AS Chemistry Unit 1 : Section 1 - Atomic Structure

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138 Terms

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What are all elements made of?
atoms
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What are all atoms made up of?
protons, neutrons, electrons
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What takes up most of the volume of an atom?
The orbitals and the spaces between them
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True or false : electrons are static outside in their energy levels outside the nucleus
False - they whizz around the nucleus in orbitals
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Where is most of the mass of an atom located?
inside the nucleus - despite its diameter being 1/10000 of the whole atom
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What is the relative charge of a proton?
+1
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What is the relative charge of a neutron?
0
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What is the relative charge of an electron?
-1
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What is the relative mass of a proton?
1
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What is the relative mass of an electron?
1/2000
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What is the relative mass of a neutron?
1
12
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What is the mass number?
the total number of protons and neutrons in a nucleus.
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What is the atomic number?
number of protons in the nucleus
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What is special about the proton number?
All atoms of the same element p have the same number of protons?
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For a neutral atom...
the number of protons equals the number of electrons
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How do you work out the number of neutrons?
mass number - atomic number
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How do atoms from ions?
By gaining or losing electrons
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Negative ions have \____ protons than electrons
less
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Positive ions have \______ protons than electrons
more
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What are isotopes?
atoms with the same number of protons but different number of neutrons
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Do isotopes of the same element have the same chemical properties?
Yes , they have the same configuration of electrons , so they have the same chemical properties
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Do isotopes of the same physical properties?
No - these differ slightly as they tend to depend on the mass of the atom
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Give 2 examples of physical properties
Density , rate of diffusion , boiling point , SHC etc
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What did John Dalton describe atoms as ?
Solid spheres that made up different elements
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In 1897, what did J J Thompson Conclude from his experiments ?
An atom must contain even smaller , negatively charged particles - electrons. The solid sphere idea of the atom had to be changed
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What was J.J. Thomson's model called?
Plum pudding model
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Describe the plum pudding model
The plum pudding model suggested that an atom is a ball of positive charge with negative electrons in embedded in it
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What experiment did Rutherford conduct?
Gold foil experiment
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Describe the process of the gold foil experiment
They fired alpha particles (positively charged) at a thin sheet of gold
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What did Rutherford expect to see based off the plum pudding model?
They expected to see most of the particles to be deflected slightly by the positive 'pudding' that made up the atom
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What are the results of the gold foil experiment?
Most of the a,pua particles past straight through the ms and a very small number were deflected backwards. Therefore the Plum pudding model couldn't be right
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What did Rutherford conclude? What did his new model consist off?
Most of the atom is empty space. His model consisted of a tiny positively charged nucleus at the centre surrounded by a cloud of negative electrons
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What 4 basic principles did Niels Bohr propose with his new model:
1. Electrons only exist in fixed orbits (shells) and not anywhere in between
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2. Each shell has a fixed energy

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3. When an electron moves between shells electromagnetic radiation is emitted or absorbed

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4. Because the energy of shells is fixed the radiation will have a fixed frequency

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What did scientists after Bohr discover?
Not all the electrons in a shell had the same energy - they refined Bohrs model to include sub shells
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What is the most accurate model of the atom we have today based on?
Quantum mechanics
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What is the relative atomic mass?
The average mass of an atom of an element compared to one twelfth of the mass of an atom of carbon 12.
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What is relative isotopic mass?
The mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
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What is relative molecular mass?
The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12
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What 3 things can a mass spectrometer be used to find?
Relative atomic mass of elements
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Relative molecular mass of compounds

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Relative abundance of isotopes

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What are the 4 stages of mass spectrometry
Ionisation, acceleration, ion drift, detection
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What are the 2 ways of ionising a sample
Electrospray ionisation
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Electron impact ionisation

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Describe electrospray ionisation
The sample is dissolved and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing each particle to gain a H+ ion. The sample is turned into a game made up of positive ions
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What happens in electron impact ionisation?
The sample is vaporised and an 'electron gun' is used to fire high energy electrons at it. This knocks one electron off each particle, so they become +1 ions.
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Describe the acceleration period during mass spectrometry
The positively charged ions are accelerated by an electric field so that they all have the same kinetic energy (this means that the lighter ions will end up moving faster than the heavier ions
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What happens during ion drift?
The ions enter a region with no electric field , so they just drift through it. Lighter ions will drift through faster than heavier ions
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Describe how a detector works
A detector records the different ions as they arrive at the detector. At the detector each positive ion gains an electron which generates a current. The size of the current is proportional to the abundance of each ion.
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What happens during detection (mass spectrometry)
Because the ions that have a lower/mass charge ratio travel at higher speeds in the drift region, they reach the detector in less time than ions with a higher mass/ charge ratio. The detector detects charged particles and a mass spectrum is produced
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ions with a lower mass/charge ratio travel through drift region at ..... speeds
higher
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Ions with a higher mass / charge will take \__ time to reach the detector
More
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Why must a vacuum be used during mass spectrometry?
We don't want the ions to collide with other particles in air
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If electron impact ionisation was used how do you find the relative mass of an isotope from the mass spectrum
The mass / charge ratio of the peak is the same as the relative mass of that isotope
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If electrospray ionisation was used how do you use the mass spectrum to find the relative mass of that isotope
A H+ ion would have been added to each particle to for, +1 ions so the mass charge ratio of each peak would be one unit greater than the relative mass of each isotope
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What 3 steps must thou take to calculate the relative atomic mass from a mass spectrum
1. For each peak read the the % relative isotopic abundance from the y axis and the relative isotopic mass from the x axis . Multiply them together to get the total mass for each isotope
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2. Add up these totals

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3. Divide by 100 (as percentages were used)

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What should you do if the relative abundance is not given as a percentage
The total abundance may not add up to 100 . Do steps 1 and 2 and then divide by the sum of the relative abundances
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True or false: many elements only have 2 stable isotopes
False many elements only have 1 stable isotope
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On a mass spectrum , what is on the y axis
% abundance of isotopes
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On a mass spectrum, what should go in the x axis
Mass / charge
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If the sample is an element what does each line represent (on a mass spectrum)
A different isotope of the element
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explain how you can get a mass spectrum for a molecular sample
1) a molecular ion , M+ is formed in the mass spectrometer when one electron is removed from the molecule
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2. This gives a peak in the spectrum with a mass/charge ratio equal to the relative molecular mass of the sample

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3. This can be used to help identify an unknown compound

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What is a molecular ion peak?
The peak with the highest m/z ratio in the mass spectrum - this represents the mass/charge ratio of the molecule being analysed
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Electron shells are made up of...
sub-shells and orbitals
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Electrons have \____ energies
Fixed
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What is the number given to each shell called?
Principal quantum number
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the further the shell is from the nucleus
the higher it's energy and the larger it's principal quantum number
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True or false: Electrons in the same sub shell have the same energy
True
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True or false : the sub shells in the same shell have the same energy
False : sub shells have slightly different energies
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How many electrons can each orbital hold?
2 electrons
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How many orbitals does an s sub shell have!
1
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What is the maximum number of electrons in an s sub shell
2
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How many many orbitals does a p sub shell have?
3
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What is the maximum number of electrons in a p sub shell
6
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How many orbitals does d have?
5 orbital
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What is the maximum number of electrons in a d sub shell
10
84
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How many rebuttals does an f sub shell have
7
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What is the maximum number of electrons in a f sub shell
14
86
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What is the maximum number of electrons in the first energy level
2 electrons
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What is the maximum number of electrons in the second principal energy level?
8
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What is the maximum number of electrons in the 3rd energy level?
18
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What is the maximum number of electrons in the 4 th energy level?
32
90
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Name all the sub shells in the 1 st energy level
1s
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Name all the sub shells in the second energy level
2s 2p
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Name all the sub shells in the third energy level
3s 3p 3d
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Name all the sub shells in the 4th energy level
4s 4p 4d 4f
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Electrons fill up the \____ energy sub shells first
Lowest
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What are the 3 rules of electron configuration
1) electrons fill up the lowest energy sub shells first
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2) electrons fill orbitals singly before they start sharing

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3. For the configuration of ions from the s and p block of the periodic table, just remove or add electrons to or from the higher st energy occupied sub shell

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What can you use for shorthand sub shell notation
Noble gases
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Describe how chromium and copper are exceptions to electronic configuration rules
They donate one if their 4s electrons to the 3D sub shell, because they're happier with a more stable full or half full d sub shell
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What else is unusual about transition metals (electron configurations)
When they become ions , they lose their 4s electrons before their 3d electrons