1. Copy and complete the following statements:
The _____ and _____ are located in the nucleus.
A neutral atom has the same number of _____ and _____.
The mass of an atom is determine by the number of _____ and ____.
The number of _____ in an atom determines the name of the element.

2. The Structure of an Atom
Section 4.2

3. Subatomic Particles
Protons, neutrons and electrons are the three basic subatomic particles.
They can be distinguished by mass, charge, and location in an atom.

4. Protons Located in nucleus Positive Charge (Charge of +1)
Relatively heavy. (Relative mass of 1)

5. Electrons Negative Charge (charge of -1)
Small (relative mass of about 1/2000)
Found in the electron cloud that surrounds the nucleus.

6. Neutron Located in the nucleus. Has no charge
About the same mass as proton (relative mass of 1)

7. Properties of Subatomic Particles
Symbol
Relative
Charge
Mass
(Proton=1)
Actual
(g)
Electron e-
9.11 x 10-28
Proton p+
1.674 x 10-24
Neutron n
1.675 x 10-24

8. Atomic Number
The atomic number of an element equals the number of protons in the nucleus.
Atoms of different elements have different numbers of protons.
Because atoms are neutral, the number of protons in an atom equals the number of electrons.

9. Mass Number
Mass number is the sum of the protons and the neutrons in the nucleus of an atom.
Mass number = Protons + Neutrons
If you know the atomic number and the mass number of an atom you can find the number of neutrons by subtracting.
Number of Neutrons = Mass Number – Atomic Number or
Number of Neutrons = Mass Number – Number of Protons

10. Sketch an atom with an atomic number of 4 and a mass number of 9.
What element is this?

11. Sketch an atom with an atomic number of 6 and a mass number of 13.
What element is this?

12. ELEMENT
ATOMIC
NUMBER
MASS
# of
PROTONS
ELECTRONS
NEUTRONS
Lithium 7 15 17 28 14 53
128 23 50
Copper 35