Atoms and their structure Labs n Labs are now online is a Google Docs folder n You can view the lab if you lose it (and you can copy and paste the procedure.

Atoms and their structure

Labs Labs are now online is a Google Docs

folder You can view the lab if you lose it (and

you can copy and paste the procedure – so stop whining about having to rewrite it)

You can submit your Labs via Google Docs by sharing them with me ([email protected])

mailto:[email protected]

Another Greek Aristotle - Famous philosopher All substances are made of 4 elements

–Fire - Hot–Air - light–Earth - cool, heavy–Water - wet

If you blend these in different proportions you can get all substances

Who’s Next? Late 1700’s - John Dalton- England. Elements are substances that can’t be

broken down

Dalton’s Atomic Theory1 All matter is made of tiny indivisible

particles called atoms.2 Atoms of the same element are identical,

those of different atoms are different.3 Atoms of different elements combine in

whole number ratios to form compounds.4 Chemical reactions involve the

rearrangement of atoms. No new atoms are created or destroyed.

Law of Definite Proportions Each compound has a specific ratio of

elements. It is a ratio by mass. Water is always 8 grams of oxygen for

each gram of hydrogen.

Parts of Atoms J. J. Thomson - English physicist. 1897 Made a piece of equipment called a

cathode ray tube.– It is a vacuum tube - all the air has

been pumped out.–A limited amount of other gases are

put in

Thomson’s Experiment

Voltage source

+-

Metal Disks

After connecting a battery to the tube, a beam appeared start at the negative end and move to the positive end


Voltage source

+-

Voltage source


He created an electrical charge around the tube and the beam always bent towards the positive

+

-

Voltage source


He determined the beam was made of negative particles

+

-

Thomson’s Experiment Used many different metals and gases The beam was always the same By the amount it bent he could find the

ratio of charge to mass It was the same with every material

Thompson’s Model Found the electron. Couldn’t find

positive particle(for a while).

Said the atom was like plum pudding.

A bunch of positive stuff, with the electrons able to be removed.

Millikan’s Experiment

Atomizer

Microscope

-

+

Oil

Metal Plates


Oil

Atomizer

Microscope

-

+

Oil droplets


X-rays

X-rays give some drops a charge by knocking offelectrons

-


+


They put an electric charge on the plates

++

--


Some drops would hover

++

--


+

+ + + + + + +

- - - - - - -

Some drops would hover


From the mass of the drop and the charge on the plates, he calculated the charge on an electron

++

--

Rutherford’s Experiment Ernest Rutherford English physicist.

(1910) Believed the plum pudding model of the

atom was correct. Wanted to see how big atom are Shot alpha particles at gold foil which can

be made a few atoms thick. Alpha particles - positively charged

particles.

Rutherford’s experiment When the alpha particles hit a florescent

screen, it glows.

Lead block

Uranium

Gold Foil

Flourescent Screen

He Expected The alpha particles to pass through

without changing direction very much.

What he expected

What he got

How he explained it

+

Atom is mostly empty space. Small dense,

positive piece at center.

Alpha particles are deflected by it if they get close enough. (like charges repel)

+

Bohr Model Planetary model Electrons in definite fixed orbits How we currently draw atoms

Wave-Mechanical Model Most modern model of the atom Gives electrons properties of both

particle and wave Electrons with distinct amounts of

energy moving in orbitals Orbitals = region in which electron is

likely to be located

Modern View The atom is mostly

empty space. Two regions. Nucleus- protons

and neutrons. Electron cloud-

region where you might find an electron.

Atoms and their structure Labs n Labs are now online is a Google Docs folder n You can view the lab if you lose it (and you can copy and paste the procedure.

Documents