The Atom

An atom is the smallest particle of matter that still has the same properties of that element.

What is an atom?

Atoms = Building Blocks

Na

Mg

H

1. Protons Positively charged particles inside the nucleus

What makes up an atom?

2. Neutrons Neutrally charged particles inside the nucleus

3. Electrons Negatively charged particles outside the nucleus

Atomic Number: tells the number of protons in the nucleus.

Each element is unique- no two elements have the same number of protons/ atomic number.

Counting Atoms

Mass number: tells the total number of particles in the nucleus.

Mass # = #p + #n

Helpful Information

How to read the Periodic Table

How to write symbols

11

Na

22.989770

Atomic #

Element Symbol

Average Atomic Mass

Mass #

X11Atomic #

Example 1

Element

Atomic #

Mass # # proton

s

# neutro

ns

# electro

ns

symbol

Oxygen 8 16 8 8 8 16

8O

P + N = Mass8 + N = 16N = 8

# electrons = # protons

Example 2

Element

Atomic #

Mass # # proton

s

# neutro

ns

# electro

ns

symbol

3 7 4 3 7

3Li

P + N = Mass3 + N = 7N = 4

If the atomic # is 3, look at the PT to find out which element is 3

The atomic # tells us the # p in the nucleus

3Lithium

Example 3

Element

Atomic #

Mass # # proton

s

# neutro

ns

# electro

ns

symbol

22 18 40

18Ar

P + N = Mass18 + N = 40N = 22

If the symbol is Ar, the element name is Argon

From the symbol, the top number is 40 (mass #)

From the symbol, the bottom number is 18 (atomic #)

The atomic # tells us the # p in the nucleus

184018Argon

# electrons = # protons