Chem - Counting atoms and Compounds/Elements Lesson

Chem - Counting atoms and Compounds/Elements Lesson

Remember that ELEMENTS have only ONE type of atom (one element) in them

• Aluminum (Al)

• Gold (Au)

• Nitrogen gas (N₂) - a Molecular Element (one of the 7 diatomic elements)

• Sulfur (S₈) - molecular Sulfur, also a Molecular element

Remember that COMPOUNDS have TWO or MORE different types of atoms (elements) in them

• Aluminum Oxide (Al₂O₃)

• Copper (I) Nitrate (CuNO₃)

• Dihydrogen monoxide = water (H₂O)

• Sulfur dioxide (SO₂)

• Glucose (C₆H₁₂O₆)

Multiple Choice

Which of the following is a compound?

• Co

• O₂

• C

• CO₂

Multiple Choice

Which of the following is an element?

• CO

• O₂

• CH₄

• CO₂

Multiple Choice

Element or Compound?

C₂H₈O

• Element

• Letters

• Numbers

• Compound

Remember that when Counting atoms, you have look at the SUBSCRIPTS on each element, and pay attention to what you are being asked to count

• Aluminum Oxide (Al₂O₃) = 2 Aluminum atoms + 3 Oxygen atoms = 5 TOTAL ATOMS.... 2 different ELEMENTS

• Water (H₂O) = 2 Hydrogen atoms + 1 Oxygen atom = 3 TOTAL ATOMS.... 2 different ELEMENTS

• Glucose (C₆H₁₂O₆) = 6 Carbon atoms + 12 Hydrogen atoms + 6 Oxygen atoms = 24 TOTAL ATOMS.... 3 different ELEMENTS

Multiple Choice

What are the small numbers that go AFTER an element symbol called? Like the 2 in H₂O ?

• subscript
• symbol
• coefficient
• superscript

Multiple Choice

How many Hydrogen atoms are in C₆H₁₂O₆?

• 1

• 6

• 12

• 24

Multiple Choice

How many Total atoms are in C₆H₁₂O₆?

• 1

• 6

• 12

• 24

Multiple Choice

How many elements are in C₆H₁₂O₆?

• 1

• 2

• 3

• 4

Multiple Choice

How many Oxygen are in H₂O?

• 1

• 2

• 0

• 4

If you have a chemical formula with PARENTHESES, you have to MULTIPLY EVERYTHING INSIDE the parentheses by the SUBSCRIPT on the outside of the Parenthesis.

• Copper (II) Nitrate = Cu(NO₃)₂ = Cu(NO₃)(NO₃)

• .........= 1 Copper atom + [2*1 Nitrogen atoms + 2*3 Oxygen atoms]

• .........= 1 Copper atom + [2 Nitrogen atoms + 6 Oxygen atoms]

• ........ = 9 TOTAL atoms

• ........ = 3 Different ELEMENTS

One more chemical formula with PARENTHESES:

• Magnesium Phosphate = Mg₃(PO₄)₂ = Mg₃(PO₄)(PO₄)

• ....= 3 Magnesium atoms + [2*1 Phosphorus atoms + 2*4 Oxygen atoms]

• ....= 3 Magnesium atoms + [2 Phosphorus atoms + 8 Oxygen atoms]

• .... = 13 TOTAL atoms

• .... = 3 Different ELEMENTS

Multiple Choice

How many Aluminum atoms are in Al₂(SO₄)₂

• 1

• 2

• 4

• 8

• 12

Multiple Choice

How many Oxygen atoms are in Al₂(SO₄)₂

• 1

• 2

• 4

• 8

• 12

Multiple Choice

How many Total atoms are in Al₂(SO₄)₂

• 3

• 7

• 9

• 12

• 14

Multiple Choice

Number of N in (NH₄)₂CrO₄

• 1

• 2

• 6

• 8

• 16

Multiple Choice

Number of H in (NH₄)₂CrO₄

• 2

• 4

• 6

• 8

• 16

Multiple Choice

Number of Total atoms in (NH₄)₂CrO₄

• 4

• 10

• 12

• 15

• 20

The NUMBER IN FRONT of the FORMULA, is called the COEFFICIENT.

The COEFFICIENT tells us how many UNITS (molecules or formula units) we have, so MULTIPLY the COEFFICIENT by every element in the formula.

• Al₂O₃ = 2 Aluminum atoms + 3 Oxygen atoms = 5 TOTAL ATOMS

• 4 Al₂O₃ = Al₂O₃ + Al₂O₃ + Al₂O₃ + Al₂O₃

• 4 Al₂O₃ = 4*2 Aluminum atoms + 4*3 Oxygen atoms = 4*5 TOTAL ATOMS

• 4 Al₂O₃ = 8 Aluminum atoms + 12 Oxygen atoms = 20 TOTAL ATOMS

One more example with a COEFFICIENT :

Remember, we MULTIPLY the COEFFICIENT by the formula.

• Mg₃(PO₄)₂ = Mg₃(PO₄)(PO₄)

• Mg₃(PO₄)₂ = 3 Magnesium atoms + 2 Phosphorus atoms + 8 Oxygen atoms = 13 TOTAL ATOMS

• 4 Mg₃(PO₄)₂ = 4*3 Magnesium atoms + 4*2 Phosphorus atoms + 4*8 Oxygen atoms = 4*13 TOTAL ATOMS

• 4 Mg₃(PO₄)₂ = 12 Magnesium atoms + 8 Phosphorus atoms + 32 Oxygen atoms = 52 TOTAL ATOMS

Multiple Choice

What is the number that is in FRONT of a formula called? Like the 3 in 3H₂O

• subscript
• coefficient
• symbol
• superscript

Multiple Choice

How many Hydrogen are in

4H₂O?

• 1

• 2

• 4

• 6

• 8

Multiple Choice

How many Total atoms are in

4H₂O?

• 4

• 6

• 7

• 12

• 16

Multiple Choice

Number of H in

3 (NH₄)₂CrO₄

• 4

• 8

• 12

• 18

• 24

Multiple Choice

Number of O in

3 (NH₄)₂CrO₄

• 1

• 3

• 4

• 12

• 24

Multiple Choice

How many atoms of aluminum are on each side of the following equation:

4Al + 3O₂ ==> 2Al₂ O₃

• 2

• 3

• 4

• 6

• 10

Multiple Choice

How many atoms of oxygen are on each side of the following equation:

4Al + 3O₂ ==> 2Al₂ O₃

• 2

• 3

• 4

• 6

• 10

Multiple Choice

How many total atoms are on each side of the following equation:

4Al + 3O₂ ==> 2Al₂ O₃

• 3

• 4

• 6

• 10

• 12