Atomic structure

sub-atomic particles

  • atom is the smallest indivisible particle of an element that can take part in chemical reaction

  • sub-atomic particles

    • proton

    • neutron

    • electron

behaviour of particles in an electric field

  • protons - deflected towards the negative plate

  • electron - deflected towards the positive plate

  • neutrons - not deflected at all (uncharged)

extent of deflection

  • angle of deflection

    • a=charge/mass

  • electron has much smaller mass than proton, the extent of deflection of electron toward the positive plate in electric field will be greater

atomic number and mass number

  • nuclide - used to describe an atomic species of which the atomic number (proton number) and mass number (nucleon number) is specified

  • atomic number (proton number) - number of protons present in an atom

  • mass number (nucleon) - number of protons and neutrons

  • in an atom, the number of electrons is equal to the number of protons - said to be electrically neutral

  • mass of atom is largely attributed to the presence of protons and neutrons in the nucleus - electrons have negligible mass

isotopes

  • atoms of the same element with different number of neutrons

  • same atomic number but different mass number

  • isotopes of the same element have the same chemical properties - they have the same number of electrons

    • have slightly different physical properties (melting/boiling point, density) - due to different relative masses of the isotopes

  • most elements occur naturally as isotopes - each isotope exists in different relative abundance

  • relative atomic mass (Ar) - takes into consideration the mass of the natural occurring isotopes and their respective relative abundance

    • no units and is recorded to 1 d.p.

noble gases

  • tend to be unreactive

  • electron arrangements of noble gases are relatively stable - exists as monatomic elements

  • atoms of noble gases have eight electrons in their outer shells (stable octet configuration)

    • except helium - stable duplet configuration

  • octet rule - when atoms react to form compounds, they tend to combine in such a way that they each have eight electrons in their outer shell, giving them octet configuration (same electronic configuration as noble gas)

formation of ions

  • formed when an atoms loses or gains electrons - acquires an electrical charge (as number of protons and electrons are no longer equal)

  • atoms lose/gain electrons to obtain duplet/octet configuration in order to achieve greater stability

arrangement of electrons in atoms

  • electrons in the innermost shell (1st shell, closest to nucleus) have the lowest energy

  • electrons in the outermost/valence shell (furthest away from nucleus) have the highest energy