1. Basic Atomic Structure
AP Chem. Chapter 2

2. Atomic Particles Particle Charge Mass (amu) Mass (kg) Location
Electron -1
1/1000 = 0
9.109 x 10-31
Electron cloud
Proton +1 1
1.673 x 10-27
Nucleus
Neutron
1.675 x 10-27

3. Format for writing isotopes of atomsA X Z
element symbol (X)
atomic number (Z) = number of protons
mass number (A) - atomic number (Z) = number of neutrons.

4. Mass Number Nuclide p+ n0 e- Mass # (Z)
Mass number is the number of protons and neutrons in the nucleus of an isotope.
Mass # (z)= p+ + n0
Nuclide p+ n0 e-
Mass # (Z)
Oxygen - 10 - 33 42
- 31 15 18 8 8 18
Arsenic 75 33 75
Phosphorus 16 15 31

5. Isotopes
Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.
Isotope
Protons
Electrons
Neutrons
Nucleus
Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2