•What is a model?

•Uses familiar ideas to explain unfamiliar facts observed in nature.

•It can be changed if you get new info.

•Evidence you get about an object without actually seeing or touching the object.

•You get a mental picture or a model of the object.

•In the 5th century BC, Democritus believed that matter could be divided into smaller & smaller pieces forever until you got to the smallest possible piece called an atom (uncuttable).

•In 1803, Dalton published his atomic theory from studying weather & the composition of air.

•1) All matter is made of atoms 2) Different elements have different kinds of atoms 3) Compounds are formed by joining atoms of 2 or more elements.

•He discovered the electron & figured it was part of an atom.

•Invented the Plum Pudding Model•The atom was a positively charged ball with lots of negatively charged electrons stuck into it like “plums in pudding.”

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•In 1908, Rutherford discovered the nucleus.

•He stated that the atom was mostly empty space made up of a positively charged nucleus with negative electrons scattered around it.

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• In his experiment, Rutherford fired a stream of alpha particles at a sheet of gold foil and found that:

1. Most of the bullets passed right through the gold sheet without changing course which meant that the gold atoms were made up of empty space.

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2. Some bullets bounced back from the sheet which meant that like charges repel. The alpha particles were positive so the nucleus must then be positively charged.

•Bohr fixed up Rutherford’s theory.

•He stated that electrons orbited the nucleus on definite paths like the planets around the sun.

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•Based on a prediction of where the electrons actually are using math formulas.

•Basic idea of waves.

•Subatomic Particles- particles smaller than an atom

•3 Main Subatomic Particles: Protons, Neutrons, Electrons

Nucleus•The tiny center of atom•99.9% of atom’s weight is the nucleus but it is 100,000 times smaller than the entire atom.

•Like a bee in Yankee Stadium

Protons•Positively Charged particles (+)

•Found in nucleus•Weighs 1 AMU

Neutrons•Neutral particles •Found in nucleus•Weighs 1AMU+

AMU•ATOMIC MASS UNIT•Special unit used to measure the mass of subatomic particles.

•1 proton = 1AMU

Atomic Number•Number of protons in nucleus of atom

•Determines what the element is

•Hydrogen’s Atomic number is 1 = 1 proton

•Carbon’s Atomic Number is 6 = 6 protons

Isotopes•Atoms of same element that have the same number of protons but a different number of neutrons

•C12- C14- difference-2 more neutrons

MASS NUMBER•Sum of protons & neutrons

•distinguishes one isotope from another

•Carbon = Mass# 12 6P + 6N= 12 total.

•Uranium238 146N + 92P = 238 Uranium235

143N + 92P = 235

Atomic Mass •Average mass of all isotopes of that element, usually a decimal located on the bottom of each card.

•Atomic mass of carbon=12.011

Electrons•Number of protons = number of electrons outside nucleus.

•Electron fills cloud. Electrons can be anywhere within the space around nucleus

•Electrons are arranged in energy levels according to how much energy they contain

•Electrons with lowest energy are in level closest to nucleus.

•Electrons with high energy are in levels farther from nucleus.

•Each level can only hold so many electrons: 1st-2 2nd-8 3rd-18 4th-32 5th-18

Chemical makeup•Properties of elements depend on how many electrons are in the various energy levels.

•Bonding: some do/some don’t

•Quarks-3particles that make up protons & neutrons