1. Inside an Atom

3. All matter is made up of one or more elements
Element: substance that cannot be broken down into smaller substances
Examples: Hydrogen, Carbon, Oxygen
Atom: the smallest unit of an element

4. Parts of an Atom Proton – positive charge (+)
Neutron – neutral (no charge)
Electron – negative charge (-)

5. Electrons are moving rapidly in a cloud around the nucleus
Protons and neutrons are found in the nucleus in the center of the atom
Electrons are moving rapidly in a cloud around the nucleus
Different energy levels around the nucleus
Electrons may “hang out” in these levels
Valence electrons – those that are farthest from the nucleus and most loosely held

7. Properties of Atoms
An atom is neutral when it has an equal number of protons (+) and electrons (-).
Sometimes when one atom reacts with another atom, it gains or loses an electron giving it a positive or negative charge
This charged particle is called an ION

8. Properties continued…
If an atom loses an electron (-), it now has a positive charge (cation)
If an atom gains an electron (-), it now has a negative charge (anion)

9. More Properties Atomic Number – number of protons
Identifies and determines the element
Carbon: atomic # 6
Sodium: atomic # 11
Gold: atomic # 79
Atomic mass – average mass of one atom of an element

10. Atomic Mass Unit (amu)
SI unit used to measure the mass of particles in atoms
Protons and Neutrons = 1 amu
Approximately 2000 Electrons = 1 amu
Almost all of an atom’s mass is in the nucleus

11. Isotopes
The number of protons for a certain atom never changes, but sometimes an atom may have different numbers of neutrons
Mass Number – sum of protons and neutrons

12. Hydrogen Isotopes