elements of life

formule, equations and amounts of substance
1. an amount of a substance
  1. 6.02 X10^23 -avogardos constant
  2. number of moles = number of 'things'/number of 'things' in a mole (6.02X10^23)
  3. molecular mass is the same as relative molecular mass, but with gmol^-1 at end
  4. number of moles = mass of substance/molar mass
  5. you can use balanced equations to work out masses, by working out moles of one molecule you can work ou the moles of others, so can work out the mass used of them
2. empirical and molecular formulae
  1. empirical formulae gives the smallest whole number ratio of atoms in a compound
  2. molecular formulae gives the actual number of atmoms in an molecule
  3. you might need to wotk out the molecular formula using the empirical formula and the Mr
  4. to work out the empirical formula work out moles of substance then make a ratio using smallest amout of moles.
    1. if you are given a percentage pretend it is out of a 100g
atomic structure
1. the atom is made up of neutrons, protons and electrons
  1. neutrons have no charge and have a relative mass of 1.
  2. protons have a positive charge and have a relative mass of 1.
  3. electrons have a negative charge and have a negliable mass (1/2000)
  4. neutrons and protons make up the nucleus while the electrons orbit it
2. history of the atom structure
  1. 1-the ancient greeks came up with the idea of atoms. all matter is made of indivisible particles.
  2. 2-john dalton came up with the biliard ball model. atoms are hard spheres which are indivisible and react in whole numbers.
  3. 3-J.J.Thomson came up with the plum pudding model. electrons are particles within a positive atom like a plum pudding
  4. 4-Ernest rutherford came up with the planetary model. atoms have a small nucleus of protons, surrounded by a cloud of electrons. mosty of the atom is empty
  5. 5-Neils Bohr came up with the quantum model.the cloud of electrons was refined to electrons in fixed (quantised) orbitals or shells.
3. relative mass
  1. The relative isotopic mass is the mass of one atom of an isotope compared to one twelfth of the mass of one atom of carbon-12
  2. The relative Atomic mass is the average mass of one atom of an element compared to one twelfth of the mass of one atom of carbon-12
  3. Isotope - atoms with thr same atomic number but different mass number
  4. relative molecular mass is the sum of the relative atomic masses of the atoms in the formula of a molecule
4. nuclear radiation
  1. fusion is two lighter nuclei joining together to form a single heavier nucleus of a new element
    1. as both nuclei are positive extreamly high tempratures and pressures are needed (in stars)
    2. in stars there is a plasma instead of atoms
    3. in a supernova atoms cool and atract electrons to become atoms, ions and molecules
  2. ionising radiation
    1. Alpha - He nucleus, 2p+2n, relative mass 4, 2+ charge, strongly ionising, stopped by paper, few centermeters in air, low deflection by electric feild
    2. Beta - electron, fast moving electron, very small relative mass. moderately ionising, stopped by foil,few meters in air, high delfection in electric feild
    3. gamma - very short wavelength, no mass, no charge, weekly ionising, large distances, stopped by lead sheet, not deflected by electric feild.
    4. gamma-does not change nucleus just makes it more stable.alpha takes 2p+2n away beta- takes a neutron and turns it into a proton
    5. a half life is the time taken half the nuclei of the isotope sample to undergo radioactive decay
  3. uses
    1. medical tracers
      1. e.g. radioactive iodine for cheaking a persons thyroid gland
      2. half lives shouldnt be too long or short. it could be dangerous if too long and unconveinient if its too short. also alpha is useless as it cant leave the body
    2. archeological dating
      1. radiocarbon dating involves mesuring how much radioactive carbon there is in the sample
      2. when organism dies the amount of carbon-14 starts to decay
5. atomic spectra
  1. when energy is provied to electrons they are caused to jump into a different energy level. Having to work against or with the pull of the nucleus energy is gained or lost by the electron.
  2. whith emision spectra the electron firstly gains energyto move further from the nucleus from either heat or high voltage, then it emits energy as it jumps back downto a lower energy level closer to the nucleus. the region of EM spectrum which is emmited can be in the visible and so we a coloured flame or discharge tube and there are also frequencys of UV that we cannot see
  3. the difference in energy between the levels produces different frequencies by the equation AE=hf
    1. AE is the difference in the energy between enrgy levels n=1 and n=2
    2. f=frequency
    3. h=planks constent
  4. the energy levels in all different elements is different because the pull of the nucleus is different for each element
  5. in the absorbtion spectrum if eletromagnetic radiation is passed througha gaseous element, certian frequences are absorbed coresponding to the differences between energy levels. frequencys are missing from the EM spectrum.
  6. the first set of lines are electrons droping to ground state (UV part), the second is droping to n=2 (visible) and third is to n=3 (IR)
  7. from this we can see: There are several shells of electrons, the energy levels are fixed, the lines get closer together because enrgy levels do, there are more groups of lines showing there are a number of energy shells but these groupings are due to all the electron transitions to a particular energy level, different element have different frequencies
mass spectroscopy
1. 1-sample is vaporised into a gas.
2. 2-a beam of electrons is passed over the sample to ionise it. The positive ions are produced by giving an electron the suffcient energy to leave an atom
3. 3- an electricaly charged surface accelerates the positive ions. How fast the ions go depend on their mass (f=ma)
4. 4-the flight tube. a vacuum is created for the atoms to fly(so ions dont coiled with atoms in the air). the lighter ions travle faster than heaver ones.
5. 5- a detector creates an electrical signal when stuck by ions, the signal being proportial to the number of ions
6. 6- a computer collects the information from the detector and produces a spectrum showing the masses of the ions produced from the sample and the abundance.
7. calculating relative atomic mass from atomic mass spectrum: relative atomic mass = (Sum of(relative isotopic mass)X(relative abundance))/100
8. molecular mass spectrum
  1. molecules can break up into fragments when ionised in a mass spectrum.
  2. the peak at the highest mass is known as the molecular ion. it gives us the relative molecular mass
  3. peaks at lower masses are fragments
bonding and structure
1. ionic bonding
  1. metalic and non-metalic
  2. metal atoms lose their outer electrons to become a positive ion, while the non-metal gains the electrons to become negative ions
  3. the oposite charges attract each other. this is known as electrostatic atraction. it results in a regulary aranged lattice.
  4. the bonds (electrostatic atraction) are very strong. alot of energy is needed to separate the ions
    1. high melting and boiling points
    2. solid at room temprature
  5. conduct electricity when molten or dissolved-ions free to move
  6. often dissolve in water - because water is polar
2. covalent bonding
  1. non-metal and non-metal
  2. they share electrons in their outer shells
  3. atoms do not become charged
  4. the convalent bond consists of the attraction between the negative shared electrons and the pull of the nucleus of the atom on either side
    1. this is eletrostatic attraction. huge amounts of energy is needed to break the bonds
  5. covalently bonded molecules have week IMB so have low melting/boiling points
  6. some elements form giant covalent networks which have extremely high boiling points e.g. dimond, silicon dioxide
    1. no IMB form just covalent
  7. dative covalent bonds
    1. both electrons in the shared pair are contributed by just one of the atoms
    2. an arrow stands as a dative covalent bond
3. metalic structures
  1. they have electrostatic attraction between the delocalised electrons and the positive metal ions.
  2. the delocalised electrons explain why metals conduct electricity
4. shapes of molecules
  1. 2 groups around centeral atom = 180 degrees, linear
  2. 3 groups around centeral atom = 120 degrees, trigonal planar
  3. 4 groups around centeral atom = 109.5 degrees, tetrahedral
  4. 6 groups around centeral atom = 90 degrees, octagonal
  5. groups of outer-shell electrons around an atom repel each other and move as far as part as possible.
inorganic chemistry and the periodic table

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elements of life

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	Created by greencat about 10 years ago