1. ATOMIC STRUCTURE
S.MORRIS 2006

2. (greek for indivisible)
HISTORY OF THE ATOM
Democritus develops the idea of atoms
460 BC
he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called
ATOMOS
(greek for indivisible)

3. 384-322BC Aristotle and fellow Greeks
According to him:
According to him everything consisted of 4 elements, fire, water, earth, and air.
His theory was accepted for a long period of time.
Drawback:

4. HISTORY OF THE ATOM ATOMS John Dalton SOLID SHPERE MODEL 1808
Revisited Democritus’s idea
suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them
ATOMS

5. HISTORY OF THE ATOM ELECTRON Joseph John Thompson
PLUM PUDDING OR RAISIN BUN MODEL
1898
Conducted Cathode ray tube experiment
found that atoms could sometimes eject a far smaller negative particle which he called an
ELECTRON

6. PLUM PUDDING / RAISIN BUN
HISTORY OF THE ATOM
1904
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
like plums surrounded by pudding.
PLUM PUDDING / RAISIN BUN
MODEL

7. HISTORY OF THE ATOM Ernest Rutherford 1910 EMPTY SPACE MODEL
Performed the GOLD FOIL EXPERIMENT and discovered
NUCLEUS

8. HISTORY OF THE ATOM Gold foil experiment
helium nuclei
Gold foil experiment
He fired Helium nuclei at a piece of gold foil which was only a few atoms thick.
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.

9. HISTORY OF THE ATOM However, this was not the end of the story.
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.

10. HISTORY OF THE ATOM Niels Bohr ORBIT MODEL / PLANETARY MODEL 1913
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.

11. Bohr’s Atom
electrons in orbits
nucleus

12. HELIUM ATOM + - + - Shell proton neutron electron
What do these particles consist of?

13. 1908 Robert Millikan He was by far the most famous American scientist.
He proved electrons were negatively charged by performing an experiment where he measured effect of electric field on oil droplets.

14. 1920’s Electron Cloud Model
Discovered by Erwin Schrödinger and Werner Heisenberg. They said an atom consists of a dense nucleus and many proton and neutrons and is surrounded by electrons, but they all have different energy levels, and different charges.

15. 1932 James Chadwick James discovered the existence of the neutron.
He found this out because when he was looking at alpha waves(positive charge), bounced off the nucleus, saying there was no charge in the neutron.

16. Atoms
Matter is anything that takes up space and has mass. All matter is made of atoms.
Atoms are the basic building blocks of matter. They make up everything around us; Your desk, the board, your body, everything is made of atoms!
Atoms are too small to see without powerful microscopes.

17. Atomic Structure
There are two basic components in every atom: Electron Cloud Nucleus

18. Subatomic Particles Three subatomic particles make up every atom:
Charge
Location
Proton
Positive (+)
Nucleus or “Core”
Neutron
No Charge (0)
Electron
Negative (-)
Electron Cloud

19. Subatomic Particles Electron Cloud: Electrons orbit the nucleus.
Nucleus or “Core”:
Protons and Neutrons are found in the nucleus.

20. number of electrons = number of protons
ATOMIC STRUCTURE He 2
Atomic number
the number of protons in an atom 4
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons

21. ATOMIC 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

22. ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge 1
neutron
No charge 1
electron
-ve charge
nil

23. 1. Electronic Configuration
ATOMIC STRUCTURE
There are two ways to represent the atomic structure of an element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams

24. ELECTRONIC CONFIGURATION
With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example;
Nitrogen
configuration = 2 , 5 7
2 in 1st shell
5 in 2nd shell N
= 7 14

25. ELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40
2,8,8,2
2,8,1
2,6 17 14 5 Cl Si B d) e) f) 11 35 28
2,8,7
2,8,4
2,3

26. N DOT & CROSS DIAGRAMS Nitrogen
With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X
Nitrogen N 7 X X N X X 14 X X

27. DOT & CROSS DIAGRAMS O Cl
Draw the Dot & Cross diagrams for the following elements; X 8 17 X O Cl a) b) X 35 X 16 X X X X X Cl X X X X X X X O X X X X X X X X X X

28. SUMMARY The Atomic Number of an atom = number of
protons in the nucleus.
The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
The number of Protons = Number of Electrons.
Electrons orbit the nucleus in shells.
Each shell can only carry a set number of electrons.

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