Unit 1:Elements of Life

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Atomic number
Number of protons/electrons in the nucleus, all atoms of the same element have the same number of protons
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Mass number
Total number of protons and neutrons in the nucleus
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Isotope
Atoms with the same atomic number but different atomic mass
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One mole is roughly 6.02x10 23
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Relative isotopic mass
Mass of an atom of an isotope of an element relative to an atom of carbon-12 with a mass of 12
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Relative atomic mass
The average mass of an atom of an element relative to an atom of carbon-12 with a mass of 12
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Relative formula mass
The average mass of an ionic compound relative to an atom of carbon-12 with a mass of 12. (add up Ar of all the ions, top number)
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Relative molecular mass
The average mass of a molecule relative to an atom of carbon-12 with a mass of 12. (add up top numbers)
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Mass of substance calculations
Mass of substance (number with grams) = Number of moles (amount present/molar mass, total top number) x molar mass (total top number)
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Empirical formulae
Smallest whole number ratio of atoms in a compound i.e C4H3O2
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Molecular formulae
Actual numbers of atoms in a molecule i.e C8H6O4
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How to calculate molecular formula
1) Relative mass (total top numbers), 2) Molecular mass (given in question) / relative mass. 3)Times this number by those in empirical formula
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Percentage Composition calculation
Percentage by mass of each element in a compound i.e water=20% H, 80% O
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Percentage Composition calculation
1) Work out formula mass of compound in question (total top numbers) 2) Then divide the atomic mass of the element you're asked about (top number) by the formula mass worked out in step 1
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Protons
Mass = 1, Charge = +1, Bottom number, All atoms of same element have same no. of protons
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Neutrons
Mass = 1, Charge = 0, Top number - Bottom number
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Electrons
Mass = 0, Charge = -1
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Structure of atoms
Protons + Neutrons are in the nucleus, most of the mass of the atom is concentrated in the nucleus. Electrons whizz around the nucleus in shells, these shells take up most of the volume of the atom.
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Electrons absorb or release energy in fixed amounts
Atoms at ground state have electrons at lowest energy level. If atoms electrons take in energy, they move to higher energy levels, away from nucleus. At higher levels, electrons are excited.
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Electrons absorb or release energy in fixed amounts 1
Electrons then release energy by dropping to lower energy level. These energy levels have certain fixed values - they're discrete. Electrons jump to energy levels by absorbing or releasing a fixed amount of energy.
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Absorption Spectra
Energy's related to frequency. When electromagnetic radiation's passed through gaseous element, electrons absorb certain frequencies, corresponding to differences between energy levels.
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Absorption Spectra 1
Meaning radiation passing through has certain frequencies missing. The missing frequencies show up as dark bands on a coloured background.
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Emission Spectra
When electrons drop to lower energy levels, they give out certain amounts of energy. The frequencies in an emission spectrum are those that're missing in absorption spectra. These're coloured bands on black background.
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Similarities between absorption and emission spectra
Both line spectra. Lines become closer at higher frequencies. Sets of lines representing transitions to or from particular level.
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Differences between absorption and emission spectra
Either coloured lines on black background or black lines on coloured background.
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Energy is related to frequency calculation
Difference in energy between two shells (triangleE) = Planck's constant (h) x Frequency (V)
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Planck's Constant
6.63 x 10^-34
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Sub shell sequence
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6 etc
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How many electrons can fill each sub shell
S=2 P=6 D=10 and F=14
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Unstable atoms
If an atom is unstable, (it has too many neutrons, not enough neutrons or too much energy in nucleus), it'll break down to become stable. This is radioactive decay. Alpha, Beta or Gamma radiation can be emitted.
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Alpha properties
Helium nuclei, ^4HE2, Stopped by paper, Strong ionising ability, Slight deflection in electric field and few cm range in air
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Beta properties
Fast moving electrons, ^0e-1, Stopped by thin aluminium sheets, Moderate ionising ability, Large deflection in electric field and few metres range in air.
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Gamma properties
Very short wave electromagentic waves, Stopped by very thick lead, Weak ionising ability, Not deflected in electric field and very long range in air.
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Half-life
Time taken for half the radioactive nuclei in a sample to decay. The half-life is fixed for any given isotope.
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Half-life calculation
Number of years ago / Half-life. This number is equal to how many times the mass of sample should be multiplied by 2.
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Nuclear fusion
Two small nuclei combine under high temperature and pressure, to make one large nucleus. In stars, hydrogen nuclei combine, making helium nuclei, releasing large amounts of energy. When H+ ions run out, temp and pressure rises = heavier elements form
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As tracers move round body, there position is detected. Long half-life is dangerous as could be exposed to radiation for long time. Short half-life is inconvenient as wouldn't last long enough. Alpha emitters would ionise atoms inside body.
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Plants photosynthesise and absorb a bit of carbon-14, as it decays, it's replaced by more. When dead, the percentage of C-14 decreases. The smaller the %, the older it must be.
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Greeks atom structure
Thought all matter was indivisible 'atomos'
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John Dalton
19th century - Dalton said atoms were solid spheres, and said different spheres made up different elements.
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J J Thompson
1897- His measurements of charge and mass showed an atom must contain small, negatively charged particles - electrons. His model was a positively charged sphere with negative electrons embedded in it - plum pudding model
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Ernest Rutherford, Hans Geiger and Ernest Marsden Gold foil experiment
1909- Gold foil experiment = fired positively charged alpha particles at thin sheet of gold, expecting them to deflect slightly by positive charged pudding. But most a particles passed straight through, some deflected backwards more than 90 degrees.
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Rutherfords nuclear model
Nuclear model - Tiny, positively charged nucleus at centre with most of atoms mass, it's surrounded by a cloud of negative electrons. Most of atom is empty space.
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Henry Moseley
Discovered the charge of the nucleus increased from one element to another in units of one.
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Rutherfords further investigation
Found nucleus contained positive particles 'protons'. This explained charges of nuclei of different atoms - atoms of diff elements have diff number of protons in nucleus. Predicted other particles in nucleus with mass but no charge.
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Discovered the neutron
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Niels Bohr
Bohr Model - Electrons exist in fixed orbits/shells, shells have a fixed energy, when electrons move between shells electromagnetic radiation is emitted/absorbed, cause energy of shells is fixed radiation has a fixed frequency.
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How does the Bohr Model show that some elements are inert?
Shells of an atom can only hold fixed numbers of electrons, and an elements reactivity is due to electrons. When an atom has full shells, it's stable and doesn't react.
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Dot and Cross diagrams for ionic compounds
The atom that's lost an electron has a + outside the square, the atom that's gained the electron has a dot to represent the new electron, and a - outside the square.
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Ionic Bonding
Ions are formed when electrons are transferred from one atom to another. Happens between a metal and a non-metal. Can't conduct electricity in solid as in fixed position by strong ionic bonds, dissolve in H20 as molecules pull ions away from lattice.
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Dot and Cross diagrams for covalent bonding
The shells of each atom are connected to each other, with a dot of a lone pair connecting to a cross of a lone pair from the other atom.
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Covalent Bonding
Molecules are formed when 2+ atoms bond together. Two atoms share electrons so they both have full outer shells. Happens between non-metals. Weak bonds, no charge carriers free to move so don't conduct electricity, insoluble
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Dot and Cross diagram for Dative Covalent Bonding
All atoms are in the square with an arrow pointing to the donor atom, a + is outside the square.
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Data Covalent Bonding
One atom donates both electrons to a bond
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Dot and cross model limitations
Most bonds aren't purely ionic/covalent they're in between, so compounds have a mixture of ionic and covalent properties.
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Simple model of Metallic bonding
Positive metal ions in a sea of delocalised electrons. Electrons pass kinetic energy so good thermal conductors, ductile as no bonds so ions can slide over each other, strong metallic bonding so high m/b.p.t
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Electron pair repulsion principle
Lone pair - Lone pair = Biggest bond angle. Lone pair - Bonding pair = second biggest bond angle. Bonding pair - Bonding pair = smallest bond angle
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2 electron pairs on central atom, no lone pairs
Linear - 180 degrees
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3 electron pairs on central atom, no lone pairs
Trigonal planar - 120 degrees
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3 electron pairs on central atom, one lone pair
Bent - 120 degrees
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4 electron pairs on central atom, no lone pairs
Tetrahedral - 109.5 degrees
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4 electron pairs on central atom, one lone pair
Trigonal pyramidal - 107 degrees
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4 electron pairs on central atom, two lone pairs
Bent - 104.5 degrees
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5 electron pairs on central atom, no lone pairs
Trigonal Bipyramidal - 90 degrees and 120 degrees
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6 electron pairs on central atom, no lone pairs
Octahedral - 90 degrees
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How is the Periodic Table layed out?
Lists elements in order of atomic number, and groups elements together according to their common properties.
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Trends in groups of the Periodic Table
Across periods 2 + 3, metals (- Li, Be, Na, Mg + Al ) m/b.p.t increase across period as the metal-metal bonds get stronger as there's an increasing no. of delocalised electrons and a decreasing radius making a higher charge density.
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Trends in groups of the Periodic Table 1
Then the simple molecular substances (N2, O2, F2, P4, S8 and Cl2) have decreasing m/b.p.t as strength of intermolecular forces weaken.
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Position of element in the Periodic Table
Elements within a period have the same number of electron shells. Elements withing the same group have the same number of electrons in their outer shell, so similar physical and chemical properties.
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Mendeleev
1869 - Mendeleev developed Periodic Table by leaving gaps and rearranging some elements from their atomic mass order. Subsequent research validated this knowledge.
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Difference between Group 1 and Group 7 elements
Group 1 reactivity increases DOWN the group, to Fr. Group 7 reactivity increases UP the group, to F.
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Group 2 elements react with water...
When react with water, ion with 2+ charge is formed, as there are 2 outer shell electrons. This reaction gives a metal hydroxide + a hydrogen. Reactivity increases down group as outer electrons further from nucleus.
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Group 2 oxides and hydroxides
Oxides of G2 react with water and form metal hydroxide, which dissolve and OH- ions make solution strongly alkaline. MgO reacts slowly and OH- isn't very soluble. Stronger alklaines form down the group as OH- gets more soluble.
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Group 2 oxides and hydroxides 1
As they're bases, the oxides and OH- neutralise dilute acids, forming solutions of corresponding salts.
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Solubilities of hydroxides and carbonates
Singly charged - ions, (Hydroxides) increase in solubility down group, Doubly charged - (carbonate) ions decrease in solubility down the group.
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Thermal decomposition + Thermal Stability
T.D = a substance breaks down when heated. T.S = the more T.S it is, the more heat's needed to break it down.
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Thermal stability of the carbonates in Group 2...
Carbonate ions = large anions, can get unstable by a cation. It draws electrons on carbonate ion towards itself (polarises it), distorting the carbonate ion. Greater distortion = less stability of carbonate ion.
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Thermal stability of the carbonates in Group 2... 1
Large cations = less distortion, so further down the group, the carbonate ion is more stable.
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Time-of-flight mass spectrometer
Vaporisation-sample turned to gas. Ionisation-particles hit with high-energy electrons=ionise them, electrons knocked off particles = +ve ions. Acceleration-+ve ions accelerated by electric field. Detection-Time taken for +ve ions to reach detector
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What does detection in mass spectrometry depend on?
Mass and charge. Light, highly charged ions reach detector fastest.
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How to calculate relative atomic mass (Ar) from mass spectrum if given as a percentage
Read % relative isoptopic abundance from Y-axis and relative isotopic mass from X-axis. Multiply them together to get total mass for each isotope. Add totals, then divide by 100
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How to calculate relative atomic mass (Ar) from mass sepcturm if not given by %
Do steps 1 and 2 from question 81. Then divide by the total relative abundance instead of 100.
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How to calculate %relative isotopic abundance for each atom
Relative abundance/total relative abundance x 100
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How to work out relative molecular mass (Mr) from mass spectrometer
It's the peak in the spectrum with the highest mass, when ignoring the isotopes.
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How does a fragmentation pattern occur in mass spectrometry
Caused by fragments of molecules that have broken when bombarded with electrons.
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Other cards in this set

Card 2

Front

Total number of protons and neutrons in the nucleus

Mass number

Card 3

Front

Atoms with the same atomic number but different atomic mass

Card 4

Front

One mole is roughly 6.02x10 23

Card 5

Front

Mass of an atom of an isotope of an element relative to an atom of carbon-12 with a mass of 12

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