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Chemistry > 1a:Atoms,Elements,Compounds and Mixtures > Flashcards

1a:Atoms,Elements,Compounds and Mixtures Flashcards

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1
Q

what is the radius of atoms?

A

0.1 nanometres

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2
Q

what is an atom?

A

the smallest indivisible part of an element that all substances are made up of.

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3
Q

what is an element?

A

an element only contains one type of atom

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4
Q

what is a compound

A

contains two or more elements chemically bonded together in fixed positions throughout the compound

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5
Q

what is the nucleus?

A

the central part of an atom which contains protons and neutrons

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6
Q

what is the relative charge and mass of protons?

A

relative charge:+1
relative mass:1

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7
Q

what is the relative charge and mass of neutrons?

A

relative charge:0
relative mass:1

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8
Q

what is the relative size of the nucleus compared to the atom?

A

the nucleus is 1/10000 of the size of an atom

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9
Q

where are electrons found?

A

electrons occupy shells around the nucleus

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10
Q

what is the relative charge and mass of electrons?

A

relative charge:-1
relative mass:very small

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11
Q

why are atoms uncharged?

A

the number of protons are the same as the number of electrons in an atom.The charge on the electron(-1) is the same size as the charge of the proton(+1) which cancel each other put which means atoms have no charge overall

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12
Q

what particle determines what an element is?

A

proton because different elements have atoms with a different number of protons
eg. lithium is an element which is made up of only lithium atoms.each lithium atom contains three protons

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13
Q

what are isotopes?

A

isotopes are different forms of an element which bas the same number of protons but a different number of neutrons(so same atomic number,different mass number)

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14
Q

why is relative atomic mass used?

A

many elements have more than in isotope so when referring to the mass of elements ,relative atomic mass is used

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15
Q

what is relative atomic mass?

A

an average mass that takes into account the abundance of the isotopes of the element

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16
Q

what is the formula to work out the relative atomic mass of an element?

A

relative atomic mass=

sum of(isotope abundance x isotope mass number) _______________________________________
sum of abundances of all isotopes

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17
Q

what is different about isotopes?

A

their chemical properties are identical but their physical properties differ(eg. density,diffusion rates)

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18
Q

how do you separate compounds?

A

once a compound is formed,the elements can’t be separated by physical processes.The only way to reform the elements is by more chemical reactions

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19
Q

what happens during a chemical reaction?

A

bonds between atoms break and the atoms from the reactant rearrange themselves to form different chemicals which are called products.

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20
Q

what is a mixture?

A

substance which consists of two or more elements or compounds which aren’t joined by chemical bonds

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21
Q

what is different about the properties of compounds compared to properties of mixtures?

A

the properties of compounds are different from the properties of the original elements whereas the chemical properties of a substance in a mixture aren’t affected by the fact that it’s apart of a mixture(they are unchanged)

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22
Q

why can mixtures be separated with physical methods?

A

because the components in a mixture aren’t chemically combined

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23
Q

what are physical methods of separation in a mixture?[5]

A
  1. chromatography
  2. filtration
  3. crystallisation
  4. simple distillation
    5.fractional distillation
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24
Q

what can chromatography be used for?

A

to separate mixtures made up of liquids of different colours

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25
how do you carry out paper chromatography?(REQUIRED PRACTICAL)[7]
1.draw a pencil line near the bottom of a sheet of filter paper 2.spot the ink on the line in a single place 3.place the sheet upright in a beaker of solvent(most likely water) and make sure the side of the paper doesn’t touch the beaker.Also make sure the ink isn’t touching the solvent initially so it’s not washed away 4.place a lid onto the beaker to prevent the solvent from evaporating 5.the solvent will seep up the paper ,carrying the ink 6.the different dyes in the ink will travel up the paper at different rates so the dyes will separate out and form spots in different places.If any dyes are insoluble in the solvent,they’ll stay baseline 7.the point the solvent has reached as it moves up the paper is the solvent front.When the solvent front has reached near the top of the paper,take the paper out of the beaker and draw a pencil line along the front and leave to dry
26
why is the lines in chromatography drawn with pencil?
pencil marks are insoluble and wont dissolve in the solvent
27
why does the solvent used depend on whats being tested in chromatography?
some compounds dissolve well in water but sometimes other solvents need to be used eg.ethanol
28
how do you calculate the Rf value?
Rf= distance moved by substance ________________________________ distance traveled by solvent
29
what does the Rf value say about the solubility of a substance in chromatography ?
the higher the Rf value,the more soluble the substance
30
what does the Rf value say about how long a substance spends in the mobile phase in chromatography?
the higher the Rf value,the more time the substance spends in the mobile phase
31
why can’t Rf values be greater than 1?
if the Rf value was greater than 1,then the substance would be greater than the substance which isn’t possible.
32
what is the pattern of spots on the filter paper during chromatography called?
chromatogram
33
what can the spots on a chromatogram mean?
the number of spots can tell you how many substances there are in the mixture at least(sometimes the number of spots don’t match the number dyes in the ink eg.two dyes could travel around the same distance so the filter paper would only show one spot)
34
what can filtration be used for?[2]
1.to separate the desired insoluble solid from a liquid reaction mixture 2.for purification(solid impurities in a reaction mixture can be removed with filtration)
35
what are the steps to filtration?[4]
1.fold a piece of filter paper into a cone 2.place the filter paper point down into a filter funnel thats sitting im the neck of a conical flask 3.pour the mixture containing the insoluble solid into the funnel lined with the filter paper 4.the liquid will pass through the filter paper but the solid will be left behind in the funnel
36
what can evaporation be used for?
separating a soluble salt that doesn’t decompose when heated from a solution
37
what are the steps of evaporation?[4]
1.pour the solution into an evaporating dish 2.place the evaporating dish onto a tripod and place a bunsen burner underneath 3.slowly heat the solution.The solvent will evaporate and the solution will her more concentrated until the solid will start to form 4.keep heating the evaporating dish until all that is left in a dry solid
38
what can crystallisation be used for?
to separate a soluble solid that could decompose when heated from a solution and crystallise the soluble solid
39
what are the steps to crystallisation?[6]
1.place an evaporating dish onto a tripod with a gauze mat.place a bunsen burner underneath the tripod 2.pour solution into the dish and gently heat it.Some solvent will evaporate and solution will get more concentrated 3.once the solution is more saturated ,let it cool slowly 4.the salt crystals should start to form as solution solubility decreases 5.filter the crystals and wash the with distilled water to remove impurities 6.leave them in a warm place to dry or using a drying oven or a desiccator
40
how could salt and sand be separated?[4]
1.grind the mixture to make sure the salt crystals are small and so will dissolve quickly 2.put the mixture in water so that the salt could dissolve and heat it so that the salt would be able to dissolve but the sand wouldn’t 3.filter the mixture so that the salt is collected in the filter paper whereas the salty water would pass through the filter paper 4.evaporate the water from the salt so that it forms dry salt
41
what can simple distillation be used for?
to separate out a liquid from a mixture of liquids with significantly different boiling points
42
what is the stationary phase in paper chromatography?
the chromatography paper
43
what is the mobile phase in paper chromatography?
the solvent
44
what affects how long molecules spend in each phase in paper chromatography?[2]
1.their solubility 2.how much they’re attracted to the chromatography paper
45
what are the steps to simple distillation?
1.a flask is set up on a tripod with a bunsen burner underneath it.A thermometer it put into the bung on the flask.A Liebig condenser is attached to the flask and is directed to a beaker 2.the mixture inside the flask is heated.The liquid in the mixture that has the lowest boiling point evaporates 3.as the vapour rises ,it passes into the condenser which has cold water in the glass around it.when it is cooled,the liquid condenses and is collected into the beaker 4.components of the mixture with higher boiling points are left behind in the flask
46
what are the cons of simple distillation?
it can only be used when the boiling points of the liquids are completely different because if they are close together,the temperature may rise above more than one of the substances and they’ll mix again
47
what can fractional distillation be used for?
separating a mixture of different liquids and is especially useful when the boiling points of the liquid are close together
48
what are the steps to fractional distillation?[8]
1.set the apparatus up similarly to the one in simple distillation however this time,the flask is attached to a fractionating column filled with glass rods which is attached to a thermometer 2.heat the mixture inside the flask 3.both mixtures will start to evaporate but the liquid with the lower boiling point evaporates easier so it’s mainly the lower boiling point liquid evaporating 4.the vapours travel up towards the fractionating column 5.when they reach the fractionating column,they condense and drip back into the flask and start to evaporate again 6.this repeated process increases the amount of the lower boiling point liquid in the fractionating column 7.when the thermometer matches the boiling point of the lowest boiling point liquid,the vapour of the lowest boiling point (and a little of other liquids)passes into the condenser where it will then cool and can be collected as a liquid 8.when the first liquid is collected,the temperature can be raised to the next lowest boiling point of the liquids in the mixture
49
who came up with the theory of the ‘plum pudding model’?
J J Thomson
50
who discovered the nucleus?
Ernest Rutherford and his student Ernest Marsden in 1909
51
what experiment did Ernest Rutherford and Ernest Marsden conduct?
the Ernests conducted the alpha particle scattering experiment in which they fired positively charged alpha particles at a thin sheet of gold.
52
who proposed the idea of shells?
Niels Bohr
53
who discovered neutrons?
James Chadwick
54
what are the differences between the plum pudding model and the nuclear model?
in the plum pudding model,there is a positive sphere with electrons in bedded in the sphere.There is no empty space.In the nuclear model,there is positive middle(the nucleus) surrounded by electrons with lots of empty space.
55
how are electrons arranged in atoms?
electrons occupy shells and the shells with the lowest energy are filled first(closest to the nucleus)
56
what does ‘Na’ represent?
1 atom of sodium
57
how are compounds formed?
from elements by chemical reactions
58
what can be said about the chemical properties of each substance in a mixture?
they are unchanged
59
what do chemical reactions always involve?[2]
1.formation of one of more substances 2.often a detectable energy change
60
how can you separate mixtures?
with physical processes
61
what was believed about atoms before the discovery of electrons?
they were solid,tiny spheres that could not be divided
62
how did JJ Thompsons discovery of the electron change the ‘solid sphere’ of atomic structure?
his experiments showed that an atom must contain electrons which changed the solid sphere idea of atomic structure to the plum pudding model.
63
what was the plum pudding model?
a sphere of positive charge with smaller negatively charged particles(electrons)
64
what did Ernest Rutherford and Ernest Marsden expect from their experiment?
They expected the particles to pass through the sheet or be slightly deflected because of the positive charge was thought to be spread through the ‘pudding’ of the atom(from the plum pudding model)
65
what was the outcome of Ernest Rutherford and Ernest Marsden experiment?
most alpha particles did go through the gold sheet ,some deflected more than expected and some deflected backwards so the plum pudding model had to be wrong.
66
what idea did Rutherford come up with to explain the outcome of his experiment?
came up with the idea of tint positively charged nucleus at the centre of atoms where most mass is concentrated.(nuclear model)
67
what evidence did Niels Bohr have to back up his claim about electrons orbiting the nucleus?
theoretical calculations agreed with experimental observations.
68
how was the idea that the nucleus could be divided come up with?
later experiments by Rutherford and others
69
how were protons discovered?
experiments showed the positive charge of the nucleus could be divided into smaller particles ,each with the same amount of positive charge
70
what are the differences between the plum pudding model and nuclear model?[2]
In the plum pudding model, there is a positive sphere with randomly embedded negative charge with no empty space. In the nuclear model, there is a central positive nucleus, with mostly empty space with a cloud of negative electrons around the nucleus. The mass in the plum pudding model is distributed equally throughout the sphere. The mass in the nuclear model is concentrated in the nucleus.
71
what is atomic number?
number of protons in an atom
72
where is most of the mass in the atom?
in the nucleus.
73
what is the mass number?
sum of protons and electrons
74
do physical methods of separation form new substances?why/why not?
physical methods do not form nee substances because no chemical reaction takes place since no chemical bonds are being broken or formed

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