ATOMS & ISOTOPESMrs. Page

Chemistry10

Parts of presentation modified from a PowerPoint presentation prepared by J. Crelling, Southern Illinois University

LEARNING OBJECTIVES• You will be able to define what an isotope is.• You will be able to determine the number of protons,

neutrons, and electrons in different isotopes of the same element.

• You will understand that atomic mass• You will understand what radioactivity is the average of

the naturally occurring isotopes of an element.• You will be able to give examples of how radioisotopes

are used in industry and medicine.

ATOMS Contain protons, neutrons, and

electrons Protons & neutrons are found in

the nucleus The nucleus contains most of the

mass of an atom Electrons are distributed around

the nucleus in energy levels/shells/orbitals (which make up the electron cloud)

The outermost electrons in the shell farthest from the nucleus are called valence electrons

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ELECTRONS

First subatomic particle discovered 1897 J.J. Thomson used the cathode

ray tube to discover the electron Has a negative charge (-1) Mass = 9.110 x 10-28 g (0.0005 amu) Electrons are located in energy

levels which make up the electron cloud

Electrons in the outermost energy level are called valence electrons

Valence electrons are responsible the for the reactivity of an atom.

PROTON

Observed by E. Goldstein in 1896 Observed by E. Goldstein in 1896

Rutherford is given credit for showing Rutherford is given credit for showing

that atoms contain both negatively and that atoms contain both negatively and

positively charged particles (gold foil positively charged particles (gold foil

experiment)experiment)

Has a charge of +1 Has a charge of +1

Relative Mass of 1 AMU (1.673 x 10Relative Mass of 1 AMU (1.673 x 10-24-24 g) g)

NEUTRON

Third major subatomic Third major subatomic particle discovered (1932 particle discovered (1932 James Chadwick)James Chadwick)

No charge (neutral)No charge (neutral) Relative Mass of 1 AMU Relative Mass of 1 AMU

(1.675 x 10(1.675 x 10-24-24 g) g)

ISOTOPES

Atoms of the same element Atoms of the same element have the same atomic number have the same atomic number (# of protons) and the same (# of protons) and the same chemical properties.chemical properties.

However, atoms of the same However, atoms of the same element may have different element may have different numbers of neutrons (and numbers of neutrons (and therefore different atomic therefore different atomic mass)mass)

IsotopesIsotopes are atoms of the same are atoms of the same element having different element having different number of neutronsnumber of neutrons

NATURALLY OCCURRING ISOTOPES

Every element has naturally occurring Every element has naturally occurring isotopesisotopes

Hydrogen has 3 naturally occurring Hydrogen has 3 naturally occurring isotopesisotopes Protium is the most abundant isotope of Protium is the most abundant isotope of

hydrogen (99.985%) has 1 proton, 0 hydrogen (99.985%) has 1 proton, 0 neutrons, and 1 electronneutrons, and 1 electron

Deuterium (0.015%) has 1 proton, 1 Deuterium (0.015%) has 1 proton, 1 neutron, and 1 electronneutron, and 1 electron

Tritium (0.0001% ?) has 1 proton, 2 Tritium (0.0001% ?) has 1 proton, 2 neutrons, and 1 electronneutrons, and 1 electron

ISOTOPE EXAMPLE

35Cl 37Cl17 17

chlorine - 35 chlorine - 37

ISOTOPES OF CARBON Naturally occurring carbon consists of three isotopes, 12C,

13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#P _______ _______ _______

#N _______ _______ _______

#E _______ _______ _______

SOLUTION

12C 13C 14C 6 6 6

#P __6___ _ 6___ ___6___

#N __6___ _ _7___ ___8___

#E __6___ _ 6___ ___6___

ZINC PROBLEM

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

B. Number of neutrons in the zinc atom

C. What is the mass number of a zinc isotope

with 37 neutrons?

ATOMIC MASS

Listed on the periodic table

Gives the mass of “average” atom of each element

compared to 12C

Average atom based on all the isotopes and their

abundance %

Atomic mass is not a whole number … mass number

is a whole number

Na22.99

CALCULATING ATOMIC MASS

Percent(%) abundance of isotopes

Mass of each isotope of that element

Weighted average =

mass isotope1(%) + mass isotope2(%) + …

100 100

ATOMIC MASS OF MAGNESIUM

Isotopes Mass of Isotope Abundance

24Mg = 24.0 amu 78.70%

25Mg = 25.0 amu 10.13%

26Mg = 26.0 amu 11.17%

(24)(.787) + (25)(.1013) + 26(.1117) =

18.888 + 2.5325 + 2.9042 = 24.3 amu

ISOTOPES

Two CategoriesTwo Categories Unstable – isotopes that Unstable – isotopes that

continuously and spontaneously continuously and spontaneously break down/decay in other lower break down/decay in other lower atomic weight isotopesatomic weight isotopes

Stable – isotopes that do not Stable – isotopes that do not naturally decay but can exist in naturally decay but can exist in natural materials in differing natural materials in differing proportionsproportions

USES OF RADIOISOTOPES Carbon 14 Dating (Geologic Time)Carbon 14 Dating (Geologic Time)

When the organism dies it stops taking in When the organism dies it stops taking in 1414C which C which disappears as it decays to disappears as it decays to 1414NN

Americum-241Americum-241 Used in smoke detectors Used in smoke detectors

Cesuim-137 Cesuim-137 Used to treat cancerous tumorsUsed to treat cancerous tumors

Californium-252Californium-252 Used to inspect luggage for Used to inspect luggage for explosivesexplosives

Cobalt-60 Cobalt-60 Used to sterilize surgical equipmentUsed to sterilize surgical equipment

Iodine-123Iodine-123 Used to treat thyroid disorders Used to treat thyroid disorders

Plutonium-238Plutonium-238 Used to power NASA Used to power NASA spaceshipsspaceships