Atomic structure and the periodic table - 1

• Atoms contain protons, neutrons and electrons. The nucleus contains protons and neutrons and has a positive charge. It contains almost the whole mass of the atom. The electrons move around the nucleus in energy levels. They have virtually no mass.
• Atoms are neutral because they have the same number of protons and electrons.
• Electrons have a mass of very small and a charge of negative one. Neutrons have mass of one and a charge of zero. Protons have a mass of one and a charge of positive one.
• Mass number is the big number and tells you the number of protons and neutrons combined. The atomic number tells you how many protons there are.
• An isotope is a different form of an element which have the same number of protons but a different number of neutrons
• Relative atomic mass ( Ar ) = sum of ( isotope abundance x isotope mass ) / sum of abundance
• A compound is two or more different elements chemically bonded together
• Mixtures are made up of two or more different substances that aren’t chemically bonded together
• Chromatography

  Draw a line near the bottom of the chromatography paper, using a pencil because pencil is insoluble

  Add a spot of ink to the line and place the sheet in a beaker of solvent, the solvent must be underneath the pencil line so the ink doesn’t dissolve into the solvent

  The end result is called a chromatogram
• Filtration can be used to separate an insoluble solid from a liquid. Use filter paper and a funnel
• Evaporation can be used to separate a soluble solid from a liquid, but the liquid will be lost in the process.

  Pour the solution into an evaporating dish

  Slowly heat the solution using a Bunsen burner, the solvent will evaporate and the solution will become more concentrated, crystals will start to form.

  Keep heating until dry crystals are left
• Crystallisation can be used to separate a soluble solid from a liquid, although the liquid will be lost through the process

  Pour the solution into an evaporating dish and gently heat the solution

  Some solvent will evaporate and the solution will become more concentrated

  When crystals start to form remove the dish from the Bunsen burner and leave the solution to cool

  Filter the crystals out of the solution and leave in a warm place to dry
• Simple distillation is used to separate a liquid from a solution. The solution is heated and the part of the solution that has the lowest boiling point evaporates first. The vapour then condenses and cools in the condensing tube.

  The condensing tube has cold water running around the outside to cool it.

  The problem is that you can only use liquids with very different boiling points.
• • In the 19th century John Dalton described atoms as solid spheres.
  • In 1897 JJ Thomson discovered the Plum Pudding Model - A solid, positive sphere with electrons spread evenly throughout
  • In 1909 Rutherford conducted the alpha particle scattering experiments and concluded that there was a tiny positively charged nucleus in the centre of the atom and a cloud of electrons surrounded it ( nuclear model), he also discovered the proton
  • Bohr discovered the nuclear model, suggesting the electrons were in fixed shells
  • James Chadwick discovered the neutron
• Dmitri Mendeleev arranged the elements in the periodic table. He organised them mainly in order of atomic weight but did move some to align with the properties of the other elements. Gaps were left to make sure there was room for elements that weren’t discovered yet. The gaps allowed Mendeleev to predict the undiscovered element’s properties
• • Group 1 are the alkali metals
  • Group 7 are the halogens
  • Group 8 are the noble gasses
• Metals are strong but malleable

  They are great at conducting heat and electricity

  They have high boiling and melting points
• The alkali metals have one electron in their outer shell which makes them very reactive, and gives them similar properties. They are soft and have low density.

  Going down the group, they increase in reactivity as the outer electron is more easily lost due to the attraction between the nucleus and the outer shell decreasing. They have lower melting and boiling point Down the group
• When alkali metals react with water, they react vigorously and produce hydrogen gas and metal hydroxides. The more reactive the metal is the more violent the reactions.
• When alkali metals react with chlorine, they react vigorously and from meta; chloride salts

  As reactivity increases down the group, The reaction gets more vigorous
• When alkali metals react with oxygen, they form a metal oxide
• As you go down the group of the halogens - they become less reactive

  They have higher melting and boiling points down the group
• The Nobel gasses are all inert, colourless gasses

  They are inert because they have eight electrons in their outer shell.
• The boiling point of the noble gasses increases down the group because of the increase in the number of electrons leading to greater intermolecular forces which need to be broken