1. Aim: What is an atom? DRAW IMAGES DO NOW: Identify X, Y, and Z as
a mixture, compound or element.
DRAW IMAGES

2. The Atom 1) The atom is the basic unit of matter.
2) Each element is composed of atoms that have different number subatomic particles compared to another element

3. Atomic Structure
A) Nucleus
Proton
Neutron
B) Cloud
3) Electron

4. The Three Fundamental Subatomic Particles
Name
Symbol
Charge
Mass (amu)
Mass (g)
Location
Proton p+ 1+
1.007
1.673 x 10-24
Nucleus
Neutron n0
1.009
1.675 x 10-24
electron e- 1-
5.486 x 10-28
9.109 x 10-28
Outside nucleus

5. Nucleus 1) Contains most of the mass of the atom; very dense
2) Has a positive charge (nuclear charge)

6. Proton Has a positive charge Atomic # = # of protons only
Atomic mass or mass # is both neutron and proton
The number of protons is called the nuclear charge

7. Proton cont. In a neutral atom, the # of electrons = # of protons
The protons “hold the electrons in the atoms”
The # of protons in an atom is specific to only that element; # of protons determines type of element

8. Neutron Has no charge; neutral
Has a mass of 1 atomic mass unit; the neutrons along with the protons make up most of the mass of the atom.

9. Sample Problems
1. Lithium has 3 protons and 4 neutron. What is the mass number?
Mass # = # of protons + # of neutrons
Mass # = 3 + 4
Mass # = 7
2. An atom has a mass number of 9 and has 5 neutrons. How many protons does it have?
9 = # of protons + 5
# of protons = 4