Counting Atoms Let’s Learn!

Intro: Wednesday Which property are the elements in the periodic table arranged? A. Atomic Number B. Atomic Mass C. Valence Electrons D. Conductivity

Which property are the elements in the periodic table arranged? A. Increasing Atomic Number B. Atomic Mass C. Valence Electrons D. Conductivity

Definitions Atom: the basic building blocks of matter that make up everything Element: a pure substance that cant be broken down Molecule: 2 or more atoms joined

Definitions Subscript: a number written after an element’s symbol. Tells the number of atoms of that element. Coefficient: number in FRONT of an element that tells the number of molecules

COUNT ATOM How to count atoms

2H2O COEFFICIENT SUBSCRIPT

The coefficient gets applied to the ENTIRE formula 2H2O The coefficient gets applied to the ENTIRE formula -this means that there are 2 molecules of water present! -you MULTIPLY this number by every subscript in the formula

2H2O 2MOLECULES!!!!

The subscript only gets applied to the element it follows 2H2O The subscript only gets applied to the element it follows -If there is no subscript present, it is assumed that there is only 1 atom of that element in the molecule.

2H2O 4 2 How many hydrogen atoms are present? How many oxygen atoms are present? 2

The easiest way to count atoms: 1. Write down all of the symbols for all of the elements present in the formula 2. If there is a coefficient, write this number next to each of the symbols 3. Multiply the coefficient by the subscripts of each of the elements present in the formula

Let’s try an example: 4CaCO3

4CaCO3

1. Write down symbols 4CaCO3 Ca C O

Write down the coefficient next to each symbol 4CaCO3 Ca C O 4

Multiply by the subscript 4CaCO3 Ca C O 4 X 1 3

Multiply… 4CaCO3 Ca C O 4 X 1 3 = 4 12

Add totals together to get the total amount of atoms 4CaCO3 Ca C O 4 X 1 3 = 4 12 20 atoms

3CO2

3CO2

2C6H12O6 GLUCOSE

2C6H12O6

6K2SO4

6K2SO4

CaMg(CO3)2

CaMg(CO3)2

3Pb(NO3)2

3Pb(NO3)2