This document discusses the structure of atoms and subatomic particles. It explains that atoms were once thought to be indivisible but are actually made up of subatomic particles, including electrons, protons, and neutrons. Each element is defined by its atomic number, or number of protons, while the mass number refers to the total number of protons and neutrons. Key subatomic particles are electrons, which have a negative charge; protons, which have a positive charge; and neutrons, which have no charge.

1. electron
shell
neutron
proton
nucleus

2. ATOMS AND SUBATOMIC
PARTICLES

3. Atom
• is the fundamental unit of
element.
• Is atom indivisible?
• NO!

4. Structure of Atom
Positively
charged
No charges
Negatively
charged

5. Subatomic
particles
Charge
Mass (g) ~size (m)
Coulumb Charge unit
electron -1.6022 x 10-19 -1 9.10939 x 10-28
Not known
exactly
(~1 x 10-18)
proton +1.6022 x 10-19 +1 1.67262 x 10-24 1 x 10-15
neutron 0 0 1.67493 x 10-24 1 x 10-15

6. • Elements differ in the number of protons, electrons, and neutrons.
• Identity of an element is based on the number of protons equates to the
atomic number.
EXAMPLE:
Atomic number = number of
protons
For neutral atom:
Number of protons = number of electrons
Number of electrons = 11

7. Elements are generally represented by a nuclide symbol:
• Mass number = number of protons + number of neutrons
• Number of neutrons = mass number – atomic number
N = A - Z

8. What is the difference between mass number and atomic number?
ELEMENTS
Na K Mg Al N
Mass number 23 24 14
Atomic Mass
Identify the atomic mass and mass number of the following elements:

9. ELEMENTS
Na K Mg Al N
Mass number 23 39 24 27 14
Atomic Mass 22.9898 39.0983 24.305 26.9815 14.0067