atomic structure

Question 1

what was the Greek philosophers’ model of the atom

Answer 1

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

Question 2

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

Answer 2

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

Question 3

what is the plum pudding model

Answer 3

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

Question 4

what are subatomic particles

Answer 4

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

Question 5

what is the mass of a proton

Answer 5

1.673 x 10 -27

Question 6

what is the mass of a neutron

Answer 6

1.675 x 10 -27

Question 7

what is the charge of electrons and protons

Answer 7

+/- 1. 602 x 10-19

Question 8

what is the mass of an electron

Answer 8

0.911 x 10 -3 (very nearly 0)

Question 9

what is the position of the electons

Answer 9

around the nucleus

Question 10

what is the position of the neutrons and protons

Answer 10

in the nucleus

Question 11

what is the charge of a neutron

Answer 11

0

Question 12

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

Answer 12

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

Question 13

what is the arrangement of subatomic particles

Answer 13

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

Question 14

what are the nuclear forces

Answer 14

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

Question 15

what is the mass spectrometer

Answer 15

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

Question 16

on what scale are relative atomic masses measured on

Answer 16

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

Question 17

what is the equation for the relative atomic/molecular mass

Answer 17

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

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

Question 18

what principle do all mass spectrometers follow

Answer 18

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

Question 19

what happens in a time of flight mass spectrometer

Answer 19

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

Question 20

what are the steps behind the flight mass spectrometer

Answer 20

1. IONISATION
2. ACCELERATION
3. FLIGHT TUBE
4. DETECTION

Question 21

how are large molecules ionised in TOF

Answer 21

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

Question 22

how are smaller molecules/ atoms ionised in TOF

Answer 22

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-

Question 23

what happens in the 2nd stage of ionisation

Answer 23

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

Question 24

what happens in the 3rd stage of TOF spectrometer

Answer 24

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

Question 25

what happens in the 4th and final stage of TOF

Answer 25

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

Question 26

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

Answer 26

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

Question 27

what is the relative atomic mass

Answer 27

the relative atomic mass is: | mean mass of an atom/ mass of 1 atom x 12

Question 28

what is the atomic number Z

Answer 28

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

Question 29

why are atoms neutral

Answer 29

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

Question 30

what determines the chemical properties of an atom

Answer 30

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

Question 31

what does the atomic number of an element show

Answer 31

chemical identity of an element and the number of protons

Question 32

what are isotopes

Answer 32

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

Question 33

how do different isotopes of the same element react

Answer 33

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

Question 34

how are electrons arranged

Answer 34

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

Question 35

what are the different sub shells

Answer 35

there are 4 sub shells | s,p,d,f which increase in energy level

Question 36

what do each sub levels consists of

Answer 36

each sub level consists of electron orbitals

Question 37

what are orbitals

Answer 37

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

Question 38

how many electrons can orbitals consists of

Answer 38

each orbital can hold up to 2 electrons with opposite spin

Question 39

how are electron orbitals filled up

Answer 39

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

Question 40

what is the maximum number electrons in each sub level

Answer 40

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

Question 41

what electron is lost first when positive ions are formed

Answer 41

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)

Question 42

what are the two elements that do not follow the trend

Answer 42

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

Question 43

what is ionisation energy

Answer 43

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

Question 44

what are successive ionisation energies

Answer 44

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

Question 45

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

Answer 45

provides evidence for electron energy sub- levels

Question 46

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

Answer 46

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

Question 47

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

Answer 47

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.

Question 48

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

Answer 48

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

Question 49

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

Answer 49

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

Question 50

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

Answer 50

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)