Untitled Lesson

1.1 Inside the atom

06/17/2024

Structure of the atom

A hundred years ago people thought that the atom
looked like a “plum pudding” – a sphere of positive
charge with negatively charged electrons spread
through it…

I did an experiment that proved this idea was wrong.

I called it the “Rutherford Scattering Experiment”

Ernest Rutherford, a New Zealander working in Manchester:

Rutherford’s team:

Ernest Rutherford and his team of scientists performed a famous experiment in
Manchester:

They fired some alpha particles at a piece of thin gold foil (only a few atoms
thick):

If the ‘Plum Pudding’ model of
the atom was correct, the alpha

particles should pass straight
through and only be slightly

deflected.

This did not

happen.

The Apparatus

Expected Plum Pudding results

Actual Experiment Results

Drag and Drop

The value of the electron rest mass is

Placeholder

Drag these tiles and drop them in the correct blank above

9.11 × 10^-31 kg

1.67 × 10^-27 kg

1.67 × 10^-24 kg

9.11 × 10^-28 kg

Multiple Choice

What is the unit for the Planck constant?

• J s

• N m^2 kg^-2

• F m^-1

• H m^-1

Multiple Choice

What is the value of the proton charge/mass ratio?

• 9.58 × 10^7 C kg^-1

• 1.76 × 10^11 C kg^-1

• 1.67 × 10^-27 kg

• 8.31 J K^-1 mol^-1

Multiple Choice

What is the symbol for the molar gas constant?

• R

• N_A

• k

• σ

06/17/2024

The Rutherford Scattering Experiment

Alpha particles
(positive charge)

Thin gold

foil

Some particles passed

through, some were deflected

backwards

Conclusion – atom is made up of a very tiny central nucleus

surrounded by electrons orbiting in shells

Multiple Choice

What is the value of the permeability of free space?

• 4π × 10^-7 H m^-1

• 8.85 × 10^-12 F m^-1

• 6.63 × 10^-34 J s

• 1.60 × 10^-19 C

Rutherford’s conclusions

Observation

Conclusion

Most alpha particles went
straight through the foil.

A few were deflected
through large angles.

A very few were reflected
straight back.

Atoms are mostly space.

The nucleus is very small
compared to the size of
the atom and it contains
most of the mass and all
the positive charge.

Multiple Choice

What is the unit for the Boltzmann constant?

• J K^-1

• W m^-2 K^-4

• m K

• N m^2 kg^-2

Label the helium atom and fill in the table:

P_____

N_____

E_____

{

N_____

Particle

Mass

Charge

Proton
Neutron
Electron

eutron

lectron

roton
ucleus

1

1

1/1840th

+1

none

-1

NOTE - Particles found in the nucleus Protons & Neutrons)
Are called collectively NUCLEONS

Multiple Choice

What is the value of the neutron rest mass?

• 1.67(5) × 10^-27 kg

• 9.11 × 10^-31 kg

• 1.67(3) × 10^-27 kg

• 1.661 × 10^-27 kg

06/17/2024

The structure of the atom

Particle

Relative Mass

Relative
Charge

Proton

1

1

Neutron

1

0

Electron

0

-1

MASS NUMBER = number of protons + number of

neutrons

SYMBOL

PROTON NUMBER = number of protons (obviously)

Multiple Choice

What is the symbol for the permittivity of free space?

• ε_0

• μ_0

• c

• e

06/17/2024

General form

MASS NUMBER = number of protons + number of

neutrons

SYMBOL

PROTON NUMBER = number of protons (obviously)

Note –
•For a neutral atom there are the same number of electrons as protons

(giving an overall charge on the atom as zero)
•The number of neutrons in a particular atom is found by ‘A – Z’

Multiple Choice

What is the overall charge of a neutral atom?

• Positive

• Negative

• Zero

• Depends on the atom

Till now, we have used relative (to proton)
masses. Actual masses of the sub-atomic

particles are on the data sheet

Multiple Choice

What happens to an atom when it becomes an ion?

• It gains or loses protons

• It gains or loses neutrons

• It gains or loses electrons

• It gains or loses both protons and neutrons

Multiple Choice

What is the charge on an electron as given in the data sheet?

• 1.6 x 10^-18 C

• 1.6 x 10^-19 C

• 1.6 x 10^-20 C

• 1.6 x 10^-21 C

Atoms and electron changes

Unlike atoms, ions have an electrical charge because they
contain an unequal number of protons and electrons.

Atoms that lose electrons have more protons
than electrons and so have a positive charge.

They are called positive ions or cations.

Atoms that gain electrons have more electrons

than protons and so have a negative charge. They

are called negative ions or anions.

Multiple Choice

If a carbon-12 atom loses two electrons, what will be the charge of the resulting ion?

• 1.6 x 10^-19 C

• 3.2 x 10^-19 C

• 4.8 x 10^-19 C

• 6.4 x 10^-19 C

Specific Charge

• Applies to charged particles
• Is simply the charge of the particle divided by its mass
• Specific charge = Q / m (data sheet, = e/me for electron or =

e/mp for proton)

• Units = Coulomb per kilogram (Ckg-1)
• Given on data sheet for the Proton and the electron (why not

Neutron?)

• NOTE – Be especially careful when reading any questions on

this – is it asking you for (a) the charge of an Ion, (b)the
specific charge of the ION or (c)the specific charge of the
NUCLEUS

Multiple Choice

How many negative electrons does a carbon-12 ion have after losing two electrons?

• Six

• Four

• Two

• Eight

Multiple Choice

How is the specific charge of an ion found?

• By its mass divided by its charge

• By its charge divided by its mass

• By the number of protons divided by the number of neutrons

• By the number of electrons divided by the number of protons

(a) The Charge of an Ion

• However, an Ion has either gained or lost

electrons

• The charge on an ion will always be a

multiple of the magnitude of the charge
on the electron on the data sheet (= 1.6 x
10-19 C)

• Let’s assume the atom of carbon 12

opposite has lost two electrons to
become an ion

• It now has only four negative electrons

but still six positive protons.

• This means the ion has an unbalanced

positive charge equal to the two electrons
it has lost

ie 2 x (1.6 x 10-19 C) = 3.2 x 10-19 C

A neutral atom has equal numbers
of positive protons and negative
electrons

Therefore, its overall charge is Zero

Multiple Choice

What is the mass number of the nucleus in the diagram shown?

• 6

• 12

• 18

• 24

(b) The Specific Charge of an Ion

• The specific charge of the ion is found

by its charge divided by its mass

• Its charge will be a multiple of the

number of electrons it has lost (as in
the previous slide)

• Its mass will be the mass number of

the nucleus (‘12’ in the diagram
shown ) multiplied by 1.67 x 10-27 kg
(on data sheet as the rounded figure
for the ‘proton (or neutron) rest
mass’)

• NOTE - The mass of the electrons are

relatively insignificant so can be
ignored

Multiple Choice

What is the value of the mass of a proton or neutron used in the calculation of the specific charge?

• 1.67 x 10^-27 kg

• 1.67 x 10^-24 kg

• 1.67 x 10^-30 kg

• 1.67 x 10^-20 kg

Multiple Choice

Why can the mass of electrons be ignored when calculating the specific charge of an ion?

• Because electrons have a positive charge

• Because electrons are not part of the nucleus

• Because the mass of electrons is relatively insignificant

• Because electrons do not affect the charge of the ion

(c) The Specific charge of the Nucleus

•For the specific charge of the nucleus, the electrons can be completely
ignored

•The charge will be the proton number multiplied by 1.6 x 10-19 C (ie
‘magnitude of the charge of the electron’ on the data sheet, which is equal
in magnitude to the charge of the proton)

•The mass will be the mass number multiplied by 1.67 x 10-27 kg

•Thus, The specific charge for the carbon 12 nucleus mentioned earlier would
be: (6 x 1.6 x 10-19 C ) / (12 x 1.67 x 10-27 kg) = 4.8 x 107 C kg-1

Multiple Choice

What is the value of the speed of light in vacuo?

• 3.00 x 10^8 m s^-1

• 4.00 x 10^8 m s^-1

• 3.00 x 10^7 m s^-1

• 4.00 x 10^7 m s^-1

Multiple Choice

What is the symbol for the gravitational constant?

• g

• G

• h

• R

Multiple Choice

What is the unit for the Planck constant?

• J s

• N m^2 kg^-2

• F m^-1

• H m^-1

Multiple Choice

What is the value of the electron rest mass?

• 9.11 x 10^-31 kg

• 1.67 x 10^-27 kg

• 1.60 x 10^-19 C

• 8.85 x 10^-12 F m^-1

Multiple Choice

What is the value of the Avogadro constant?

• 6.02 x 10^23 mol^-1

• 8.31 J K^-1 mol^-1

• 1.38 x 10^-23 J K^-1

• 5.67 x 10^-8 W m^-2 K^-4

Multiple Choice

What is the unit for the permittivity of free space?

• F m^-1

• H m^-1

• N m^2 kg^-2

• J K^-1

Multiple Choice

What is the value of the proton rest mass?

• 1.67(3) x 10^-27 kg

• 1.67(5) x 10^-27 kg

• 9.11 x 10^-31 kg

• 1.60 x 10^-19 C

Multiple Choice

What is the symbol for the Boltzmann constant?

• k

• R

• G

• h

Multiple Choice

What is the value of the gravitational field strength?

• 9.81 N kg^-1

• 9.81 m s^-2

• 6.63 x 10^-34 J s

• 1.38 x 10^-23 J K^-1

Multiple Choice

For the specific charge of the nucleus, which particles can be completely ignored?

• Protons

• Neutrons

• Electrons

• All particles

Multiple Choice

What is the charge of the proton number multiplied by?

• 1.6 x 10^-19 C

• 1.67 x 10^-27 kg

• 1.6 x 10^-27 C

• 1.67 x 10^-19 kg

Multiple Choice

What is the mass of the mass number multiplied by?

• 1.6 x 10^-19 C

• 1.67 x 10^-27 kg

• 1.6 x 10^-27 C

• 1.67 x 10^-19 kg

Multiple Choice

What is the specific charge for the carbon 12 nucleus?

• 4.8 x 10^7 C kg^-1

• 4.8 x 10^6 C kg^-1

• 4.8 x 10^8 C kg^-1

• 4.8 x 10^5 C kg^-1