Modern Periodic Table
-A perioid is a horizontal row of elements in the periodic table, showing trends.
-A group is a vertical column, showing similar chemical properties and the same number of outer-shell electrons.
-Perioidicity is the trend in properties across each period, for example elements change from metals to non-metals.
-Similarities in electron structure leads to chemical similarity, each element in a vertical group has the same number of outer-shell electrons and type of orbital.
Periodicity: Ionisation Energies/Atomic Radii
Across a perioid:
-There is a general increase in ionisation energy.
-The number of protons increases, so there is more attraction to electrons.
-Electrons are added to the same shell, drawing it inwards with no electron shielding change.
-Noble gases have the highest ionisation energies.
In general there is a decrease in atomic radii (bar the noble gases), as increased electron number pulls the outer shell inwards; with a sharp decrease in first ionisation energy from the end of the last period to the begining of the next, due to the addition of a shell.
Down a group:
-The number of shells increases, so shielding increases.
-Atomic raddi increases.
-Thus first ionisation energy decreases.
Periodicity: Boiling Points
Across the periodic table, metals go to non-metals and solids to gases, with this trend:
-General increase in boiling points from 1-4. (giant structures)
-Sharp decrease form 4-5, as giant structures go to simple molecules.
-Comparitively low boiling points from 5-0. (simple molecules)
-Silicon is a semi-metal (Hard to classify).
-Group 1-3 in general are giant metallic structures with metallic bonding (strong).
-Group 4 is usually covalent, which are strong.
-Group 5-0 are simple molecules with weak van der Waals's forces.
The melting/boiling points of metals increase because:
-Ionic charge increases.
-Ionic size increases.
-Number of electrons increased in the lattice.
Group 2: Redox
-Reasonably high melting and boiling points.
-Light metals with low densities.
-Form colourless compounds.
-Together with Group 1 form the s-block of the perioidic table.
-Two electrons more than the noble gas and an outer shell with two electrons.
-Reactive metals and strong reducing agents.
-Are oxidised in reactions, losing two electrons. (e.g. Mg -> Mg2+ + 2e-)
Reaction with oxygen:
-Ionic oxide with general formula MO, where M is the group 2.
-E.g. 2Ca + O2 -> 2CaO, so Ca is oxidised and O reduced.
Reaction with water:
-The M is ox is oxidised and one of the H reduced.
Group 2: Compounds Reactions
Group 2 form oxides and hydroxides which are bases, with hydroxides:
-Down the group solubility increases.
-Down the group alkilinity increases, greater -OH concentration.
-Hydroxides can be used to neutralise soil or to relieve indigestion.
Group 2 carbonates are decomposed by heat to form metal oxides and CO2, down the group ease of thermal decomposition decreases.
Group 7: Redox
-Low melting and boiling points.
-The exist as diatomic molecules.
-van der Waals' forces increase down the group.
-So boiling/melting points increase down the group (gas->liquid->solid).
-Seven electrons in outer shell, halogens have one less than a noble gas; in the p sub-shell.
-These are the most reactive elements in the periodic table, and are oxidising agents.
E.g. 1/2Cl2 + e- -> Cl-
-Halogens become less reactive down the group, so oxidising power decreases.
-This is due to smaller atomic radii, greater electron shielding.
-Halogens take place in displacement reactions, where a more-reactive element displaces a less-reactive element (e.g. Cl2 + 2Br- -> 2Cl- + Br2)
-So Cl is more reactive than Br, and Br more than I.
Group 7: Uses/Halide Tests
-Bonding = covalent diatomic molecules.
-Structure = simple molecular, with weak van der Waals' forces.
-Redox = Oxidising agents to form halide ions.
-Reactivity = Decreases down group.
-Flourine is VERY reactive, hard to contain.
-NaCl is table salt.
-NaF is added to toothpaste.
-Crystals of CaF2 are used to make lenses to focus IR light.
Halide test -> Chloride is white, bromide is cream and iodide yellow: