1. CHAPTER 15 Introduction to Atoms

2. ATOMS are the building block of all matter.

3. Structure Atoms are made of small particles Consist of
Protons, neutrons and electrons (subatomic particles)
Consist of
nucleus – made of protons (+) and neutrons (neutral) makes up most of the mass of an atom
Electron cloud – contains electrons (-) that move around the nucleus (1/10,000 the size of a proton or neutron)
Same number of protons and electrons, atom has a neutral charge.

4. Draw a picture of an atom in your note. Label the electron cloud.

5. Electron Cloud Sphere shaped region surrounding the nucleus
Low energy electrons = closer to nucleus
Higher energy electrons = farther away.
VALENCE ELECTRONS – electrons far from the nucleus, can move to other atoms
Composes most of the volume of an atom.
Made mainly of “empty space” – absolutely nothing

6. Atoms and Elements
Elements – type of matter that cannot be broken down, consist of one kind of atom
Each atom is unique
has its own 
ATOMIC NUMBER – number of protons in the nucleus (carbon 6, oxygen 8), also tells the number of electrons

7. Atomic mass – average mass of all the atoms of an element
measured in atomic mass units (amu) proton= 1amu, 1 neutron= 1amu
We use the Mass Number – rounded atomic mass

8. ATOM MATH RULES Atomic # = #protons = #electrons
Atomic Mass = #neutron + #protons
Atomic Mass - #protons = #neutrons

9. How many different kinds of atoms are there in the world?
Atoms are like letters, you put them together to make compounds or molecules (words)