The Periodic Table

• Periods: the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1-7 (e.g. elements in period 2 have two electron shells, elements in period 3 have three electron shells
• group: the vertical columns that show how many outer electrons (also known as valency electrons) each atom has and are numbered from I-VII, with a final group called Group 0 (instead of VIII)

  • eg. Group IV elements have atoms with 4 electrons in the outermost shell, Group VI elements have atoms with 6 electrons in the outermost shell and so on
• the group number can help determine the charge that metal and non-metal ions form

  • for metals, the group number corresponds to the number of electrons it will lose to achieve a full outer shell and the charge of the metal ion (e.g. sodium is in Group 1, it will lose 1 electron and form an ion with a 1+ charge)
  • for non-metals in Group VII and VI, will gain 1 and 2 electrons respectively to gain a full outer shell (e.g non-metals in Group VII gain 1 electron to form ions with a 1-charge, and in Group VI gain 2 electrons to form ions with a 2- charge)
• Valency (or combining power) tells you how many bonds an atom can make with another atom or how many electrons its atoms lose, gain or share, to form a compound

  • e.g. carbon has a valency of 4 as it is in Group IV so a single carbon atom can share 4 electrons to make 4 single bonds or 2 double bonds
  • in ionic compounds, the valency of each ion is the same as its charge
  • in covalent molecules, the vaency is the number of bonds that atom makes
• The metallic character of elements decreases as you move across a Period on the Periodic Table (left to right), and it increases as you move down a Group

  • this trend occurs due to atoms more readily accepting electrons to fill their valence shells rather than losing them to have the previous, already full, electron shell as their outer shell
• Group I (alkali metals)

  • form alkaline solutions with high pH values when reacted with water
  • all contain just one electron in their outer shell
  • soft and easy to cut, getting even softer and denser as you move down the Group (sodium and potassium do not follow the trend in density
  • have shiny silvery surfaces when freshly cut
  • conduct heat and electricity
  • all have low melting point and densities compared to other metals, and the the melting point decreases as you move down the group
• Chemical properties of alkali metals

  • react readily with oxygen and water vapour in air so are stored under oil to stop them from reacting
  • will react similarly with water, reacting vigorously to produce an alkaline metal hydroxide solution and hydrogen gas
  • get more reactive as you go down the group
• Group VII non-metals that are poisonous

  • a.k.a the halogens
  • halogens are diatomic meaning they form molecules of two atoms (F2, Cl2, Br2, I2 and At2)
  • have 7 electrons in their outer shell
  • form halide ions by gaining one more electron to complete their outer shells
• Halogens

  • Physical state changes from gas to liquid to solid as you go down the group
  • Density increases as you go down the group
• Halogens at room temperature (20°C)

  • Chlorine is a pale yellow-green gas
  • Bromine is a red-brown liquid
  • Iodine is a grey-black solid
• As you go up Group VII non-metals

  Reactivity increases
• Reason for increased reactivity up Group VII

  Number of shells of electrons decreases, so outer electrons are closer to the nucleus and there are stronger electrostatic forces of attraction which help to attract the extra electron needed
• Solid iodine is dark grey-black, iodine vapour is purple and aqueous iodine is brown
• • the m.p and b.p of the halogens increases as you go down the group (flouring has the lowest m.p and astatine has the highest)
  • the halogens become denser as you go down the group (fluorine will be a gas and astatine a solid)
  • the color of halogens becomes darker as you go down the group (flourine is yellow and astatine is black)
• A reaction in which a more reactive element displaces a less reactive element from a solution a less reactive element from a solution of its salt

  • A halogen displacement occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
• Chlorine and bromine

  • if you add chlorine solution to colorless potassium bromide solution, the solution becomes orange as bromine is formed
  • chlorine is above bromine in Group VII so is more reactive and will therefore displace bromine from and aqueous solution of the metal bromide
  • the least reactive halogen always ends up in the elemental form
  • potassium bromide + chlorine  →  potassium chloride + bromine
  • 2KBr (aq) + Cl2 (aq) → 2KCl (aq) + Br2 (aq)
• Bromine and iodine

  • bromine is above iodine in Group VII so is more reactive and will therefore displace iodine from an aqueous solution of metal iodide. The solution will turn brown as iodine is formed
  • magnesium iodide + bromine  →  magnesium bromide + iodine
  • MgI2 (aq) + Br2 (aq)  → MgBr2 (aq) + I2 (aq)

  
• General properties of the transition metals

  • very hard and strong metals
  • good conductors of heat and electricity
  • have very high m.p. and are highly dense metals
  • form colored compounds
  • often have more than one oxidation state such as iron readily forming compounds of both Fe2+ and Fe3+
  • often used as catalysts to improve the rate of reaction in industrial processes (Transition element catalysts of platinum or rhodium are also used in car exhausts in the 'catalytic convertor' to reduce the levels of nitrous oxides and carbon monoxide produced)
• • Compounds containing transition elements in different oxidation states will have different properties and colours

  
• uses of the transition elements

  • used extensively as catalysts due to their ability to interchange between a range of oxidation states
  • this allows them to form complexes with reagents which can easily donate and accept electrons from other chemical species within a reaction system
  • used in medicine and surgical applications such as limb and joint replacement (titanium is often used for this as it can bond with bones due to its high biocompatibility)
  • They are also used to form coloured compounds in dyes and paints, stained glass jewellery
• Group VIII or 0

  • a.k.a noble gases
  • very low m.p. and b.p
  • all monoatomic, colorless gases
  • all have full outer shells
  • this electron configuration is extremely stable so these elements are unreactive and inert (does not react chemically with any other substance)

  Electronic configurations of the noble gases:

  • He: 2
  • Ne: 2,8
  • Ar: 2,8,8
  • Kr: 2,8,18,8
  • Xe: 2,8,18,18,8