1. Introduction to Atoms

2. What are atoms?
An atom is the smallest particle into which an element can be divided and still be the same substance.

3. History of the Atom

4. History
Democritus – first person to use the word atom, comes from the Greek word atoma, means “indivisible”
John Dalton came up with the atomic theory
JJ Thomson did experiments using a cathode ray tube, came up with model that included positive and negative charges
Ernest Rutherford did the Gold Foil experiment, which changed the model to a positive nucleus surrounded by electrons
Niels Bohr determined that electrons move in specific distances from the nucleus based on how much energy they have

5. Atomic theory The atomic theory states 5 things:
All matter is made up of atoms
Atoms are neither created nor destroyed in chemical reactions (Law of conservation of mass)
Atoms of different elements combine in whole-number ratios
Each element is made of a different kind of atom
The atoms of different elements have different mass and properties

6. Parts of an atom
Protons – positively charged particles found in all atoms
Neutrons – particles found in all atoms that do NOT have a charge (neutral charge)
Electrons – negatively charged particles found in all atoms

8. Nucleus
Center of the atom that is extremely dense, positively charged region that contains BOTH protons and neutrons
Protons and neutrons = mass number

9. Electron clouds
Regions inside the atom, located outside surrounding the nucleus with negatively charged particles (electrons)
Bohr proposed that electrons move in paths at certain distances around the nucleus = BOHR MODEL

11. Next time – Atoms and the periodic table

12. Atomic mass unit (amu)
The SI unit used to express the masses of the particles of an element
Each proton has a mass of 1 amu
Each neutron has a mass of 1 amu
Electrons are so small that they have a mass unit of almost zero

13. Atomic number How can you tell which elements these atoms represent?
Atomic number – number of protons in the nucleus of an atom

14. Isotopes Are all atoms of an element the same? NO
Isotopes – atoms that have the same number of protons but different number of neutrons
Each element has a limited number of isotopes that occur naturally

15. Mass number Protons + neutrons = mass number
Used to determine if an element is an isotope

16. Atomic mass
Weighted average of masses of all the naturally occurring isotopes of an element
MATH BREAK – pg 316 , do in your science journal

17. Physical Property Color, odor, mass, volume Physical Properties
Definition
Example
Thermal conductivity
The ability to transfer thermal energy from one area to another
Plastic foam is a poor conductor, so hot chocolate in a plastic foam cup will not burn your hand.
State
The physical form in which a substance exists , such as a solid, liquid, or gas
Ice is water in its solid state.
Malleability
The ability to be pounded into thin sheets
Aluminum can be rolled or pounded into sheets to make foil.
Ductility
The ability to be drawn or pulled in a wire
Copper is often used to make wiring.
Solubility
The ability to dissolve in another substance
Sugar dissolves in water.
Density
Mass per unit volume
Lead is used to make sinkers for fishing line because lead is more dense than water.

18. Physical vs. Chemical Properties
Substance
Physical property
Chemical property
Helium
Less dense than air
nonflammable
Wood
Grainy texture
flammable
Baking soda
White powder
Reacts with vinegar to produce bubbles
Powdered sugar
Does not react with vinegar
Rubbinmg alcohol
Clear liquid
Red food coloring
Red color
Reacts with bleach and loses color
Iron
malleable
Reacts with oxygen
Tin