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Topic 2: Bonding, structure and properties of matter (Nano particles (Uses…
Topic 2: Bonding, structure and properties of matter
Ionic bonding
Metal and non metal
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Sodium Chloride - Na + Cl === Cl- + Na+ 
Ionic compounds
Giant ionic lattice - the oppositely charged ions form a regular lattice with strong electrostatic forces of attraction.
Properties: They all have high boiling and melting points due to the many bonds between the ions this takes a lot of energy to overcome. When solid the ions cannot conduct electricity however when they are molten the ions are free to move and so can conduct electricity. Ionic compounds dissolve very easily in water and in an aqueous solution they can also carry an electric current.
Empirical formula - work out ion charges of each element in the compound. (eg: Na+ and O-2) Then balance these out. Make them neutral charges. (eg: You would need 2 Na atoms to balance the 1 O atom so the empirical formula would be Na2O.)
Covalent
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Simple covalent substances - elements that naturally travel in pairs (eg: Hydrogen, Oxygen, Chlorine and Nitrogen)
Properties: Held together by very strong bonds yet the forces of attraction are weak. Melting and boiling points are very low as they have weak forces of attraction which are easily broken. Can't conduct electricity as they are not charged with no free electrons.
Metalic
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Electrons in the outer shell are delocalised. This means that they can conduct electricity very well and they can also carry heat energy so are good thermal conductors too. Very high melting and boiling points generally solid at room temp because the electrostatic forces between the metal atoms and the sea of delocalised electrons are very strong. Most pure metals are malleable because they have layers which can slide over each other.
Alloys - these are a mixture of different metals which means they are harder. The different sized atoms cannot slide over one another making them harder and less malleable. Alloys are used for example in copper coins.
Nano particles
Uses: Discovering new catalysts. New coatings. New computer parts. Stronger and lighter building materials. Sensors that detect individual substances in tiny amounts. Used in sun cream because they block ultraviolet light rays which are harmful to the skin. Titanium Dioxide is used in house paint and sweet coated chocolate.
Properties: They have a very large surface area compared to their volume. They are also able to react very quickly which makes them good catalysts as they also speed up reactions. Nano particles do not reflect visible light so they cannot be seen.
Coarse particles - diameter between 2500nm and 10,000nm. Dust is an example.
Fine particles - diameter between 100nm and 2500nm.
Nano particles - diameter between 1nm and 100nm.
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