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Chem > Elements of life > Flashcards

Elements of life Flashcards

1
Q

What in an atom determines an elements chemical properties and how does it affect isotopes?

A

The number and arrangement of electrons
Isotopes have the same configuration of electrons so have the same chemical properites

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2
Q

What in an atom determines an elements physical properties and how does it affect isotopes?

A

Its mass
Isotopes have different properties becuase they have a different mass

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3
Q

Describe the plum pudding modle of the atom

A

Positivley charged solid sphere with negative electons embedded in it

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4
Q

Descaribe the gold foil experiment

A

Alpha particles were fired at a thin sheet of gold
Most of them when straight through showing the atom is mostly empty space
Some reflected off the positivley charged nucleus
Leading to the nuclear modle of a tiny positively charged nucleus with the elctrons surrounding it in a cloud

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5
Q

Describe the bohr modle of the atom

A

electrons can only exist in fixed orbitals or shells and no where in between
Each shell has a fixed energy
When an electron moves between shells electromagnetic radiation is emmited or absorbed
Full shells are not reactive

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6
Q

What does a mass spectrometer do?

A

Measures the relative atomic mass, relative molecular mass, relative isotopic abundance, molecular structure

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7
Q

How do mass spectrometers work?

A

1) Vapourisation - the sample is turned into a gas using an electrical heater
2) Ionisation - the gas particles are bombarded with high energy electrons to ionise them. Electrons are knocked off the partciles leaving positive ions
3) Acceleration - the positive ions are accelerated by an electric field
4) Detection - the time taken for the positive ions to reach the detector is measured. This depends on an ions mass and charge - light, highly charged ions will reach the detector first, heavier ions with a smaller charge will take longer
5) A mass spectrum is produced

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8
Q

Describe a mass spectrum

A

Y axis - abundance of ions
For an element the height of each peak gives the relative isotopic abundance
If the sample is an element each line will respresent a different isotope of that element
X axis - mass/charge ratio (m/z) - most charges at +1 so we can assume the x axis is just the relative mass

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9
Q

How do you work out relative atomic mass from a mass spectrum?

A

1) For each peak read the percentage of relative atomic abundance (Y axis) and the relative isotopic mass (X axi) and multiply them together to get the total mass for each isotope
2) Add up these totals
3) Divde bt 100 because percentages were used

If the relative abundance is not a precentage just add them together and divide by that new total instead of 100

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10
Q

What are the four moles equations

A

Solid -
mole = mass/mr
Liquid -
mole = concentraton x volume
Gas -
(RTP) mole = volume / 24
(not RTP) Pv = nRT

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11
Q

What is the equation for percentage yeild?

A

percentage yeild = actual yeild/ theoretical yeild x 100

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12
Q

What is a standard solution?

A

A solution with a known concentration

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13
Q

How do you make a standard solution?

A

E.g make 250cm3 of a 6.00 mol dm-3 solution of sodium chloride
1) First work out how many moles of solute you need
n = c x v, n = 6 mol dm-3 x 0.25dm-3 = 1.5 mol
2) Work out how many grams of solute is needed
mass = mol x mr = 1.5 x 58.5 = 87.75g
3) Weigh a beaker note down the mass then add the correct mass of solute
4) add some distilled water to the beaker and stir until all the solute has dissolved
5) tip the solution into a volumetric flask using a funnel
6) Rinse the beaker and stirring rod with water and add to the flask
7) Top up flask with the correct volume (250cm3) using a pipette drop by drop when you get near the top
8) Put a stopped on and shake

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14
Q

How do you change the standard solution to a differernt concentration?

A

Divide the concentration you want by the concentration you have and multiple by the volume you want. This gives you the amount of solution to use.

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15
Q

What are the colour changes in methyl orange and phenolphthalein?

A

Methyl orange
acid - red
alkali - yellow
Phenolphthelein
acid - colourless
alkali - red

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16
Q

What are all the subshells names, number of orbitals and maximum electrons?

A

Subshell Orbitals Electrons
s 1 2
p 3 6
d 5 10
f 7 14

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16
Q

Draw out the table of energy levels 1 - 4

A

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14

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17
Q

What is an orbital?

A

the bit of space that an electron moves in
orbitals within the same sub shell has the same energy
electrons in each orbital spin in opposite directions (spin - pairing)

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18
Q

What shape are s and p orbitals

A

S - spherical
P - 3 dumbell shapes all at right angles to each other

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19
Q

How do electrons fill up in energy levels?

A

They fill up from the lowest energy level first
4s sub shell has a lower energy level than 3d sub shell so 4s fills up first
They fill up singly before pairing up

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20
Q

What is meant by a giant lattice structure?

A

A reqular structure which is a repeating unit

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21
Q

What are the properties of ionic compounds?

A

Conduct electricity when molten or dissolved (not solid)
High melting points
Soluble in water

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22
Q

What are the properties of simple covalent compounds?

A

Low melting and boiling point and liquids or gasses at RTP as there is not giant lattice to break down
(To melt or boil them energy only has to overcome weak intermolecular forced not covalent forces)
Don’t conduct electricity as no del e are free to move
Insoluble in water

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23
Q

What is a dative bond?

A

Both electrons in the bond come from one atom

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24
Q

What are the properties of giant covalent structures?

A

High metling points
Hard
Good thermal conductors - vibrations travels easily though thr stiff lattice
Insouble - doesn’ contain ions and the covalent bonds mean the atoms are more attracted to the lattice
Can’t conduct electricity - no free electrons (apart from graphite)

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25
Q

Describe a metallic structure

A

A sea of delocalised electrons leaving a positive metal ion

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26
Q

Describe and explain the properties of metallic bonding

A

High metling points - more delocalised electrons the stronger the attraction, also affected by the size of the metal ion and the lattice struture
Ductile - no bonds holding specific ions together so layers can slide over each other
Good thermal conductors - del e can pass kinetic energy to each other
Good electrical conductors - del e can pass charge between each other - impurities reduce this by reducding the number of electrons that are free to move
Insouble - strong metallic bonds

27
Q

What are the bond angles for:
4 + 0
3 + 1
2 + 2
5 + 0
6 + 0

A

109.5
107
104.5
120 + 90
90

28
Q

What do elements in the same period and group have in common?

A

Period - Same amount of electron shells
Group - same number of electrons in their outer shell and similar physical and chemical properties

29
Q

What are the reactivity trends in group 1 and 7?

A

Going down the group
Group 1 reactivity increases
Group 7 reactivity decreases

30
Q

What are the trends across period 2 and 3?

A

Melting point increases across the period for the metals (Li Be Na Mg Al) becuase the metallic bonds get stronger because the metal ions have an increasing number of del e (increasing charge) and decreasing ionic radius (electrons are pulled in closer as the protons increase)
This leads to a higher charge density which attracts the ions together more strongly
The elements with giant covalent structures (C and Si) have strong covalent bonds
Carbon (as graphite or diamond) and silicon have the highest melting points
Next are the simple molecular substances (N2 O2 F2 P4 S8 Cl2) . Their melting points depend on the strength of their intermolecular forces which are weak.
More atoms in a molecule mean stronger intermolecular forces (S8)
Noble gases have the lowest melting points becuase they exist as individual atoms so weak intermolecular forces

31
Q

What is ionisation enthalpy?

A

The energy needed to remove an electron from each atom in 1 mole of gaseous atoms to form 1 mole of gasous 1+ ions

32
Q

Write an equation for the first ionisation enthalpy in magnesium

A

Mg(g) –> Mg+(g) + e-

33
Q

State and explain what effects the size of ionisation enthalpies

A

Atomic radius - the further away the outershell electrons are from the positive nucleus the less they’ll be attrected towrds it so the ionisation enthalpy will be lower
Nuclear charge - the more protons the more it will attract outer electrons so it will be harder to remove them so ionisation enthalpy will be higher
Electron shielding - inner electron shells sheild the outer shell electrons from the attrective force of the nucleus so ionisation enthalpy will be lower

34
Q

What is the trend with ionisation enthalpy down a group and why?

A

Decreases down a group
because there is less attrection between the nucleus and outer electrons
As you go down the group the outer electrons are in shells further from the nucleus
Sheliding increses as there are more shells
Although number of protons increases down the group its a less important factor than the others so doesn’t have an effect

35
Q

What is the trend with ionisationenthalpy across a period and why?

A

Increase across a period
Number of protons is increasing
Outer shell electrons are in the same energy level

36
Q

What do group 2 metals form when they react with water?

A

metal hydroxide + hydrogen

37
Q

What is the reactiviy trend down group 2 and why?

A

Increases because the outer electron gets further away from the nucleus so its more easilly lost

38
Q

How to group 2 metals react with oxygen?

A

They burn to form metal oxides which are white solids

39
Q

Group 2 oxide + water =
descibe its properties

A

Metal hydroxide
dissolves in water to make alkaline solutions (execpt magnesium)

40
Q

Whats the solubility trend down group 2?

A

Depends on the anion
Single charge (OH-) solubility increases down the group
Double charge (CO3 2-) solubility decreases down the group

41
Q

What do group 2 carbonates decompose to?

A

CO2 + metal oxide

42
Q

What is the trend in thermal stability down group 2 carbonates and why?

A

Increases
The more thermally stable something is the more heat it will take to break down
Carbonate ions are larger anions and cna be made unstable by a group 2 metal cation. The cation draws the electrons on the carbonate ions towards itself (polarises it). This distorts the carbonate ion, the greater the distortion the less stable it is
Large cations cause less distortion as they have a low charge density so down the group the cations get larger so less distortion so more stablilty

43
Q

What of the following are soluble or insoluble:
Lithium salts
carbonates
halides
sulfates
nitrates
hydroxides
sodium salts
ammonium salts
potassium salts

A

Soluble
Lithium, sodium, potassium, ammonium salts
nitrates
halides (exept for silver halides)
sulfates (exept barium, calcium, lead)

Insoluble
hydroxides (execpt lithium, sodium, potassium)
carbonates (except lithium, sodium, potassium, ammonium)

44
Q

What reaction makes salts?

A

Precipitation reaction

45
Q

How do you do a precipitation reaction?

A

Pick two solutions that contain the ions you need mix and filter the ppt out and dry

45
Q

How do you make a soluble salt?

A

React an acid plus a metal or an insoluble base (metal hydroxide or metal oxide) filter and crystalised. You can tell when the right amount of of metal has been addded as it will no longer dissolve.

With alkalis (soluble bases) you won’t know when enough has been added. Find this out by titrating using an indicator so you know when the acid has been neutralised and then repeat with the correct amount of alkali without the indicator. Crytsalise like normal.

46
Q

How do you carry out a flame test?

A

Used to find the metal cation in a compound
1) Dip a nichrome wire loop in concentrated HCl
2) Then into the sample of the compund
3) Hold the loop in a blue part of the bunsen flame
4) Observe colour change

47
Q

What are the metal cations and their colours in flame test?

A

Lithium - crimson
Sodium - yellow
Potassium - lilac
Calcium - brick red
Barium - green
Copper - blue green

48
Q

What are the colours of ppt for the metals in sodium hydroxide and the compound?

A

Silver - brown Ag2O
Calcium - white Ca(OH)2
Copper - blue Cu(OH)2
Lead - white Pb(OH)2
Iron (II) - green Fe(OH)2
Iron (III) - brown Fe(OH)3
Zinc - white at first and dissolves to be colourless Zn(OH)2 and then Zn(OH)3-
Aluminium - white at first and dissolves to be colourless Al(OH)3 and then Al(OH)4-

49
Q

What is the test for carbonate ions?

A

With dilluet HCl carbonate ions will fizz to give off carbon dioxide and then can test for carbon dioxide with limewater which turns cloudy

50
Q

How do you test for sulfates?

A

Add HCl and barium chloride solution which would give a white ppt of barium sulfate

51
Q

How do you test for ammonium compounds?

A

Ammonia gas is alkaline which can be tested with damp red litmus paper which will turn blue
Ammonium ions can be tested by adding sodium hydroxide and gentley heat and ammoia gas will be given off

52
Q

How do you test for hydroxides?

A

Add red litmus paper to the solution and if a hydroxide is present the paper will turn blue

53
Q

How do you test for halides?

A

Add nitric acid and then silver nitrate solution
Chloride gives a white ppt - silver chloride
Bromide gives a cream ppt - silver bromide
Iodide gives a yellow ppt - silver iodide

54
Q

How do you test for nitrates?

A

Warm with sodium hydroxide and aluminium foil
They will react to give ammonium gas and water which can be tested with damp red litmus paper and turn blue

55
Q

What order should you do the test for ions so avoid false positives?

A

1) Carbonates test
2) Sulfate test
3) Halide test

56
Q

What is the electromagnetic spectrum?

A

Electromagnetic radiation is energy that is transmitted as waves
Along the spectrum frequency increases and wavelength decreases:
1) Radio waves
2) Microwaves
3) Infrared
4) Visible light
5) UV
6) X rays
7) Gamma rays

57
Q

How do electrons behave in energy levels (shells) when absorbing or releasing energy?

A

If an atoms electrons takes in energy from their surroundings they can move to higher energy levels and the electrons are said to be excited
An electron can release energy by dropping down an energy level
Energy levels are discrete - they all have certain fixed values

58
Q

Describe the absorption spectra and how it forms

A

Dark lines on a coloured background
When electromagnetic radiation is passed through a gaseous element the electrons only absorb certain frequencies corresponding to differences between energy levels
This means the radiation passing through has certain frequencies missing which form the dark lines

59
Q

Describe the emission spectra and how it forms

A

Coloured lines on a dark background
When electrons drop to lower energy levels they give out a certain amount of energy producing the coloured lines
Each spectrum is unique to their element

60
Q

What do the lines in absorption and emmision spectra represent?

A

Electrons moving to or from a differernt energy level
When the lines get closer together the frequency increases

61
Q

What is the equation for energy difference between two shells?

A

E = hv
E - energy difference between two shells (J)
h - plancks constant (JHz-1)
v - frequency (Hz or s-1)

62
Q

What is the equation for frequnecy?

A

C = vY
C - speed of ligth (m/s)
v - frequency (Hz or s-1)
Y - wavelength (m)

63
Q

What is nuclear fusion?

A

When two small nuclei combine under high temperature and pressure to make one large nucleus releasing huge amounts of energy

Chem (5 decks)

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