AtomsAtoms&&

Isotopes Isotopes NOTES NOTES

Reading the Periodic TableReading the Periodic Table

A

EM

Atomic Number

Average Atomic Mass

Element Symbol

Reading Atoms & Isotopes

EA

M

Element Name – M

Element Symbol

Mass Number

Atomic Number

Or

Atomic Number• The number of Protons in the

nucleus of a given atom

• Remember – All atoms as a whole want to have a Neutral electrical charge.

Atomic # the # of Protons

the # of electrons

==

Mass Number• The sum of the number

of protons and number of neutrons in the nucleus of an atom.

• Example:

Carbon - 12 6 n

6 p

+

12

Isotopes• Atoms that have the same

number of Protons but different numbers of Neutrons.

Example:

Bromine - 79 = 35p and 44n

Bromine - 80 = 35p and 45n

Average Atomic MassAverage Atomic Mass• The average mass of all isotopes of an

element. Example:

• In a sample of 100 Carbon atoms:• 99 of them are Carbon-12 & • 1 is a Carbon-14.

What’s the Average Atomic Mass?

12.0212.02

Finding the # of Neutrons:

# of Neutrons = Mass # - Atomic #

•Use the formula below:

3

Li6.94

Name:

# p :

# e :

# n :

Lithium

33

4

Unit of Measurement Unit of Measurement (MASS):(MASS):

Atomic Mass Unit (amu) • one-twelfth the mass of a carbon-

12 atom. (6P & 6N)• 1 amu = 1.665402 x 10-27 Kg• 1p = 1.007280 amu• 1n = 1.008670 amu• 1e = 0.000549 amu

Practice Problems

Element: _________ Symbol: _________Protons: _________ Protons: ________Electrons: _________ Electrons: ________Neutrons: _________ Neutrons: ________

50

Sn118.71

Tin50

6950

Mg12

1212

Magnesium-24

More Practice Problems

Element: _________ Element: _________

Protons: _________ Protons: ________

Electrons: _________ Electrons: ________

Neutrons: _________ Neutrons: ________

Cr24

52Au79

197

Chromium24

2824

Gold79

11879

More Practice Problems

Element: _________ Element: _________

Protons: _________ Protons: ________

Electrons: _________ Electrons: ________

Neutrons: _________ Neutrons: ________

Cl17

37Cl17

35

Chlorine17

1817

Chlorine17

2017