What do I need to know for the test?

Atomic Theory

Democritus460 BC-created the 1st Atomic Theory of Matter (not

modern atomic theory however)

HIS THEORYMatter is composed of empty space through which

atoms moveAtoms are solid, homogeneous, indestructible, and

indivisibleDifferent kinds of atoms have different sizes and shapesThe differing properties of matter are due to the size,

shape, and movement of atomsChanges in matter result from changes in groupings of

atoms and NOT from changes in the atoms themselves

John Dalton

Dalton revived Democritus’s ideas in the 19th century. Much time has passed.

Dalton’s Model

Father of the Modern Atomic Theory5 parts

Each element is composed of tiny, indestructible particles called atoms

All atoms for a given element have the same mass and properties

Atoms cannot be created, divided into smaller particles, or destroyed

Atoms combine in whole number ratios to form compounds

In a reaction, atoms are separated, combined, and rearranged

John Dalton

J.J. Thompson

J.J. ThomsonHe used a cathode ray tube experiment to

discover electrons. He measured both magnetic and electric fields

on the cathode rays and observed that there was a teeny tiny particle, much smaller than the Hydrogen atom Electron

Plum Pudding ModelNegatively charged electrons are distributed

throughout a uniform positive charge

Plum Pudding Model

Cathode Ray

Robert Millikan

Robert MillikanDiscovered the charge (-1) of an electron by

doing the oil drop experimenthttp://www.suite101.com/content/millikan-oil-drop-

experiment-a124624

Oil Drop

Ernest Rutherford

He was interested in studying how alpha particles (+ charge ) interact with atoms

Rutherford thought that, in his experiments, only a few positively charged alpha particles would slightly deflect and the rest would go straight through.

Using the Gold Foil Experiment he discovered that some of those particles deflected at large angles and even bounced straight back at him.

Ernest Rutherford

That means that the plumb pudding model was wrong and there was a small dense center to an atom called a NUCLEUS!

Which means that the electrons floated around in empty space….so he also discovered the orbital theory of electrons, in other words, electrons orbit the nucleus (small charge) in circular paths

Gold Foil Experiment

Mendeleev’s Periodic Table (Side Note)Mendeleev was the first to put all the known

elements into some sort of arrangement. His periodic table is NOT the periodic table we know today. He arranged the table in order of atomic mass,

NOT number.

Henry Moseley

Arranged the periodic table according to atomic number NOT atomic mass (Mendeleev)This is our periodic table that we use today

Periodic Law-Elements close to one another have similar properties.

Henry Moseley

Niels Bohr

Niels BohrBohr’s Model is based on the light emission

spectrum of Hydrogen…He proposed that a hydrogen atom has only

certain allowable energy levels. (energy is quantized)Lowest energy level is ground stateWhen an electron is excited it moves up to an

excited state

He proposed that electrons can only orbit in certain circular paths (like planets)Each path is a different energy level

Bohr’s Energy Levels

When an electron falls from an excited state to the ground state, light is emitted….

His model explained Hydrogen’s spectrum, but not any other element

Louis De Broglie

Louis went one step further than Bohr…Theorized that all moving particles have wave

like characteristics, even electrons!

Louis De Broglie

Erwin Schrödinger

Went further with the wave/particle theoryDiscovered electron clouds (s, p, d, f)Explains that electrons move like waves and

not in a fixed patterns

Erwin Schrödinger

At any given time, an electron can be found somewhere within its electron cloud. (90% of the time)

James Chadwick

Essentially discovered neutrons (no charge) and how it pairs with protons in a mass called a nucleus

James Chadwick