Counting Atoms

Counting Atoms

Counting Atoms:

Let's discuss a few terms before we can start counting atoms. Bit first, why do we need to count atoms???

Imagine...

You are the proud owner of a new toy company. Your current main product is matchbox cars. You have to order several parts to put them together. But how do you know how many wheels to get to produce 50,000 cars? How many axles? To do this, you have to know how to calculate the numbers you need.

Chemists:

Scientists need to know how to count atoms to produce different compounds or complete different types of chemical reactions. Just like a toy manufacturer has to calculate the number of wheels, so a chemist has to calculate the appropriate number of atoms for correct measurements.

Multiple Choice

So... why do scientists count atoms?

• They have nothing better to do.

• They use the knowledge to mix chemicals in proper quantities for reactions.

• Because they are the count! Ah Ah Ah!!!

• They want to make toy cars.

Terminology: Element

A chemical that cannot be broken down into another substance

Each unique capital letter represents a different element.

Terminology: Atom

The smallest part of a chemical element

Combining atoms creates molecules.

Terminology: Molecule

Two or more atoms stuck together

Multiple Choice

A chemical that is pure and can't be broken into any other substance

• Element

• Atom

• Molecule

Multiple Choice

Smallest particle you can break a substance into and still be that element

• Element

• Atom

• Molecule

Multiple Choice

Two or more atoms stuck together; can be of the same element or different elements.

• Element

• Atom

• Molecule

Molecular Formulas

• An expression that states the number and type of atoms present in a molecule of a substance.

• H2 tells you there are 2 atoms of hydrogen.

• H2O tells you there are 2 atoms of hydrogen and 1 atom of oxygen.

• There is 1 TYPE of element in H2; Hydrogen. There are 2 types in Water: Hydrogen and oxygen.

Subscripts

• The small numbers after the element’s name

• No subscript means there is only one atom present. (A "1" is not needed- it is redundant.)

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Subscripts + Coefficients

• The big number at the  beginning of this formula is a coefficient

• Involved in counting atoms

• Represents the number of molecules for that compound

• Important when balancing      equations

Subscripts + Coefficients.

This formula means there are 2 H2SO4 molecules.

We know in each molecule there are:

   2 hydrogens

   1 sulfur

   4 oxygens

To find the total number of atoms, multiply each of these atoms by 2.

Total atoms for this formula = 14

Subscripts + Coefficients.

This formula means there are 2 H2SO4 molecules.

We know in each molecule there are:

   2 hydrogens x2 = 4

   1 sulfur x2 = 2

   4 oxygens x2 = 8

To find the total number of atoms, multiply each of these atoms by 2.

Total atoms for this formula = 14

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Parentheses

This formula means aluminum is bonded to a molecule of sulfur and oxygen.  

We know in this molecule there are:

   2 aluminums 

   1 sulfurs

   4 oxygens

To find the total number of atoms, multiply 3 by each element in the parenthesis.

Total atoms for this formula = 17

Parentheses

This formula means aluminum is bonded to a molecule of sulfur and oxygen.  

We know in this molecule there are:

    2 aluminum (not in parentheses!)

1 sulfurs x3 = 3

4 oxygens x3 = 12

To find the total number of atoms, multiply 3 by each element in the parenthesis.

Total atoms for this formula = 17

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