Atomic structure and the periodic table

• what is an atom?

  smallest part of an element that can exist
• what is an element?

  substance of only one type of atom
• what 2 groups can elements be classified into?

  metals and non-metals
• What is a compound?

  two or more elements combined chemically in fixed proportions which can be represented by formulae
• do compounds have the same properties as their constituent elements?

  no, they have different properties
• what is a mixture? Does it have the same chemical properties as its constituent materials?

  • mixture consists of two or more elements or compounds not chemically combined together
  • does have the same chemical properties
• what are the methods through which mixtures can be separated? Do these involve chemical reactions?

  • filtration, crystallisation, simple distillation, fractional distillation, chromatography
  • don’t involve chemical reactions
• describe and explain simple distillation

  • used to separate liquid from a solution - the liquid boils off and condenses in the condenser
  • thermometer will read the boiling point of the pure liquid, get to keep the liquid
• describe and explain crystallisation

  • solution is heated and some of the solvent evaporates, leaving behind a saturated solution
  • saturated solution is allowed to cool and crystals to form
  • crystals can be separated by filtration
• describe and explain evaporation

  • technique for separation of a solid dissolved in a solution from a solvent (eg salt from H2O)
  • solution is heated until all the solvent evaporates, the solids stays in the vessel
• describe and explain fractional distillation

  • technique for separation of a mixture of liquids, works when liquids have different boiling points
  • the fractionating column contains glass beads, helps to separate the compounds
  • industry - mixtures are repeatedly condensed and vaporised
  • column is hottest at bottom and coldest at top
  • liquids will condense at different heights
• describe and explain chromatography

  • place a piece of paper with a spot containing a mixture in a beaker with some solvent
  • bottom of paper has to be in contact with the solvent
  • solvent level will slowly start to rise, separating the spot into few spots
• what is a separating funnel?

  • apparatus for separating immiscible liquids
  • two immiscible liquids of different densities will form two distinct layers in the separatory funnel
  • can run off the bottom layer (liquid with greater density) to a separate vessel
• describe the plum-pudding model?

  atom is a ball of positive charge with negative electron embedded in it
• describe the Bohr/nuclear model and how it came about

  suggests that electrons orbit the nucleus at specific distances (shells) - came about from the alpha scattering experiments
• what did the work of James Chadwick provide evidence for?

  existence of neutrons in the nucleus
• relative masses and relative charges of the proton, neutron and electron

  • Masses: 1, 1, very small
  • charges: 1, 0, -1
• radius of an atom

  0.1 nm
• radius of a nucleus and what is it compared to that of the atom

  1x10-14 m and 1/10000
• name given to the number of protons in the nucleus

  atomic number
• atoms of the same element have the same number of which particle?

  protons
• what is the mass number?

  total number of protons and neutrons
• equation for the number of neutrons using mass number and atomic number

  subtract atomic number from the mass number
• what is an isotope? Do isotopes of an element have the same chemical properties?

  • atoms of the same element that have a different number of neutrons
  • have the same chemical properties as they have the same electron structure
• what is the relative atomic mass?

  average mass value which takes the mass and abundance of isotopes of an element into account, on a scale where mass of 12C is 12
• what are ions?

  • charged particles
  • formed when atoms lose (positive ions) electrons or gain (negative ions) electrons
• properties of metals

  • high boiling/melting point
  • conducts heat and electricity
  • shiny
  • malleable
  • high density
  • basic oxides
• properties of non-metals


  • low boiling/melting point
  • don't conduct heat or electricity - minus graphite
  • dull
  • brittle
  • low density
  • acidic oxides
• what is formed when a metal reacts with a non-metal?

  ionic compound (made of positive and negative ions)
• what is formed when a non-metal reacts with a non-metal?

  • molecular compound containing covalently bonded atoms
  • atoms share electrons, as opposed to transferring electrons between each other
• group 0 elements are known as

  noble gases
• what makes the periodic table periodic?

  similar properties of elements occur at regular intervals
• elements in the same group have the same number of electrons in their outer shell; what does this tell us about their chemical properties?

  they have similar chemical properties
• early periodic tables were arranged by..

  increasing atomic mass
• knowledge of what made it possible to explain why the order based on atomic weights was not always correct?

  isotopes
• elements that react to form positive ions are

  metals
• elements in group 1 are known as..

  alkali metals
• state three characteristics of the alkali metals

  • 1 electron in outer shell
  • low density
  • are stored under oil to prevent reactions with oxygen or water
  • soft, can be cut with a knife
• how do group 1 elements react with non-metals? Why are these reactions similar for the different group 1 elements?

  • form ionic compounds which are soluble white solids which form colourless solutions
  • all have 1 electron in outer shell
• how do group 1 elements react with water?

  • release hydrogen and form hydroxides which dissolve to form alkaline solutions
  • react vigorously with water fizzing and moving around on the surface of water