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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