THE ATOM The smallest part of an element that has

properties of that element.

In 1981, a type of microscope called a scanning tunneling microscope (STM) was developed.

Photo courtesy National Institute of Standards and Technology (NIST)

<http://www.howstuffworks.com/framed.htm?

parent=atom.htm&url=http://nist.gov>

STM image of a single zigzag chain of cesium atoms (red) on a gallium-arsenside surface (blue)

Copperatoms

nanotechweb.org/articles/news/3/9/8/1/niststm1

MODEL

A way scientists explain something unknown by relating it to something

that can be seen or understood.

What are some reasons scientists use models?

You have certainly had experience with models in science in your past. Name one of the models you have used in science class.

Model of an atom.

Why is our current understanding of the atom still considered a model or a theory?

Empedocles (49- 432 BC) argued that all matter was composed of four elements: fire, air, water, and earth. The ratio of these four elements affected the properties of the matter.

Atomic Model Timeline

Democritus2500 years agoFirst idea of an atom"atomos" (invisible)

He suggested that atomos were eternal and could not be destroyed.

Democritus theorized that atomos were specific to the material that they made up, meaning that the atomos of stone were unique to stone and different from the atomos of other materials, such as fur.

Democritus

This was a remarkable theory that attempted to explain the whole physical world in terms of a small number of ideas.

Middle Ages, 1200-1600

Goal was to change cheap elements into gold

Philosopher’s Stone

 Alchemy

The philosophers' stone is a legendary alchemical substance, said to be capable of turning base metals, especially lead, into gold; it was also sometimes believed to be an elixir of life, useful for rejuvenation and possibly for achieving immortality .

The Scientific Revolution1600-1700’s

 Copernicus-the Sun  is the center of the   Solar System.

Galileo-advanced telescopes & experimental physics Newton-

Laws of Motion & Gravity

Copernicus

John Dalton

early 1800’s

“Father of theAtomic Theory”

John Dalton

School Teacher from England

19th Century (1807)

He combined the idea of elements with the Greek theory of atoms.

Dalton’s Atomic Theory

All matter is made of atoms

Atoms can’t be created or destroyed

All atoms of one element are the same

Atoms of different elements can combine to form new substances

John Dalton pictured the atom as a hard sphere with the same makeup throughout the entire atom.

William Crookes

English Scientist 1870'sTested Dalton's theory of the atom.

Experimented with an airless glass tube with two metal pieces hooked to a battery.

Cathode ray tube + CRTSame type of mechanism found in tv's and computer monitors

Saw a "beam" of something from the negatively charged cathode to the positively charged anode.

The beam looked like a grennish-yellowish light, but Crookes said it was a beam of particles.

He couldn't prove it!!! (bummmer!)

J. J. Thomson

1897 English physicist

Worked on Crooke's experiments. Use a magnet next to the glass tube.

Proved that the beam was not light...Light can not be bent with a magnet.The beam bent towards the magnet.....Opposite charges attract.Knew that the particles were negatively charged. HOW?

Named the negatively charged particles ELECTRONS.

J J Thomson's model of the atom.

"Plum Pudding Model of the Atom"

Your assignment is to begin filling out the Study Guide from your reading the Atomic Theory Handout from the science site.

Read the material again if needed. Write out rough draft paragraphs of John Dalton, William Crookes, and JJ Thomson's work on the atom and atomic theory.

Use your flash cards Element Test is Monday, Dec 14th!!

Science Work for Dec 1 ......