P4 - Atomic Structure

What is the radius of an atom?

1x10^-10m.

What is the radius of a nucleus?

1x10^-14m.

When might electron arrangements change?

Through absorbing/emitting radiation

Define isotope.

Atoms with the same number of protons (and electrons) but a different number of neutrons

Who designed the plum pudding model

JJ Thomson.

Relative Mass of a proton.

1

Charge of a proton.

+1 (positive)

Relative Mass of a neutron

1

Charge of a neutron

0. (no charge/neutral)

Relative Mass of an electron

near 0 (negligible).

Charge of an electron

-1 (negative)

What maintains the electron's position around the nucleus

Electrostatic forces.

What is activity

The rate at which a source of unstable nuclei decays.

What do Bequerels measure

Activity

What does an alpha particle have in its nucleus?

2 protons 2 neutrons. (Helium)

Relative mass of an alpha particle.

4.

Relative charge of an alpha particle.

+2

Ionising power of an alpha particle

Very easy and strong.

Range in air of alpha particles

~5cm

What are alpha particles stopped by

Paper.

What are beta particles made of

Fast moving electrons.

Relative mass of beta particle

1/2000 (negligible)

Relative charge of a beta particle.

-1

Ionising power of a beta particle

Medium

What stops beta radiation

Aluminium.

What does gamma radiation consist of?

Electromagnetic waves

Where is the majority of mass of an atom concentrated

The nucleus

Which shell of an atom would have the electrons with the most energy

The 1st (closest to the nucleus).

What stops gamma rays

Lead

Atomic number is the same as the

protons and electrons.

What did the plum pudding model suggest?

Electrons were embedded in a ball of positive charge

Who conducted the gold foil experiment?

Rutherford

What was fired at gold foil

A beam of alpha particles.

What was expected to happen in the gold foil experiment

All of the alpha particles to pass straight through the foil

What happened in the gold foil experiment?

Most alpha particles went straight through.

Some were deflected at angles.

Few came right back off the foil

What did the gold foil experiment prove?

Atoms are mainly empty space

The nucleus must be positive as any that hit it repelled

The plum pudding model was wrong.

What was the difference between Bohr and Rutherford's models

Rutherford's shows no clear energy levels or shells

Who discovered the neutron?

James Chadwick.

What would you use to represent alpha decay in an equation

Helium

What would you use to represent beta decay in an equation?

An electron

Why is there no change of element when gamma rays are emitted

Gamma rays are not impacting the nucleus in any way and any excess energy is emitted as photons

Define: Stable Nuclei.

Nuclei with a low amount of nuclear energy so it doesn't need to decay.

Define: Unstable Nuclei.

Nuclei with too much energy they need to decay in order to lose some nuclear energy

Beta ray range in air.

~ 1m.

Count rate after n lives =.

initial count rate / 2^n

Define irradiation.

The exposure to penetrating radiation when all or part of the body is exposed to unshielded sources.

Does irradiation make you radioactive?

No

Define external contamination.

Radioactive material is on skin or clothing

Which type of radiation is worst in external contamination

Gamma because it can penetrate skin and the whole body.

Define internal contamination.

Radioactive material is ingested, swallowed, breathed in or absorbed through open wounds.

Which type of radiation is worst in internal contamination

Alpha because it is the most ionising and will ionise cells faster.

What are the dangers of contamination

Ionising and dividing cells

Permanent.

Fatal.

Why was the gold foil suspended by a vacuum?

Because it guaranteed that all the deflections were from the atoms and foil and not anything else.

Why was gold foil chosen

It can be rolled very thin without breaking and is malleable.

Supermarket fruit can be preserved by exposing them to...

Gamma radiation

Name places background radiation could come from

Cosmic Rays

Medical Uses.

Radon Gas (rocks).

Food and Drink

Nuclear disasters

Nuclear weaponry fall out

Gamma range in air.

infinite

Why do some isotopes decay

They have too many neutrons in their nucleus and need to decay to become stable.

What is radiation?

energy emitted by a decaying nucleus.

What is count rate?

The number of decays recorded each second by a detector

How do you measure count rate

Geiger counter.

What is half life

length of time required for half of the radioactive atoms in a sample to decay

What would the gradient of a half-life graph show?

Activity

What type of nuclear radiation has the greatest penetrating power

Gamma.

Who discovered the electron

JJ Thomson.

Who discovered the nucleus?

Rutherford

What is the Bohr model

Model that suggests that electrons orbit the nucleus of an atom in fixed proportions.

key points of alpha particles.

highly ionising

weakly penetrating.

key points of beta particles

medium ionising

medium penetrating.

key points of gamma particles.

weak ionising

highly penetrating.

What is nuclear fission

The splitting of a large and unstable nucleus

When does nuclear fission occur?

When it absorbs a neutron.

What is emitted in nuclear fission?

What fuels a nuclear power station

Uranium (235)

What length of half life would an unstable nuclei have?

Short half life.

How does nuclear fission start

The Uranium nucleus absorbs a neutron

Describe nuclear fusion.

The joining of 2 or more lighter nuclei to form a heavier nucleus.

What changes in alpha decay?

Mass number decreases by 4, atomic number decreases by 2

What changes in beta decay

no change in mass number, atomic number decreases by 1.

What changes in gamma decay?

Nothing.

Describe beta decay.

A fast moving electron that is emitted as a neutron becomes a proton

Describe gamma radiation

Pure energy with no mass or charge

Gamma symbol.

Y

Define activity

The overall rate of decay of all the isotopes in a sample

1 Becquerel=

1 decay per second.

Half life definition

Time taken for the number of radioactive nuclei in a sample to halve

Is contamination in itself a problem?

No; only when the particles decay

What three things determine how harmful radiation is? (TAW.)

Type (ionising or not?)

Where (you are exposed to it)

Amount (time, distance, radioactivity.)

What type of nuclear fission is uncommon

Spontaneous.

When does an unstable nuclei split into two daughter cells?

When it absorbs a neutron.

What is it called when an unstable nuclei split into two daughter cells?

Nuclear fission

What is produced in nuclear fission

2 or 3 neutrons, large amounts of gamma waves and energy

What is occurring in a nuclear bomb?

Chain reaction.

Name two isotopes that can undergo fission when they absorb a neutron.

Uranium and Plutonium.

Is fission green

Yes - no greenhouse gases emitted

Why does fusion release so much energy

some of the lost mass from the smaller nuclei are converted into energy.

Why is fusion not possible (currently) on earth

It can only happen under extremely high temperatures and pressures.

Which type of radioactivity is used in smoke detectors?

Alpha

Which type of radiation is made up of high energy electrons?

Beta radiation

What does a beta particle consist of?

one electron