3.1.1 Atomic Structure

Question 1

What was Robert Boyle’s idea about the atom? and what date?

Answer 1

1661 - Robert boyle proposed that there could not be a substance that can be made simpler. (These were chemical elements).

Question 2

What was John Dalton’s description of the atom? and what date?

Answer 2

1803 - John Dalton suggested that 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.

Question 3

What was Henri Becquerel’s description of the atom? and what date?

Answer 3

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

Question 4

What was Ernet Rutherford’s description of the atom? and what date?

Answer 4

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

Question 5

What was J J Thomson’s discovery?

Answer 5

in 1897, Thomson discovered the electron (the first sub-atomic particle discovered). He showed that electrons were negatively charged and electrons from all the elements were the same. He believed that there must have been a positive charge (because of negative charge) and electrons were lighter than whole atoms so something must have took the mass of the whole atom-> He suggested electrons were located within the atom in circular arrays, ;ole plums in a pudding of positive charge.

Question 6

What 3 fundamental particles are atoms made of?

Answer 6

Protons, Neutrons and electrons/

Question 7

Structure of atom

Answer 7

protons and neutrons are in the centre of the atom, held together by strong forces called the ‘strong nuclear force’. Electrons surround the nucleus by ‘electrostatic forces’ of attraction, that hold electrons and protons together in the atom, so it overcomes the repulsion between the protons in the nucleus. Strong nuclear force is more strong than electrostatic forces of attraction, however this acts only over very short distances - within the nucleus.

Question 8

What are nucleons?

Answer 8

Protons and Neutrons, because they are found in the nucleus.

Question 9

Relative mass and relative charge of protons

Answer 9

relative mass= 1, relative charge= +1

Question 10

Relative mass and relative charge of neutrons

Answer 10

relative mass= 1, relative charge= 0

Question 11

Relative mass and relative charge of electrons

Answer 11

relative mass= 1/1840, relative charge= -1

Question 12

Why are the standard measures of masses and charges of sub-atomic particles used?

Answer 12

Because the masses and charges of these particles are so small that it is easier to use standard measures and compare the rest to them - hence the term ‘relative’ is used.

Question 13

What does A and Z stand for, for an element?

Answer 13

A- the mass number is the total number of protons and neutrons in the nucleus of an atom.
Z- the atomic number (proton number) is equal to the number of protons in the nucleus of an atom.

Question 14

What happens when an atom loses an electron or gains an electron

Answer 14

It becomes a positively charged ion, if it loses an electron. It becomes a negatively charged ion, if it gains an electron.

Question 15

What is an isotope?

Answer 15

Isotope is an element are atoms with the same number of protons but a different number of neutrons but have the same chemical properties element.

Question 16

What is Time of flight (TOF) mass spectrometer?

Answer 16

A mass spectrometer is an analytical instrument used to give accurate information, about relative isotopic mass and relative abundance of isotopes. It can be used to help identify elements and to determine relative molecular mass.

Question 17

What are the processes that occur in a TOF mass spectrometer?

Answer 17

1) Vacuum
2) ionisation
3) Acceleration
4) Ion drift
5) Detection
6) Data analysis

Question 18

What happens in ionisation?

Answer 18

• Substance is dissolved in a volatile solvent and forced through a fine hollow needle - connected to the positive terminal of a high voltage supply.
• Tiny positively charged droplets are produced (because of loss of electrons to positive charge of supply).
• The solvent evaporates from the droplets into the vacuum; leaving behind (original droplets) single positive ions.

Question 19

What happens in acceleration in TOF?

Answer 19

The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed, because they are accelerated to a constant kinetic energy.

Question 20

What happens in Ion drift in TOF?

Answer 20

The ions pass through a hole in the negatively charged plate, forming a beam and travel along the tube, call the flight tube (there is no electric field here), to a detector. The ions are separated based on their speed; the smaller, first ions travel through the flight tube most rapidly and reach the detector first.

Question 21

What happens in detection in TOF?

Answer 21

When the ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector, which causes a current to flow.

Question 22

What happens in data analysis in TOF?

Answer 22

The flight times are analysed and recorded as a mass to charge ratio (m/z).

Question 23

Outline how the TOF mass spectrometer is able to separate two ions with different m/z values to give two peaks.

Answer 23

The ions are accelerated by the electric field to constant kinetic energy and the ion with a smaller mass moves faster and arrives at the detector first.

Question 24

What is the relative isotopic mass?

Answer 24

The relative isotopic mass of a single isotope of an element relative to the mass of an to carbon-12

Question 25

What does it mean when a mass spectrometer has four peaks?

Answer 25

It means if has four isotopes

Question 26

How can you find out the abundance of each isotope from the results of TOF mass spectrum?

Answer 26

The abundance of each isotope is given by the height of the peak. The numbers above the peaks indicate the relative abundance of each ion detected. The bigger the number, the higher the abundance.

Question 27

What is the formula of the relative atomic mass (Ar)?

Answer 27

Ar = Average mass of 1 atom of an element ÷ 1/12 mass of one ^12C.

Question 28

How can the relative atomic mass of an element be calculated?

Answer 28

Ar = ∑ (mass of isotopes x relative abundance) ÷ ∑ (relative abundance)

Question 29

Why is Mass spectrum complicated for compounds?

Answer 29

The molecule breaks up and produce a small iron is called fragments, which also give peaks.

Question 30

How is the relative molecular mass of a compound determined by mass spectrum?

Answer 30

It is determined by looking at the pic with the largest m/z value - molecular ion peak. The molecular iron is the ion formed by the removal of one electron from a molecule. The mass value of the molecular ion peak is the same as the relative molecular mass of the compound.

Question 31

How to work out the relative molecular mass from a given mass spectrum?

Answer 31

Give the m/z value of the peak furthest to the right - the molecular ion peak.

Question 32

How are energy levels labelled for an atom?

Answer 32

The energy levels are labelled n = 1 (closest to the nucleus), n = 2, n = 3 etc.

Question 33

What are energy levels subdivided into? give examples and what other features does each one have?

Answer 33

They are subdivided into subshells, s, p, d, (and f), which are made up of orbital. Two electrons occupy each orbital.

Question 34

What is the maximum number of electrons and orbitals in each subshell?

Answer 34

s - 2 electrons and 1 orbital
p - 6 electrons and 3 orbitals
d - 10 electrons and 5 orbitals
(f - 14 electrons and 7 orbitals)

Question 35

What subshells do n=1, n=2 and n=3 have?

Answer 35

only s subshell in n=1, s and p subshells in n=2 and s, p, and d subshells in n=3.

Question 36

State how electrons fill up an atom?

Answer 36

Electrons fill up the lowest energy subshells first. (The 4s subshell is lower in energy that the 3d, so it fills before 3d).

Question 37

Give the order is which subshells fill up, and give the order it has to be written in; from 1s to 4p.

Answer 37

1s 2s 2p 3s 3p 4s 3d 4p

1s 2s 2p 3s 3p 3d 4s 4p

Question 38

What electrons do transition metals lose first?

Answer 38

4s electrons

Question 39

When atoms form positive ions, what is the order of subshells in which the electrons are lost from?

Answer 39

4p 4s 3d 3p 3s 2p 2s 1s

Question 40

The 2+ ion of transition metals is caused by the lose of which electrons? (subshell)

Answer 40

4s^2 electrons

Question 41

The electron configuration and iron atom

Answer 41

filling: 1s2 2s2 2p6 3s2 3p6 4s2 3d6
writing: 1s2 2s2 2p6 3s2 3p6 3d6 4s2

Question 42

Give the electron configuration of an iron ion

Answer 42

atom: 1s2 2s2 2p6 3s2 3p6 3d6 4s2
ion: 1s2 2s2 2p6 3s2 3p6 3d6

Question 43

Give the electron configuration of a bromide ion

Answer 43

atom: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5
ion: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6

Question 44

What are the two exceptions for our electrical figuration?

Answer 44

Chromium and copper atoms

Question 45

Give the electron configuration for a chromium atom

Answer 45

1s2 2s2 2p6 3s2 3p6 3d5 4s1 (not 3d4 4s2)

Question 46

Give the electron configurations for a copper atom

Answer 46

1s2 2s2 2p6 3s2 3p6 3d10 4s1 (not 3d9 4s2)

Question 47

What happens in vacuum in TOF mass spectrometry?

Answer 47

The whole apparatus is kept under a high vacuum to prevent the ions produced colliding with molecules from the air.

Question 48

What was Niels Bohr’s idea about the atoms and electrons and what year was this idea introduced?

Answer 48

1913 - Niels Bohr put forward the idea that the atom consisted of a tiny positive nucleus orbited by negatively-charged electrons to form an atom like a tiny solar system. The electrons orbited in shells of fixed size and the movement of electrons from one shell to the next explained how atoms absorbed and gave out light. This was the beginning go what is called quantum theory.

Question 49

What was Erwin Schödinger’s idea about the atoms and electrons and what year was this idea introduced?

Answer 49

1926 - Erwin Schödinger, a mathematical physicist, worked out an equation that used the idea that electrons had some of the properties of waves as well as those of particles. This led to a theory called quantum mechanics which can be used to predict the behaviour of sub-atomic particles.

Question 50

What was James Chandwick’s discovery and what year was this idea introduced?

Answer 50

1932 - He discovered the neutron.

Question 51

What was Gilbert Lewis’ ideas about bonding?

Answer 51

• The inertness of the noble gasses was related to their having full outer shells of electrons.
• Ions were formed by atoms losing or gaining electrons to attain full outer shells.
• atoms could also bond by sharing electrons to form a full outer shell.

Question 52

Explain different models of the atom that chemists use for different purposes

Answer 52

• Dalton’s model can still be used to explain the geometries of crystals.
• Bohr’s model can be used for a simple model of ionic and covalent bonding.
• The charge cloud idea is used for a more sophisticated explanation of bonding and the shapes of molecules.
• The simple model of electrons orbiting in shells is useful for many purposes, particularly for working out bonding between atoms.

Question 53

What formula tells us how many electrons can be found at each energy level?

Answer 53

2n² where n is the number of the main level.

Question 54

What is an electron considered to be?

Answer 54

a cloud of negative charge.

Question 55

What happens to the energy at each main shell?

Answer 55

The energy increases as the main shell increases, e.g. the second main shell has higher energy than the first main shell; and the third has higher than the second.

Question 56

2 rules of spin

Answer 56

• Two electrons in the same orbital must have opposite spins.
• The electrons are usually represented by arrows point up or down to show the different directions of spin.

Question 57

3 rules for allocating electrons to atomic orbitals.

Answer 57

1) atomic orbitals of lower energy a field first - so the lower main level is filled first and, within this level, sub-levels of the lower energy of filled first.
2) atomic orbitals of the same energy fill singly before pairing starts. This is because electrons repel each other.
3) no atomic orbital can hold more than two electrons.

Question 58

What is ionisation energy?

Answer 58

The energy required to remove a mole of electrons from a mole of atoms in the gaseous state and is measured in KJ mol^-1

Question 59

Why is it called ionisation energy?

Answer 59

because as the electrons are removed, the atoms become positive ions.

Question 60

What is the abbreviations of ionisation energy?

Answer 60

IE

Question 61

How can you measure the energies required to remove electrons one by one in IE?

Answer 61

It starts from the outer electrons working inwards
*The first electron needs the least energy to remove it because it is being removed from a neutral atom. This is the first IE.
*The second electron needs more energy than the first because it is being removed from a +1 ion. This is the second IE.
*The third needs more… and so on.
They are called successive ionisation energies.

Question 62

How can you find the group number of an atom by looking at its ionisation energies?

Answer 62

The group number is one less that the big jump in successive ionisation energy.

Question 63

Trends in ionisation energies across a period in the Periodic Table

Answer 63

Ionisation energies generally increase across a period because

• the nuclear charge is increasing and this makes it more difficult to remove an electron
• the shielding is similar as the electron is being removed from the same shell.
• there is a smaller atomic radius, as the outermost electrons is held closer to the nucleus by the greater nuclear charge.

Question 64

In going from magnesium (1s² , 2s² , 2p⁶ , 3s² ) to aluminium (1s² , 2s² , 2p⁶ , 3s² , 3p¹ ), the ionisation energy actually goes down, despite the increase in nuclear charge. Explain why

Answer 64

This is because the outer electron in aluminium is in a 3p orbital which is of a slightly higher energy than the 3s orbital.

Question 65

Why is there a drop of ionisation energy between phosphorus (1s² , 2s² , 2p⁶ , 3s² , 3p³) and Sulfur (1s² , 2s² , 2p⁶ , 3s² , 3p⁴)?

Answer 65

In phosphorus, each of the three 3p orbitals contains just one electron. While in sulfur, one of the 3p orbitals must contain two electrons. The repulsion between these paired electrons makes it easier to remove one of them, despite the increase in nuclear charge.

Question 66

Trends in ionisation energies down a group in the Periodic Table

Answer 66

Down a group the first IE decreases because:

• there is an increase in atomic radius
• there is more shielding of the outer electron from the nucleus charge due to the increased number shells
• there is less nuclear attraction for the outer electron because of the increased atomic radius and increased shielding

Question 67

Why does successive ionisation energies get larger when removing from an ion?

Answer 67

To remove an electron from a positive ion requires more energy as the outermost electron is closer to the nucleus and there is the same number protons for fewer electrons, resulting in a greater nuclear attraction for the electrons.