Atomic structure.

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  • Created by: sydjow17
  • Created on: 14-12-19 13:38
Why do we assume there are equal number of protons and electrons in an atom?
The atom is neutral, so the number of protons and electrons must be the same, because their charge is equal in size and opposite in charge.
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What force holds together protons and neutrons in the centre of the atom?
The strong nuclear force.
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Which is stronger in an atom, the strong nuclear force or the electrostatic forces of attraction?
The strong nuclear force.
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Describe electrostatic forces.
The forces of attraction and repulsion between electrically charged particles.
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Define isotope.
Atoms with the same number of protons but different numbers of neutrons.
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Do isotopes react chemically in the same way?
Yes - they have the same electron configuration.
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What did Dalton suggest?
(1803) Elements were composed of indivisible atoms. All the atoms of a particular element had the same mass and atoms of different elements had different masses.
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What did Becquerel discover?
(1896) Radioactivity, which showed that particles could come from the inside of the atom.
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What did Thomson discover?
(1897) The electron and showed that they were negatively charged, which meant there had to be some source of positive charge; the plum pudding model.
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What did Rutherford find?
(1911) That most of the mass of an atom and all its positive charge was concentrated in a tiny nucleus.
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What idea did Bohr put forward?
That the atom consisted of a tiny positive nucleus orbited by negatively-charged electrons. The electrons orbited in shells of fixed size and the movement of electrons from one shell to the next explained how atoms absorbed and gave out light.
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What did Schrodinger work out?
An equation that used the idea that electrons had some properties of waves as well as those of particles. This led to the theory called quantum mechanics.
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What did Chadwick discover?
The neutron.
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How do you work out the number of electrons a shell can hold?
2n^2, where n is the number of the shell.
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Define relative atomic mass, Ar.
Average mass of an atom / 1/12th mass of 1 atom of 12C.
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Why do no other isotope, other than carbon-12, have a relative atomic mass that is exactly as whole number?
Neither the proton nor the neutron has a mass of exactly 1.
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What is mass spectrometry?
An analytical technique that measures the mass-to-charge ratio of one or more ions/molecules present in a sample.
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What does a mass spectrometer tell us?
It gives accurate information about relative isotopic mass and also about the relative abundance of isotopes.
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What are the principles of a time of flight (TOF) mass spectrometer?
Ionisation, acceleration to give all ions constant kinetic energy, ion drift, ion detection and data analysis.
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Why is the TOF mass spectrometer apparatus kept under a high vacuum?
To prevent the ions that are produced colliding with molecules from the air.
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What are the two types of ionisation used?
Electrospray ionisation and electron impact.
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What determines which type of ionisation is used?
Electron impact is used for elements and low Mr compounds. Electrospray ionisation is used for high Mr compounds (e.g. proteins).
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Describe the process of electron impact.
High energy electrons are fired at the sample from an electron gun. This knocks off one electron from each atom/molecule to form 1+ ion.
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What happens during acceleration of ions?
The ions are accelerated using an electric field so that all the ions have the same kinetic energy (where kinetic energy = 0.5mv^2)
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What happens during the separation of ions?
Ion drift - the ions then enter the flight tube (length d). Ions with different masses (mass m) have a different time of flight. The light ions travel faster and take less time to reach the detector, where t= √(m/2KE).
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What is the difference between high and low resolution mass spectrometry?
Low resolution mass spectrometry is to one decimal point, whereas high resolution mass spectrometry is to five decimal places.
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How do you find the average mass of atoms from a mass spectrum?
= total mass of all the atoms / total number of atoms.
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Why is there a small peak at Mr+1 of a mass spectrum when finding Mr of molecules?
Due to a small number of molecules containing carbon-13 or hydrogen-2 atoms; due to isotopes.
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Define atomic orbital.
A region of space around the nucleus where there is a high probability of finding an electron.
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What is different about the 4s sub-level of an atomic orbital?
It is of slightly lower energy than the 3d sub-level for neutral atoms, although this can change when ions are formed.
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How many electrons can an orbital hold?
2 electrons with opposite spin.
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Give the electron arrangement for chromium (24 electrons).
1s2 2s2 2p6 3s2 3p6 3d5 4s1
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Give the electron arrangement for copper (29 electrons).
1s2 2s2 2p6 3s2 3p6 3d10 4s1
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Define ionisation energy.
The energy required to remove a mole of electrons from a mole of atoms, in the gaseous state (kJ/mol).
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What are the three factors that affect the ionisation energy?
Atomic radius (distance from nucleus), nuclear charge and shielding.
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Other cards in this set

Card 2

Front

What force holds together protons and neutrons in the centre of the atom?

Back

The strong nuclear force.

Card 3

Front

Which is stronger in an atom, the strong nuclear force or the electrostatic forces of attraction?

Back

Preview of the front of card 3

Card 4

Front

Describe electrostatic forces.

Back

Preview of the front of card 4

Card 5

Front

Define isotope.

Back

Preview of the front of card 5
View more cards

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