Early Models of the Atom History of the Atom Standard Atomic Notation Some Intro Songs for your entertainment: The Atom Song:

Early Models of the Atom

History of the AtomStandard Atomic

Notation

Some Intro Songs for your entertainment:

The Atom Song: http://www.youtube.com/watch?v=vUzTQWn-wfE&NR=1 (3 min)

HISTORY OF THE ATOMHISTORY OF THE ATOM

460 BC Democritus develops the idea of atoms

- ancient Greek philosopher

-suggested that matter was made up of

tiny particles called:

- his theory was not accepted for 2000

years

ATOMOSATOMOS

(greek for indivisible)


1808 John Dalton

- working with gases, reconsidered

Democritus’ theory that particles are

indivisible

- Described matter as tiny spheres that were

able to bounce around with perfect elasticity

and called them:ATOMSATOMS

History of the Atom

Dalton’s Atomic Model:1) All matter is made up of atoms, which are

particles too small to see2) Each element has its own kind of atom, with its

own particular mass3) Compounds are created when atoms of different

elements link to form molecules4) Atoms cannot be created, destroyed, or

subdivided in chemical changes

Problem with Dalton’s Theory:

– unable to explain the Electrical nature of matter:

Like charges repelUnlike charges attract

History of the Atom

1879 William Crookes- worked with cathode ray tubes- beam of particles was attracted to a

positive plate- these particles were called:

ELECTRONS

- have a negative charge

History of the Atom

1886 Eugen Goldstein

-most samples of matter are NOT charged

-the atom must contain positively charged particles

-used cathode ray tubes to prove this and they were called:

PROTONS


1898 Joseph John Thompson

- atom had a positive core and electrons

were embedded in this


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

Or

RAISIN BUN MODEL


1910 Ernest Rutherford

- designed an experiment using RADIUM (this element spits out positive ALPHA particles)

- he placed a piece of gold foil in front of

the beam, surrounded by a screen to

detect the path of the particles

- they found that although most of them

passed through, about 1 in 10,000 hit


gold foil

helium nuclei

They found that while most of the particles passed

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

their surprise, some particles bounced straight back.

helium nuclei

Rutherford’s Gold Foil ExperimentRutherford & Bohr (4 min)

http://videos.howstuffworks.com/hsw/25133-icons-of-science-bohr-and-the-structure-of-the-atom-video.htm


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 the

central nucleus. This held the electrons in place by

electrical attraction, so the electrons swarm around the

nucleus.

However, this was not the end of the story.

History of the Atom

1932 Chadwick- Nucleus contains another particle which

has NO charge (neutral) called a:NEUTRON

- This particle and the proton have approximately the same mass, but the electron is very small. It takes 1837 electrons to have the same mass as ONE proton or neutron.


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.

Bohr’s Atom

electrons in orbits

nucleus

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

What do these particles consist of?

ATOMIC STRUCTUREATOMIC STRUCTURE

SubatomicParticle

Location Charge Mass

Protons In nucleus Positive 1

Neutrons In nucleus Neutral 1

Electrons Orbit around nucleus

negative None (1/1837)

STANDARD ATOMIC NOTATIONSTANDARD ATOMIC NOTATION

the number of protons in an atom

the number of protons and neutrons in an atomHeHe

22

44 Mass number

Atomic number

Atomic number = number of electrons = number of protons

mass number – atomic number = number of neutrons


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

• fourth shell assume up to 8

electrons


There are two ways to represent the atomic

structure of an element or compound;

1. Electronic Configuration

2. Bohr-Rutherford Diagrams

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

With electronic configuration, elements are

represented numerically by the number of

electrons in their shells and number of shells. For

example;

N

Nitrogen

7

142 in 1st shell

5 in 2nd shell

configuration = 2 , 5

2 + 5 = 7

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

Write the electronic configuration for the following elements;

Ca O

Cl Si

Na20

40

11

23

8

17

16

35

14

28

B11

5

a) b) c)

d) e) f)

2,8,8,2 2,8,1

2,8,7 2,8,4 2,3

2,6

SUMMARYSUMMARY

1. The Atomic Number of an atom = number of

protons in the nucleus.

2. The Atomic Mass of an atom = number of

Protons + Neutrons in the nucleus.

3. The number of Protons = Number of Electrons.

4. Electrons orbit the nucleus in shells.

5. Each shell can only carry a set number of electrons.

This powerpoint was kindly donated to www.worldofteaching.com

http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.

S.Morris 2006 – outline of this powerpoint

Documents

Early Models of the Atom History of the Atom Standard Atomic Notation Some Intro Songs for your entertainment: The Atom Song: