1. Distinguishing Between Atoms
Lecture I
Atomic Structure Review

2. I. Atomic Structure Review
Rutherford Model of the Atom
Three subatomic particles
Nucleus: Center of atom-contains
Protons:
(+) charge
1 atomic mass unit
Neutrons:
no charge
Orbitals:
Paths around nucleus-great distance from nucleus-contain
Electrons:
(-)charge
1/1840 amu

3. II. Atomic Number Atomic Number: The number of protons in the nucleus.
Elements differ because of different number of protons
Because atoms are neutral, (+) charge =
(- )charge / protons = electrons
Element
Atomic
Number
Protons
Elec-
trons K 19
____ 5 S 16 V 23

4. III. Mass Number
Mass Number: The total number of protons and neutrons in an atom.
Most mass is concentrated in nucleus-that is where these particles are located
If you know the atomic number and mass number you can determine atom’s composition.
# neutrons = mass # - atomic number
Shorthand Notation / Nuclear Notation
Symbol with mass as superscript 197Au
atomic number as subscript 79

5. 1H 1 197Au 79 35Cl 17 38Cl Element Hydrogen oxygen # protons
# electrons
# Neutrons
Mass Number
Atomic Number
Nuclear Notation 1H 1
197Au 79
35Cl 17
38Cl

6. Gold Chlorine 1 8 79 17 118 18 21 16 197 35 38 1H 8 O 197Au 35Cl 38Cl
Element
Hydrogen
oxygen
Gold
Chlorine
# protons 1 8 79 17
# electrons
# Neutrons
118 18 21
Mass Number 16
197 35 38
Atomic Number
Nuclear Notation 1H
8 O
197Au
35Cl
38Cl

7. IV. Isotopes
Isotopes: atoms that have the same number of protons and electrons but different number of neutrons.
Different masses mean they have different mass numbers
Chemical behavior is the same
Three isotopes of hydrogen: hydrogen, deuterium, tritium

8. 2H 3H 1H 1 Isotope Nuclear Notation Protons Electrons Neutrons
Mass Number
Protium 1H 1
Deuterium 2H
Tritium 3H

9. V. Atomic Mass
Because mass of atoms so small and inconvenient to work with (fluorine X 10-23) it is more useful to compare relative masses of atoms using a reference isotope as a standard. Carbon-12 is used.
Atomic Mass Unit (amu) = 1/12 mass of carbon atom.
Atomic mass: weighted average mass of naturally occuring isotopes.
Estimate atomic mass: look at relative abundance
Calculate atomic mass: multiply the mass of each isotope by its natural percent abundance (expressed as a decimal) also known as the relative abundance, and add products.

10. Calculate Atomic Mass of Sulfur
Nuclear Notation
Natural Percent Abundance
Mass (amu)
Relative Abundance
32S 16
95.002
31.972
33S
0.76
32.971
34S
4.22
33.967
36S
0.014
35.967
Calculate atomic mass: multiply the mass of each isotope by its relative abundance and add products.

11. VI. The Periodic Table-A Preview
The periodic table allows you to easily compare one element to another.
Horizontal rows are called periods.
Vertical columns are called groups or families.