Unit 1.6

• All nitrates are soluble
• All group 2 carbonates are insoluble
• Hydroxide become more soluble as you go down the group
• Sulfates become less soluble as you go down the group
• Magnesium hydroxide is insoluble
• Barium hydroxide is soluble
• Lead is insoluble
• Magnesium sulfate is soluble
• Barium sulfate is insoluble
• Ionisation energy increase across a period as there is an increase in nuclear charge in the same energy level, so there is little extra shielding and therefore a greater attraction between the nucleus and outer electron
• Ionisation energy decreases down a group. The outer electron has increased shielding from inner electrons and is further from the nucleus. This outweighs the increase in nuclear charge.
• Electronegativity increases across a period. There is an increase in nuclear charge, and the outer electrons are always shielded by the same inner electrons, so there is a greater attraction between the nucleus and bond pair.
• Electronegativity decreases down a group the bonding pair have increased shielding from the nucleus, which decreases the attraction between the nucleus and bond pair.
• Elements which have metallic bonding have the greater melting points. The metal ions have a greater charge and there is an increase is delocalised electrons as you go across a period. The more electrons in a metals outer shell, the stronger the metallic bond.
• Elements with giant covalent structures have high melting points due to the large amount of energy needed to break the strong covalent bonds.
• Elements with a simple molecular structure have low melting points. The covalent bonds holding the atoms in the molecule togther are strong, however the intermolecular forces holding the molecules are easily broken.
• Elements which exist as separate atoms (such as Argon) have very low melting and boiling points as atoms are held together by weak temporary dipoles.
• Gravimetric analysis is a technique that uses mass to determine the amount of a substance in a sample. It depends on comparing the masses of two compounds containing the analyte (the ion being analysed). The mass of an ion in a pure Covent compound can be determined and then used to find the percentage of mass of the same ion in a known quantity of an impure compound.
• All s-block elements (apart from magnesium) may be identified with a flame test. A clean metal wire (or splint) is moistened with hydrochloric acid, dipped in the compound and then held in a non-luminous bunsen flame.
• Lithium would burn red
• Sodium would burn yellow/orange
• Potassium would burn lilac
• Magnesium has a colourless flame
• Calcium burns brick red
• Strontium burns crimson
• Barium burns apple green
• The test for halides is silver nitrate. This test has to be done in a solution, so if you start from a solid, it must first be dissolved. Silver nitrate is added to the solution and the different colours of the precipitate ca identify the halide.
• Chlorine and silver nitrate produce a white precipitate.
• Bromine and silver nitrate produce a cream precipitate
• Iodine and silver nitrate produce a yellow precipitate.
• AgCl dissolves in dilute NH3
• AgBr dissolves in concentrated NH3
• AgI is insoluble in NH3
• In general, metal oxides are basic, and non-metal oxides are acidic.
• S-block elements are metals that form basic oxides. They are reducing agenst, so they donate electrons and form cations easily. Their melting point decreases down the group.
• P-block elements are non metals that form acidic oxides. They are oxidising agents, those in group 6 and 7 can accept electrons and form anions easily. Their melting point increases down the group.
• P-block elements are non metals that form acidic oxides. They are oxidising agents, those in group 6 and 7 can accept electrons and form anions easily. Their melting point increases down the group.
• A redox reaction is when oxidation and reduction occur in the same chemical reaction.
• An oxidising agent is a species that accepts electrons, thereby helping oxidation while being reduced in the process.
• A reducing agent is a species that donates electrons, thereby helping reduction while becoming oxidised in the process.