1. Atomic Structure

3. Relative masses/charges of protons, neutrons and electrons
Sub-atomic particle
Relative Mass
Relative Charge
Proton (p) 1 +1
Neutron (n)
Electron (e)
5 x 10-4 -1

4. Protons
Neutrons
Electrons
Electronic Configuration

5. Isotopes
Isotopes are atoms of the same element with the same ________(same number of protons) but different __________(different no. of neutrons).
Isotope
Protons
Neutrons
Electrons
Pg 57 Test yourself

6. Isotopes react the same way (same chemical properties) N2 + 3H2 2NH3
N D ND3
have different physical properties
has a boiling pt of -2530C whereas
has a boiling pt of -2500C
Chemical properties – the same number and arrangement of
electrons
Why?
Different mass of the 2 hydrogen isotopes will move at different speed.
Physical properties – different masses hence move at
diferent speed

7. Radioactive Isotopes
Many isotopes are radioactive as the nuclei of these atoms break down spontaneously, emitting radiation.
3 different forms of radiation
Gamma radiation : highly penetrating
Alpha radiaton : can be stopped by a few cm of air
Beta radiation : can be stopped by a thin sheet of aluminium.

8. Radioactive Isotopes nuclear power generation
sterilization of surgical instruments in hospitals
crime prevention
finding cracks and stress in metals and
preservation of food

9. Carbon Dating
By measuring the relative isotopic mass of C-14 in a given organic – possible to calculate the age of a living organism from the % of C-14 remaining in the sample. (how decay and half life).

10. The mass spectrometer Positive ions are accelerated
in an electric field.
Atoms/molecules are bombarded by high energy electron.
Atoms are ionised by
knocking one or more
electrons off to give a positive ion.
M(g) + e  M+(g) + 2e
Ions are deflected by
a magnetic field.
The beam of ions is detected electrically

11. Heaviest ions
Lightest ions
Different ions are deflected by the magnetic field by different amounts.
The amount of deflection depends on:
the mass
positive charge on the ion.
Lighter ions are deflected more than heavier ones.
Ions with 2 (or more) positive charges are deflected more than
ones with only 1 positive charge.
The lower the mass/charge (m/z) ratio,
the more the ions are deflected

12. Which ion will deflect the most in a mass spectrometer?

13. The mass spectrometer measures the relative abundance of
different isotopes (atoms) of an element. The output is a
mass spectrum.
The mass spectrum shows that iron has 4 isotopes as follows: Calculate the relative atomic mass of iron.
Pg 61 Test yourself

14. An element has an atomic number of 24
An element has an atomic number of 24. The natural element consists of four isotopes.
The mass spectrum of the element X produced the following peaks of three of its isotopes on the chart recorder.
What is element X classified in the Periodic Table?
Calculate the isotopic mass of the 4th isotope if the relative atomic mass of element X is

15. Bohr Model
In 1913, Neils Bohr proposed that the electrons in atoms are a in orbits of differing energy around the
nucleus (think of planets orbiting around the sun
B used energy levels(shells) to describe orbits of different energy. Energy of an atom is quantized – can have 1 level or another – nothing between them.
n = 1 is closest to the nucleus of the atom and of lowest energy.
When the electron occupies the energy level of lowest energy the atom is said to be in its ground state.
An electron can move from ground state to a higher level energy level by absorbing energy.
After excited, e can return to the ground state by releasing energy it has absorbed.
Sometimes, the energy released by electrons occupies the position of the electromagnetic spectrum (with a range of wavelength) that human detect as visible light. Slight variation in the amount of energy are seen as light bu differing colours.
An atom can have only one ground state. If the electron occupies one of the higher energy levels then the atom is in an excited state. An atom has many excited states.

16. Bohr Model
Electron can gain energy by moving to a higher energy level or
lose energy by moving to lower energy level
Transitions of electrons between two discrete energy levels will produce a line spectrum.
Line spectrum – evidence for electrons being in energy levels (shells).

17. Emission Spectrum (larger value of n) would fall into a
An electron in a higher energy level
(larger value of n) would fall into a
lower energy (stable).
This process would involve a loss of
energy.
To conserve energy, a particle called a
photon carries away the excess
energy in this transition.
The energy of this photon
= difference in the energy levels of the electron transition ( E2 – E1 )
To identify this photon with the light found when atoms emit light,we need to know the frequency of the emitted light.
Energy = h x frequency
h : Planck's constant

18. For a given atom,
there can be many types of transitions from higher to lower energies, and thus many different energies of emitted photons and,
subsequently, many different frequencies of light waves.

19. When electrons return to the first level (n = 1) the series of lines occurs in the ultraviolet region (Lyman series )as this involves the largest energy change.
The visible region (Balmer series )spectrum is formed by electrons dropping back to the n = 2 level and the first series in the infrared (Paschen series) is due to electrons falling to the n = 3 level. The lines in the spetrum converge because the energy levels themselves converge.
Page 56

20. Such series of distinct spectral lines are observed experimentally when a gas such as hydrogen is heated up –
the added heat energy excites the electrons, which subsequently fall into lower energy levels,
emitting photons of various energies and,
thus, light of various frequencies.
The observed frequencies correspond very well to what is predicted in the Bohr model.

21. Line Spectrum
When energy is supplied to individual elements they emit a spectrum which only contains emssions at particular wavelengths.
Each element has its own characteristic spectrum known as a line spectrum.

22. The visible hydrogen spectrum
The spectrum consists of discrete lines and that the lines converges towards the high energy (violet) end of the spectrum.
Energy = h x frequency
Energy = h x speed of light / wavelength
The lines in the spectrum get closer together at higher
frequency / energy
Page 63

23. Continuous Spectrum
White light is made up of all the colours of the spectrum.
When it is passed through a prism, a continuous spectrum of all the colours can be obtained.
A continuous spectrum contains all wavelengths from a band of the electromagnetic spectrum.

24. Electron Arrangements
Electrons in an atom are arranged in energy levels(shells).
Max no. of electrons in each shell = 2n2
Main energy level no. 1 2 3 4 5
Max no. of electrons 8 18 32 50

25. The energy levels are called shells with numbered 1, 2, 3, 4, etc
The energy levels are called shells with numbered 1, 2, 3, 4, etc. (principal quantum numbers, n)
n correspond to the no. of rows (periods) in the PT.
For a given element, electrons are added to the shells as follows:
Up to 2 electrons in shell 1
Up to 8 electrons in shell 2
Up to 18 electrons in shell 3

26. s,p, and d-orbitals

27. Modern Atomic Structure2p 3p 4p 3d 4d 4f
Sublevel designation
n = 1
n = 2
n = 3
n = 4
An orbital for a hydrogen
atom. The intensity of the
dots shows that the electron
spends more time closer to
the nucleus.
The first four principal energy
levels in the hydrogen atom.
Each level is assigned a
principal quantum number n.
The types of orbitals on each
of the first four principal
energy levels.
Hein, Arena, Foundations of College Chemistry, 2000, page 202

28. Energy Level Diagram of a Many-Electron Atom
6s p d f 32
5s p d 18
4s p d
Arbitrary
Energy Scale 18
3s p 8
2s p
Original reference: Pimental, Chemistry An Experimental Science, (CHEM Study), 1969, page 266. 8 1s 2
NUCLEUS
O’Connor, Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 177

29. Atomic no. (electron config.)H 1 He 2 Li 3 Be 4 B 5 C 6 N 7 O 8 F 9 Ne 10 Na 11 Mg 12 Al 13 Si 14 P 15