Download atomic and nuclear structure notes

Atomic and Nuclear Structure Notes
Atoms
 atomic number
- location: top part of element box
- identifies the element – every element has its own unique atomic number




proton
- location: in the nucleus (center of atom)
- positive one charge
- number of protons = atomic number
- number of protons determines what element it is
neutron
- location: in the nucleus (center of atom)
- neutral charge
- number of neutrons = atomic mass – number of protons
atomic mass (mass number)
- location: bottom part of element box
- the average mass of all the element’s isotopes
- measured in atomic mass units (amu)
electron
- location: outside of nucleus
- negative one charge
- number of electrons = atomic number
Atomic number equals
Protons and
Electrons
Mass number minus
Atomic number equals
Neutrons
Isotopes
 forms of the same atom with the same number of protons, but different numbers
of neutrons  different mass
 example: carbon

isotope symbols
- phosphorus-24
24
P
15
24
P
24 is the mass number; 15 is the atomic number
24 is the mass number; 15 is the atomic number
24 is the mass number; 15 is the atomic number
Average Atomic Mass
 the mass you see on the Periodic Table
 to find for a certain element, we take into account all of the isotopes that exist and
the percentage of each type
 steps for solving average atomic mass
1. change percentages to decimal numbers by dividing by 100 or moving the
decimal two places to the left
2. multiply each decimal number from Step 1 by the mass of that particular isotope
3. add up all of the products from Step 2
4. your answer should match the mass on the Periodic Table
 example problem: Given the following table, calculate the average atomic mass for
oxygen.
Isotope
Relative Abundance
Mass
oxygen-16
99.759%
15.99491 amu
oxygen-17
0.037%
16.99913 amu
oxygen-18
0.204%
17.99916 amu
1. oxygen-16
99.759% = 0.99759
oxygen-17
0.037% = 0.00037
oxygen-18
0.204% = 0.00204
2. oxygen-16
0.99759 x 15.99491 = 15.956
oxygen-17
0.00037 x 16.99913 = 0.00629
oxygen-18
0.00204 x 17.99916 = 0.0367
3. 15.956 + 0.00629 + 0.0367 = 15.99899
4. answer matches what is on the Periodic Table? Yes
Nuclear (Radioactive) Particles
 Alpha particle (2He, α)
4
o
o
o
o

Beta particle (0e, β)
-1
o
o
o
o

Mass = 4amu
Charge = +2
Penetrating power = low
Shielding = paper or clothing
Mass = 0 amu
Charge = -1
Penetrating power = medium (4mm into body tissue)
Shielding = aluminum foil or wood
Gamma particle (γ)
o Mass = 0 amu
o Charge = 0
o Penetrating power = high (most dangerous)
o Shielding = lead or concrete
Half-Life
The time required for half of a radioisotope’s nuclei to decay into it’s products.
# ½ lives
0
1
2
3
4
5
6
Amount remaining
100%
50%
25%
12.5%
6.25%
3.125%
1.5625%
Example: Gold-198 has a half-life of 2.7 days. How much of a 96g sample of gold-198 will
be left after 8.1 days? __12g__
# ½ lives
0
2.7
5.4
8.1
Amount
96g
48g
24g
12g
Electron Configuration
 electrons exist in different orbitals: s, p, d, f (write on periodic table)
· s orbitals hold a maximum of 2 electrons
· p orbitals hold a maximum of 6 electrons
· d orbitals hold a maximum of 10 electrons
· f orbitals hold a maximum of 14 electrons
 example: electron configuration for Ar = 1s22s22p63s23p6
o (adding superscripts gives you the total number of electrons for that element)
 Rules
o Aufbau’s principle

All electrons fill the orbitals in the lowest energy level first.
o Pauli’s Exclusion principle

No two electrons can have the same quantum numbers.

That is, the two electrons must face opposite directions.
o Hund’s rule

If two or more orbitals of equal energy are available, electrons will
occupy them singly before filling them in pairs.