Chemistry unit 7

• Isotope

  Atoms of the same element with the same atomic number but a different atomic mass due to a change in the number of neutrons.
• Uses of Hydrogen isotopes

  • Hydrogen-1 used to make ammonia and turn unsaturated/liquid fats into solid fats
  • Hydrogen-2 used to produce hydrogen bombs
  • Hydrogen-3 used in nuclear fusion reactions and as an artificial radioactive tracer
• Calculating relative atomic mass using isotope abundances

  
  

  = (mass number x abundance %) + (mass number x abundance %)

  100
• Stable nuclei

  Stable nuclei have a balanced number of protons and neutrons.

  Elements with naturally stable nuclei are located in the lighter section of the periodic table.

  All nuclei with proton numbers under 83 are naturally stable.
• Unstable nuclei

  Unstable nuclei have an unbalanced number of protons and neutrons, too much of either.

  Unstable nuclei are generally heavy due to an excess number of protons and neutrons. Because of this they decay and emit particles in order to achieve a balanced state.

  All nuclei with proton numbers over 83 are unstable and radioactive.
• Decay series

  Series of decays where a radioactive element is decomposed into different elements until a stable atom is formed
• Parent and daughter isotope

  Parent isotope: The initial radioactive isotope that occurs before decay starts to form daughter isotope.

  
  

  daughter isotope: The new isotope formed from the decay of the parent isotope. This results in different atomic masses for isotopes of the same element.
• Half-life

  The time taken for the radioactivity of an isotope to decay into half of the original value
• Transuranium elements

  Elements with radioactive isotopes that decay to form stable atoms, with atomic numbers greater than 92 (Uranium). they are all unstable/radioactive.
• Star life cycle- we are all star dust

  The statement 'we are all star dust' refers to the fact that many of the elements present in our bodies were formed through nuclear fusion processes in stars. Elements heavier than hydrogen and helium were created in stars and supernovae before being incorporated into planets and life forms on Earth.
• Geiger counter

  1. Geiger counters are devices used to detect for radioactive emissions in industries where radioactive elements are used. Geiger counters can detect all types of radiation emissions but are most commonly used to detect beta and gamma radiation.

  
  

  2. The counter consists of a tube filled with an inert gas that become unnaturally conductive of electricity when impacted by high - energy particles or radiation. Records the number of radiation reaching it in one second (activity).
• star life cycle

  Fusion reaction: Fusion is a nuclear reaction in which two light atomic nuclei combine to form a heavier nucleus, releasing a large amount of energy. Fusion powers stars like our sun. 
• Examples of isotopes (carbon)

  Carbon-12, Carbon-13, and Carbon-14 for the element carbon.

  - Carbon-12 is the standard relatives for all atomic masses, carbon-14 is used in carbon dating and radio labelling.
• Isotopes with correct notation

  when writing: carbon-12

  
• what happens to the chemical and physical properties of isotopes?

  Same chemical properties

  Different physical properties (density, boiling/melting point, rate of diffusion
• Alpha decay

  A form of decay in which 2 protons and neutrons are emitted.

  An alpha particle is like a helium nucleus as it contains 2 neutrons and protons.

  
• Beta decay

  A form of decay in which a neutron transmutes into a proton and electron.

  A beta particle is like an electron which increases the atomic number of the isotope.

  
• Gamma decay

  A form of decay in which gamma rays are emitted.

  Gamma decay usually occurs after alpha or beta decay.

  Gamma rays are usually photons or electromagnetic energy that is released from isotopes.

  
• Compare the three decays?

  Alpha particles are positively charged particles moving at high speeds. strong ionizing power. weak penetrating power

  Beta particles are negatively charged. weak ionising power and average penetrating power

  Gamma rays: very weak ionising power, strong penetrating power
• what does an unstable nuclei do?

  If a nucleus is unstable, it will emit radiation to gain stability. A stable atom has enough binding energy to hold the nucleus together permanently. The nuclei is unstable because the strong nuclear forces do not produce enough binding energy to hold the nucleus together. Radioactivity results from having an unstable nucleus, when nuclei lose energy and break apart, decay occurs. Radioactive decay releases energy from the nucleus as radiation. Radioactive atoms release energy until they become stable.
• What does the stability of an isotope depend on?

  the ratio of protons to neutrons
• What is the decay series

  Decay series is a series of decay in which radioactive elements is decomposed in different elements until it produces one stable atom.