Counting Atoms in Formulas

​Counting Atoms in Formulas

Define the law and counting atoms in formulas.​

​Law of Conservation of Mass states that in a chemical reaction mass is not created or destroyed.

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This means that the mass you start with (reactants) is the same as the mass you end with (products).

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This law holds true whether it is a chemical or a physical change.​

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Make sure you copy the slide into your journal​

​Title for Notes: Counting Atoms in Formulas

​Elements, Molecules and Compounds

Element: Any substance that cannot be broken down into a simpler substance, its a pure substance made up of only one type of atom.

• Examples: H, Ne, F, B, He, O​

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Molecule: A particle made of two or more atoms bonded together.

• Examples: O₂, H₂O, CO₂, CH₄, Cl₂, H₂, O₃

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Compound: A substance formed by two or more elements​ bonded together in a set ratio.

• Examples: H₂O, CO₂, CH₄, H₂O₂, ​C₆H₁₂O₆

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Multiple Choice

The Law of Conservation of Mass says that matter can neither be __________ or __________.

• created; destroyed

• recycled; renewed

• subtracted; added

• joined; separated

Multiple Choice

Table Salt (NaCl)

• element

• compound

• mixture

Multiple Choice

Elements are made of 

• many types of atoms 

• the periodic table

• one type of atom 

• molecules 

Multiple Choice

Are these molecules also compounds?

• YES

• NO

Multiple Choice

Which of the following cannot be broken down into something simpler?

• a compound

• an element

• a chemical formula

• a mixture

​Subscripts

Subscripts are numbers that are written below and to the right of a chemical symbol. Subscripts tell you the number of atoms of an element.​ If an element does not have a subscript, it is understood that it is 1.

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​Formula	​N
​Elements	​# of Atoms
​N	​ 2
​Total Atoms	​2
​Elements	​1
​Molecules	​1

​Formula	​C
​Elements	​# of Atoms
​C	​6
​H	​12
​O	​6
​Total Atoms	​24
​Elements	​3
​Compounds	​1

​Formula	​H
​Elements	​# of Atoms
​H	​2
​O	​1
​Total Atoms	​3
​Elements	​2
​Compounds	​1

​Coefficients

Coefficients ​are whole numbers that appear in front of a formula that tell how many compounds or elements you have. The distributive property is used - the coefficient is multiplied by the subscript of each element.

​Example:

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​Formula	​4H
​Elements	​#of Atoms
​H: 4x2	​8
​O: 4x1	​4
​Total Atoms	​12
​Elements	​2
​Compounds	​4

​Formula	​3HCO
​Elements	​#of Atoms
​H: 3x1	​3
​C: 3x1	​3
​O: 3x3	​9
​Total Atoms	​15
​Elements	​3
​Compounds	​3

​Formula	​5H
​Elements	​#of Atoms
​H: 5x2	​10
​P: 5x1	​5
​O: 5x4	​20
​Total Atoms	​35
​Elements	​3
​Compounds	​5

Multiple Choice

How many elements are in the compound Fe₂O₃?

• 0

• 1

• 2

• 3

Multiple Choice

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

• 0

• 2

• only 1

• 1 million

Multiple Choice

How many atoms of Iron are in this compound?

• 1

• 2

• 3

• 4

Multiple Choice

How many different elements are present in H₂COCH₂

• 5

• 4

• 3

• 2

Multiple Choice

How many atoms are there TOTAL in H₂SO₄ ?

• 6

• 5

• 7

• 3

Multiple Choice

How many Magnesium atoms are in 10MgCl₂?

• 10

• 5

• 20

Multiple Choice

How many total POTASSIUM atoms are in this formula?

• 8

• 2

• 4

• 12

Multiple Choice

Which is the correct formula for:
 three hydrogen (H)
one sulfur (S)
four oxygen (O)

• H₃SO₄

• HSO₄

• H₄S₃O

• H₂O

Multiple Choice

What does the subscript in a chemical formula tell you?

• How many molecules are present

• How many atoms are present

• How many elements are present

• How many neutrons are present

Multiple Choice

How many atoms of Hydrogen are in this compound?

• 1

• 2

• 3

• 4

Multiple Choice

The red numbers in the image below represent ________

• subscripts

• coefficients

• I don't know, and don't want to try

• None of the answers are correct

Multiple Choice

The blue numbers in the image below represent ________

• I don't know, and don't want to try

• coefficients

• subscripts

• none of the answers are correct

Multiple Choice

How many elements are in this formula?

Li₂O

• 1

• 2

• 3

• 4

Multiple Choice

Which of the following shows the elements with correct numbers of ATOMS for this molecule

H₂SO₄

• H = 2, S = 4, O = 4

• H = 2, S = 1, O = 4

• H = 8, S = 4, O = 4

• H = 2, SO = 4

​Parenthesis in a formula are used to show that atoms in a particular structure are repeated in the molecule.

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Parenthesis in a formula:​

​Formula	Al
​Elements	​#of Atoms
​Al: 1x2	​2
​S: 1x1x3	​3
​O: 1x4x3	​12
​Total Atoms	​17
​Elements	​3
​Compounds	​1

​Formula	5(NH
​Elements	​#of Atoms
​N: 5x1x2	​10
​H: 5x4x2	​40
​O: 5x1	​5
​Total Atoms	​55
​Elements	​3
​Compounds	​5

​Formula	2Ca
​Elements	​#of Atoms
​Ca: 2x3	​6
​P: 2x1x2	​4
​O: 2x4x2	​16
​Total Atoms	​26
​Elements	​3
​Compounds	​2

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 O's are in Al₂(SO₄)₃

• 4

• 12

• 7

• 24

Multiple Choice

How many atoms of oxygen(O) are in

3Fe₂O₃

• 6

• 9

• 1

• 3

Multiple Choice

What are the 3 particles that make-up the atom?

• protons, neutrons, and isotopes

• neutrons, isotopes, and electrons

• positives, negatives, and electrons

• protons, neutrons, and electrons

Multiple Choice

Which of the following chemical formulas represents a compound? 

• C₃

• O₂

• CH₃CHO

• H₂

Multiple Choice

A ______ is a number written in front of a chemical formula.

• Coefficient

• Subscript

• Exponent

• Coordinator