Compounds

Compounds

Counting Atoms

Compounds

• A compound is a substance that has two or more chemical elements whose atoms are bonded together. These atoms are chemically bonded in specific ways and in detailed proportions, and the substances cannot be readily separated through simple physical means.

Chemical Formulas

• Chemical formulas are used to describe the types of atoms and their number in an element or compound

Goal:

By the end of this lesson you should be able to identify how many atoms of each element are present in a chemical formula by using the subscripts and coefficients.

Subscript

The small 2 at the bottom of the oxygen is a subscript They apply only to the atom to their right, which is oxygen in this case. In this compound there are 2 oxygens.

Subscript

If there is no subscript that means there is 1 atom. There is 1 sulfur atom in this compound.

Subscript

In this compound there is 1 sulfur and 2 oxygens.

There are 3 atoms in this compound.

1 + 2 = 3

Elements

An element is a pure substance which cannot be broken down by chemical means. The periodic table lists the known elements. In this chemical formula there are two elements, sulfur and oxygen.

Multiple Choice

How many Oxygen atoms are in H₂O?

• 1

• 2

• 0

• 4

Multiple Choice

How many Hydrogen atoms are in H₂O?

• 1

• 2

• 0

• 4

Multiple Choice

How many total atoms are in H₂O?

• 1

• 2

• 3

• 4

Multiple Choice

How many elements are in H₂O?

• 1

• 2

• 3

• 4

Multiple Choice

The number of Na's in Na₂CO₃

• 1
• 2
• 3
• 6

Multiple Choice

The number of carbons in Na₂CO₃

• 1

• 2

• 3

• 6

Multiple Choice

The number of oxygens in Na₂CO₃

• 1

• 2

• 3

• 6

Multiple Choice

The total number of atoms in Na₂CO₃

• 1

• 2

• 3

• 6

Multiple Choice

The total number of elements in Na₂CO₃

• 1

• 2

• 3

• 6

Multiple Choice

How many hydrogen atoms are there in:

H₂SO₄

• 6

• 5

• 2

• 3

Multiple Choice

How many sulfur atoms are there in:

H₂SO₄

• 1

• 5

• 2

• 3

Multiple Choice

How many oxygen atoms are there in:

H₂SO₄

• 1

• 5

• 2

• 4

Multiple Choice

How many atoms are there TOTAL in:

H₂SO₄

• 6

• 5

• 7

• 3

Multiple Choice

How many elements are there in:

H₂SO₄

• 6

• 5

• 7

• 3

Brackets

In this example the 4 only applies to the hydrogen.

The 2 outside the bracket applies to everything inside the bracket.

Total Count:

N: 1 x 2 =2

H: 4 x 2 = 8

O : 1

Total: 11 atoms

Multiple Choice

Number of N in (NH₄)₂CrO₄

• 1
• 2
• 8
• 16

Multiple Choice

Number of H in (NH₄)₂CrO₄

• 1

• 2

• 8

• 16

Multiple Choice

Number of Cr in (NH₄)₂CrO₄

• 1

• 2

• 8

• 16

Multiple Choice

Number of O in (NH₄)₂CrO₄

• 1

• 2

• 8

• 4

Coefficients

The big 5 out in front of the compound is called a coefficient. That number applies to the entire compound. Whatever atom counts we have is now multiplied by 5.

Total Count:

N: 1 x 2 x 5 = 10

H: 4 x 2 x 5 = 40

O: 1 x 5 = 5

Total: 55 atoms

Multiple Choice

How many Hydrogen are in 4H₂O?

• 6
• 8
• 2
• 4

Multiple Choice

How many oxygen are in 4H₂O?

• 6

• 8

• 2

• 4

Multiple Choice

How many carbon atom/s are present in the compounds CaCO₃?

• 1
• 2
• 3
• 4

Multiple Choice

How many carbon atom/s are present in the compounds 4CaCO₃?

• 1

• 2

• 3

• 4

Multiple Choice

How many oxygen atom/s are present in the compounds 4CaCO₃?

• 7

• 12

• 3

• 4