ATOMIC THEORYThe history and structure of the atom

ATOMS

Atoms are the fundamental building block of ordinary matter.

They are smallest identifiable unit of an element.

They are so small you can’t even see them with a microscope.

THE GREEKS

Democritus Proposed elements consist of tiny solid particles

that cannot be subdivided.

THE HISTORY OF THE ATOM

Dalton’s Atomic Theory (1808) Each element is composed of tiny, indestructible

particles called atoms. All atoms of a given element have the same

mass and other properties that distinguish them from the atoms of other elements.

Atoms combine in simple, whole-number ratios for form compounds.

Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms change the way that

they are bound together with other atoms to form a new substance.

THE HISTORY OF THE ATOM

Scientists set out to prove Dalton’s theory Late 1800’s J.J. Thompson’s Cathode Ray

Experiment discovered the electron. The cathode ray tube is a tube with partially

vacuumed air. In the tube there are two plates

one with a positive charge the other with a negative charge

When high voltage wires are attached an electrical charge is produced.

Rays are produced and can be seen when they hit a fluorescent material at the end of the tube.

THE HISTORY OF THE ATOM

THE HISTORY OF THE ATOM

What Thompson found The streams of light traveled in straight lines They were independent of the cathode plate

material used They carried a negative electrical charge.

These negatively charged particles he called Electrons. The mass of these particles was much less than

that of Hydrogen the lightest element. This meant that there were smaller particles than the

atom.

Movie Click on movie link for cathode ray tube.

THOMSON MODEL 1904

Plum pudding model

THE HISTORY OF THE ATOM

Millikan’s Oil Drop Experiment (1909) Found the Charge of the electron Fine droplets of oil were sprayed into a drum with

two electrical plates The drops were allowed to fall through a small

hole into the lower portion of the drum The air was then bombarded with energy

producing electrons The negatively charged drops interacted with the

negatively charged plate at the bottom of the drum As the charge on the plate was varied the drops

slowed, stopped, or reversed. By measuring the voltage on the plate when the drops

were stopped the charge of each electron would be found.

THE HISTORY OF THE ATOM

THE HISTORY OF THE ATOM

Rutherford’s Gold Foil Experiment (1909) Rutherford shot alpha particles at a sheet of gold

foil thinking that the particles would just past through.

He found that some of the particles were deflected .

This lead him to propose that the majority of the mass of the atom and the positive charge of the atom were all in the center of the atom NOT spread throughout. There were large amounts of empty space in the atom.

THE HISTORY OF THE ATOM

RUTHERFORD MODEL, 1911

THE HISTORY OF THE ATOM

Nuclear Theory of the AtomMost of the atom’s mass and all of its

positive charge are contained in a small core called the nucleus.

Most of the volume of the atom is empty space, throughout which tiny, negatively charged electrons are dispersed.

There are as many negatively charged electrons outside the nucleus as there are positively charged particles (named protons) within the nucleus, so that the atom is electrically neutral.

THE HISTORY OF THE ATOM

There was still unaccounted mass from the atom presented in Rutherford’s findings. This mass was explained by James

Chadwick as neutrons. Neutrons are electrically neutral particles that also reside in the nucleus.

THE ATOM

ELECTRON CLOUD MODEL

BEYOND THE SUBATOMIC PARTICLES

Scientists next question was what makes up protons, neutrons, and electrons?

The answer- Quarks! Found by smashing protons together to break

them apart. Using a TEVATRON Six different types.

http://scienceblogs.com/startswithabang/files/2012/07/atom_zoom_b.jpeg

FOLDABLE OF PARTS OF THE ATOM AND THEIR MATHEMATICAL RELATIONSHIPS

0

PROTONS = ELECTRONS

http://www.passmyexams.co.uk/GCSE/physics/what-is-radioactivity-and-structure-of-atom.html

structure-of-atom.html

ATOMIC NUMBER

The number of Protons in an element. Find which number changes by one as you move left to right on the periodic table.

Do any elements have the same atomic number?

If the atomic number ( # of protons )changes then element changes.

MASS NUMBER

Look at your periodic table. Is there another number larger than the atomic number?

This is the mass number. The sum of protons and neutrons in the nucleus. Gives the mass of an atom.

P+ + NO = mass number

ATOMIC MASS NUMBER

DRAW THE NUCLEUS OF OXYGENTHE CORRECT NUMBER OF NEUTRONS AND PROTONS

DRAW THE NUCLEUS OF BERYLLIUM

DRAW THE NUCLEUS OF LITHIUM

http://www.green-planet-solar-energy.com/images/Lithium-7.gif

ISOTOPES: WHAT IS THE SAME AND WHAT IS DIFFERENT FOR THE ATOMS OF CARBON?

http://www.slideshare.net/ulcerd/chemical-structure-structure-of-matter-elements-ions-isotopes

Therefore the atomic mass will be different but the atomic number will be the same ( same element)

BUILD AN ATOM PHET SIMULATION

Go to link under chapter 4 in Phy Sci resources

ELECTRON CLOUD MODEL

Electrons move in a less predictable way Electron cloud is area around nucleus where

electrons are moving Atomic Orbitals – space where an electron is

most likely to be found

4.3 MODERN ATOMIC THEORY

Bohr’s Model of the Atom Better description of electrons Electrons orbit around nucleus in energy levels

like planets 1st Level = holds up to 2 electrons 2nd Level = holds up to 8 electrons 3rd level = holds up to 18 electrons Electrons can move to different energy levels if

atom gains or loses energy

HOW TO DRAW ELECTRONS IN THE FIRST THREE ENERGY LEVELS

18 total we are not counting 1,2nd

8 total in 2nd

2 total

ELECTRONS IN ENERGY SHELLS

ELECTRONS CAN MOVE

Electrons can move when they gain or lose energy.

Therefore we use the electron cloud model to show where electrons maybe located.

ELECTRON CLOUD MODEL

Electrons move in a less predictable way Electron cloud is area around nucleus where

electrons are moving Atomic Orbitals – space where an electron is

most likely to be found

Practice sheet for filling orbits

FLAME TEST DEMO LAB