This document discusses atomic theory and subatomic particles. It defines atoms as building blocks of elements made up of protons, neutrons and electrons. The key subatomic particles are electrons, protons and neutrons, which have specific masses and charges. Atoms are identified by their atomic number and mass number. Isotopes are atoms of the same element with different numbers of neutrons. The document also discusses radioactive decay and the three main types of radiation emitted: alpha, beta and gamma radiation. It describes their properties including mass, charge, penetrating power and ability to ionize. Decay laws regarding changes in nucleon number and proton number during alpha, beta and gamma decay are also summarized.

1. LecturePLUS Timberlake 1
Atomic Theory
 Atoms are building blocks of elements
 Similar atoms in each element
 Different from atoms of other elements
 Two or more different atoms bond in simple ratios to
form compounds

2. LecturePLUS Timberlake 2
Subatomic Particles
Particle Symbol Charge
Mass
Electron e- 1- 1/1840
Proton p+ + 1
Neutron n 0 1
Charge measure in terms of electronic charge: e=1.6x10^-19
Mass is measure in unified atomic mass: units(u)
1 u is 1/12 of the mass of a carbon-12 atom.

3. LecturePLUS Timberlake 3
Location of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cm
nucleus

4. LecturePLUS Timberlake 4
Atomic Number
Counts the number
of
protons
in an atom

5. LecturePLUS Timberlake 5
Atomic Symbols
 Show the mass number and atomic number
 Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11

6. LecturePLUS Timberlake 6
Number of Electrons
 An atom is neutral
 The net charge is zero
 Number of protons = Number of electrons
 Atomic number = Number of electrons

7. LecturePLUS Timberlake 7
Subatomic Particles in Some Atoms
16 31 65
O P Zn
8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n
8 e- 15e- 30 e-

8. LecturePLUS Timberlake 8
Isotopes
 Atoms with the same number of protons, but
different numbers of neutrons.
 Atoms of the same element (same atomic
number) with different mass numbers
Isotopes of chlorine
35Cl 37Cl
17 17
chlorine - 35 chlorine - 37

9. LecturePLUS Timberlake 9
Learning Check
Naturally occurring carbon consists of three isotopes,
12C, 13C, and 14C. State the number of protons,
neutrons, and electrons in each of these carbon atoms.
12C 13C 14C
6 6 6
#p _______ _______ _______
#n _______ _______ _______
#e _______ _______ _______

10. Nuclear Density
• Mass of proton m(p)=1.67 x 10^-27 kg
• Radius of proton r = 0.80 x 10^-15 m
• Find the density=

11. Isotopes
Atoms made of protons, neutrons and electrons.
Neutrons+ Protons: Nucleus
• Electron + Proton # influences-> Chemical Properties
• Protons+ Neutron # influences-> Physical Properties
Isotopes
Atoms with same number of protons but different
number of protons are Isotopes.

12. Radioactivity
• A stable nuclei emits radiations. Radiation was
discovered by Henri Becquerel in 1896. These
radiations are not influenced by any outside
conditions such as temperature or pressure.
• It is a spontaneous process, but it occurs at
fixed intervals. Hence a proportion of sample
decay will occur in that time interval.

13. Three particles present in these
Radiations:
• Alpha, Beta And Gamma
Alpha
Beta
Gamma

14. • We know that nuclei consists of protons and
neutrons, if the balance between these two
types of particles is too far to one side, the
nucleus may emit alpha or B radiations.
• Gamma emitted after alpha or B radiation to
release excess energy.

15. A third conserved quantity
• In radioactive decay, both nucleon number A
and proton number Z are conserved.
• On comparison b/w mass before and after
decay, we witness a decrease in mass.
• This is because energy lost caries mass- recall
E=mc^2, so we witness a net decrease in
energy.

16. Properties of Ionizing radiation
• On moving past atoms, alpha or B collide/rub with
them and this as a result causes to knock or drag away
electrons from an atom.
• This process is called Ionization.
• Now, Energy is lost during ionization.
Size: Motion: Ionization Ability:
• Alpha: more mass &charge | slow | Most
• Beta: lighter | faster | Moderate
• Gamma: no charge | Least

17. Lesson Contents
1. Physical properties of a, b and g
2. Penetrating power of a, b and g
3. N v Z graphs
4. Decay laws

18. Alpha Radiation
Alpha particles contain two protons
and two neutrons

19. Alpha Radiation
a has the same constitution as a
helium nucleus
Alpha particles may be written as
They have a double positive charge
and a mass of 4 u

20. Alpha
• Since most effective ionization therefore,
most energy is lost during travel, hence cover
least distance and in a cloud chamber, most
prominent tracks are formed.

21. Detection of all three:

22. Beta-minus Radiation
Beta-minus particles are electrons

23. Beta-minus Radiation
b- is produced when a neutron decays
Beta-minus particles may be written
as
They have a negative charge and a
mass of 1/1800 u

24. Beta-minus Radiation
b- is produced when a neutron decays
The surplus mass is released as
kinetic energy in the b- and as an
antineutrino
+ Energy

25. Gamma Radiation
Gamma rays are a form of electro-
magnetic radiation

26. Gamma Radiation
g release is often associated with a
or b decay
Gamma rays remove energy from
an unstable nucleus

27. Type of
radiation
emitted &
symbol
Nature of the
radiation
(higher only)
Nuclear
Symbol
(higher only)
Penetrating power, and what will block it
(more dense material, more radiation is
absorbed BUT smaller mass or charge of
particle, more penetrating)
Ionising power - the ability to remove electrons
from atoms to form positive ions
Alpha
a helium nucleus of 2
protons and 2
neutrons, mass = 4,
charge = +2
Low penetration, biggest mass and
charge, stopped by a few cm of air or
thin sheet of paper
Very high ionising power, the biggest mass and
charge of the three radiation's, the biggest
'punch'!
Beta
high kinetic energy
electrons, mass =
1/1850, charge = -1
Moderate penetration, 'middle' values of
charge and mass, most stopped by a few
mm of metals like aluminium
Moderate ionising power, with a smaller mass
and charge than the alpha particle
Gamma
very high frequency
electromagnetic
radiation, mass = 0,
charge = 0
Very highly penetrating, smallest mass
and charge, most stopped by a thick
layer of steel or concrete, but even a few
cm of dense lead doesn't stop all of it!
The lowest ionising power of the three, gamma
radiation carries no electric charge and has
virtually no mass, so not much of a 'punch'
when colliding with an atom

28. Penetrating power

31. Effect of Magnetic Fields

33. Decay laws - alpha
When an isotope emits an a particle
 Its nucleon number decreases by 4
 Its proton number decreases by 2
For example:

34. Decay laws – beta-minus
When an isotope emits a b- particle
 Its nucleon number is unchanged
 Its proton number increases by 1
For example:

35. Decay laws – beta-plus
When an isotope emits a b+ particle
 Its nucleon number is unchanged
 Its proton number decreases by 1
For example:

36. Decay laws
Try writing the nuclear equations for
the decay of these isotopes

37. Decay laws
Answers

38. Decays

39. Randomness and Decay:
Spontaneous:
• Decays not effected by the presence of other
nuclei.
• No chemical reaction, external factors like
pressure and temperature effect the decay.
• Random:
• Impossible to predict the time
• Each nucleus has an equal probability to decay