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# Isotopes - PowerPoint PPT Presentation

Isotopes. Definition. All atoms of the same element have the same atomic number, but may have different masses. Having the same atomic number, means having the same number of protons (and electrons).

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## PowerPoint Slideshow about ' Isotopes' - abby

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### Isotopes

• All atoms of the same element have the same atomic number, but may have different masses.

• Having the same atomic number, means having the same number of protons (and electrons).

• The difference in mass is due to the difference in the number of neutrons a specific atom may have.

Examples

### Isotopes

• Carbon-12

• Carbon-13

• Carbon-14

Atomic number

12C

13C

14C

35Cl

37Cl

• Chlorine-35

• Chlorine-37

17

17

6

6

6

• Atomic mass – Atomic number = # neutrons

### Isotopes

Examples

Atomic mass

12 – 6 = 6 no

12C

14C

6

6

Atomic number

14 – 6 = 8 no

• So the atomic mass refers to the average mass of all the atoms of an element.

### Atomic mass calculations

Example

100 total atoms of carbon:

99 atoms of carbon-12

1 atom of carbon-13

99 x 12 = 1188 u

1 x 13 = 13 u

Total 1201 u

Average mass = 1201 u / 100 = 12.01 u

### Atomic mass calculations

98.89 %

1.11 %

Example a

Steps

mass of carbon-12 => 12 x 0.9889 = 11.8668 u

mass of carbon-13 => 13 x 0.0111 = 0.1443 u

Average mass of

naturally occurring Carbon 12.0111 u

12C

13C

6

6

Calculate the atomic mass given the information:

Isotope Abundance (%) Mass (u)

Cl-35 75 35

Cl-37 25 37

### Atomic mass calculations

Steps

mass of Cl-35 => 35 x 0.75 = 26.25 u

mass of Cl-37 => 37 x 0.25 = 9.25 u

Average mass of Cl 35.50 u

If 50 % of Bromine atoms have a mass number

of 79 and 50 % have a mass number of 81.

Calculate the average mass (atomic mass ) of Bromine atoms.

### Atomic mass calculations

Steps

79 x 0.50 = 39.50 u

81 x 0.50 = 40.50 u

Average mass of Bromine 80.00 u

If 80 % of Boron atoms have a mass number

of 11. The rest have a mass number of 10.

What is the atomic mass of Boron?

### Atomic mass calculations

Steps

11 x 0.80 = 8.8 u

10 x 0.20 = 2.0 u

Average mass of B 10.8 u

Calculate the atomic mass of Fe.

73 % of the atoms have a mass of 55.

15 % of the atoms have a mass of 56.

12 % of the atoms have a mass of 54.

### Atomic mass calculations

Steps

55 x 0.73 = 40.15 u

56 x 0.15 = 8.40 u

54 x 0.12 = 6.48 u

Average mass of Fe 55.03 u