The AtomThe Atom

Atomic Number and Mass Atomic Number and Mass NumberNumber

IsotopesIsotopes

RadioactivityRadioactivity

Half LifeHalf Life

Structure of the atomStructure of the atom

nucleusprotonneutron electrons

Subatomic Particles of the Subatomic Particles of the AtomAtom

ParticleParticle Symbol Symbol Charge Charge

ElectronElectron e e-- negativenegative

ProtonProton p p++ positive positive

NeutronNeutron n noo no chargeno charge

Location of Subatomic Location of Subatomic ParticlesParticles

1010-13 -13 cmcm

electronselectrons

protonsprotons

neutronsneutrons

1010-8 -8 cmcm

nucleus

DefinitionsDefinitions Atomic numberAtomic number – the total number of protons in – the total number of protons in

an atoman atom Mass numberMass number – the sum of the number of – the sum of the number of

protons and the number of neutrons in an atomprotons and the number of neutrons in an atom IsotopeIsotope – elements can exist with same number – elements can exist with same number

of protons but different numbers of neutrons.of protons but different numbers of neutrons. Size of atomSize of atom -If the atom was the size of the -If the atom was the size of the

MCG, the nucleus would be the size of a pea in MCG, the nucleus would be the size of a pea in the middle of the oval and electrons would move the middle of the oval and electrons would move over the entire field over the entire field

Number of ElectronsNumber of Electrons

An atom is neutral An atom is neutral The net charge is zeroThe net charge is zero Number of protons = Number Number of protons = Number

of electronsof electrons Atomic number = Atomic number = Number of Number of

electronselectrons

Atomic SymbolsAtomic Symbols

Show the Show the mass number and atomic mass number and atomic

numbernumber

Give the symbol of the elementGive the symbol of the element

mass numbermass number

23 23 NaNa sodium-sodium-2323

atomic numberatomic number 1111

IsotopesIsotopes

Atoms with the same number of protons, Atoms with the same number of protons,

but different numbers of neutrons. but different numbers of neutrons.

Atoms of the same element (same Atoms of the same element (same

atomic number) with different mass atomic number) with different mass

numbersnumbers

Isotopes of chlorineIsotopes of chlorine

3535ClCl 3737ClCl1717 1717

chlorine - 35 chlorine - 37chlorine - 35 chlorine - 37

Learning Check PointLearning Check Point

Naturally occurring carbon consists of Naturally occurring carbon consists of three isotopes, three isotopes, 1212C, C, 1313C, and C, and 1414C. State C. State the number of protons, neutrons, and the number of protons, neutrons, and electrons in each of these carbon atomselectrons in each of these carbon atoms. .

1212CC 1313CC 1414CC 66 6 6 6 6

#P _______ _______ _______ #P _______ _______ _______

#N _______ _______ _______#N _______ _______ _______

#E _______ _______ _______#E _______ _______ _______

SolutionSolution

1212CC 1313CC 1414CC 66 6 6 6 6

#P #P __6_____6___ _ 6____ 6___ ___ ___66___ ___

#N __#N __66___ ____ _ __77___ ______ ___88___ ___

#E #E __6_____6___ _ 6____ 6___ ___ ___66___ ___

Learning Check PointLearning Check Point

An atom has 14 protons and 20 neutrons.An atom has 14 protons and 20 neutrons.A.A. Its atomic number isIts atomic number is

1) 141) 14 2) 162) 16 3) 3) 3434

B. Its mass number isB. Its mass number is1) 141) 14 2) 162) 16 3) 3)

3434

C. The element isC. The element is1) Si1) Si 2) Ca2) Ca 3) Se3) Se

D.D. Another isotope of this element isAnother isotope of this element is

1)1) 3434X X 2)2) 3434X X 3)3) 3636XX 16 16 14 14 14 14

SolutionSolution

An atom has 14 protons and 20 neutrons.An atom has 14 protons and 20 neutrons.A.A. It has atomic numberIt has atomic number

1) 141) 14

B. It has a mass number ofB. It has a mass number of3) 343) 34

C. The element isC. The element is1) Si1) Si

D.D. Another isotope of this element would beAnother isotope of this element would be

3) 3) 3636XX 1414

Are elements stable?Are elements stable?

Alchemists searched for the ability Alchemists searched for the ability to change substances into to change substances into gold.gold.

There are elements that change into There are elements that change into leadlead over time. These are usually over time. These are usually referred to as radioactive elements.referred to as radioactive elements.

Are elements stable?Are elements stable?

As the mass number gets larger the As the mass number gets larger the element is less stableelement is less stable

Look at the difference in protons and Look at the difference in protons and neutrons for calcium and iodine…neutrons for calcium and iodine…

In a nucleus there are two types of In a nucleus there are two types of forces acting.forces acting.

One is the One is the electrostatic forceelectrostatic force of of repulsion that acts between protons.repulsion that acts between protons.

On its own, it would blow the nucleus On its own, it would blow the nucleus apart.apart.

This force is reduced (in part) by the This force is reduced (in part) by the presence of neutrons…but really presence of neutrons…but really there must be something elsethere must be something else

Why radioactive nuclei are Why radioactive nuclei are unstableunstable

In a stable nucleus, the nuclear force In a stable nucleus, the nuclear force ‘balances’ the electrostatic force of ‘balances’ the electrostatic force of repulsion.repulsion.

When this force is ‘unbalanced’, the When this force is ‘unbalanced’, the nucleus becomes unstable and hence nucleus becomes unstable and hence radioactive.radioactive.

The nuclear force exists between nucleonsThe nuclear force exists between nucleons Proton to protonProton to proton Proton to neutronProton to neutron Neutron to neutronNeutron to neutron

Nuclear ForceNuclear Force

Nuclear ForceNuclear Force

The nuclear force only acts at very short The nuclear force only acts at very short rangerange

It stops the nucleus collapsing in on It stops the nucleus collapsing in on itselfitself

It is the strongest force knownIt is the strongest force known

gravitygravity

electrostaticelectrostatic

nuclearnuclear

The four forcesThe four forces

Radiation: The process of emitting energy in the form of waves or particles.

Where does radiation come from?Radiation is generally produced when particles interact or decay.

A large contribution of the radiationon earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial).

Radiation is going through you atthis very moment!

http://www.atral.com/U238.html

RadiationRadiation

Unstable nuclei will decay.Unstable nuclei will decay. They breakdown and give out radiation.They breakdown and give out radiation. Many isotopes are radioactive. They are

called radioisotopes. This instability in the nucleus; in an attempt This instability in the nucleus; in an attempt

to become more stable, the nucleus will to become more stable, the nucleus will literally “spit out” a particle or some energyliterally “spit out” a particle or some energy

A more stable nucleus is formed.A more stable nucleus is formed.

RadioactivityRadioactivity

Types of RadiationTypes of Radiation

There are three types of radiation: alpha () beta ()

gamma () All three are ionising. This means that

they can interact with other atoms and dislodge electrons from them. (Complete nature of radioactive particles worksheet)

How well they can interact How well they can interact is described as ionising is described as ionising ability.ability.

Ionising radiation is Ionising radiation is considered dangerous.considered dangerous.

EXERCISEEXERCISE

Use the internet to Use the internet to complete the types of complete the types of radioactivity worksheet.radioactivity worksheet.

Ionising AbilityIonising Ability

Alpha particles contain two protons Alpha particles contain two protons and two neutronsand two neutrons

has the same components as a has the same components as a helium nucleus and can be written as helium nucleus and can be written as

Alpha RadiationAlpha Radiation

They carry a double charge and as a They carry a double charge and as a result have result have high ionisinghigh ionising ability. ability.

They are the most ionising but have They are the most ionising but have the lowest penetrating power, they the lowest penetrating power, they can be stopped can be stopped by paperby paper

Properties of Alpha Properties of Alpha RadiationRadiation

There are two types: There are two types:

Beta-minus (Beta-minus (-) are electrons-) are electrons

Beta-plus (Beta-plus (+) are anti-electrons +) are anti-electrons (positrons)(positrons)

Beta RadiationBeta Radiation

Beta particles carry a single charge Beta particles carry a single charge and so are moderately ionising. and so are moderately ionising.

Beta particles can be stopped by Beta particles can be stopped by a thin a thin sheet of aluminiumsheet of aluminium

Properties of Beta Properties of Beta RadiationRadiation

Gamma radiation is often associated Gamma radiation is often associated with alpha and beta decay.with alpha and beta decay.

Gamma rays remove energy from Gamma rays remove energy from the nucleus.the nucleus.

They can be written as:They can be written as:

Gamma RadiationGamma Radiation

Gamma ray image of the milky way

Gamma rays have no mass and no Gamma rays have no mass and no charge and as a result have low charge and as a result have low ionising ability.ionising ability.

They carry a high amount of They carry a high amount of energy.energy. They are very penetrating and They are very penetrating and

require require much lead or concretemuch lead or concrete to to stop them.stop them.

Properties of Gamma Properties of Gamma RadiationRadiation

Penetrating ability of Penetrating ability of particlesparticles

alpha particles stopped by paperalpha particles stopped by paper beta particles stopped by 5 mm of aluminumbeta particles stopped by 5 mm of aluminum gamma rays stopped by 30 cm of dense leadgamma rays stopped by 30 cm of dense lead

Geiger-Muller tube and rate-meter.

Detecting RadiationDetecting Radiation

Background radiationBackground radiation

Smoke alarmsSmoke alarms Sterilising hospital equipmentSterilising hospital equipment Thickness controlThickness control Radioactive datingRadioactive dating Radioactive tracersRadioactive tracers Food preservationFood preservation Cancer treatmentCancer treatment

Uses of Radioactive Uses of Radioactive SourcesSources

Radiation may be absorbed by the body it passes through.

All living things contain living cells. We have many different types of cells which perform different functions including:

Skin cells. Red blood cells (they transport oxygen around the body) White blood cells (they fight infection). Nerve cells. Muscle cells. Brain cells. Sperm cells

Radiation can kill living cells or change the nature of living cells.

Ionising radiation can kill or change the nature of living cells.

The effects of the damage inflicted by the ionising radiation may:

be severe and cause immediate effects, or not become apparent for a long time.

The biological effect of radiation depends on:

The type of radiation. The type of body tissue or body organ that absorbs the radiation. The total amount of energy absorbed.

The Effects of Ionising The Effects of Ionising RadiationRadiation

During the Second World War, two atomic bombs were dropped on Hiroshima and Nagasaki in Japan.

Those people who survived the blast were exposed to a large dose of radiation. Such doses caused severe damage to cells all over the body, especially in the skin, blood, bone tissue and gut.

WW2 – Hiroshima and Nagasaki

Fat Man

Many of these people died within a few weeks. Those people who were exposed to a smaller dose recovered from such immediate effects.

WW2 – Hiroshima and Nagasaki

135 000 people were removed from an area within a radius of 30 km.

The smoke and radioactive debris reached a height of 1200 m and travelled across Russia, Poland and Scandinavia.

Chernobyl Nuclear Power Station

A cloud of material from the accident reached the UK and, with heavy rain, there was material deposited on parts of North Wales, Cumbria and Scotland. This caused certain farm animals (e.g. lambs) to be banned from sale as they had absorbed radiation from the grass.

(View Chernobyl: You Tube)

Chernobyl Nuclear Power Station

These effects take longer to become apparent and can be caused by much lower levels of radiation.

One of the most important long-term effects of radiation is that of cancer in various parts of the body.

Long term effects of Long term effects of Ionising RadiationIonising Radiation

Uranium miners tended to get lung cancer due to breathing in gases which emitted alpha particles.

People who painted the dials of clocks with luminous paint developed oral cancer from using their lips to make points on the brushes.

Long term effects of Long term effects of Ionising RadiationIonising Radiation

Exposure to ionising radiation causes cancer ?

The mechanisms for cancer occurring are poorly understood at the moment. One theory is that the ionising radiation affects the DNA material within us – our genetic make-up.

Our DNA contains instructions which control the cells. If ionising radiation alters these instructions in the DNA, there is a chance that cancer will develop.

Genetic damage can be caused to cells by radiation, including cells which are involved in reproduction.

Using radioisotopesUsing radioisotopes

Using the internet find out about two Using the internet find out about two of the followingof the following

Medical scanningMedical scanning Cancer treatmentCancer treatment Carbon datingCarbon dating Rock datingRock dating Nuclear powerNuclear power

Reducing exposureReducing exposure

Your exposure to radiation can be Your exposure to radiation can be reduced by:reduced by: