1. Atomic Theory

2. Atoms Matter is made of atoms
Atoms are the basic building block of matter

3. History of the Atom 400 BC Democritus
THE ATOM IS AN INDIVISIBLE PARTICLE
the atom is the smallest particle of matter
1808 Dalton
THE SOLID SPHERE MODEL
atoms are solid , indestructible spheres (like billiard balls)
1897 J.J. Thompson
THE RAISIN BUN MODEL
atoms are solid spheres made up of solid positive mass with tiny negative particles embedded in the positive

4. History of the Atom 1911 Rutherford THE PLANETARY MODEL
the atom is composed of a positive nucleus and negative electrons which surround the nucleus
atom is mostly empty space
Gold foil experiment

5. The Gold Foil Experiment by Rutherford
Prediction
In accordance to the J.J. Thomson model of an atom, the alpha particles should have passed directly through the gold foil for all instances.
Observation
most of the alpha particles passed straight through the foil, a small percentage of them were deflected at an angles and some were even backscattered.
Conclusion
two conclusions: one, an atom is mostly empty space and scattered electrons and two, an atom must have a positively charged centre that contains most of its mass

6. History of the Atom 1913 Niels Bohr
electrons orbit the nucleus in different energy levels
electrons can move from one level to another by gaining or losing packets of energy
electrons are more stable when they are closer to the nucleus
1932 Sir James Chadwick
the nucleus contains particles called neutrons and positively charge protons

7. History of the Atom

8. Structure of the Atom Consists of sub-atomic particles. protons
neutrons
electrons
Protons and neutrons are located in the nucleus
Electrons orbit the nucleus

9. Determining the number of subatomic particles
Each element has an atomic number and a mass number
Atomic number = no. of protons
= no. of electrons
Mass number = no. of protons + no. of neutrons
Therefore, no. of neutrons = mass number – atomic number

10. Example: How many protons, neutrons and electrons does carbon have?
Atomic number = 6
Mass number = 12
Number of protons: 6
Number of neutrons: 12-6 = 6
Number of electrons: 6

11. Atomic Symbol
An international recognized system that allows anyone to commuicate information about the atom
mass number A E
chemical symbol Z
atomic number

12. Isotopes and ions
Isotope is an atom of an element with a different number of neutrons and hence a different mass number.
An Ion is an atom that has lost or gained electron/s.

13. The Bohr Model
Electrons move around the nucleus in fixed energy levels called shells.
Shells close to the nucleus are lower in energy while shells farther away are high in energy.
Shells are number outwards from the nucleus (1,2,3..) and are also lettered (K,L,M,N...)

14. Number of electrons in shells
Different shells hold different numbers of electrons. The maximum number of electrons that can fit into a shell is 2n2 (n = shell number)
Shell number (n) Representative letter Maximum number of electrons
in this shell (2n2)
1 K X = 2
2 L X = 8
3 M X = 18
4 N X = 32

15. Drawing Atoms Bohr diagram
number of protons and neutrons written in the center
electrons drawn in circular orbits around the nucleus
10 P
10 N

16. Example: Chlorine Atomic number is 17. Mass number is 35.
17 protons and electrons
17 P
18 N
Mass number is 35.
= 18 neutrons

17. Subshells Subshells are energy levels found within shells.
There are four different types of subshells
Named- s, p, d, f .
Subshell energy: s<p<d<f
subshell
Number of electrons s 2 p 6 d 10 f 14

18. Shells and subshells

20. Electron configuration
The way in which electrons are arranged around the nucleus of an atom is called the electron configuration of the atom.

21. Aufbau Principle
Electrons occupy orbitals of lower energy first.

22. Order of electron filling
Electrons fill shells and subshells of lowest energy first.

23. Write the full electronic configuration of:
Aluminum – 13 electrons
Calcium – 20 electrons
Iron – 26 electrons
Bromine – 35 electrons

24. Answers Aluminum – 13 electrons Calcium – 20 electrons
1s22s22p63s23p1
Calcium – 20 electrons
1s22s22p63s23p64s2
Iron – 26 electrons
1s22s22p63s23p64s23d6
Bromine – 35 electrons
1s22s22p63s23p64s23d104p5

25. ShellSubshell Orbital
Orbital is the 3 dimensional space around a nucleus in which electrons are most likely to be found
Each orbital can hold up to 2 electrons.
Timberlake LecturePLUS 2000

26. Orbitals s subshell: spherical 1 orbital-2 electronsz
p subshell: pair of lobes
3 orbital- 6electrons x y
Shape represents electron density (not a path the electron follows)

27. d subshell: double dumpbells 5 orbital-10 electronsx y xy yz xz z2
x2-y2

28. Ground state and excited state
At ground state the electron is at its lowest possible energy level (electrons are as close to the nucleus as possible).
Example: Sodium (Z=11)
Ground state electron configuration: 2, 8, 1

29. Evidence for the Bohr Model
If atoms are given large amounts of energy (heat, light or electricity), the electrons can jump to an orbit further away from the nucleus. The atom is then in an excited state.
Fluorine
Ground state
F: 1s2 2s2 2p5
Exited state
F*: 1s2 2s1 2p5 3s1

30. Evidence for the Bohr Model
When the electrons return to the ground state, they release this energy in the form of light. The light released has a specific wavelength corresponding to the difference between the energy levels.

31. Frequency A
n = 3
Frequency B
n = 2
Frequency C
n = 1

32. Electromagnetic Energy

33. Evidence for the Bohr Model
Emission Spectra are emissions of light from atoms that have been heated or provided with energy.

34. Evidence for the Bohr Model
Emission Spectra are different for each material. Fe
They can be used to determine the identity of an unknown sample of an element.

35. Hydrogen
Helium
Practise
1) Draw 2 Bohr-Rutherford diagrams for lithium; one in the ground state and one in the excited state. Make sure to include the energy put into the system, and energy released.
2) Explain why different elements have different emission line spectrums.

36. Practise
Identify each of the unknown gases based on the emission line spectrums provided. The 4 possibilities are oxygen, hydrogen, helium and neon. A B C D