properties and structures of atoms

• the nucleus contains most of the atoms mass, but only takes up a very small amount of space in comparison to the rest of the atom
• protons are positively charged, positive and have equal mass to a neutron
• neutrons are neutral subatomic particles that have no charge and are found in the nucleus of an atom and have the same mass as a proton
• an electron is found in the electron shell, is negatively charged and its mass is 1/1800 to the mass of a proton
• isotopes have the same number of protons but different number of neutrons (they have two different mass numbers)
• isotopes have similar chemical properties but different physical properties
• chemical properties include reactivity and bonding
• physical properties include melting point and mass
• john dalton created the solid sphere model in 1803 and the theory stated that atoms are indivisible, those of given elements are identical and compounds are combinations of different types of atoms/elements
• Thomson created the plum pudding model in 1904, he discovered electrons within atoms, theorised that electrons were scattered about a cloud of positive charge
• Rutherford created the nuclear model in 1911, he crafted an experiment that separated electrons and protons/neutrons, which led to the discovery of a central nucleus within an atom
• Niels Bohr created the planetary model in 1913, which proposed that electrons move around the nucleus in orbits and they must gain or lose energy to move between these orbit levels
• James Chadwick in 1932 discovered the neutron as being a neutrally charged sub atomic particle in the nucleus that had the same mass as a proton
• relative atomic mass is the average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12
• isotopes have the same atomic number but differing mass numbers due to varying amounts of neutrons
• relative atomic mass = (abundance % * atomic mass) + (abundance % * atomic mass) / 100
• if you are given the relative atomic mass, sub into the equation to figure out the isotopic abundancies
• core charge is the measure of attraction between nucleus (+) and valence electrons (-)
• 2 factors determine electrostatic attraction, the distance between charges and the magnitude of the charge
• core charge = protons - inner electron shells
• atomic radius is the distance from the nucleus to the boundary of the outer electron shell
• atomic radius decreases across a period, as the core charge imcreases across a period
• atomic radius increases down a group, there are more energy levels
• ionisation energy is the energy required to remove one electron from an atom in its ground state
• ionisation energy increases across a period as the core charge increases therefore the attraction between the nucleus and the valence electrons so more energy is required to remove them from the atom
• ionisation energy decreases down a group, as there are a larger amount of energy levels, so less energy is required to remove an electron
• electronegativity is the ability of an atom to form bonds with an electron
• electronegativity increases across a period, as an increased core charge increases the attraction between the nucleus and the outer electrons
• electronegativity decreases down a group because the atomic radius increases and the attraction between the nucleus and the valence electrons also decreases
• electron affinity is the ability to gain an electron (anion)
• electron affinity increases across a period due to increase in core charge
• electron affinity decreases down a group
• metallic character is the ability to lose an electron (cation)
• metallic character decreases across a period, as it is harder to lose an electron is there is a large amount of core charge
• metallic character increases down a group because the atomic radius decreases and the nuclear charge increases
• ground state is when all electrons are in the lowest levels of the atom
• excited state is when electrons are in a higher energy level than the ground state, so they are more likely to be emitted
• mass spectroscopy


  1 sample is vapourised/ionised

  2 sample if accelerated and separated according to their mass-to-charge ratios

  3 detector counts the amounts of each isotope
• atomic absorption spectroscopy


  1 sample is sucked into gas stream to the AAS in a flame

  2 target metal atoms freely absorb light from the cathode lamp

  3 samples are filtered through wavelength filter from desired light from the beam

  4 amplifier/signal detector determines how much light has been absorbed, the absorption is directly proportional to the concentration of the sample
• calibration curve

  compares the absorption to the concentration of each solution. If a concentration of a sample in unknown, it can be plotted on the curve, which determines the concentration