1. ATOMIC STRUCTURE

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
ATOMAS
(greek for indivisible)

3. HISTORY OF THE ATOM John Dalton 1808
He said elements consisted of tiny particles called atoms.
He said that the reason an element is pure is because all atoms of an element were identical and they had the same mass.
He also said that the reason elements differed from one another was that atoms of each element were different from one another and had different masses.
Atoms combine to form compounds

4. HISTORY OF THE ATOM ELECTRON Joseph John Thompson 1898
Found that atoms could sometimes eject a far smaller negative particle which he called an
ELECTRON

5. HISTORY OF THE ATOM Ernest Rutherford 1910
Performed the gold foil experiment where he fired Helium nuclei (alpha particles) at a piece of gold foil which was only a few atoms thick.
Assumed that the positively charged particles were bounced back if they approached a
positively charged atomic nucleus head-on (Like charges repel one another)

6. HISTORY OF THE ATOM
gold foil
helium nuclei
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.

7. HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus.
He suggested that nearly all of the mass and all of the positive charge of an atom is contained in a very small "nucleus" at the center of the atom. The negative charges, or electrons, orbit around this nucleus.

8. HISTORY OF THE ATOM Niels Bohr 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.

9. Bohr’s Atom
electrons in orbits
nucleus

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

11. ATOMIC STRUCTURE Particle Charge Mass proton + charge neutron1
1.673x10-27kg
neutron
No charge 1
1.675x10-27kg
electron
- charge
nil

12. He 2 4 ATOMIC STRUCTURE Atomic number (Z)
the number of protons in an atom 4
Atomic mass
the number of protons and
neutrons in an atom

13. Number of electrons determines the charge of an atom
When a NEUTRAL atom
number of electrons = number of protons
Number of electrons determines the charge of an atom
When charged, called an ION!!!
Cation=positive ion (lost electron(s))
Anion=negative ion (gained electron(s))

14. The atomic number tells you the number of PROTONS in one atom of an element.
It also tells you the number of ELECTRONS in a neutral atom of that element.
The atomic number gives the “identity” of an element as well as its location on the periodic table. No two different elements will have the SAME atomic number.

15. How to Find the Number of Neutrons
The mass number is used to calculate the number of NEUTRONS in one atom of an element.
Neutrons = Atomic Mass - Atomic Number.
For example:
Number of neutrons in iron = 56 (atomic mass) - 26 (atomic number) = 30 neutrons

16. Isotopes
An atom that has a different number of neutrons and therefore is an atom that has a different mass
All elements of the same element have the same # of protons (atomic number), but may vary in the number of neutrons
Although isotopes have different masses, they do not differ significantly in their chemical behavior
Example: Hydrogen
Protium (hydrogen-1) Deuterium (hydrogen-2) Tritium (hydrogen-3)

17. Designating Isotopes 168O, 178O, 188O
1. Hyphen notation-Mass number is written after the name of the element
hydrogen-2
Normal carbon is carbon-12. Those atoms have 6 neutrons
Carbon-14 actually has 8 neutrons (2 extra). C-14 is considered an isotope of the element carbon.
2. Nuclear Symbol-Composition of the nucleus using the element's symbol
168O, 178O, 188O

18. How to calculate atomic mass average
(percent 1 * atomic weight) + (percent 2 * atomic weight) + (percent 3 * atomic weight) = atomic mass average
(0.789 * 24) + (0.100 * 25) + (0.111 * 26) = ( ) =
Percent abundance
Atomic mass
78.9%
Mg(24)
10.0%
Mg(25)
11.1%
Mg(26)

19. Formula for Electron Capacity = 2n2
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 18 electrons
4th shell -32 electrons
Formula for Electron Capacity = 2n2
The variable n represents the Principal Quantum Number, the number of the energy level in question.

20. 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

21. 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
Number of electrons in the outermost shell=number of valance electrons N
= 7 14

22. 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

23. 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

24. 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

25. 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.