Atoms
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Atoms

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Atoms Atoms Presentation Transcript

  • Atoms
  • This is a diagram of a CD. The diameter of its hole is one-eighth of the diameter of theCD.
  • Diagrams of atoms look very similar.
  • But the nucleus at the centre of an atom is very much smaller.
  • The diameter of the nucleus is around 100 000 times less than the diameter of the atom.
  • This is equivalent to a CD with a normal-sized hole and an overall diameter of 1.5 km.
  • Each atom has a nucleus at its centre, containing sub-atomic particles called protonsand neutrons.
  • Sub-atomic particles called electrons are arranged around the nucleus.
  • What are the properties of these sub-atomic particles?
  • Their masses are incredibly small.
  • The proton and electron have incredibly small electric charges and the neutron has nocharge.
  • To make sense of the tiny masses, we use relative masses. The proton’s relative massis 1.
  • The electron is nearly 2000 times lighter than the proton and neutron.
  • To make sense of the tiny charges, we use relative charges. The proton’s relativecharge is +1.
  • Protons and electrons have equal but opposite charges.
  • The nuclear symbol for lithium is 7Li. 3
  • The bottom number is the atomic number or proton number, Z.
  • The top number is the mass number, A.
  • These numbers mean that this atom has 3 protons, and ...
  • … the number of protons added to the number of neutrons is 7.
  • So there are 7 − 3 = 4 neutrons.
  • 2 4 3There are an equal number of protons and electrons in an atom, so there are 3electrons.
  • The three protons are found in the nucleus.
  • The four neutrons are also found in the nucleus.
  • The three electrons are arranged around the nucleus.
  • 3517 Cl is an isotope of chlorine. It is often called chlorine-35.
  • Its mass number is 35.
  • Its atomic number is 17.
  • So there are 35 − 17 = 18 neutrons.
  • 3717 Cl is another isotope of chlorine. It is often called chlorine-37.
  • Its mass number is 37.
  • Its atomic number is 17.
  • So there are 37 − 17 = 20 neutrons.
  • Both isotopes have 17 protons and 17 electrons but different numbers of neutrons.
  • Isotopes of an element are chemically identical but have different physical properties.