To compare isotopes

Science - Atomic Structures

Draw and provide the atomic number and mass number for these isotopes:

2

Oxygen-16

Oxygen-17

Oxygen-18

Your turn:�Boron has two isotopes, which occur in natural relative abundances as per the information below. Calculate the relative atomic mass of boron.

Boron-10: 19.9%

Boron-11: 80.1%

3

Your turn:�A sample of magnesium was tested and shown to contain the following isotopes in abundance listed below. Calculate the relative atomic mass of magnesium in the sample and round to two decimal places.

Magnesium-24: 78.20%

Magnesium-25: 10.11%

Magnesium-26: 11.69%

4

Your turn:�A sample of lithium contains two isotopes - Lithium-6 (6.85% abundance) and Lithium-7 (93.15% abundance).�Calculate the relative atomic mass of lithium in the sample to the appropriate number of significant figures.

Lithium-6: 6.85%

Lithium-7: 93.15%

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5

1. Draw (nucleus only) and name (e.g. carbon-12) the following isotopes:

a)

​

b)

​

c)

6

• A sample of bromine contains 50.7% bromine-79 and 49.3% bromine-80.

Calculate the relative atomic mass of the sample to one decimal place.

7

• A sample of carbon contains 98% carbon-12, 1.5% carbon-13 and 0.50% percent carbon-14. Calculate the relative atomic mass to the correct number of significant figures.

8

9

Answers

Draw and provide the atomic number and mass number for these isotopes:

10

Oxygen-16

Oxygen-17

Oxygen-18

9 protons

9 protons

9 protons

7 neutrons

8 neutrons

9 neutrons

Your turn:�Boron has two isotopes, which occur in natural relative abundances as per the information below.

Calculate the relative atomic mass of boron.

Boron-10: 19.9%

Boron-11: 80.1%

19.9/100 x 10 = 1.99

80.1/100 x 11 = 8.811

1.99 + 8.811 = 10.801 uamu

11

Your turn:�A sample of magnesium was tested and shown to contain the following isotopes in abundance listed below. Calculate the relative atomic mass of magnesium in the sample and round to two decimal places.

Magnesium-24: 78.20%

Magnesium-25: 10.11%

Magnesium-26: 11.69%

78.20/100 x 24 = 18.768

10.11/100 x 25 = 2.5275

18.768 + 2.5275 + 3.0394 �= 24.3349 uamu

11.69/100 x 26 = 3.0394

12

Your turn:�A sample of magnesium was tested and shown to contain the following isotopes in abundance listed below. Calculate the relative atomic mass of magnesium in the sample and round to two decimal places.

Magnesium-24: 78.20%

Magnesium-25: 10.11%

Magnesium-26: 11.69%

78.20/100 x 24 = 18.768

10.11/100 x 25 = 2.5275

18.768 + 2.5275 + 3.0394 �= 24.33 uamu (2 d.p)

11.69/100 x 26 = 3.0394

13

Your turn:�A sample of lithium contains two isotopes - Lithium-6 (6.85% abundance) and Lithium-7 (93.15% abundance).�Calculate the relative atomic mass of lithium in the sample to the appropriate number of significant figures.

Lithium-6: 6.85%

Lithium-7: 93.15%

​

6.85/100 x 6 = 0.411

93.15/100 x 7 = 6.5205

0.411 + 6.5205�= 6.9315 uamu

3 sig figs

4 sig figs

14

Your turn:�A sample of lithium contains two isotopes - Lithium-6 (6.85% abundance) and Lithium-7 (93.15% abundance).�Calculate the relative atomic mass of lithium in the sample to the appropriate number of significant figures.

Lithium-6: 6.85%

Lithium-7: 93.15%

​

6.85/100 x 6 = 0.411

93.15/100 x 7 = 6.5205

0.411 + 6.5205�= 6.93 uamu

3 sig figs

4 sig figs

3 sig figs

15

• Draw (nucleus only) and name (e.g. carbon-12) the following isotopes:

a)

​

b)

​

c)

Nitrogen-14

​

Boron-10

​

Beryllium-7

Drawing must contain 5 protons and 9 neutrons

Drawing must contain 4 protons and 6 neutrons

Drawing must contain 3 protons and 4 neutrons

e.g.

16

• A sample of bromine contains 50.7% bromine-79 and 49.3% bromine-80. Calculate the relative atomic mass of the sample to one decimal place.

79 x 50.7/100 = 40.053

80 x 49.3/100 = 39.44

40.053 + 39.44 = 79.493

= 79.5 uamu (1 d.p.)

17

• A sample of carbon contains 98% carbon-12, 1.5% carbon-13 and 0.50% percent carbon-14. Calculate the relative atomic mass to the correct number of significant figures.

12 x 98/100 = 11.76

13 x 1.5/100 = 0.195

14 x 0.50/100 = 0.07

11.76 + 0.197 + 0.07 = 12.027

All original values: 2 sig figs

=12 (2 sig figs)

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