elements of life part 2

covalent bonding
1. when non-metallic elements it is not energetically favourable to form ions eletrons are shared between tthe atoms of the elements in these compunds
2. when two pairs of electrons form covalent bond it's called a double bond
3. dative bond
  1. carbon monoxide has a tripple bond. two pairs are formed by the carbon and oxygen atoms contributing one electron to the pair.however both electrons in the third pair come from oxygen atom. this is called a dative bond
4. covalent intermolcular bonds within simple molcules like water are strong , however the electrostatic attractions between simple molcules are weak, this means that small amounts of energy is needed to seperate one molecule from another
  1. elements and compunds with a simple structure have low melting and boiling pointsbeacuse there is no charged particles and simple covalent structutres do not conduct electricity they mostly do not dissolve in water
shape of molecules
1. electron pair repulsion
  1. in methane there is 4 electrons groups attached to the carbon because similar charges repel they arrange themselves so that they can be the furthest away from each other
    1. the furthest they can get apart from each other is 109 degrees apart. this means it is tetrahedral
      1. all carbons surrounded by four single bonds have tetrahedral arrangement
  2. lone pairs
    1. molecules such as ammonia and water have lone pairs in the outer shells of nitrogen and oxygen, the lone pairs repel the electron pairs in ammonia and water adopt a tetrahedral shape. but one or more lone pairs are in the conners.
    2. the simple rule for covalent molecules is that groups of electrons on the outer shell repel each other and move apart as far as each other
    3. lone pairs repel more strongly than electrons involved in bonding
2. other shapes
  1. linear molecules
    1. there are two groups of electrons around the central atom because there is fewer molecules they can go further apart, the furthest they can get apart is 180 degress.
      1. planar molecules
        there are three groups around the central atom, the bond angle is 120 degrees it is flat and shaped like a triangle is described as a triangular planar
        bipyramidal molecules
        five groups of electrons around a central atom gives us a trigonal bipyramidal shape.with electrons at the five corners of the shape.bond angles are about 120 or 90 degrees depending on their position
        octahedral molecules
        six groups of electrons around a central atom where electrons are directed to the corners of an octahedron
amount of substance
1. relative atomic mass
  1. amount of moles=mass/molar mass
  2. moles of formula units
    1. amount in moles of formula units=mass/molar mass
    2. Avogardro's constant
      1. is 6.02x10^23
      2. percentage yield
        this reduce the amount of product produced
        loss of production from reaction vessels , particularly if there are several stages,side reactants occuring ,unwanted product
        impurities in reactants,changes in temperature a pressure,if the reaction is an equilibrium system
        percentage yield =experimental yield/theoretical yield
chemical bonding
1. group one and two have only one or two outer shell electrons these get taken away to form cations
  1. non-metal have more than 3 outer shell electrons they are able to gain electrons and to form negatively charged ions called anions
    1. having a doubly charged anion is hard because the charges are both negative and getting a -3 anion is extremely difficult and hardly happens
  2. cations with 4+ are very unknown
2. ionic bonding
  1. when metals react with nonmetals ions are formed if the overall charge is favorable
    1. the cations and anions formed are held together by their opposite charges in a electrostatic bond
      1. in a compound the ions attract many of the opposite charges creating a giant lattice
  2. ionic salts
    1. acid + alkali= salt + water
      1. acid + base =salt + water
        acid + carbonate= salt + water + c02
        acid + metal= salt + hydrogen
    2. ionic substances in solution
      1. many ionic substances dissolve in water
        the ionic substances that don't dissolve
        barium,lead,calcium silver sulphates
        silver and lead halides ( chlorides, bromides iodies)
        metal hydroxides apart from group one hydroxides and amonimum hydroxide
        the ions become surrounded by the water and spread out through the solution . once they are seperated from each other they are independant of each other.
        the presence of the hydrated ions explain why aquesous solution of salts can conduct electricity
    3. ionic equations
      1. most reactions happen to only have two types of ion
        e.g if you have a solution of silver nitrate to a solution of sodium chloride you get a white percipitate of silver chloride
        the na and the no3- is not involved in the reaction therefore is not put into the equation they are called spectator ions
      2. bonding,structure and properties
        ionic bonding
        they are normally solids at room temperature and pressure,and have lattice structures that consist of negative and positive ions in al 3 demensions
        because of this they form regularly shaped crystals
        the electrostatic attractions are strong this is why ionic compounds have high melting points, once melted the ions are free to move and can conduct electricity.
        metallic bonding
        metals have a lattice structure, the most important characteristic is the electron sea model
        the model is pictured as a giant lattice structure of metal cations in a sea of delocalised electrons.
        covalent bonding
        insoluble in water and do not conduct electricity

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elements of life part 2

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	Created by Shontel McLaughlan almost 7 years ago