Counting AtomsOctober 21st

Let’s Review!

Atoms are made of protons, neutrons, and electrons

Elements are made of the same kind of atom

The number of protons = the atomic number of the element

Chemical symbols on the periodic table either has:

One capital letter

One capital and one lowercase

It NEVER NEVER NEVER NEVER NEVER NEVER has 2 capitals together. Did I say NEVER? I will try to trick you on your test and so will our friends who make the STAAR.

What is an element?

Element = a pure substance; the same kind of atom

Elements can exist as one atom or hundreds of atoms

All atoms of an element are the SAME no matter what the quantity

Elements are only found on the periodic table.

If it is NOT on the periodic table, it is NOT an element

Examples of elements: Oxygen, Nitrogen, Carbon

Not Elements: air, fire, earth, water (any of your game “stuff”)

If you ever answer air, fire, earth, or water I will make you do text book work until you remember the above point. 70 pages await you if you choose the wrong answer.

Molecules & Compounds

Molecules = more than 1 atom

Can be a molecule of an element

You can have 2 atoms of hydrogen to make a molecule of pure hydrogen H2

It is not one atom, so it is a molecule

It is not a compound because there is only one type of element

Compounds = more than one element

Think “complicated” for compound

Water, H20 is a compound because there are 2 elements (hydrogen and oxygen) in it.

How can you count atoms in molecules and compounds?

Subscripts = add

The small number to the bottom right of the chemical symbol is called the subscript.

Sub = under Script = Writing

To count atoms:

Look at the subscripts

No subscript? Write in the number 1

You may need to add the subscripts depending on what the question is

Let’s Practice: What elements are here?

1. H4

2. H2O

3. CH4

4. NaCl

5. CaCO3

Let’s Practice: How many of each element?

1. H4

2. H2O

3. CH4

4. NaCl

5. CaCO3

Exit Practice: Which elements are present and how many of each element:1.CO2

2.LiCl

3.H2O2

Coefficients and counting atoms

Coefficients = multiplying

It’s the large number in the front; I call it the “Mamba Jamba”

In math, it looks like this: 2x3 The number two is the coefficient and 3 is the superscript

Distributive property (if you don’t know about it yet, get ready….its coming)

In chemistry, you will use the coefficient to multiply all of the subscripts

You distribute the coefficient to all of the elements

Each element gets multiplied by the coefficient

The coefficient tells you how many molecules you have

Doodle this: 3 water moleculesDraw what Mrs. Szymanski does

Wouldn’t it be lame to have to write:

H2O + H2O + H2O

Instead, we write:

3 H2O

You can do it two ways! You’ve got options!!! Its your lucky day.

Way #1: 3 CaCl2 Multiply all elements by 3

Calcium = 3

Chlorine = 6

Total atoms = 6 + 3 = 9

Way #2: 3 CaCl2 Add all of the elements first

Calcium = 1

Chlorine = 2

1 + 2 = 3

Multiple the answer by the coefficient:

3 times 3 = 9

Practice with Coefficients:

1. 3 H4

2. 2 H2O

3. 4 CH4

4. 2 NaCl

5. 5 CaCO3

Exit Ticket:

What is the difference between a subscript and a coefficient?