S.MORRIS 2006. Papercuts This piece of paper is 28cm x 2.5 cm How many times would you have to cut this piece of paper to be the same width as an atom?

S.MORRIS 2006

Papercuts

• This piece of paper is 28cm x 2.5 cm• How many times would you have to cut this

piece of paper to be the same width as an atom?• Once you cut a piece in half, you have to discard

one half and then use the other piece to continue this process

• Repeat this until you can no longer cut the paper.

• How many cuts did you make?

Width of an Atom

• The average width of an atom is 130 picometers

• 1pm = 10-12 m = 1/1 000 000 000 000 of a meter

•  1 millimeter = 1 000 000 000 picometers

• That’s teeny tiny !

Who are these dead dudes?

How did they contribute to our

present day model of an atom?

HISTORY OF THE ATOMHISTORY OF THE ATOM

460 BC Democritus develops the idea of atoms

he pounded up materials in his pestle and

mortar until he had reduced them to

smaller and smaller particles which he

called

ATOMAATOMA

(greek for indivisible)

This theory was ignored and forgotten for more than 2000 years!

HISTORY OF THE ATOMHISTORY OF THE ATOM

1808 John Dalton

suggested that all matter was made up of

tiny spheres that were able to bounce

around with perfect elasticity and called

them

ATOMSATOMS

Dalton’s Theory 1. all elements are composed of atoms.

2. atoms of the same element are exactly alike.

3. atoms of different elements are different.

4. compounds are formed by the joining of atoms of two or more elements.

Fill this in on your Notes sheet

Dalton’s Atom

HISTORY OF THE ATOMHISTORY OF THE ATOM

1898 Joseph John Thompson

found that atoms could sometimes eject a

far smaller negative particle which he

called an

ELECTRONELECTRON

HISTORY OF THE ATOMHISTORY OF THE ATOM

Thompson develops the idea that an atom was made up of

electrons scattered unevenly within an elastic sphere

surrounded by a soup of positive charge to balance the

electron's charge

1904

like plums surrounded by pudding.

PLUM PUDDING

MODEL

HISTORY OF THE ATOMHISTORY OF THE ATOM

1910 Ernest Rutherford

oversaw Geiger and Marsden carrying out

his famous experiment.

they fired Helium nuclei at a piece of gold

foil which was only a few atoms thick.

they found that although most of them

passed through. About 1 in 10,000 hit

HISTORY OF THE ATOMHISTORY OF THE ATOM

gold foil

helium nuclei

They found that while most of the helium nuclei passed

through the foil, a small number were deflected and, to

their surprise, some helium nuclei bounced straight back.

helium nuclei

HISTORY OF THE ATOMHISTORY OF THE ATOM

Rutherford’s new evidence allowed him to propose a

more detailed model with a central nucleus.

He suggested that the positive charge was all in a

central nucleus. With this holding the electrons in place

by electrical attraction

However, this was not the end of the story.

HISTORY OF THE ATOMHISTORY OF THE ATOM

1913 Niels Bohr

studied under Rutherford at the Victoria

University in Manchester.

Bohr refined Rutherford's idea by

adding that the electrons were in

orbits. Rather like planets orbiting the

sun. With each orbit only able to

contain a set number of electrons.

The Bohr model was a modification of the Rutherford model.

Bohr the electrons in certain circular orbits around the nucleus called shells.

Bohr’s Atomic Theory

+

Scientists had learned a lot about the atom, but couldn’t figure out what made it so

heavy. In 1932 James Chadwick solved the mystery by coming up with the idea of neutrons, neutral particles that

live in the nucleus with protons. The new improved Bohr model

includes these particles.

0

Neutrons

Bohr Model of a HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

New Bohr Model

ATOMIC STRUCTUREATOMIC STRUCTURE

Particle

proton

neutron

electron

Charge

+ charge

- charge

No charge

1 amu

1 amunil

Mass

Use your periodic table to help you Use your periodic table to help you find the ATOMIC STRUCTUREfind the ATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

HeHe22

44 Atomic mass

Atomic number

Charge = # of protons + # of electrons

= (+ number) + (- number)

If the number of protons is the same as the number of electrons, what is the charge of the atom?

ATOMIC STRUCTUREATOMIC STRUCTURE

Electrons are arranged in Energy Levels

or Shells around the nucleus of an atom.

• first shell a maximum of 2 electrons

• second shell a maximum of 8

electrons

• third shell a maximum of 8

electrons

NucleusNucleus

11stst shell shell

22ndnd shell shell

33rdrd shell shell

Adapted from http://www.sciencespot.net/Media/atomsfam.pdf

Created by G.Baker www.thesciencequeen.net

So let’s try it….• How to draw a Lithium atom

• First, look at the Periodic Table

• Second, How do you find the number of protons?

• Then determine the number of neutrons• Then determine the number of electrons

3

Li

Lithium

7

Created by G.Baker www.thesciencequeen.net

So let’s try it….

3

Li

Lithium

7

++

++++

Protons = 3

Neutrons = 4

(7-3=4)

--

--

--

Electrons = 3 Electrons = 3

2 in the 12 in the 1stst shell, 1 in the shell, 1 in the 22ndnd shell shell