Atomic Structure - Unit 1

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  • Created on: 10-05-15 09:40
Relative charge and mass of a proton
Relative charge = 1 Relative mass = !+
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Relative charge and mass of a neutron
Relative charge = 1 Relative mass = 0
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Relative charge and mass of an electron
relative charge = -1 Relative mass = 1/2000
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What is the mass number
the number of protons and neutrons found in the nucleus of an atom
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What is the atomic number
the number protons found in an atom
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What are isotopes
Isotopes of an element are atoms with the same number of protons but different number of neutrons
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What does the electronic configuration of an atom control
The chemical properties,hence isotopes have the same electronic configuration. But physical properties alter slighly due to different densities and rates of diffusion. This is because physicalproperties tend to depend on more on the mass of the atom
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In the 19th century, how did John dalton describe atoms
As solid spheres and said that diffent spheres made uo different elements
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What did JJ Thompson conclude from this
Atoms weren't solid and indivisible. his measurements of charge and mass showed that an atom must contain smaller, negatively charged particles. The new model was known as the 'plum pudding model'
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What new evidence did Ernest Rutherford's famous 'gold foil' experiment provide?
there is a tiny positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons - most of the atom is empty space
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What were the modifications of Niels Bohr' model
- Electrons only exist in fixed orbitals and not anywhere in between. - Each shell has a fixed energy - When an electron moves between shells electromagnetic radiation is emitted or absorbed - Energy of shells is fixed,
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How was Bohr' model no quite right?
not all elctrons has the same energy, so scientist refiened the model to have sub shells. Bohrs' model explained why some elememts are inert due each shell can hold a fixed number of electrons and an element's re activity is due to its electrons.
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What is the main advantage of the the quantum model
You never know where an electron really is or which direction it is going in also an electron can act as a wave and a particle. therefore scientists use which ever model is relevant for what they are investigating.
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What is relative atomic mass
The relative atomic mass,Ar, is the average mass of an atom of an element on a scale where an atom of carbon 12 is exactly 12. The relative atomic mass of each element is exactly 12
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What is meant by relative isotopic mass
the relative atomic mass is the mass of an atom of an isotope of an element on a scale where an atom of carbon - 12 is exactly 12.
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How do you calculate relative atomic mass
isotopic masses x percentages divided by total percentages
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What is meant by relative molecular mass and how do you work it out?
the average mass, Mr of a molecule on a scale where an atom of carbon 12 is exactly 12. To find Mr, just add up the relative atomic mass values of all atoms in the molecules
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what is the relative formula mass and how do you work it out
average mass of a formula unit on a scale where an atom of carbon 12 is exactly 12.
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What is the first step of Mass Spectroscopy
Vaporization - The sample is turned into gas (vaporized) using an electrical heater
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What is the second step of Mass spectroscopy
ionisations - The gas particles are bombarded with energy electrons to ionise them. Electrons are knocked off the particles, leaving positive ions.
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What is the the third step of Mass spectroscopy
Acceleration - positive ions are accelerated by an eletric field
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What is the fourth step of Mass spectroscopy
The positive ions paths are altered with a magnetic field. Lighter ions have less momentum and a re deflected more that heavier ions. For a given magnetic field, only ions with a particular mass/charge ratio make it to detector
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What is the fifth step to Mass spectroscopy
Detection - Magnetic field is slowly increased. As this happens, ions with increasing mass can reach the detector. As th eions hit the detector they cause a current to flow. The bigger the current the more isotope present in the sample
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What does a mass spectrometer find out about
Relative atomic mass, relative molecular mass, relative isotopic mass, relative isotopic abundance, molecular structure.
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Calculating relative molecular mass
A molecular ion M+ is formed when electrons bombard the molecule. An electron is removed from teh molecule resulting in a peak in the mass spectrum with the highest mass. The mass of M+ gives Mr for the molecule.
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Cont
However bombarding with electrons causes fragmentation of the molecule hece show up one mass spectrum as fragmentation patterns
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Definition of Ionisation Energy
The first ionistation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1 + ions
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What Factors effect ionistation energy
Nuclear charge - More protons there are in a nucleus, the more positively charged the nucleus is and much more strongly attracted thatn one further away.
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Cont
Distance from nucleus - Attraction falls off very rapidly with distance. An electron close to the nucleus will be mor strongly attacted than one further away.
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Cont
Shielding - Number of electron between outer electrons and ucleus increases, outer electrons feel less attraction towards the nuclear charge. This lessens the pull of the nucleus by inner shell s of electrons .
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Definition of second ionisation energy
The energy needed to remove an electron from each ion in 1 mole og gaseous 1+ ions
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Why is second ionisation energy higher
because the electron is being removed from a positive ion, which requires more energy. The electronic configuration also plays a role in how much lager the second ionisation energy is that the first
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What is the Ionisation trend down group 2
First ionisation energy decreases down group 2. This provides evidence that electron shells do exist. If each element down group 2 has an extra electron shell compared to the one above , the extra inner shells will shield the outer electrons.
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Cont
from the nucleus, also extra shells mean that outer electrons are further away from the nucleus so nucleus attraction is reduced. Hence makes it easier to remove electrons therefore ionisation energy will be reduced
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First Ionisation energy across period 3
Increases. Number of protons is increasing therefore nuclear charge is increasing which means stronger nuclear attraction. All the extra electrons are roughly around the same energy level therefore little sheilding involved.
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Exceptions - drop between Grop 2 and 3
Aluminium's outer elctron is in a 3p orbital rather than a 3s orbital. The orbital has a slightly higher energy than a 3s orbital, so the electrons in average are found further away from nucleus
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Cont
The 3p orbital has additional shielding provided by the 3s2 electrons. Both these factors are strong enough to override the effetc of increased nuclear charge. Hence IE decreases
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drop between group 4 and 6
The shielding is identical in teh phosphourous and sulfur atoms and the electron is being removed from an identical orbital.
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cont
In phosphourous case the elctron is being removed from a singly occupied orbital. But in sulphur electron is being removed from an orbital containig 2 electrons. Repulsion between the two electrons means the electrons are easier to remove from shared
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