1. e- p+ n0 0 amu 1 amu 1 amu Electron proton Neutron
Subatomic Particle
Symbol
Charge
Mass (amu)
Where is it found?
Negative
(-1)
Electron Cloud e-
0 amu
Electron
proton p+
Positive
(+1)
1 amu
Nucleus n0
1 amu
Nucleus
Neutral
(0)
Neutron
Atomic mass unit (AMU)- the SI unit used to express the mass of the particles in an atom.

2. Two regions of an atom: Nucleus Electron cloud
Where most of the mass is found
Has protons and neutrons
Central dense region of an atom
Electron cloud
Possible region where e- can be found around the nucleus

3. More about atoms
All elements are different from each other because of the number of p+, e- and n0 they have.
Elements are said to be “electrically neutral” # of e- = # of p+
If an atom has different numbers of e- and p+ then they are called IONS
Ions – atom with a charge (can be + or - )

4. How to determine # of e-, n0 & p+:
Atomic Number = # of protons
(if an atom, then p+ = e-)
Find atomic number on periodic table.

5. H 1 Hydrogen 1.00794 Atomic Number # of Protons Which then tells us:
ELEMENT SYMBOL
What does the
atomic number tell us
About a typical atom? 1 H
Hydrogen
# of Protons
Which then tells us:
# of electrons
AVERAGE ATOMIC MASS

6. Element
# of protons
# of Neutrons
# of Electrons
Atomic Mass
Atomic number H He Ar 1 1
1.0079 1 2 2 2 2
4.0026 18 22 18 18
39.95