ISOTOPIC NOTATIONisotopes are atoms with the same number of

protons but different number of neutrons

A

Z X

A = mass number (the total number of protons + neutrons)

Z = atomic number (the total number of protons)

X = element symbol

READING ISOTOPIC NOTATIONREADING ISOTOPIC NOTATION 46

21 Sc

46 = mass number (the total number of protons (2121) + neutrons

(2525)

21 = atomic number (the total number of protons (2121))

Sc = element symbolIn a neutral atom, the number of

electrons (21) is equal to the number of protons.

PRACTICE PROBLEMS

15N # protons = ____ # neutrons= ____ #electrons = ___

35P # p = ____ # n= ____ #e- = ___

62Cu2+

# p = ____ # n= ____ #e- = ___

76Se3-

# p = ____ # n= ____ #e- = ___

7 8 7

15 20 15

29 33 27

34 42 37

Writing ISOTOPIC NOTATION1. Write the symbol for the atom with an

atomic number of 21 and a mass number of 48.

2. Give the complete chemical notation for the nuclide with 23 protons, 26 neutrons and 20 electrons.

3. Write the isotopic notation fora.Z = 46 A = 110b.An atom containing 24 protons, 28

neutrons, and 21 electronsc. Titanium-50

48 Sc

49V3+

110Pd

52Cr3+

50Ti

PRACTICE PROBLEMS1. 196 Pt4+

# p = _____ # n = _____ #e- = _____

mass number = ________ atomic number = _______

atomic mass = ________ name of element = _______

2. Indicate the appropriate atomic mass of an element with 30 protons, 30 neutrons, and 28 electrons.

78 118 74

196 78

195.1 amu platinum

65.39 amu

Atomic Mass• The atomic mass of an element represents the average

mass of all the isotopes found in nature. No element exists with only one possible isotope. Hydrogen has the smallest number of isotopes: 1H protium, 2H deuterium, 3H tritium. Its atomic mass is 1.0079 amu (atomic mass units). The atomic mass is calculated by adding the % of 1H mass found in nature to the % of 2H mass found in nature plus the % of 3H mass.

• % 1H + % 2H + % 3H = average mass (atomic mass)• Generally the formula used is:

% X + % Y + % Z… = atomic mass. An instrument called the mass spectrometer is generally

used to determine the percentages and individual masses of each isotope.

Atomic Mass• Silver is found to have two stable isotopes, one has an atomic

mass of 106.904 amu and the other weighs 108.905 amu. The first isotope represents 51.82 % of the mass of the element and the second represents 48.18 %. What is the atomic mass of the element silver?

The equation to use is %X + % Y = average

And remember to turn your percents into fractions before multiplying.

(0.5182) 106.904 amu + (0.4818) 108.905 amu =?

55.398 amu + 52.470 amu =?

107.868 amu !!

Now look at the periodic table to verify the answer.

PRACTICE PROBLEMS # 81. A sample of neon contains three isotopes,

neon-20 (with an isotopic mass of 19.9924 amu), neon-21 (20.9939 amu) and neon-22 (21.9914 amu). The natural abundances of these isotopes are 90.92%, 0.257 %, and 8.82 %. Calculate the atomic weight of neon.

2. There are only two naturally occuring isotopes of copper, 63Cu and 65Cu. Copper has an atomic mass of 63.55 amu. What is the natural abundance of each isotope?

3. There are only two naturally occuring isotopes of gallium, 69Ga and 71Ga. What is the natural abundance of each isotope?

20.17 amu

65Cu = 30% & 63Cu = 70%

69Ga = 60% and 71Ga = 40%

GROUP STUDY PROBLEM #8_______1. The element with atomic number 53 contains

a) 53 neutrons b) 53 protons C) 26 neutrons & 27 protons d) 26 protons & 27 neutrons

_______2. The mass of one atom of an isotope is 9.746 x 10-23 g. One atomic mass unit has the mass of 1.6606 x 10-24 g. The atomic mass of this isotope is

a) 5.870 amu b) 16.18 amu c) 58.69 amu d) 1.627 amu

108

_______3. The number of neutrons in an atom of 47 Ag is

a) 47 b) 108 c) 155 d) 61

27

_______4. The number of electrons in an ion of 13 Al3+ is

a) 13 b) 10 c) 27 d) 14

_______5. What is the relative atomic mass of boron if two stable isotopes of boron have the following mass and abundance:

10.0129 amu (19.91%) & 11.0129 (80.09%)

a) 10.81 amu b) 10.21 amu c) 10.62 amu d) 10.51 amu