Atomic Structure
- Created by: Former Member
- Created on: 10-04-14 13:01
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- Atomic Structure
- The Atom
- All elements are made up of atoms.
- Atoms are made up of protons and neutrons in the nucleus, and electrons orbiting the nucleus.
- Protons have a mass of 1 and a charge of +1.
- Neutrons have a mass of 1 and a charge of 0.
- Electrons have a mass of 0 and a charge of -1.
- In neutral atoms there is the same number of protons and electrons.
- Ions are charged particles that have either lost or gained electrons.
- Isotopes of an element are atoms with a different number of neutrons.
- Atomic Models
- Dalton and Thomson's model (the plum pudding) suggested that protons were large, solid, positive particle with small negatively charged particles inside.
- Rutherford's model suggested that an atom is a positively charged nucleus surrounded by smaller negatively charged particles.
- Rutherford disproved the 'plum pudding' via the gold foil experiment.
- Bohr's model is similar to Rutherford's model however suggests that electrons are found in fixed energy levels.
- Relative Mass
- Relative atomic mass is the average mass of an atom of an element on a scale where an atom of C12 is exactly 12.
- Relative isotopic mass is the average mass of an isotope of an element on a scale where an atom of C12 is exactly 12.
- Relative molecular mass is the average mass of a molecule on a scale where an atom of C12 is exactly 12.
- Relative formula mass is the average mass of a formula unit on a scale where an atom of C12 is exactly 12.
- Mass Spectrometry
- Mass spectrometers can tell you relative atomic mass, relative molecular mass relative isotopic abundance and molecular structure.
- 1. Vaporisation - the sample is turned into a gas.
- 2. Ionisation - The gas particles are bombarded by electron which knock electrons off the particles leaving positively charged ions.
- 3. Acceleration - The ions are accelerated by an electric field.
- 4. Deflection - Lighter ions are deflected by a magnetic field as they have less momentum so only ions with a specific mass/charge ratio are detected.
- 5. Detection - As ions hit the detector a current flows which produces a mass spectrum.
- A mass spectrum has abundance on the y axis and mass/charge on the x axis.
- Mass spectrometers can tell you relative atomic mass, relative molecular mass relative isotopic abundance and molecular structure.
- Electronic Structure
- Electrons are found in orbitals, within sub shells, within energy levels.
- Different energy levels contain different sub shells.
- The 1st energy level contains a 1s sub shell.
- The 2nd energy level contains a 2s and 2p sub shell.
- The 3rd energy level contains a 3s, 3p and 3d sub shell.
- The 4th energy level contains a 4s, 4p, 4d and 4f sub shell.
- Energy level diagrams and sub-shell notations are used to represent electronic structure.
- There are rules to electron structure.
- Electrons fill lowest energy sub shells first.
- Electrons fill orbitals singularly before sharing.
- When electrons are lost, they are lost from the highest possible energy level.
- Cu and Cr rather have a half or full 3d then a full 4s.
- 4s sub shell is filled before 3d.
- Ionisation Energies
- The first ionisation energy is the energy needed to remove 1 electron form each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
- There are 3 main factors that affect ionisation energy.
- Nuclear Charge - the higher the positive charge in the nucleus the greater the pull (so ionisation energy increases).
- Distance from nucleus - The greater the distance the less attraction between the nucleus and outer electron (so ionisation energy decreases).
- Shielding - the greater the number of electrons between the nucleus and outer electron the smaller the attraction (so ionisation energy decreases0.
- Down group 2 ionisation energy decreases as shielding and distance increases.
- Ionisation energy increases across a period as nuclear charge increases however decreases slightly as a new sub shell starts to fill.
- The Atom
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