Access to Science – Chemistry - periodicity Prepare for learning: pens, notebooks bags and stuff to side benches

Learning aims for the session: Reflective Learner Effective Participator Team worker Learning aims for the session: Describe the variation of atomic radius, first ionisation energy and electronegativity of group 1 elements. Describe the reactions of group 1 elements with oxygen, chlorine and water. Carry out qualitative analysis of common cations and anions. Liteion racy and Numeracy News!

Physical data for Group I elements Atomic radius /nm 1st Ionisation energy/kJ mol-1 Melting point/ºC Lithium Sodium Potassium Rubidium Caesium 0.123 519 180 0.157 494 98 0.203 418 64 0.216 402 40 0.235 376 29

Changes down Group 1 increases Atomic radius increases because of the increasing number of energy levels 1st Ionisation energy decreases because of increasing size and shielding Melting point Because of increasing size between adjacent atoms and increased nuclear shielding resulting in longer, weaker metallic bonds. decreases

Group 1 elements They are typical metals – forming largely ionic compounds with other elements They release electrons to form positive ions Na  Na+ + e- So, will form ionic bonds with other elements such as oxygen, water and chlorine for example. They are reducing agents i.e. They donate electrons to oxidising agents

OILRIG They release electrons to form positive ions Na  Na+ + e- They are reducing agents i.e. They donate electrons to oxidising agents Oxidation Is Loss; Reduction Is Gain When a substance is oxidised it loses electrons, so becomes more positively charged The substance that is oxidised is known as a reducing agent because in the process of being oxidised / losing electrons it causes reduction or the giving electrons to another substance. When substance is reduced it gains electrons, so becomes more negatively charged The substance that is reduced is known as an oxidising agent because in the process of being reduced / gaining electrons it is causing oxidation or taking electrons from another substance. 4Na + O2 2 Na2O Here sodium has lost it’s outer electron to oxygen, so is oxidised. Sodium is acting as a reducing agent because it is giving its electrons to oxygen. Oxygen can be defined as being reduced in the process because it has gained electrons. Oxygen can also be described as an oxidising agent as it has caused reduction / loss of electrons from sodium in the process.

Reactivity of group 1 elements Reactivity increases down the Group because… the outer electron becomes easier to remove as the atomic size increases and the nuclear shielding increases.

Reactivity of group 1 Demo http://www.youtube.com/watch?v=m55kgyApYrY Individuals - Describe what you witnessed for the reactivity of the group 1 metals during the demo and video. Pair – describe to a partner Share - describe to the group. Make your notes

Reaction with water 2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g) lithium hydroxide 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g) sodium hydroxide 2K(s) + 2H2O(l)  2KOH(aq) + H2(g) potassium hydroxide 2Rb(s) + 2H2O(l)  2RbOH(aq) + H2(g) http://www.bing.com/videos/search?q=sodium+and+acid&FORM=HDRSC3#view=detail&mid=7672B61AF0AA4E596DE67672B61AF0AA4E596DE6 rubidium hydroxide 2Cs(s) + 2H2O(l)  2CsOH(aq) + H2(g) caesium hydroxide click for sodium + acid

Solubility in organic solvents Solubility of the halides – salts of group 17 (fluorides, chlorides, bromides and iodides) Solubility in water Solubility in organic solvents Lithium halides Other Group 1 halides slightly soluble slightly soluble very soluble insoluble Lithium salts are anomalous because of the small size of the cation, they tend to draw anions closer leading to more covalent properties present in the salts.

Thermal decomposition of nitrates 2LiNO2  Li2O + 2NO2 + ½O2 lithium nitrate lithium oxide nitrogen dioxide 2NaNO3  2NaNO2 + O2 sodium nitrate sodium nitrite The anomalous character of lithium nitrite is due to its covalent character, it’s more like group 2 carbonates, that also decompose this way on heating.

Summary LiNO3  LiNO2 + Li2O NaNO3  NaNO2 KNO3  KNO2 RbNO3  RbNO2 CsNO3  CsNO2

Carbonates Thermal decomposition of lithium carbonate 2LiCO3  Li2O + CO2 Again, the anomalous character of lithium carbonate is due to its covalent character, it’s more like group 2 carbonates, that also decompose on heating.

Summary The Group 1 metals are reactive and form ionic salts. Compounds are generally soluble in water, insoluble in organic solvents and are thermally stable. Lithium compounds exhibit anomalous properties.

http://aschool.us/random/random-pair.php Siobhan Naomi Leyton Kevin Sean Andrew Nicola Laura Hannah Rebekha Jacob Anthony Maria Joe Gemma Sarah Glen Amanda Abigail Hasib Eamon Stephen Inna http://aschool.us/random/random-pair.php

Qualitative analysis of salts What’s in a salt? An anion and a cation e.g. Na+ Cl- We have looked at a way of finding out what metal cation is present – flame tests However, this doesn’t work for all cations – some do not give coloured flames, or give similar colours so it is difficult to distinguish between them. We are now going to look at some other ways of telling what is in a substance.

Tests can be grouped For cations: often we can distinguish between metal cations by adding a alkali such as sodium hydroxide or ammonium hydroxide (ammonia in solution). For anions: we can test for carbonates, sulphates, nitrates and halides by using simple tests too. demo

Read first! Pairs! There are lots of tests to analyse compound to identify what is present, here are a few of them......... Work slowly through the analysis and record what you find… You will do this again in a few weeks with some unknowns as part of your assignment, so make clear notes of results and you might want to take photographs too. http://aschool.us/random/random-pair.php

Results

Periodic Table click to return