1. Components of the Atom Nucleus: Nuclear Forces:
Small densely packed area located at the center of the atom
Nuclear Forces:
Forces that allow protons and neutrons to exist close together in the nucleus
Electron Cloud (orbitals)
The large volume area that surrounds the nucleus
Subatomic particles
Particles that make up the atom
Quantity of these parts determine an element’s chemical/physical properties

2. Subatomic Particles Particle Charge Symbol Location Grams AMU* Proton
Positive p+
Nucleus
1.673e-24 1
Neutron
Neutral n0
1.675e-24
Electron
Negative e-
Cloud
9.11e-28
* AMU = atomic mass unit

3. Characteristics of Atoms
All matter is composed of atoms
Atoms of one element differ in properties from atoms of another element
Atoms are neutral (p+ = e-)
Atoms are mostly made of empty space.

4. Element Symbols 12
Mass Number C 6
Atomic Number
C-12
Mass Number

5. Examples:
Atomic number
Mass number p+ e- n0 O 30
238
146 8 8 16 8 8 Zn 65 30 30 35 U 92 92 92

6. Difference between an Atom, Ion, and Isotope
Charged particles (positive or negative)
# of electrons change (p+ ≠ e-)
Isotope:
# of neutrons change
Masses are different since the # of neutrons are different
** If the # of protons change, the element changes **

7. Isotopes Where to find the mass number of isotopes:
Information will be given either 3 ways
Name: carbon-14 or C-14
Symbol: 14C
Adding given # no to p+ (or atomic #)
The Atomic Mass of an Isotope will be given. It can not be taken from the periodic table.

8. Atomic Masses
The weighted average of all the isotopes masses known for an element
Masses found on periodic table are atomic masses
All elements have isotopes: some are radioactive
What you are given when trying to calculate atomic mass
Each known isotope and it’s atomic mass
The percent abundance (how often it occurs) for each element

9. Atomic Masses The atomic mass is 27.9 amu
Calculate the atomic mass of Si based on the following isotopes of Silicon:
Si-28 Mass: %
Si-29 Mass: %
Si-22 Mass: %
1) Multiple the mass of each isotope by the abundance
Note: the percent must be in decimal form
2) Add the products above to find the atomic mass
The atomic mass is 27.9 amu