Chemical Formulas

Chemical Formulas

TEKS 8.5D

Chemical Formulas

TEKS 8.5D:

“ Students will recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts”

Chemical Formulas - What?

A chemical formula is a description of the number and kind of atoms found in a molecule of a substance

Can have up to 3 parts:

●Chemical Symbol

●Subscript

●Coefficient

Chemical Formulas - Why?

●Scientists use chemical formulas because they are shorter and more specific than using a common name or compound name

●For example, it is easier for a scientist to say NaCl, than “table
salt” or “sodium chloride”

●Chemical formulas are universally understood, no matter the language of the scientist

Chemical Formulas - Examples

Some chemical formulas you may be familiar with:

H2O (water)

CO2 (carbon dioxide)

HC2H3O2 (acetic acid or vinegar)

NaHCO3 (sodium bicarbonate or baking soda)

NH4 (ammonia)

C6H12O6 (?????)

Chemical Formulas - Explanation

H2O

Symbol for
Hydrogen

Symbol for

Oxygen

Number of hydrogen
atoms (the subscript

number)

Number of oxygen atoms

(no subscript number

means one atom)

Chemical Formulas - How many elements?

●If asked how many elements are in a molecule, remember the correct way to write chemical symbols is with a capital letter followed by a lowercase letter!

●Be careful not to count an element twice if repeated in the formula

Chemical Formulas - How many atoms?

To count the total number of atoms in a formula, count each
symbol without a subscript as one atom and then add together all of the subscript numbers.

HC2H3O2

Chemical Formulas - How many atoms?

How many atoms?

HC2H3O2

Chemical Formulas

HC2H3O2

8 total atoms

● 4 H
● 2 C
● 2 O

Chemical Formulas - Parenthesis

If part of the formula is enclosed in a parenthesis with an outside subscript number to the right of the parenthesis pair, the subscript number should be multiplied by the subscript numbers for each symbol within.

Chemical Formulas - Parenthesis

How many atoms?

CO(NH2)2

Chemical Formulas - Parenthesis

In CO(NH2)2 there are a total of 8 atoms:

●1 Carbon

●1 Oxygen

●2 Nitrogen

●4 Hydrogen

Chemical Formulas - Coefficients

Coefficients - Just like in math, a co-efficient is a number that appears at the beginning of a formula that applies to all elements in the formula.

3 H2O

In this example, the 3 gets applied to both the hydrogen and the oxygen and the numbers are multiplied.

So, there would be 6 total hydrogen atoms and 3 total oxygen atoms

Chemical Formulas - Coefficients

How many atoms?

3 H2O

Chemical Formulas - Coefficients

3 H2O

In this example, the 3 gets applied to both the hydrogen and the oxygen and the numbers are multiplied.

So, there would be 6 total hydrogen atoms and 3 total oxygen atoms for a total of 9 atoms in the molecule

Multiple Choice

How many elements are in asbestos?

H₄Mg₃Si₂O₉

• 4

• 18

• 5

• 20

Multiple Choice

How many total atoms are in H₂O₂

• 2

• 3

• 4

• 5

Multiple Choice

How many elements are in this chemical formula?

$$H_2SO_4$$  

• 1

• 2

• 3

• 4

Multiple Choice

How many atoms of Carbon are in this formula? $$C_{6\ }H_{12}O_6$$  

• 6

• 1

• 12

Multiple Choice

What is the total number of atoms in this formula? $$H_2O_2$$  

• 2

• 4

• 3

Multiple Choice

2H₂ + O₂ ----> 2H₂O What is the product?

• ------>
• 2H₂O
• 2H₂+ O₂

Multiple Choice

2H₂ + O₂ --------> 2H₂O What  are the reactants?

• ----->
• 2H₂O
• 2H₂ +O₂

Multiple Choice

How many O's are in Al₂(SO₄)₃

• 4
• 12
• 7
• 24

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 total atoms are in H₂SO₄

• 7

• 3

• 4

• 6

Multiple Choice

How many total atoms are in

Na₂HCO₃

• 4

• 5

• 6

• 7

Multiple Choice

How many atoms are in

Ca₃(PO₄)₂

• 3

• 10

• 13

• 11