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atomic structure Flashcards

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1
Q

what was the Greek philosophers’ model of the atom

A

Greek philosophers had a model in which matter was made up of a single continuous substance that produced the four elements - earth, fire, water and air

the idea that matter was made of individual atoms was not taken seriously for another 2000 years

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2
Q

what were the steps taken that lead to the current atom model

A

1661:
Robert Boyle proposed there were some substances that could not be made more simpler. These were the chemical elements, as we know them

1803:
John Dalton suggested elements were composed of indivisible atoms.
All the atoms of a particular element had the same mass and atoms of different elements had different masses.
Atoms could not be broken down

1896:
Henri Becquerel discovered radioactivity. Radioactivity showed that particles could come from inside the atom. Therefore the atom was not indivisible

1897:
J.J Thomson discovered the electron. This was the first sub- atomic particle to be discovered. He showed that the electrons were negatively charged and electrons from all elements were the same

This lead to the creation of the plum- pudding model (J.J Thomson)

1911
Ernest Rutherford and his team found that most of the mass and all the positive charge of the atom in a tiny nucleus

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3
Q

what is the plum pudding model

A

as electrons are negatively charged, there had to be some source of positive charge. Furthermore, electrons are much lighter than the whole atom meaning there much be something that account for the rest of the atom.

Thompson therefore suggested that the electrons were located within the atom in circular arrays surrounded by positive charge, like plums in a pudding of positive charge

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4
Q

what are subatomic particles

A

the fundamental particles that atoms are made up of

these particles are:
protons
neutrons
electrons

the protons and nucleus make up the neutrons (sometimes referred to as nucleons)

electrons surround the nucleus

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5
Q

what is the mass of a proton

A

1.673 x 10 -27

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6
Q

what is the mass of a neutron

A

1.675 x 10 -27

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7
Q

what is the charge of electrons and protons

A

+/- 1. 602 x 10-19

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8
Q

what is the mass of an electron

A

0.911 x 10 -3 (very nearly 0)

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9
Q

what is the position of the electons

A

around the nucleus

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10
Q

what is the position of the neutrons and protons

A

in the nucleus

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11
Q

what is the charge of a neutron

A

0

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12
Q

what are the relative values of the mass and charges of protons neutrons and electrons

A

as the actual charges and masses are small, we use relative values

relative charges of proton and electron: +/- 1

relative mass of proton and neutron : 1

relative mass of electron:
1/1840

relative charge of neutrons: 0

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13
Q

what is the arrangement of subatomic particles

A

protons and neutrons are in the centre of the atom, held together by a force called the strong nuclear force.

electrons surround the nucleus
electrons are found in a series of levels (referred to as orbitals or shell)

the levels get further and further away from the nucleus

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14
Q

what are the nuclear forces

A

protons and neutrons are in the centre of the atom, held together by the strong nuclear force. This force is stronger than the electrostatic forces of attraction that hold electrons and protons together i the atom, so it overcomes the repulsion between the protons in the nucleus
- force only acts within the nucleus

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15
Q

what is the mass spectrometer

A

the mass spectrometer is the most useful instrument for the accurate determination of relative atomic Ar (relative atomic mass)

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16
Q

on what scale are relative atomic masses measured on

A

relative atomic masses are measured on a scale which the mass of an atom of C12 is defined as exactly 12

No other isotope has a realtive atomic mass that is exactly a whole number. This is because neither the proton or the neutron has a mass of exactly 1

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17
Q

what is the equation for the relative atomic/molecular mass

A

average mass of 1 atom/ 1/12 of mass of atom

average mass of 1 molecule/ 1/12 of mass of atom

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18
Q

what principle do all mass spectrometers follow

A

there are several types of mass spectrometer but all work on the principle of forming ions
- separating ions according to the ratio of their charge to their mass

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19
Q

what happens in a time of flight mass spectrometer

A

substance(s) in the sample are converted to positive ions

accelerated to high speed which depend on their mass to charge ratio)

they then arrive at the detector

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20
Q

what are the steps behind the flight mass spectrometer

A
  1. IONISATION
  2. ACCELERATION
  3. FLIGHT TUBE
  4. DETECTION
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21
Q

how are large molecules ionised in TOF

A

IONISATION

two types of ionisation:

ELECTROSPRAY
Is for larger molecules. 1.The sample is dissolved in a volatile solvent
2.forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply. This produces tiny, positive charged droplets that have gained a proton from the solvent
3.Solvent evaporates from the droplet into the vacuum and the droplets get smaller and smaller until they can contain no more a singley positively ion

22
Q

how are smaller molecules/ atoms ionised in TOF

A

the 2nd type of ionsiation is ELECTRON IMPACT

the sample must be a gas

1.sample is vaporised and high energy electrons are fired at it from an electron gun An electron gun is a hot wire filament with a current running through it that emits beam of high energy electrons

This usually knocks off one electron from each particle forming a 1+
the equation:
e.g.x(g) - x+ +e-

23
Q

what happens in the 2nd stage of ionisation

A

the 2nd stage is ACCELERATION

The positive ions are accelerated using an electric field so that they have the same kinetic energy

Given that all the particles have the same kinetic energy, the velocity of each particle depends on its mass
- lighter particles = faster velocity

  • heavier particles = slower velocity
24
Q

what happens in the 3rd stage of TOF spectrometer

A

The positive ions travel through a hole in the negatively charged plate into a tube. The time of flight of each particle through this flight tube depends on its velocity which in turn depends on its mass

equation to work out velocity of ions travelling through the flight tube :
t= d/v

25
Q

what happens in the 4th and final stage of TOF

A

DETECTION

the positive ions hit the negatively charged electric plate. When they hit the electron plate, the positive ions are discharged by gaining electrons from the plate. This generates a movement of electrons and hence a electric current that is measured. The size of the current gives a measure of the number of ions hitting the plate

26
Q

what doe the computer do with the data collected at the end of TOF

A

a computer uses this data to produce a mass spectrum. This shows the mass to charge ratio and the abundance of each ion that reaches the detector

given that all ions produced by electospray and most ions by electron ionsistaion have a 1+ charge, the mass to charge ratio is effectively the mass of each ion

27
Q

what is the relative atomic mass

A

the relative atomic mass is:

mean mass of an atom/ mass of 1 atom x 12

28
Q

what is the atomic number Z

A

atoms consist of a tiny nucleus made up of protons and neutrons that is surrounded by electrons

The number of protons in the nucleus is called the atomic number/ proton number Z

29
Q

why are atoms neutral

A

the number of electrons in the atom is equal to the proton number, so atoms are electrically neutral

30
Q

what determines the chemical properties of an atom

A

the number of electrons in the full outer shell of an atom determines chemical properties of an element ( how it reacts) and what sort of element it is

31
Q

what does the atomic number of an element show

A

chemical identity of an element and the number of protons

32
Q

what are isotopes

A

every single atom of any particular element has the same number of protons in its nucleus therefore the same number of electrons. However, the number of neutrons may vary

Atoms with the same number of protons but different numbers of neutrons are isotopes

33
Q

how do different isotopes of the same element react

A

different isotopes of the same element react chemically in exactly the same way as they have the same electron configuration

34
Q

how are electrons arranged

A

electrons are arranged in electrons shells (energy levels), which themselves have sub shells

35
Q

what are the different sub shells

A

there are 4 sub shells

s,p,d,f which increase in energy level

36
Q

what do each sub levels consists of

A

each sub level consists of electron orbitals

37
Q

what are orbitals

A

regions in space in which the electrons spends most of its time/ most likely to be in

38
Q

how many electrons can orbitals consists of

A

each orbital can hold up to 2 electrons with opposite spin

39
Q

how are electron orbitals filled up

A

1) AUFBAU PRINCIPLE
eletrons enter the lowest orbital available

2)HUND’S RULE
electrons prefer to occupy orbitals on their own and only pair up when no empty orbitals of the same energy are available

this is the order that orbitals fill up:
1s 2s 2p 3s 3p 4s 3d 4p

40
Q

what is the maximum number electrons in each sub level

A

s- 2
p- 6
d- 10
f- 14

41
Q

what electron is lost first when positive ions are formed

A

in ions, the electron in the highest energy levels are lost first

however there are some exceptions to this rule:
when losing electron, electrons are lost from 4s before 3d ( the energy levels are close, and when electrons fill, 4s goes before 3d)

42
Q

what are the two elements that do not follow the trend

A

Cr: 1s2 2s2 2p6 3s2 3p6 4s1 instead of 1s2 2s2 2p6 3s2 3p6 4s2 3d4

Cu :1s2 2s2 2p6 3s2 3p6 4s1 3d10 instead of 1s2 2s2 2p6 3s2 3p6 4s2 3d9

43
Q

what is ionisation energy

A

electrons can be removed from atoms and the energy it takes to remove them can be measured. This is called ionisation energy because as the electrons are removed, the atoms become positive ions

DEFINITION:
ionisation energy is the energy required to remove a mol of electrons from a mol of atoms in the gaseous state and is measured in kJ mol -1

44
Q

what are successive ionisation energies

A

you can measure the energies to remove the electrons one by one from an atom, starting from the outer electron and working inwards

1st electron needs the least energy to remove it because it is being removed from a neutral atom. This is called the first IE (ionisation energy)

2nd electron needs more energy than the first because it is being removed form a 1+ ion. This is the 2nd IE.

the third needs more and so on

These are called successive ionisation energies

45
Q

what does the pattern of ionisation energies across a period provide evidence for

A

provides evidence for electron energy sub- levels

46
Q

how can you find the number of electrons in any element without using a periodic table

A

you can find the number of electrons in each main level of any element by looking at the jumps in successive ionisation energies

47
Q

what is the general trend for ionisation energies across in the periodic table

A

Ionisation energies gradually increase across a period because the nuclear charge is increasing and this makes it more difficult to remove an electron. There is still the same number of shells - same shielding

This increase, however, is not regular - this is evident if you were to plot the ionisation energies of element across a period.

48
Q

why is the increase in ionisation energies across a period not regular

A

e.g. from magnesium ( 1s2 2s2 2p6 3s2) to aluminium (1s2 2s2 2p6 3s2 3p3), the ionisation energies actually go down despite this increase in nuclear charge.

This is because the outer electron in aluminium is in a 3p orbital which is slightly higher than the 3s orbital. It, therefore, needs less energy to remove it

there is also a dip in ionisation energy between phosphorous ( 1s2 2s2 2p6 3s2 3p3) and sulfur (1s2 2s2 2p6 3s2 3p4).
In phosphorus, each of the three 3p orbitals contains just one electron, while in sulfur, one of the orbitals contain two electrons.
The repulsion between these paired electrons makes it easier to remove them, despite the increase in nuclear charge

49
Q

what is the general trend in ionisation energies down a group in the periodic table

A

there is a general decrease in first ionisation energies down a group.
This is because the outer electron is in the main energy level that gets further from the nucleus in each case

  • more shielding
  • fewer forces of attraction felt between the positive nucleus and negative electrons
50
Q

time of flight calcualtion (work out the length of the tube

A

1) find the mass of one atom by dividing the atomic number by 1000 then dividing that number by AVAGADRO’S CONSTANT
2) work out the velocity by using the KINETIC ENERGY EQUATION
3) work out the distance (in metres) by using the SPEED EQUATION ( distance = time x speed)

chemistry a level (24 decks)

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