Atoms, elements and compounds 3.2.3-3.2.5

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  • Atoms, elements and compounds
    • Molecules and coalent bonds
      • H2,Cl2,H20, CH4,NH3, and HCL formation of single covalent bonds: The sharing of pairs of electrons leading to the noble gas configiration
      • Volatility: is a measure of how readily a substance vaporizes or transitions from a liquid phase to a gas phase
        • Covalent compounds have lower melting and boling points than ionic compounds. Ionic compounds form giant lattices covalent forces are weaker than the forces which keep the lattice of ionic compounds together. Hence the difference in volatility.
      • Solubility: the measurement of how much of a substance will dissolve in a given volume of a liquid
        • Ionic compounds are also more soluble in water than covalent compounds.
      • Electrical conductivity:  the reciprocal of electrical resistivity. It represents a material's ability to conduct electric current
        • solid ionic compounds do not conduct electricity because there are no free mobile ions or electrons, ionic compounds dissolved in water make an electrically conductive solution. In contrast, covalent compounds do not exhibit any electrical conductivity, either in pure form or when dissolved in water
    • Macromolecules
      • Uses
        • Graphite is a mineral made of loosely bonded sheets of carbon atoms, giving it a slippery texture that makes it a very effective lubricant
        • The diamond grit is very hard, and very sharp, so that it can cut through even hard materials without wearing down too quickly, offering both faster cuts and more blade life than other abrasive blades
      • Structure
        • Diamond: Diamond is organised in a giant lattice structure with strong covalent bonds between carbon atoms.  Each carbon atom has four electrons in its outer shell, all of which form covalent bonds which are strong and hard to break.
      • Silicon IV oxide (Silicon dioxide)
        • Structure: contains many silicon and oxygen atoms. All the atoms in its structure are linked to each other by strong covalent bonds. The atoms are joined to each other in a regular arrangement, forming a giant covalent structure.
        • Similarities to diamond: is hard and has a high melting point, but contains silicon and oxygen atoms, instead of carbon atoms.
          • Diamond: Diamond is organised in a giant lattice structure with strong covalent bonds between carbon atoms.  Each carbon atom has four electrons in its outer shell, all of which form covalent bonds which are strong and hard to break.
    • Molecules and covalent bonds
      • Ionic compounds have two or more elements held together with strong electro static force of attraction,therefore an immense amount of energy is needed to separate them and melt the compound whereas in covalent compounds the molecules of the compound are held together by weaker force of attraction
    • Metalic bonding
      • A lattice of positive ions in a 'sea of electrons'
      • Metals are described as malleable  because of the ability of the atoms to roll over each other into new positions without breaking the metallic bond
      • Metal particles are held by strong metallic bounds that is they have high melting and boiling points. Thus free electrons in metals can move through the metals allowing electricity to pass through the metals.

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