Physics || The Atom

Question 1

Who Discovered Electrons Could Be Moved From Atoms?

Answer 1

J. J. Thompson in 1897,

He suggested the “plum-pudding” Model where atoms were spheres of positive charge with tiny negative electrons stuck in them like fruit in a plum pudding.

Question 2

1909?

Answer 2

Rutherford and Marsden fried alpha particles at a gold sheet,

They expected the particles to just pass through or defect slightly because of the lump pudding model,

However, they did not, most particles went straight though but others deflected back the way they came.

Question 3

1909 Experiment Came To What Conclusion?

Answer 3

Most of the mass of the atom was concentrated at the centre in a tiny nucleus,

He also realised that most of an atom is just empty space,

Nucleus must have a positive change since it repelled the positive alpha particles,

This led to the creation of the nuclear model of the atom.

Question 4

A Few Years After The Nuclear Model, What Happened?

Answer 4

Niels Bohr tweaked Rutherfords idea by proposing a model where the electrons were in fixed orbits at set distances from the nucleus,

These distances are called energy levels,

Electrons can only exist in these fixed orbits (shells) and not anywhere in between,

This model is known as the Bohr model and is pretty close to our current model.

Question 5

Current Model Of The Atom?

Answer 5

Atom is a positively charged nucleus surrounded by negatively charged electrons,

Nearly all the mass of the atom is in the nucleus where all the protons and neutrons are,

The rest is empty space,

The negative electrons whizz around the outside of the nucleus in fixed orbits called energy levels or shells,

Shells give the atom the overall size,

Atoms are neutral (become ion when it becomes charged so looses or gains an electron).

Question 6

Atoms Join Together To Form?

Answer 6

Molecules.

Question 7

Proton Features?

Answer 7

Mass of 1,

Charge of 1.

Question 8

Neutron Features?

Answer 8

Mass of 1,

Charge of 0.

Question 9

Electron Features?

Answer 9

Mass of 0.0005 (nothing),

Charge of -1.

Question 10

How Do Electrons Move Energy Levels?

Answer 10

Electrons can move to different shells,

This happens when they absorb electromagnetic radiation with the right amount of energy,

It can move up shell or to an empty/partially filled shell,

When this happens, it’s said the electron is excited,

The electron then returns to its original shell and emits all the radiation it had absorbed.

Question 11

How Can You Tell What Radiation Is Emitted From The Atom?

Answer 11

Energy of the atom depended on what energy level the electron moves between,

A higher energy means a higher frequency,

This means visible light is often produced when electrons move between energy levels.

Question 12

Energy Levels Moving Further Out?

Answer 12

As you move further from the nucleus, the energy levels get closer together,

So the difference between two levels next to ea bother gets a lot smaller,

This means that an excited electron falling from the third energy level to the second would release less energy that an excited electron falling from the second the the first,

This means that frequency of the radiation decreases as you get further from the nucleus.

Question 13

Changes Of The Nucleus Releases What?

Answer 13

Changes within the nucleus lead to the production of high energy, high frequency gamma rays.

Question 14

Ionised Atom Means?

Answer 14

It loses an electron,

If an outer electron absorbs radiation with enough energy, it can move so far that it leaves the atom,

It is not a free electron and the atom is said to be ionised,

An ionised atom is positive because it has more protons then electrons,

An atom can lose more than one electron. The more it loses, the greater the positive charge.

Question 15

What Is Nuclear Radiation?

Answer 15

It’s ionising radiation which is any radiation that can knock electrons from the atoms.

Question 16

Isotopes Are?

Answer 16

Different forms of the same element,

Written as “Carbon-14” which shows the mad number (protons + neutrons) is 14,

All elements have isotope but there’s usually only one or two stable ones.

Question 17

Radioactive Decay?

Answer 17

Unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable,

This process is called radioactive decay.

Question 18

Alpha Particles?

Answer 18

Alpha radiation is when an alpha particle is emitted from the nucleus,

An alpha particle (a) consists of two protons and two neutrons (like a helium nucleus),

They don’t penetrate very far into materials,

Stopped quickly,

Only travel a few cm in air,

Absorbed by thin sheet of paper,

They are strongly ionising.

Question 19

Beta-Minus Particle?

Answer 19

Simply a fast moving electron released by the nucleus,

They have virtually no mass and a relieve charge of -1,

Moderately ionising,

Range in the air of a few metres,

Absorbed by sheet of aluminium (5mm thick).

Question 20

Beta-Plus Particle?

Answer 20

B+ is a fast moving positron,

The positron is the antiparticle of the electron,

This just mess it has exactly the same mass but with the opposite effect (positive),

Moderately ionising,

Smaller range than the B- because when they. Hit an electron, the two destroy each other and produce gamma rays - this is called annihilation.

Question 21

Annihilation?

Answer 21

Used in medical imaging,

Positrons have a smaller range than the B- because when they hit an electron, the two destroy each other and produce gamma rays - this is called annihilation.

Question 22

Gamma Rays?

Answer 22

After a nucleus has decayed, it often undergoes nucleus rearrangement and release some energy,

Gamma rays (y) are waves of EM radiation realised by the nucleus that carry away this energy,

They penetrate far into materials without being stopped and travel long distances,

They are weakly ionising because they tend to pass through rather than collide with atomsC

Eventually, they hit something and do damage,

They can be absorbed by thick sheets of lead of metres of concrete.

Question 23

What Do Nuclear Equations Show?

Answer 23

Radiative decay by using element symbols,

They’re written in the form: atom before decay —-> atom after decay + radiation emitted,

The total mass and the atomic numbers must be equal on both sides of the equation.

Question 24

Alpha Equation?

Answer 24

Loses two protons and two neutrons,

Mass number will decrease by 4 and atomic number will decrease by 2.

Question 25

Beta-Minus Equation?

Answer 25

In this decay, a neutron changes to a proton and an electron,

The mass number doesn’t change,

The atomic number increased by one.

Question 26

Positron Equation?

Answer 26

In B+ decay, a proton changes to a neutron and a positron,

The mass number doesn’t change,

The atomic number decreases by 1.

Question 27

Neutron Emission Equation?

Answer 27

When a nucleus emits a neutron,

The mass number decreases by one,

The atomic number stays the same.

Question 28

Gamma Ray Equation?

Answer 28

Gamma rays don’t change the charge or mass so there is no equation,

Gamma rays get rid of excess energy from an atom,

The nucleus goes from an excited state to a more stable state by emitting gamma,

The mass and atomic number stay the same.

Question 29

Radioactive Sources Contain?

Answer 29

Radioactive isotopes that give out radiation from the nuclei of their atoms,

This process is random.

Question 30

How Can You Predict How Many Nuclei Will Decay In A Given Time?

Answer 30

By working out their half-life.

Question 31

Activity Is?

Answer 31

The rate at which a source decays.

Question 32

How Can Activity Be Measured?

Answer 32

Geiger-Muller Tube,

Clicks every time it detects radiation,

The tube can be attached to a counter which displays the number of clicks per second (count rate),

You can also defence radiation by using a photographic film. The more radiation the films exposed to, the darker it becomes.

Question 33

What Is Activity Measured In?

Answer 33

Becquerels (Bq),

1 Bq is one decay per second.

Question 34

How Does Radioactivity Decrease Over Time?

Answer 34

Some isotopes take a few hours to decay whilst some take millions of years,

Activity never reaches zero so we have to use the idea of half life to measure how quickly the activity falls.

Question 35

Half Life Is?

Answer 35

The average time it takes for the number of radiative nuclei in an isotope to half.

Question 36

Short Half Life?

Answer 36

Means the activity falls quickly because the nuclei are very unstable and rapidly decay,

Sources with short half life’s are dangerous because of the high amount of radiation they emit at the start,

However, they quickly become safe.

Question 37

Long Half Life?

Answer 37

Means the activity falls more slowly because most of the nuclei don’t decay for a long time,

The source just sits there and realises small amounts of radiation for a long time,

This can be dangerous because nearby areas are exposed to radiation for millions of years.

Question 38

Measuring Half Life With A Graph?

Answer 38

Plot a graph with activity against time,

Will always be shaped going from top left to bottom right,

The half life is Found from the graph by finding the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis,

So if Activity is 800, half life is 400. So find 400 on the graph and find the time it takes.

Question 39

Background Radiation?

Answer 39

Is a low level radiation that’s around us all the time,

Comes from unstable isotopes which are in the air, food, building materials, rocks,

Comes from cosmic rays which are from the sun,

Comes from human activities such as fall out from nuclear explosions and nuclear waste.

Question 40

Absorbed Radiation Dose?

Answer 40

The amount of radiation your exposed to.

Question 41

Irradiation?

Answer 41

Objects that are exposed to radioactive sources,

Irradiating something does not make it radioactive.

Question 42

How Do We Reduce Irradiation?

Answer 42

Putting things in lead-lined boxes,

Standing behind barriers or being in a different room,

Using remote controlled arms,

Medical staff who work with radiation wear photographic film badges to monitor their exposure.

Question 43

Contamination?

Answer 43

When unwanted radioactive atoms get onto an object,

These contaminating atoms might then decay which releases radiation which could cause you harm,

Contamination is especially dangerous because radioactive particles could get inside you,

Gloves and tongs should be used to avoid getting particles stuck on skin or under nails,

Some industrial workers wear protective suits to stop them breathing in particles.

Question 44

Radiation Damages Cells How?

Answer 44

Radiation enters living cells and ionise atoms and molecules within them,

This can lead to tissue damage,

Higher doses and lower doses have different side effects,

Hospitals try to limit staff exposed to radiation,

Staff stand behind shielding and untreated body parts of patients,

Tracers with short half lives are used.

Question 45

Lower Doses Of Radiation?

Answer 45

Lower doses tend to cause minor damage without killing the cells,

This can give rise to mutant cells which divide uncontrollably and cause cancer,

Question 46

Higher Doses Of Radiation?

Answer 46

Higher doses tend to kill cells completely causing radiation sickness (vomiting, tiredness and hair loss).

Question 47

Which Radiation Is The Most Dangerous?

Answer 47

Outside the body, beta and gamma radiation are the most dangerous because they penetrate the body and delicate organs,

Alpha is less dangerous because it can’t penetrate the skin,

Inside the body, alpha is the most dangerous because it is strongly ionising so the damage they do is in a vey localised area,

This means that contamination, rather than irritation, is the major concern when working with alpha.