x=60.112amu

Ga-69=60.112 Ga-71= 100-60.112 =39.888

9. percentage of B-10 = 19.9%

B-11 = 100- 19.9

= 80.1%

Ar =

10.811=(19.9 x 10.0219) + (801 x X)

19.9 + 80.1

x=11.087 amu

Exercise 1.1 Atoms and Molecules (number 1 to 3)

Answers:

1. Relative mass of these sub-atomic particles :

• Proton : 1 a.m.u
• Eletron : 1/1834 a.m.u
• Neutron : 1 a.m.u

The proton is heavier than the electron because the electric charge depends on the mass time the radius of a particle and whereas the mass of the proton is heavier than the mass of electron. Thus, the product of mass time the radius is in both particles are the same and therefore they have the same charge.

2. The number of protons, neutrons, and electrons for each isotope.

²⁴⁴₉₄ Pu > Protons : 244

Neutrons : 94

Electrons : 150

⁵⁶₂₆ Fe ³⁺ > Protons : 56

Neutrons : 26

Electrons : 30

⁷⁸ ₃₄ Se^2- > Protons : 78

Neutrons : 34

Electrons : 44

3. An isotope consists of 33 protons and 42 neutrons.

³³₄₂M