Inside the Atom
Particle Physics Lesson 1
Homework (Fri
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Ernest Rutherford
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What important
experiment did he direct
in the early 20th Century?
What did Rutherford
conclude from his
analysis of the
observations?
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nd
2
Oct)
Video

In Search of Giants (1 of 15) Atoms and the
Periodic Table
Quick Exercise

Draw a diagram of a lithium atom, labelling as
many parts as you can.
Atoms in a Crystal...
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This is an image of
silicon atoms arranged
on a face of a crystal.
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The image was made
by a Scanning
Tunnelling
Microscope
Draw a lithium atom
This is the layout of a lithium atom, with three protons, three
electrons, and four neutrons. The protons and neutrons are, of
course, found in the nucleus. They are called nucleons. The
electrons are found in shells orbiting the nucleus.
Today’s Objectives

State the charge and mass in SI units and relative
units for the proton, neutron and electron.

Define specific charge and calculate its value for
nuclei and ions.

Interpret nuclide notation including the Proton
number Z and the nucleon number A.
Define what is meant by isotope.

Important Facts
It is important to understand:
 The nucleus is very small compared to the atom,
about 10 000 times smaller. The diameter of an
atom is in the order of 10-10 m, whereas the
diameter of the nucleus in the order of 10-15 m.
 The atom is a very dynamic entity. The diagram
shows a stylised representation; the reality is that
there is absolute bedlam at the atomic level.
Inside the atom…
Property
Electron
Proton
Neutron
Charge
-1e
+1e
0
Mass
9.11 × 10-31 kg 1.67 × 10-27 kg 1.67 × 10-27 kg
Relative Mass 0.0005
1.0000
1.0004
The electron and the proton have the same value of charge, but the
signs are different. We also use a quantity for the charge called
electronic charge unit, e.
1 e = 1.602 × 10-19 C.
The neutron has almost the same mass as the proton.
Quick Quiz
1) How many protons neutrons and electrons are there
in the lithium atom?
2) A carbon atom has 6 protons and 6 neutrons. Draw
out the carbon atom in a similar way to the lithium
atom in the diagram above.
3) What is the total charge of a carbon nucleus?
(a) in electronic charge units
(b) in coulombs
4) What is the total charge of the electrons?
(a) in electronic charge units
(b) in coulombs
Definition of an Isotope

Isotopes are atoms with the same number of
protons and different numbers of neutrons.
Isotope Notation
Different atoms are distinguished by their numbers of
protons and neutrons. We write the symbols using the
following notation:
A is called the nucleon number, or the mass
number. It is the total number of nucleons.
Z is the proton number or the atomic number, which
is the number of protons. The number of protons
determines the element. X is the chemical symbol
Isotope Notation
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We can determine the number of neutrons simply by
subtracting the proton number from the nucleon
number. ( No. of neutrons = A – Z).
Isotopes have the same numbers of protons, but
different numbers of neutrons.
Isotopes have the same physical and chemical
properties.
If the proton number is altered, the element changes.
Some isotopes are radioactive, as the nuclei are
unstable.
Specific Charge

The specific charge of a charged particle is
defined as its charge divided by its mass:charge
specific charge 
mass

Calculate the specific charge for:A hydrogen nucleus (1H).
A uranium nucleus (238U)
The electron.
Doubly ionised 24Mg (mass is 3.98 x 10-26 kg).
1)
2)
3)
4)
Further Question

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


An ion has a specific charge of 1.20 × 107 C kg-1
and a charge of - 3.2 X 10 to the power of
minus 19 C.
Express the charge in e
Calculate the mass?
This is likely to be an ion of which element?
What is the specific charge of the nucleus of this
ion?
What would be the charge of an atom of this
Reactions

Chemical reactions involve the electrons of the outer
shells. Nuclei are not involved in any way, and remain
totally unaltered even in the fiercest chemical
reactions.
Try this out…

Carbon 14 is an isotope of Carbon.
How many protons?
How many neutrons?
How many electrons?

Write out Carbon-14 using the isotope notation.

Carbon 14 is an unstable isotope. It decays so that one of the
neutrons turns into a proton.
Draw the new atom, what is it? Write it out using the isotope
notation.
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Don’t mix up your ‘n’ words!
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Nucleus – the massive positively charge centre
of an atom
Neutron – an uncharged particle found in the
nuclei of most atoms
Nucleon – a proton or a neutron in the nucleus
Nuclide – different types of nucleus of the same
element but with different numbers of nucleons.
Summary