AQA AS Chemistry Atomic Structure

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  • Created on: 23-10-12 10:56
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Atomic Structure
Fundamental Particles
Protons have a relative charge of 1+ and a relative mass of 1.
Electrons have a relative charge of 1- and a relative mass of 1/1836.
Neutrons have a relative charge of 0 and a relative mass of 1.
The mass number of an atom is the total number of neutrons and protons.
The atomic number is the total number of protons in an atom.
The atomic number is also the number of electrons.
Early models of the atom predicted that elements with a noble gas structure will be more stable (i.e. Group 0).
Protons, Neutrons and Electrons
There are various models to illustrate atomic structure:
The Plum Pudding Model is no longer accepted due to an experiment by Hans Geiger and Ernest
Rutherford showed that mostly empty space and nucleus is small +
Rutherford's Model suggested that the nucleus was tiny and where most of the mass was concentrated.
The electrons went around the nucleus and most of the atom is just empty space.
The Bohr Model of the atom shows us that electrons have a fixed distance and energy around the nucleus
and the modern atomic orbital model was born.
particles were used to bombard atoms and prove the existence of electrons and neutrons.
Mass Number and Isotopes
(A)- is the letter used for the relative atomic mass of an atom, it is the number on the top in a periodic table.
(Z)- is the letter used to represent the number of protons in an element. Also known as the atomic number. It
is the number on the bottom of the periodic table.
o Isotopes are elements with the same atomic number but different mass numbers.
o This means that they have a different number of neutrons.
o As a result they have the same chemical properties but different physical properties.
o The isotope with more neutrons has:
A higher m.p. and b.p.
A higher mass
A higher density
Slower rate of diffusion
Simple Mass Spectrometry
Vaporization: - They must be turned into a gaseous state so that they can be separated and move more easily.
Ionization: - The atoms are bombarded with high speed electrons from an electron gun and this in turn knocks of an
electron. This means that they have become ions with a 1+ charge.
Acceleration: - This is the process when the ions move through an electric field so that they move quickly. Also they
can be focused into a narrow beam through the acceleration chamber.
Deflection: - The ions are deflected using an electromagnet and this changes their path depending on the m/z ratio.
There are many factors which can affect deflection:
Heavier ions are deflected less than smaller ones.
Ions with a greater m/z ratio are deflected less than ions with a lower m/z ratio.
Ions with a greater velocity are deflected less.
Ions with a greater charge are deflected more.
Altering the magnetic field strength brings different ions to the detector.
Detection: - There is a negative plate at the detector which, when hit with the ions, produces an electric current. The
bigger the current, the more abundant the ion is. As we said before, altering the magnetic field strength brings
different ions to the detector.
Mass Spectrometry has many uses. It is used in space probes to analyse soil samples and also atmospheric
gases.
It is used to find out the abundance of isotopes in a sample or the different ions in a sample.

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Simple Mass Spectra
Can be used to show us the relative abundance of an atom/ion in a sample- this is along the y-axis.
Can tell us the m/z ratio of elements- this is along the x-axis.
To find out the Ar we can just read off the x-axis (as long as the charge is 1+). If not then we have to do
mass/charge to find the Ar.…read more

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Aufbau Principle- Electrons fill energy levels in order of increasing energy. This means that the 1st energy
level fills first as it has the lowest amount of energy.
Pauli Exclusion- Electrons fill in orbitals. Each orbital can only hold a maximum of 2 electrons and these fill with
opposite spins.
Hund's Rule- Electrons fill all vacant orbitals with the same spin and then once all vacant orbitals are filled then
electrons start pairing up, but they pair up with the opposite spin.…read more

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In period 3 there are abrupt drops between Mg and Al and between P and S, this offers us evidence for
sub-levels.
o The abrupt drop between Mg and Al is because Mg is (Ne) 3s2 and Al is (Ne) 3s2 3p1. This means that because
Al has the 3p sub-level it's further away from the nucleus and more shielded. This in turn means that lower
ionization energy is required.
o The abrupt drop between P and S happens due to their spin diagrams.…read more

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