1. Menzies High School
AS Chemistry
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2. AS Module 1 Atomic Structure Fundamental particles
be able to describe the properties of protons, neutrons and electrons in terms of relative charge and relative mass
Protons, neutrons and electrons
understand the importance of these particles in the structure of the atom
Mass number and isotopes
be able to recall the meaning of mass number (A) and atomic (proton) number (Z) be able to explain the existence of isotopes understand the principles of a simple mass spectrometer, limited to ionisation, acceleration, deflection and detection be able to interpret simple mass spectra of elements and calculate relative atomic mass from isotopic abundance, limited to mononuclear ions know that mass spectrometry can be used to determine relative molecular mass
Electron arrangement
be able to describe the electronic structures of atoms and ions up to Z = 36 in terms of levels s, p and d, considered as energy levels not quantum numbers understand how ionisation energies in Group II (Be - Ba) and in Period 3 (Na - Ar) give evidence for electron arrangement in levels and sub-levels
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3. AS Module 1
Periodicity
Classification of elements in s, p, and d blocks
be able to classify an element as s, p or d block according to its position in the Periodic Table
Properties of the elements of Period 3 (Na - Ar) to illustrate periodic trends
be able to describe the trends in atomic radius, first ionisation energy, electronegativity, melting and boiling points of the elements Na - Ar understand the reasons for the trends in these properties
Group II
understand the trends in atomic radius, first ionisation energy, electronegativity and melting pouint of the elements Be - Ba know the reactions of the elements Be - Ba with water and recognise the trend know the relative solubilities of the hydroxides of the elements Be - Ba and that Mg(OH)2 is sparingly soluble know the relative solubilities of the sulphates of the elements Be - Ba and that BaSO4 is insoluble and is formed in the test for sulphate ions know that beryllium is atypical, limited to covalent character (e.g. in BeCl2), the amphoteric character of Be(OH)2 and the limitation of maximum co-ordination number to four
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4. M+ M + e- M M+ What is Ionisation
The removal of an electron(s) from a gaesous atom to form an ion. +
11+
11-
10- 1+ M+ M
(g)
(g)
The overall process is represented by an equation;
(g) + e- M M+
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5. Ionisation Energy
Since the energy involved in ionising a single atom is so small we define it for...
1 mol of electrons
The 1st ionisation energy of an atom is the energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of unipositive ions
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6. Ionisation Energy - Trends
I II III IV V VI VII O
H: 1s1 1 H He
He:1s2 p
Li: 1s22s1
Na: 1s22s22p63s1
Be: 1s22s2
Mg: 1s22s22p63s2
B: 1s22s22px1
Al: 1s22s22p63s23p1 Li Be B C N O F Ne 2
C: 1s22s22px12py1
Si: 1s22s22p63s23px13py1
N: 1s22s22px12py12pz1
P: 1s22s22p63s23px13py13pz1
O: 1s22s22px22py12pz1
S: 1s22s22p63s23px23py13pz1
F: 1s22s22px22py22pz1
Cl: 1s22s22p63s23px23py23pz1 3 Na Mg
Ne: 1 s22s22p6
Ar: 1s22s22p63s23p6 Al Si P S Cl Ar d 4
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7. Ionisation Energy - Trends
I II III IV V VI VII O
K: Ar4s1
Sc: Ar4s23d1 1 H He
Ca: Ar4s2
Ti: Ar4s23d2 p
V: Ar4s23d3
Zn: Ar4s23d10
Cr: Ar4s13d5
Ga: Ar4s23d104p1 Li Be
Mn: Ar4s23d6
Ge: Ar4s23d104p2 B C N O F Ne 2
Fe: Ar4s23d7
As: Ar4s23d104p3
Co: Ar4s23d8
Se: Ar4s23d104p4
Ni: Ar4s13d10
Br: Ar4s23d104p5 3 Na Mg
Cu: Ar4s13d10
Kr: Ar4s23d104p6 Al Si P S Cl Ar d K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 4 Ba Sr
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8. Ionisation Energy - Trends
I II III IV V VI VII O
understand how ionisation energies in Group II (Be - Ba) 1 H He p
and in Period 3 (Na - Ar) Li Be B C N O F Ne 2
give evidence for electron arrangement in levels and sub-levels 3 Na Mg Al Si P S Cl Ar d K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 4 Ba Sr
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9. Ionisation Energy - Trends
Factors affecting the size of ionisation energy
The greater
the attraction between the nucleus and the outer electron
The greater will be the value of the 1st I.E. 1s 2s 2p 3s 3p
The size of that attraction will be governed by:
charge on the nucleus.
The more protons there are in the nucleus, the more positively charged the nucleus is, and the more strongly electrons are attracted to it.
distance of the electron from the nucleus.
Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away.
number of electrons between the outer electrons and the nucleus.
If there are filled shells of electrons between the outer electron and the nucleus they will ‘cut off’ some of the attractive force of the nucleus – this known as screening or shielding.
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10. Ionisation Energy - Trends
1. Look up and tabulate the 1st ionisation energies of the
a) The Period 3 elements, b) The group II elements
2. Plot, by hand, graphs of the 1st ionisation energies of...
The Period 3 elements, b) The group II elements
against their atomic numbers.
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11. Ionisation Energy - Trends
Variation in 1st Ionisation Energy with Proton Number
Proton number
Ionisation energy kJ/mol P3
Ionisation Energy - Trends
Variation in 1st Ionisation Energy with Proton Number
Ionisation energy kJ/mol P3
Proton number
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12. Ionisation Energy - Trends
Variation in 1st Ionisation Energy with Proton Number
Ionisation Energy - Trends
Ionisation energy kJ/mol P3
Proton number
1600
Variation in ionisation energy across Period 3
1400
General trend:
As the proton number increases, the 1st I.E. increases
1200
1000
1st Ionisation energy kJ/mol
800
Successive increase in nuclear charge (+ve) means the outer electrons become more strongly held and need more energy to remove them.
600
400
400
charge on the nucleus.
The more protons there are in the nucleus, the more positively charged the nucleus is, and the more strongly electrons are attracted to it.
200
Proton number
[Na Mg Al Si P S Cl Ar]
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13. Explain why boron has a lower first ionisation energy than beryllium.
Variation in 1st Ionisation Energy with Proton Number 1s 2s 2p 3s 3p
Ionisation Energy - Trends
Ionisation energy kJ/mol P3
Explain why aluminium has a lower first ionisation energy than magnesium.
Proton number
1600
Mg’s outer electron in an s (3s) orbital (1) Al’s outer electron is in a p (3p) orbital (1) 3p higher in energy than 3s – less energy needed to remove it(1)
Variation in ionisation energy across Period 3
Two places where the general trend is not followed…
1400
1200
Explain why boron has a lower first ionisation energy than beryllium.
1000
12p
13p
Be’s outer electron in an s (2s) orbital (1) B’s outer electron is in a p (2p) orbital (1) 2p higher in energy than 2s – less energy needed to remove it(1)
1st Ionisation energy kJ/mol
800
Ne3s2
600
p-orbital is higher in energy than an s orbital (further from the nucleus and screened) so the electron requires less energy to remove it; aluminium will have a lower 1st I.E. than magnesium. Even though the nuclear charge has increased this is more than off-set by the greater energy and degree of shielding of the p-orbital electron.
Ne3s23px1
400
400
200
Proton number
[Na /Li Mg/Be Al/B Si/C P/N S/O Cl/F Ar/Ne]
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14. electron lost in S is paired in a 3p orbital (1)
Variation in 1st Ionisation Energy with Proton Number 1s 2s 2p 3s 3p
15p
Ionisation Energy - Trends
Ionisation energy kJ/mol P3 P3
Explain why sulphur has a lower first ionisation energy than phosphorus.
Proton number
Proton number
1600
electron lost in S is paired in a 3p orbital (1)
electron lost in P is unpaired in a 3p orbital (1) repulsion between paired electrons (1) less energy needed to remove a paired electron than an unpaired one (1)
Variation in ionisation energy across Period 3
Variation in ionisation energy across Period 3
Two places where the general trend is not followed…
1400
1200
Ne3s23px1py1pz1 1s 2s 2p 3s 3p
16p
1000
Ne3s23px2py1pz1
1st Ionisation energy kJ/mol
800
In both cases the electron is removed from a p-orbital (same amount of shielding in both elements) but in phosphorus the electron lost is one of the unpaired p-electrons and in sulphur it is one of the paired electrons . The paired electrons repel each other and less energy is needed to remove one of them compared with the unpaired ones; sulphur therefore has a lower 1st I.E. than phosphorus.
600
400
400
200
Proton number
[Na /Li Mg/Be Al/B Si/C P/N S/O Cl/F Ar/Ne]
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15. As the proton number increases,
1000 1s 2s 4p Be 1s 2s 2p 3s
12p 1s 2s 2p 3s
20p 3p 4s 1s 2s 2p 3s
38p 3p 4s 3d 5s
Ionisation Energy - Trends
Variation in ionisation energy down Group II Mg Ca Sr
1st Ionisation energy kJ/mol
800
600
400
400
Successive increase in nuclear charge (+ve) does not make up for:
the increased degree of shielding felt by the outer s-electron
Its higher energy state
Its greater distance from the nucleus
So, the outer electrons become less strongly held and need less energy to remove them.
General trend:
As the proton number increases,
the 1st I.E. decreases
200
Proton number
[Be Mg Ca Sr Ba]
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16. LOG10(IONISATION EERGY/kJmol) ELECTRON BEING REMOVED
Ca: 1s22s22p63s23p64s2
Ca: 4s23p63s22p62s21s2
ELECTRON BEING REMOVED
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17. LOG10(IONISATION EERGY/kJmol) ELECTRON BEING REMOVED
Ca: 4s23p63s22p62s21s2
ELECTRON BEING REMOVED
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18. © KeMsoft2004