Chem1

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What is the mass number of an atom?
The totoal number of protons and neutrons in the nucleus of an atom.
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What is the atomic number of an atom?
The number of protons in the nucleus of an atom.
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What is an Isotope?
Atoms of an element with the same number of Protona but a different number of neutron. They have the same chemical properties because they have the same electon configuration and different phsical properties due to different masses.
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What is relative atomic mass?
The average mass of an atom of an element on a scale where Carbon-12 is exactly 12.
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How do you calculate relative atomic mass?
((mass x abundance)+(mass2 x abundance2)) divided by 100
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What is relative isotopic mass?
The mass of an atom of an element on a scale where carbon-12 is exactly 12.
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What is relative molecular mass?
The average mass of a molecule on a scale where carbon-12 is exactly 12.
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What is relative fromula mass?
The average mass of a formula unit on a sccale where Carbon 12 is exactly 12.
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Mass Spec step 1
The sample is turned into a gas using and electrical heater.
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Mass spec step 2
The gas particles are bombarded with electons to ionise them. Electrons are knocked off, leaving positive ions.
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Mass spec step 3
The magnetic field deflect lighter ions as they have less momentum. For a given magnetic field only ions with a particular mass/charge ratio pass through.
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Mass spec step 4
The magnetic field strength is slowly increased. As this happen different ions reacch the detector. The bigger the currentg generated, the more of that isotope there is.
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What does the y-axis of Mass Spectra shoe?
The abundance of ions.
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What does the height of each peak show?
Relative abundance
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What does the X-axis show?
Mass/charge ratio
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Define first ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to from one mole of 1+ electrons.
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How does Nuclear charge affect ionisation energy?
The more protons there are in the nucleus, the more positively charged it is so electons are more stongly attracted to it.
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How does the distance from the nucleus affect ionisation energy?
Attraction falls off rapidly with distance. An electrron close to the nucleus will be much more strongly attracted than one further away.
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How does shielding affect ionisation energy?
As the number of electrons between the outer and electrond and the nuvleus increseases, the outer electrons feel less attraction towards the nuclear charge.
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Pairing
Two electrons in the same orbital experience repulsion which offsets the atrraction from the nucleus, so that paired electrons are removed rather more quickly.
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Why does ionisation energy decrease down a group?
Each element down the group has an extra electron shell compared to the one above. The extra inner electrons will shiled the outer ones from the attraction and there will be more distance between electrons and nucleus thus reducing the attraction.
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Why does ionisation energy increase (except for Al and P) as you go across a period?
The number of protons is increasing, which means there is a stronger nuclear attraction.
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What is a mole?
6 x (10^23) paricles, it is also called Avogadro's constant.
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What is Molar mass?
The mass of one mole of something. It is the same as the relative molecular mass but its unit is gmol^-1.
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How do you calculate the number moles?
Number of moles= Mass (g)/Molar mass
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How do you calculate moles using concentration and volume?
Moles= (conc x vol in cm^3)/1000 OR (Conc x vol in dm^3)
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If temperature and pressure remain constant how do you calculate the number of moles?
moles= vol in dm^3/24 or vol in cm^3/24000
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what is the ideal gas equation?
Pressure (pa) x volume (m^3)= moles x temperature (K) x gas constant
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Define empirical formula.
The smallest whole number ratio of atoms in a compund.
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How do you find a molecular formula?
Molecular mass divided by empirical mass.
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How do you calculate percentage yield?
(actual yield/theoretical yield) x 100
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How do you calculate percentage atom economy?
(mass of desired product/mass of reactants) x 100
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How is an ionic bond formed?
When electrons are transferred from one atom to another. Electrostatic attraction hold positive and negative ions together.
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Describe the structure of Sodium Chloride.
It is a giant ionic lattice.It is made up of the same basic untis repeated over and over again. -Cl-Na-Cl-
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Describe the solubility of an Ionic compound
They tend to dissolve in water, because water is polar and "like dissolves like".
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Describe the electrical conductiviy of ionic compounds.
They conduct electricity when they are molten or dissolved but not when they are solid.
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Describe the melting point of Giant ionic Lattices.
A lot of energy is required to overcome the strong electrostatic forces so they have a high melting point.
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Describe a metallic bond.
The outermost shell of a metal atom is delocalised, so electrons are free to move. This leaves a positive metal ion which is attracted to the negatively charged delocalised electrons, forming a lattice of ions in a sea of delocalised electrons.
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How does the number of delocalised electrons affect melting point?
The more delocalised electrons there are, the stronger the bonding will be and the higher the melting point.
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Why do metals have the ability to be shaped?
There are no bonds jolding specific ions together, therefore the metal ions can slide over eachother when the structure is pulled. They are malleable and ductile.
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How do metals conduct electricity?
The delocalised electrons pass kinetic energy to eachother, making metals good conductors of heat and electricity.
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Describe the solubility of metals.
Metals are insoluble, except in liquid state. This is due to the strength of the metallic bonds.
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How does a covalent bond occur?
Formed when two atoms share electrons. There can be single, double or triple bonds. Both the positively charged nuclei are electrostatically attracted to the shared electrons.
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Why do simple covalent compounds not conduct electricity?
Because there are no free ions to carry the charge.
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Why do simple covalent compounds have a low melting point?
Because the weak forces of attraction between molucles are easily broken.
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Describe the solubility of simple covalent compounds.
Some dissolve in water depending on how polarised thee molecules are.
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Describe the structure of Graphite.
Each carbon atom makes 3 bonds. The fourth outer electron of each atom is delocalised. The sheets are bonded together by weak Van der Waals forces.
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Describe the properties of Graphite.
Sheets can easily slide over eachother because of weak bonds between sheets. An electric current can flow due to delocalised electrons. It has a low density, a high melting point (covalent bonds) and it is insoluble.
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Describe the structue of Diamond.
each carbon atom is bonded to four other carbon atoms arranged in a tetrahedral shape.
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Describe the properties of Diamond
It has a high melting point, extremely hard, good thermal conductor, it cannot conduct electricity and it is insoluble.
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What is a dative covalent bond?
When one of the atoms provides both of the shared electrons.
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What is electronegativity?
The ability to attract the bonding electrons in a covalent bond. It is measured on the pauling scale, with Fluorin being the most electronegative element.
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What is a dipole?
A difference in charge between the two atoms caused by a shift in electron density in the bond.
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Describe permanent dipole-dipole forces
the delta positive and delta negative charges on a polar molecule cause weak electrostatic forces of attraction between molecules.
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Describe Hydrogen bonding
Only happens when hydrogen is bonded to fluorine, nitreogen or oxygen, it is the strongest type of intermolecular force. The O,N and F are very electronegative so they pull electrons towards them.
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How do Permanent Permanent dipole forces occur?
These occur when a molecule has two atoms bonded together with significantly different electronegativities (polar molecules.
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What is an instantaneous dipole?
In molecules made from atoms with similar electronegativities, the electrons on the bond move more towards one atom than the other.
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How does a induced dipole occur?
A permanent dipole induces a dipole in another molecule, then the two attract eachother.
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How do Van de waals forces occur?
an instantaneous dipole induces a dipole then attracts that molecule. Present in all molecules.
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How does atomic radii change across period 3?
It decreases because as the number of protons increases, the relative charge increases. This pulls electrons closer to the nucleus. The extra electrons do not affect shielding.
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How does ionic radii change across period 3?
decreases from Ns to Si as electrons are lost. Increseease at P and the decreases to Cl as ellectons are beeing gained.
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Why does melting point increase from Sodium to Aluminium?
The charge increases from 1+ to 3+ so the number of delocalised electrons increase, increasing the strength of the metallic bond.
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Why does Silicon have a high melting point?
It has a giant covalent structure resembling diamond. Each silicon atom is covalently bonded to four others. These covalent bonds are very strong and require large amounts of energ to break.
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Why so P,S,Cl and Ar have low melting points?
Because little energy is required to overcome the van der waals forces between molecules. The strength of the van der waals forces decreases as size decreases - S^8, P^4, Cl^2, Ar
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Why does ionisation energy increase across period 3?
Because the numbe rof protons is increasing, meaning there os an increasing atraction between the outer shell and the nucleus.
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What is an isomer?
Compunds that have the same molecular formula but a different structural formula.
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What is a chain isomer?
compounds that have different arrangements of the carbon skeleton.
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What is a positional isomer?
Compounds that have the same skeleton and atoms but the atom/group is attached to a different carbon atom.
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What is a functional group isomer?
These have the same atoms arragnged into different functional groups.
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How are alkanes separated from crude oil?
Through fractional distillation. Vapours rise up the column and they are tapped off at different heights due to temperature gradients, there are bubble gaps preventing them from going back when the condense.
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Describe Catalytic cracking.
Carried out at lower temperatures (450) and pressures. Catalysts are Zeolites. It can produce many branched alkanes, cycloalkanes and aromatics. Mechanisms involve the formation of carbocations.
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Describe thermal cracking.
Uses higher temperatures (900) and pressures (7000 kpa). Produces a large proportion of Alkenes.The higher the temperature, the closer the chain breaks giving smaller alkanes. It uses a free radical mechanism.
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What is the formula for complete combustion?
Alkane + o.5nOxygen = nCarbon dioxide + n+1water
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What are the formulas for incomplete combustion?
1)alkane + oxygen = water +carbon monocide + carbon 2) alkane +oxygen =water +carbon monoxide 3) ALkane +oxygen =water +carbon
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Why is sulfur dioxide bad for the environment?
It can cause acid rain.
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How is sulfur dioxide removed from crude oil?
Flue gas desulfurization: sulfur dioxide + Calcium (hyd)roxide = calcium sulfite + water
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How is carbon monoxide formed in the internal combustion engine? why is it bad and how is it removed?
It is formed through incomplete combustion. The gas binds irreversibly to haemoglobin. It is reacted with Oxygen to produse carbon dioxide in a catalytic converter.
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How are oxides of nitrogen formed? why are they bad and how are they removed?
They are formed from high temperatures in the engine. They react with unburnt hydrocarbons to form low level ozone and contributes to acid rain. They are reacted with CO to make nitrogen and carbon dioxide.
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Why are unburnt hydrocarbons bad? How are they removed?
They react with NO gases to form low level ozone. Benzen and Buta-1-3-diene are carcinogens.
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Describe how carbon monoxide and nitrogen oxide are removed in a catalytic converter.
The CO and NO diffuse over the catalyst and are adsorbed over the surface. Temporary bonds form. The bond in the gas molecules are weakened allowing a reaction to take place. ONe they have reacted, the gas molecules Desorb from the surface and difuse
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Card 2

Front

What is the atomic number of an atom?

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The number of protons in the nucleus of an atom.

Card 3

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What is an Isotope?

Back

Preview of the front of card 3

Card 4

Front

What is relative atomic mass?

Back

Preview of the front of card 4

Card 5

Front

How do you calculate relative atomic mass?

Back

Preview of the front of card 5
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