# The Atom Atomic Number and Mass Number IsotopesPage 1

#### WATCH ALL SLIDES

Slide 1

Chapter 2 Atoms and Elements

The Atom

Atomic Number and Mass Number

Isotopes

Slide 2

## Atomic Theory

Atoms are building blocks of elements

Similar atoms in each element

Different from atoms of other elements

Two or more different atoms bond in simple ratios to form compounds

Slide 3

## Subatomic Particles

Particle Symbol Charge Relative

Mass

Electron e- 1- 0

Proton p+ + 1

Neutron n 0 1

Slide 4

10-13 cm

electrons

protons

neutrons

10-8 cm

nucleus

Slide 5

## Atomic Number

Counts the number

of

protons

in an atom

Slide 6

11

Na

Atomic Number

Symbol

Slide 7

11

Na

11 protons

Sodium

Slide 8

## Learning Check

State the number of protons for atoms of each of the following:

A. Nitrogen

1) 5 protons 2) 7 protons 3) 14 protons

B. Sulfur

1) 32 protons 2) 16 protons 3) 6 protons

C. Barium

1) 137 protons 2) 81 protons 3) 56 protons

Slide 9

## Solution

State the number of protons for atoms of each of the following:

A. Nitrogen

2) 7 protons

B. Sulfur

2) 16 protons

C. Barium

3) 56 protons

Slide 10

## Mass Number

Counts the number

of

protons and neutrons

in an atom

Slide 11

## Atomic Symbols

Show the mass number and atomic number

Give the symbol of the element

mass number

23 Na sodium-23

atomic number 11

Slide 12

## Number of Electrons

An atom is neutral

The net charge is zero

Number of protons = Number of electrons

Atomic number = Number of electrons

Slide 13

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