Inside the atom

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The structure of an atom

  • Every atom contains:
    • a postively charged nucleus composed of protons and neutrons
    • electrons that surround the nucleus.

nucleon - a proton or neutron inside the nucleus

  • Each electron has a negative charge. Because the nucleus is positively charged, the electrons are held in the atom by the electrostatic force of attraction between them and the nucleus.
  • The nucleus contains most of the mass of the atom.
  • The electron has a much smaller mass than the proton or the neutron.
  • The proton and the neutron have almost equal mass.
  • The electron has equal and opposite charge to the proton.
  • The neutron is uncharged.
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Isotopes

  • Every atom of a given element has the same number of protons as any other atom of the same element.

atomic number (Z) - the amount of protons in the nucleus eg. Z = 6 for every carbon atom, Z = 92 for every uranium atom

isotopes - atoms with the same number of protons and different numbers of neutrons

nucleon number (A) - the total number of protons and neutrons

  • We label the isotopes of an element according to their atomic number Z, their mass number A and the chemical symbol of the element:
    • Z is at the bottom left of the element symbol and gives the number of protons in the nucleus.
    • A is at the top left of the element symbol and gives the number of protons and neutrons in the nucleus.
    • The number of neutrons in the nucleus = A - Z.

nuclides - different types of nuclei

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Specific charge

specific charge = charge / mass

  •  How to calculate the specific charge of a charge particles:
    • A nucleus of hydrogen has a charge of 1.60 x 10^(-19)C and a mass of 1.67 x 10^(-27)kg. Therefore, its specific charge is 9.58 x 10^(7)C/kg.
    • The electron has a charge of -1.60 x 10^(-19)C and a mass of 9.11 x 10^(-31)kg. Therefore its specific charge is 1.76 x 10^(11)C/kg.
    • An ion of the magnesium isotope with atomic number 12 and nucleon number 24 has a charge of + 3.2 x 10^(-19)C and a mass of 3.98 x 10^(-26)kg. Therefore its specific charge is 8.04 x 10^(6)C/kg.
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