Chemistry Bonding

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  • Created by: Najeeha
  • Created on: 22-05-14 21:12

Metallic bonding

Only METALLIC  elements are metallically bonded. Metallic bonding is when there is a regular arrangement of positive metal ions in a 'sea' of delocalised electrons.

Properties and explanation of properties

  • High melting and boiling points because it takes a lot of energy to overcome the dtrong electrostatic forces of attraction and separate the positive metal ios and the negative delocalised electrons
  • Always conduct electricty because when a volatge is applied the delocalised electrons move throughout the structure.
  • Good conductors of heat because the delocalised electrons move and dissipate the heat
  • Malleable and ductile because when the solid is hammered or drawn into wires the layers slide over eachother and then settle in new equivalent positions


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New Materials(smart materials,nano-materials)

Materials are constantly being developed with novel properties including smart materials and nano particles.Smart often nickel and titanium alloys include

  • Alloys that cange shape at different temperatures, can be used to switch off kettles when water boils, to trigger fire sprinklers, springs in coffee makers to release the hot water.
  • Superclastic smart alloys that return to their original shape. These are used in spectacle frames,dental braces,medical stents, bra underwires, clips for bone fractures.
  • Nanoscale Titanium Oxide is used in self cleaning glass.

Nanoscale refers to structures that are 1-100nm in size 1nm=10   m and have a few hundred atoms. Nanoparticles have ahigh surface area to volume ratio and show different properties to the bulk material. They are being studied in the hope that they can be used in new computers, new catalysts, new coatings including anti-rusting gels, very sensitive sensors, new cosmetics such as tan creams and deodourants and stronger and lighter construction materials. Nanotubes are being studie for hydrogen fuel storage. Carbon forms fullerenes, with varying numbers of carbon atoms. Fullerenes can be used for drug delivery,lubricants, catalysts and in nanotubes for reinforing materials e.g tennis rackets.

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SALTS

Soluble Salts (Neutralisation Reaction)

This method is used to prepare soluble salts but not those of SODIUM,POTASSIUM AND AMMONIUM.

Reactive Metal + Acid                Salt + Hydrogen

Metal Oxide+ Acid                     Salt+ water

Metal Carbonate+ Acid               Salt + Water + Carbon dioxide

In all three methods exces solid is used to ensure ALL ACID REACTS. This excess solid(either metal, metal oxide or metal carbonate) is then removed by filtration

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SALTS

1. About 50cm3 of the appropriate dilute acid is added to a beaker

2. If metal or metal oxide (but not metal carbonate) is added, the acid is warmed on a hot plate.

3. The solid(metal or metal oxide or metal carbonate) is then added slowly until it is in excess. The solid is in excess when some solid remains at the bottom of the beaker. If metal or metal carbonate is used there will also be no effervesence observed as well as the solid remaining.

4. The mixture is then filtered.

5. The filtrate is then conentrated by evaporating some of the water and then left to crystallise

6. The crystals are dried by pressing between filter paper. 

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SALTS

Acid+ alkali (Titration)

This method is used to prepare salts of sodium.potassium and ammonium. It is the only way to produce these salts, and no other salts are produced by this method.

Acid + Alkali                 Salt + Water 

Alkalis are often soluble bases and are often hydroxides

Common Alkalis include:

Sodium Hydroxide NaOH

Potassium Hydroxide KOH

Ammonium Hydroxide NH4OH

other common alkalis include

Sodium Hydrogencarbonate  NaHCO3

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SALTS

1.25 cm3 of the alkali is added to a conical flask using a pipette.

2. 3 drops of indicator either methyl orange or phenolphthalein are added to the conical flask

3. The buretter is filled with acid and the volume noted- this is the initial volume

4.The acid is added to the conical flask, whilst the flask is swirled.

5. As soon as the indicator changes colour, methyl orange from yellow to orange and phenolphthalein pink to colourless the burette tap is closed and the final volume noted.

6. Volume of acid added is calculated.

7.Steps 1-6 are repeated.

8. When the volume of acid added is concordant (within 0.1cm3) steps 1,3,4 are repeated, nut with no indicator. The exact volume of acid being calculated added.

9. The salt solution is concentrated by heating and then left to crystallise10. The crystals are dried by pressing between filter paper

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SALTS

Insoluble salts can only be made by precipitation.Two solutions are chosen so that one contains the postive ion and the other contains the negative ion required. These solutions are usually soluble salt solutions but may be acid solutions providing the necessary negative ion.

1. Suitable quantities of each chosen solution are placed in separate beakers or boiling tubes.

2. The solutions are mixed resulting in the precipitation of the insoluble salt.

3.The mixture is then filtered.

4. The residue of the insoluble salt is dried by pressing between filter papers or by leaving to dry.

This method is used to remove unwanted ions from a solution e.g treating water for drinking, treating effluent.

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Analysis of Salts

Flame tests

A number of salts when heated strongly in a roaring flame produce a distinctive flame colouration.

Li+                                     Crimson

Na+                                    Yellow

K+                                      Lilac

Ca2+                                  Red

Ba2+                                  Green

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