Counting Atoms in Chemical Formulas

Counting Atoms

Coefficient vs Subscript

• Coefficient: Numbers in front of a formula which gives the total number of compounds.

• Subscripts: The small number to the bottom right of an element, which tells the number of atoms of the element immediately before it.

Multiple Choice

What is the Coefficient?

• 4

• 3

• 1

• 0

Multiple Choice

What is the subscript of Nitrogen?

• 4

• 3

• 1

• 0

Counting Atoms

• The Coefficient should be multiplied by the subscript of each element.

• The Coefficient is applied to all the elements in the compound behind the coefficient

• The subscript can only be applied to the element directly in front of it.

• * Remember if there is no number written in the subscript position it is counted as 1 atom*

Multiple Choice

How many Carbon are in the compound?

• 4

• 5

• 20

• 9

Multiple Choice

How many Bromine atoms are there in the compound?

• 4

• 7

• 12

• 6

Multiple Choice

How many Phosphorous atoms are there in the compound?

• 2

• 3

• 5

• 6

Counting Atoms: Formulas with parenthesis

• The subscript on the outside of the parenthesis applies to everything within the parenthesis.

• Multiple any subscript on the inside of the parenthesis by the subscript outside the parenthesis

• multiply all numbers by the coefficient for a total number of atoms

Multiple Choice

How many Hydrogen atoms are in the molecule?

• 3

• 4

• 12

• 1

Multiple Choice

How many Strontium atoms are in the compound?

• 6

• 2

• 3

• 5

Multiple Choice

How many atoms of oxygen are in the compound?

• 3

• 4

• 1

• 12

Multiple Choice

How many Phosphorous atoms are in the molecule?

• 2

• 4

• 1

• 8

Multiple Choice

How many Oxygen atoms are in the compound?

• 8

• 4

• 16

• 6

Multiple Choice

How many atoms of Hydrogen are in H₂O

• 1

• 2

• 3

• more than 3

Multiple Choice

How many different elements are present in H₂COCH₂

• 5

• 4

• 3

• 2

Multiple Choice

Calculate the number of Oxygen atoms in Al(OH)₃

• 1

• 2

• 3

• 4

Multiple Choice

Coefficients in chemical formulas...

• Multiply just the first atom

• Add to the subscripts at the end of the molecule

• Multiply elements without subscripts

• Multiply EVERYTHING!

Multiple Choice

C₃H₅(NO₃)₃

• C = 3, H = 5, N = 3, O = 9

• C = 3, H = 5, N = 1, O = 9

• C = 9, H = 15, N = 3, O = 9

• C = 9, H = 15, N = 1, O = 3

Multiple Choice

How many Magnesium are in 10MgCl₂?

• 10
• 5
• 20

Multiple Choice

How many O's are in Al₂(SO₄)₃

• 4
• 12
• 7
• 24

Multiple Choice

How many atoms are there TOTAL in:
H₂SO₄

• 6
• 5
• 7
• 3

Multiple Choice

How many Sodium (Na) are in 6NaCl?

• 1
• 12
• 6

Multiple Choice

Number of N in (NH₄)₂CrO₄

• 1
• 2
• 8
• 16

Multiple Choice

How many CARBONs are in this formula?

• 1

• 4

• 8

• 12

Multiple Choice

How many total POTASSIUM atoms are in this formula?

• 8

• 2

• 4

• 12