Counting Atoms and Molecules

What do the subscript (small) numbers tells us in a chemical formula?

• How big the molecule is

• The size of each atom

• How many of each atom we have

• The age of the atoms

A molecule is...

• A substance made up of only one type of atom

• When two or more atoms are chemically bonded together

• Lots of different types of atoms

Tags

NGSS.MS-PS1-1

How many Hydrogen atoms are in H₂O?

• 0

• 1

• 2

• 3

Tags

NGSS.MS-PS1-1

How many atoms are there TOTAL in H₂SO₄ ?

• 6

• 5

• 7

• 3

Tags

NGSS.MS-PS1-1

What is the total number of atoms in an ammonia (NH₃) molecule?

• 1

• 2

• 3

• 4

Answer explanation

An ammonia (NH₃) molecule consists of 1 nitrogen atom and 3 hydrogen atoms. Therefore, the total number of atoms in an NH3 molecule is 1 + 3 = 4, making the correct answer 4.

Tags

NGSS.MS-PS1-1

How many molecules are in this chemical formula?

• 5 molecules

• 4 molecules

• 2 molecules

• 6 molecules

Answer explanation

Remember, the coefficient tells you how many molecules there are, and the subscript tells you how many atoms there are per molecule!

Tags

formulas

How many Nitrogen atoms are in the in H₂C₃O₄N₅?

• 2

• 3

• 4

• 5

Tags

NGSS.MS-PS1-1

How many Aluminum atoms are in Al₂O₃?

• 3

• 2

• 5

• 1

Tags

NGSS.MS-PS1-1

How many atoms are present if there is no subscript following the element symbol?

• 0

• 2

• only 1

• 1 million

Tags

NGSS.MS-PS1-1

What is the correct formula for this compound?

• HO₂

• H₂O

• O₂H

• HOH

Tags

NGSS.MS-PS1-1