atomic structure and periodic table aqa

• What is an atom?


  An atom is the smallest part of an element that can exist.
• What defines an element?

  An element is a substance with only one type of atom.
• What is a mixture?

  A mixture consists of two or more elements or compounds not chemically combined together.
• What type of mixture can be separated by simple distillation?

  A soluble solid and a liquid, e.g., salt and water.
• What is the process of simple distillation?

  The liquid boils off and condenses in the condenser, with the thermometer reading the boiling point of the pure liquid.
• What type of mixture can be separated by crystallisation/evaporation?

  A soluble solid from a (non-flammable) liquid.
• What is the purpose of the evaporating basin in crystallisation?

  It provides a large surface area for quicker evaporation.
• What type of mixture can be separated by filtration?

  An insoluble solid suspended in a liquid, e.g., sand and water.
• What happens to the insoluble solid during filtration?

  The insoluble solid (residue) gets caught in the filter paper.
• What is the filtrate in filtration?


  The substance that comes through the filter paper.
• What type of mixture can be separated by fractional distillation?

  Soluble liquids with different boiling points, e.g., crude oil.
• How does the fractionating column work in fractional distillation?

  It has a temperature gradient, being hotter at the bottom than at the top.
• What happens when a mixture of soluble liquids is heated in fractional distillation?

  All liquids are evaporated, but the liquid with the lower boiling point forms the greatest percentage of vapour.
• What does the thermometer measure in fractional distillation?

  The temperature of the fractions before they condense.
• What was the belief about atoms before the discovery of the electron?

  Atoms were thought to be tiny spheres that could not be divided.
• What did the plum-pudding model suggest about the atom?

  It suggested that the atom was a ball of positive charge with negative electrons embedded in it.

  
• What did the Rutherford and Marsden’s alpha scattering experiments demonstrate?

  They led to the plum-pudding model being replaced by the nuclear model.
• What is the nucleus in the nuclear model of the atom?

  The center of the atom where all the mass and positive charge is located.
• How did the Bohr model adapt the nuclear model?

  It suggested that electrons orbit the nucleus at specific distances on energy levels or shells.
• How are atoms arranged in the modern periodic table?

  Atoms are arranged in order of their atomic number (proton number).
• How do you calculate the number of neutrons in an atom?

  By subtracting the atomic number from the mass number.
• Why do isotopes of an element have the same chemical properties?

  Because they have the same electronic structure.
• What does the mass number represent in the representation of an atom?

  The mass number is the total number of protons and neutrons in the atom.
• How do you calculate the relative atomic mass (R.A.M) of an element?

  1. A.M = Sum of (mass number of isotope x % abundance) / 100
• What do elements in the same group of the periodic table have in common?

  They have the same number of electrons in their highest energy levels (outer electrons).
• Why are Group 0 elements called noble gases?

  Because they are unreactive due to stable arrangements of electrons.
• What happens to the boiling points of noble gases as you go down the group?

  The boiling points increase with increasing relative atomic mass.
• what is an isotope? 


  atoms with different numbers of neutrons but the same number of protons
• give 2 reasons why the discovery of gallium helped Mendeleev’s periodic table to become accepted.

  • gallium fitted the gap he left
  • gallium's properties were predicted correctly
• Which scientist first suggested that electrons orbit the nucleus at specific distances?


  Bohr
• differences between nuclear model and plum pudding model 


  • nuclear model is mostly empty space - PPM has none
  • the nuclear model has all its positive charge in the nucleus - PPMs a ball of positive charge
  • nuclear model has mass concentrated in nucleus
  • nuclear model has electrons and nucleus separate
• what change did Bohr make to the nuclear model? 


  • electrons orbit nucleus in energy levels.
  • electrons are at specific distances from the nucleus.
  • electrons are in shells around the nucleus
• what is atomic number?

  number or protons
• Describe how the process of distillation produces pure water from salt solution. 


  • solution is heated

  • water evaporates

  • the vapour cools in the condenser

  • the vapour condenses or the vapour turns to a liquid

  • (pure) water collects in the beaker
• define mass number 


  number of protons plus neutrons
• why are alloys harder than pure metals 


  the layers in the alloy are distorted
• Why do noble gases not easily form molecules?

  Because their atoms have stable arrangements of electrons
• What trend is observed in the boiling points of noble gases as you go down the group?

  The boiling points increase with increasing relative atomic mass
• What type of vapours do halogens produce?

  Coloured vapours that are toxic
• What type of compounds do halogens form with metals?

  Ionic salts where the halide ion carries a charge of -1