4:1 Notes

Democritus

Greek Philospher Democritus (460B.C.-370B.C.) was among the first to suggest the existence of atoms (from the Greek word "atomos")

Believes atoms were indivisible and indestructible which is incorrect

Dalton's Atomic Theory

All alements are composed of tiny particles called atoms

Atoms of any one element are different from those of another element

Atoms of different element combine in simple whole-number ratios to form chemical compounds

In chemical reactions, atoms are combined, separated, or rearanged - but never changed into atoms of another element.

"Billard Ball" model

He pictures the atom as billard (pool) balls, and thought they were completely solid all the way though

J.J. Thomson

Discovered the electron

He was the first scientist to show the atom was made of even smaller things

He used the Cathode Ray Tube to discover electrons

He discovered electrons because when he passed electricity through the beam, the beam bent up toward the positive side of a magnet

Thomson's "Plum Pudding" Atom Model

It was a spherical cloud of positive charge with random electrons scattered throughout, like plum pudding

Rotherford's Gold Foid Experiment

A radioactive source shoots alpha rays at gold foil. Some rays get reflected while others path through. This happens because the alpha particles sometimes hits the nucleus. He knows that since alpha particles are positively charged, something very small but very solid that is also positively charged must be inside the atoms.

Rutherford's contribution to the atomic theory

The atom is mostly empty space.

The nucleus is a small, dense corse with a positive charge.

Structure of the Atom

Atom - the smallest porticle of an element that can exist alone

-Two regions of an atom

--Nucleus

---Center of atom

---Protons and neutrons

--Electron "cloud

---Area surrounding nucleus containing electrons

Proton - positive charge (+), 1 atomic mass unit (amu); found in the nucleus

-AMU - approximate mass of a proton or a neutron

Neutron - neutral charge (0), 1 amu; found in the nucleus

Electron - negative charge (-), mass is VERY small

Counting atoms

Number of protons in the nucleus

The number of protons determines identity of the element

6 = Atomic number

C = Symbol

12.011 = Atomic mass

Mass number (atomic mass)

number of protons + neutrons

Units are g/mol

Isotopes

-Atoms of the same element with varying number of neutrons

Different isotopes have different mass numbers because the number of neutrons is different