Introduction to

The Periodic Table

Why is the Periodic Table important to us?

• The Periodic Table is the most useful tool to a chemist.

• You get to use it on every test.

• It organizes lots of information about all the known elements.

Periodic Table

There are 92 naturally occurring elements arranged by atom size.

Periodic table

The atoms are arranged by size from smallest (H) to largest.

Elements are arranged:

Vertically into Groups

Horizontally Into Periods

We’ll learn later how this organization works.

Hydrogen is the smallest atom.

• Hydrogen has an atomic number of 1.

• Hydrogen belongs to a family of its own.

6

CCARBON

12

Each box on the Periodic Table stands for 1 of the elements.

We can get 4 pieces of information from that box.

The name of the element.

The symbol for the element.

The atomic number for the element.

The atomic mass for the element.

If you have no trouble reading the above information off the Chart, click here to skip the sample problems.

Reading the Periodic Table

Using your Periodic Table, answer these:

What is the chemical symbol for:

• Sulfur?

• Neon?

Answer all, and then click for the answers.

S

Ne

Reading the Table: Symbols

Using your Periodic Table, answer these:

What elements have these chemical symbols:

• Ag?

• Na?

Answer all, and then click for the answers.

Silver

Sodium

Reading the Table: Symbols

Using your Periodic Table, answer these:

What elements have these Atomic Numbers:

• 9?

• 56?

Answer all, and then click for the answers.

Fluorine

Barium

Reading the Table: Atomic Numbers

Let’s Review!

• Every one of these elements is made of the same particles.

• A Hydrogen proton is identical to Gold protons.

• What makes atoms different is the number of protons.

• The Atomic Number gives us the number of protons.

Atomic Number

The Atomic Number gives us the number of protons and electrons.

Use your copy of the Periodic Table for the rest of this activity.

2

1. Helium has an atomic number of 2. How many protons does it have?

2. Sodium has an atomic number of 11. How many electrons does it have?

11

Atomic Number

The Atomic Number gives us the number of protons and electrons.

Let’s try the same problems in reverse.

Phosphorus

1. What element has 15 protons?

2. What element has 92 electrons?

Uranium

Mass Number

The Mass Number is the sum of the number of protons and the number of neutrons.

Mass Number = Protons + Neutrons

35

What is the mass number of an element that has 17 protons and 18 neutrons?

Hint: Use the formula above.

What element is it?

Hint: Look at the Periodic Table.

Chlorine

Mass Number

Many Periodic Tables will use the atomic mass or atomic weight instead of the mass number. I know it sounds confusing, but they are really the same thing as the mass number.

When using these Periodic Tables, you will have to round the atomic mass off to get the mass number.

8

OOXYGEN

15.9994

The atomic mass for oxygen is 15.9994.

We round off 15.9994 to 16. Thus 16 is the mass number of oxygen.

Finding the Number of Neutrons

16

1. How many neutrons does Sulfur have?

2. How many neutrons does Aluminum have?

14

The Mass Number is the sum of the number of protons and the number of neutrons.

Mass Number = Protons + NeutronsNeutrons = Mass Number - Protons

Finding the Number of Neutrons

If you got those two questions right, click here to go to the next slide.

If you had trouble, click elsewhere on the slide to continue.

2. How many neutrons does Aluminum have? 14

Step 1: Find the Atomic Number and Mass.

Atomic Number – 13 Atomic Mass - 27

Step 2: Calculate the number of protons.

Aluminum has 13 protons because that is the Atomic Number.

Step 3: How many neutrons added to 13 would make 27?Step 3: or what is 27 – 13?

The Answer is14 neutrons.

Review Questions BeginReview Question

# 1

Which element has the smallest atom?

• Helium

• Hydrogen

• Oxygen

• Nitrogen

Answer: Hydrogen (H)

Review Question # 2

Which element has an atomic number smaller than Aluminum?

• Uranium

• Iron (Fe)

• Sodium (Na)

• Chlorine

Answer: Sodium (Na)

Review Question # 3

Which element has an atomic number greater than Iron (Fe)?

• Uranium

• Lithium

• Sodium (Na)

• Chlorine

Answer: Uranium

Review Question # 4

Which element has a nucleus with 13 protons?

• Calcium

• Aluminum

• Silicon

• Iron

Answer: Aluminum

Review Question # 5

How many protons, electrons, and neutrons does Hydrogen have?

Answer:

Protons – 1

Electrons – 1

Neutrons - 0

Review Question # 6

How many protons, electrons, and neutrons does Phosphorus have?

Answer:

Protons – 15

Electrons – 15

Neutrons - 16

Review Question # 7

How many protons, electrons, and neutrons does Argon have?

Answer:

Protons – 18

Electrons – 18

Neutrons - 22

Review Question # 8

How many protons, electrons, and neutrons does Uranium have?

Answer:

Protons – 92

Electrons – 92

Neutrons - 146

Go back to the main page,

and

open the

“Constructing an Atom” PowerPoint.