Atomic Structure

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  • Atomic Structure
    • The Atom
      • Mass & Atomic Number
        • Neutral atoms, number of electrons = number of protons.
          • Neutrons = mass no - atomic no
        • Atomic Number - Protons only in nucleus. Identifies element.
        • Ions = atoms with gained or lost electrons. Negative charge = gained. Positive = lost.
          • Isotopes have same chemical but different physical properties. E.g. Different densities and rates of diffusion because they depend more on mass of atom.
        • Mass Number  - Total number of protons & neutrons in nucleus
      • Structure of Atom
        • Elements made from atoms. Atoms made from protons, neutrons & electrons
          • Protons & neutrons in nucleus. Electrons in orbitals.
      • Isotopes
    • Relative Mass
      • Calculating Relative Atomic Mass
        • (Isotopic Masses x percentages) / 100 (total percentage)
      • Relative Isotopic Mass
        • Mass of atom of isotope on scale where carbon 12 = 12.
      • Relative Molecular Mass
        • Mr = Average mass of a molecule on a scale where carbon 12 = 12
        • Mr = add up Ar of all atoms in molecule
      • Relative Atomic Mass
        • Ar = average mass of atom on scale, carbon 12 = 12.
      • Relative Formula Mass
        • Average mass of a formula unit on scale where carbon 12 = 12
          • Used for ionic compounds. Add Ar of all molecules taking ions into account.
    • Mass Spectrometer
      • How it Works
        • 1. Electrospray Ionisation - Dissolved in polar substance, pushed through nozzle at high pressure. High voltage applied, loses electron, separated from solvent.
          • 2. Acceleration -  Positive ions accelerated by electric field. Same kinetic energy to all ions. Lighter ions accelerate more.
            • 3. Ion Drift - Ions leave electric field with constant acceleration & KE. Enter region of no electric field with same acceleration. Lighter ions travel faster.
              • 4. Detection - Lighter ions travel faster, reach the detector in less time. Detects the current created when hitting the detector. times how long in the spectrometer for. Calculates mass / charge values to produce mass spectrum.
      • Interpreting a Mass Spectrum
        • Data from spectrometer.
          • If sample is an element, each line is an isotope. Y-axis is the abundance of ions. X-axis is mass/charge ratio. All are ions (1+) presume it is the relative isotopic mass. Height of peaks is relative isotopic abundance.
      • Identifying Element
        • Elements with isotopes has more than one line, produces characteristic patterns used to identify a certain element.
    • Using Mass Spectra
      • Calculating Relative Molecular Mass
        • Mass/charge ratio = Mr, used to identify an element.
      • Calculating Relative Atomic Mass
        • 1. Read % abundance from y-axis & Relative isotopic mass from x-axis. Multiply = total relative mass for each isotope.
          • 2. Add up totals.
            • 3. Divide by 100 or the total relative abundance (may not be given as %).
    • Electronic Structure
      • Configuration of Transition Metals
        • Chromium and Copper donate a 4s electron to the 3d shell.
          • More stable with full or half full d shell.
        • Lose 4s electrons before 3d.
      • Electronic Structure & Chemical Properties
        • Outer shell electrons determine chemical properties
          • Group 1 & 2 lose electrons and become positive ions
          • Group 5, 6 & 7 Gain electrons and become negative ions
          • Group 0 doesn't gain or lose electrons so is inert.
      • Electron Shells
        • Each shell given a number called the principal quantum number
        • Shells divided into different amounts of sub-shells
          • Sub-shells have different amounts of energy (S, P, D, F).
            • Sub-shells have different numbers of orbitals that can hold up to two electrons.
              • S - 2 electrons         P - 6 electrons         D - 10 electrons          F - 14 electrons
      • Working out Configuratio-n
        • Showing electron configuration
          • Sub-shell notation
          • Arrows in boxes
          • Energy Level diagram
        • Follow Rules
          • 1. Fill lowest energy sub-shell first
            • 2. Electrons fill sub-shells singularly before sharing
              • 3. Configuring ions from s and p block, add or remove from highest energy occupied sub-shell.
    • Ionisation Energies
      • Trends - Group 2
        • 1st ionisation energy decreases down group
          • Proof for shells. Increased shielding and larger distance between electrons and nucleus.
      • Second IE
        • Energy needed to remove 1 electron from 1 mole of gaseous 1+ ions
          • Greater than 1st energy as electron is removed from ion instead of an atom.
          • Electron configuration plays role in how much larger the 2nd energy is than the 1st
      • Trends - Across Period
        • Across period, general trend is energies increase, due to more protons
          • Al & S drop slightly due to starting to fill a new shell with more shielding and a larger distance between the nucleus and outer electrons.
        • Drop between groups 5 & 6 is due to electron repulsion
      • Successive IE
        • You can remove all of the atoms from an atom. Each time an electron is removed there is a successive ionisation energy
      • Ionisation
        • 1st ionisation energy=Energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
        • 1. Enter gas symbol, measure for gaseous atoms
          • 2. Refer to 1 mole  of an atom rather than 1 atom
            • 3. Lower ionisation energy = easier to form a positive ion.
      • Affecting Ionisation Energy
        • Nuclear Charge - More protons so stronger attractive force on electrons
        • Distance from nucleus - Closer to nucleus means stronger attraction
        • Shielding - lessening of pull on outer electrons due to more electrons in inner shells
      • IE & Shell Structure
        • Can work out how many shells and what group an element is in if you know the successive IEs.
          • Within each shell, successful IEs increase as a more positive ion is formed due to less electrons. Big jumps due to new shell
            • Number of electrons removed before big jump tells us the group.
            • Count number of electrons from right to left until next big jump to tell the number of electrons in each shell. This reveals the element.

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