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The Atom Atomic Number and Mass Number IsotopesRadioactivity Half Life.

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Presentation on theme: "The Atom Atomic Number and Mass Number IsotopesRadioactivity Half Life."— Presentation transcript:

1 The Atom Atomic Number and Mass Number IsotopesRadioactivity Half Life

2 Structure of the atom nucleus proton neutron electrons

3 Subatomic Particles of the Atom ParticleSymbol Charge Electron e - negative Proton p + positive Neutron n o no charge

4 Location of Subatomic Particles cm cm electrons electrons protons protons neutrons neutrons cm cm nucleus

5 Definitions Atomic number – the total number of protons in an atom Atomic number – the total number of protons in an atom Mass number – the sum of the number of protons and the number of neutrons in an atom Mass number – the sum of the number of protons and the number of neutrons in an atom Isotope – elements can exist with same number of protons but different numbers of neutrons. Isotope – elements can exist with same number of protons but different numbers of neutrons. Size of atom -If the atom was the size of the MCG, the nucleus would be the size of a pea in the middle of the oval and electrons would move over the entire field Size of atom -If the atom was the size of the MCG, the nucleus would be the size of a pea in the middle of the oval and electrons would move over the entire field

6 Number of Electrons An atom is neutral An atom is neutral The net charge is zero The net charge is zero Number of protons = Number of electrons Number of protons = Number of electrons Atomic number = Number of electrons Atomic number = Number of electrons

7 Atomic Symbols Show the mass number and atomic number Show the mass number and atomic number Give the symbol of the element Give the symbol of the element mass number 23 Na sodium Na sodium-23 atomic number 11 atomic number 11

8 Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine Isotopes of chlorine 35 Cl 37 Cl 1717 chlorine - 35 chlorine - 37 chlorine - 35 chlorine - 37

9 Learning Check Point Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______

10 Solution 12 C 13 C 14 C #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___

11 Learning Check Point An atom has 14 protons and 20 neutrons. A.Its atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163) 34 C. The element is 1) Si2) Ca3) Se D.Another isotope of this element is 1) 34 X 2) 34 X 3) 36 X

12 Solution An atom has 14 protons and 20 neutrons. A.It has atomic number 1) 14 B. It has a mass number of 3) 34 C. The element is 1) Si D.Another isotope of this element would be 3) 36 X 14 14

13 Are elements stable? Alchemists searched for the ability to change substances into gold. Alchemists searched for the ability to change substances into gold. There are elements that change into lead over time. These are usually referred to as radioactive elements. There are elements that change into lead over time. These are usually referred to as radioactive elements.

14 Are elements stable? As the mass number gets larger the element is less stable As the mass number gets larger the element is less stable Look at the difference in protons and neutrons for calcium and iodine… Look at the difference in protons and neutrons for calcium and iodine…

15 In a nucleus there are two types of forces acting. In a nucleus there are two types of forces acting. One is the electrostatic force of repulsion that acts between protons. One is the electrostatic force of repulsion that acts between protons. On its own, it would blow the nucleus apart. On its own, it would blow the nucleus apart. This force is reduced (in part) by the presence of neutrons…but really there must be something else This force is reduced (in part) by the presence of neutrons…but really there must be something else Why radioactive nuclei are unstable

16 In a stable nucleus, the nuclear force ‘balances’ the electrostatic force of repulsion. In a stable nucleus, the nuclear force ‘balances’ the electrostatic force of repulsion. When this force is ‘unbalanced’, the nucleus becomes unstable and hence radioactive. When this force is ‘unbalanced’, the nucleus becomes unstable and hence radioactive. The nuclear force exists between nucleons The nuclear force exists between nucleons Proton to proton Proton to proton Proton to neutron Proton to neutron Neutron to neutron Neutron to neutron Nuclear Force

17 The nuclear force only acts at very short range The nuclear force only acts at very short range It stops the nucleus collapsing in on itself It stops the nucleus collapsing in on itself It is the strongest force known It is the strongest force knowngravityelectrostaticnuclear

18 The four forces

19 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 radiation on earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial). Radiation is going through you at this very moment! Radiation

20 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 to become more stable, the nucleus will literally “spit out” a particle or some energy This instability in the nucleus; in an attempt to become more stable, the nucleus will literally “spit out” a particle or some energy A more stable nucleus is formed. A more stable nucleus is formed. Radioactivity

21 Types 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)

22 How well they can interact is described as ionising ability. How well they can interact is described as ionising ability. Ionising radiation is considered dangerous. Ionising radiation is considered dangerous. EXERCISE EXERCISE Use the internet to complete the types of radioactivity worksheet. Use the internet to complete the types of radioactivity worksheet. Ionising Ability

23 Alpha particles contain two protons and two neutrons Alpha particles contain two protons and two neutrons  has the same components as a helium nucleus and can be written as  has the same components as a helium nucleus and can be written as Alpha Radiation

24 They carry a double charge and as a result have high ionising ability. They carry a double charge and as a result have high ionising ability. They are the most ionising but have the lowest penetrating power, they can be stopped by paper They are the most ionising but have the lowest penetrating power, they can be stopped by paper Properties of Alpha Radiation

25 There are two types: There are two types: Beta-minus (  -) are electrons Beta-minus (  -) are electrons Beta-plus (  +) are anti-electrons (positrons) Beta Radiation

26 Beta particles carry a single charge and so are moderately ionising. Beta particles carry a single charge and so are moderately ionising. Beta particles can be stopped by a thin sheet of aluminium Beta particles can be stopped by a thin sheet of aluminium Properties of Beta Radiation

27 Gamma radiation is often associated with alpha and beta decay. Gamma radiation is often associated with alpha and beta decay. Gamma rays remove energy from the nucleus. Gamma rays remove energy from the nucleus. They can be written as: They can be written as:   Gamma Radiation Gamma ray image of the milky way

28 Gamma rays have no mass and no charge and as a result have low ionising ability. Gamma rays have no mass and no charge and as a result have low ionising ability. They carry a high amount of energy. They carry a high amount of energy. They are very penetrating and require much lead or concrete to stop them. They are very penetrating and require much lead or concrete to stop them. Properties of Gamma Radiation

29 Penetrating ability of particles alpha particles stopped by paper alpha particles stopped by paper beta particles stopped by 5 mm of aluminum beta particles stopped by 5 mm of aluminum gamma rays stopped by 30 cm of dense lead gamma rays stopped by 30 cm of dense lead

30 Geiger-Muller tube and rate-meter. Detecting Radiation

31 Background radiation

32 Smoke alarms Smoke alarms Sterilising hospital equipment Sterilising hospital equipment Thickness control Thickness control Radioactive dating Radioactive dating Radioactive tracers Radioactive tracers Food preservation Food preservation Cancer treatment Cancer treatment Uses of Radioactive Sources

33 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.

34 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 Radiation

35 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

36 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

37 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

38 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

39 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 Ionising Radiation

40 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 Ionising Radiation

41 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.

42 Using radioisotopes Using the internet find out about two of the following Medical scanning Medical scanning Cancer treatment Cancer treatment Carbon dating Carbon dating Rock dating Rock dating Nuclear power Nuclear power

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


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