1. Ch. 3 – Atoms: The Building Blocks of Matter
An atom is the smallest matter that can’t be divided into smaller matter.
What is an atom made up of?
Nucleus
Proton – positive charge
Neutron – neutral charge
Electron clouds (energy levels)
Electrons – negative charge
Atom is Greek for indivisible

2. Bohr’s Model Dalton’s Theory Explains the make up of an atom.
Nucleus  Protons & Neutrons
Electron Clouds  Electrons
Bohr’s Model
Show’s the make up of an atom.

3. MASS # - ATOMIC # = NEUTRONS
Atoms of different elements may combine to form chemical compounds.
In chemical reactions atoms are either combined, separated, or rearranged
Atoms cannot be created nor destroyed.
Each element can have more than 1 atom.
Ex. Cl2
MASS # - ATOMIC # = NEUTRONS

4. Atoms of the same element may have different masses
Atoms of the same element may have different masses. These are called isotopes.
Ex. Hydrogen has 3 isotopes  Protium, deuterium, tritium.
What does the atomic number tell you?
Number of protons in each atom of an element.
What does the mass number tell you?
Total number of protons and neutrons in the nucleus of an atom.
If an element has isotopes for that element they are called nuclides.

5. An atomic mass unit is a standard unit used for comparison.
Carbon has exactly 12 atomic mass units (U) and is used as a standard for comparison.
Each element on the periodic table has an average atomic mass.
Why do you suppose it is an average?
Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element.
Ex. Cu  69.17% is Cu – 63; 30.83% is Cu – 65.

6. Mole, Molar Mass, and Avogadro’s number all help describe an element.
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Mole – Roughly the mass of a substance that is has 6.02 x 1023 particles (atoms or molecules).
All of the average atomic masses on the periodic table is equal to 1 mole (mol.).
Ex. B 10.81g = 1 mol.
Ex. Zn 65.39g = 1 mol.

7. Avogadro’s number is 6.02 X 1023 particles.
The number of particles (atoms or molecules) in exactly one mole is always 6.02 X 1023.
Ex. B 10.81g = 6.02 X 1023.
Ex. Zn 65.39g = 6.02 X 1023.
Molar mass – the mass in grams of one mol. Of a pure substance.
Basically the average atomic mass in grams.
Ex. B 10.81g = 1 mol. = 6.02 X 1023.
Ex. Zn 65.39g = 1 mol. = 6.02 X 1023.

8. The molar mass of all elements will always contain the same number of atoms, which is 6.02 X 1023.
Which atoms are heavier?
Do the heavier atoms have more atoms in one mole?
Pg. 90
Sample Problems from pg