© kemsoft20041 menzies high school as chemistry © kemsoft20042 as module 1 atomic structure...
TRANSCRIPT
© KeMsoft2004 1
Menzies High School
AS Chemistry
© KeMsoft2004 2
AS Module 1
•Atomic Structure
Fundamental particlesbe 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 isotopesunderstand the principles of a simple mass spectrometer, limited to ionisation, acceleration, deflection and detectionbe able to interpret simple mass spectra of elements and calculate relative atomic mass from isotopic abundance, limited to mononuclear ionsknow 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 numbersunderstand 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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AS Module 1•PeriodicityClassification 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 ofPeriod 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 - Arunderstand 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 - Baknow the reactions of the elements Be - Ba with water and recognise the trendknow the relative solubilities of the hydroxides of the elements Be - Ba and thatMg(OH)2 is sparingly solubleknow the relative solubilities of the sulphates of the elements Be - Ba and that BaSO4 is insoluble and is formed in the test for sulphate ionsknow 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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What is IonisationWhat is Ionisation
M+
+
M (g)
The removal of an electron(s) from a gaesous atom to form an ion.
The overall process is represented by an equation;
(g)
(g) + e-M M+(g) + e-
(g)
11-11+
0
10-
1+
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Ionisation EnergyIonisation Energy
Since the energy involved in ionising a single atom is so small we define it for...
1 mol of electrons1 mol of electrons
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I II III IV V VI VII O
1
2
3
4
d
Ionisation Energy - TrendsIonisation Energy - Trendss
pp
SS
BB CC NN OO FF NeNe
AlAl SiSi PP ClCl ArAr
LiLi BeBe
MgMg
HeHe
NaNa
HHH: 1s1
He:1s2
Li: 1s22s1
Be: 1s22s2
B: 1s22s22px1
C: 1s22s22px12py
1
N: 1s22s22px12py
12pz1
O: 1s22s22px22py
12pz1
F: 1s22s22px22py
22pz1
Ne: 1 s22s22p6
Na: 1s22s22p63s1
Mg: 1s22s22p63s2
Al: 1s22s22p63s23p1
Si: 1s22s22p63s23px13py
1
P: 1s22s22p63s23px13py
13pz1
S: 1s22s22p63s23px23py
13pz1
Cl: 1s22s22p63s23px23py
23pz1
Ar: 1s22s22p63s23p6
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I II III IV V VI VII O
1
2
3
4
Ionisation Energy - TrendsIonisation Energy - Trendss
pp
SS
GaGa GeGe AsAs BrBr KrKr
BB CC NN OO FF NeNe
AlAl SiSi PP ClCl ArAr
SeSeKK CaCa
LiLi BeBe
MgMg
HeHe
ScSc TiTi VV CrCr MnMn FeFe CoCo NiNi CuCu ZnZn
BaBa
SrSr
NaNa
HHK: Ar4s1
Ca: Ar4s2
Sc: Ar4s23d1
Ti: Ar4s23d2
V: Ar4s23d3
Cr: Ar4s13d5
Mn: Ar4s23d6
Fe: Ar4s23d7
Co: Ar4s23d8
Ni: Ar4s13d10
Cu: Ar4s13d10
Zn: Ar4s23d10
Ga: Ar4s23d104p1
Ge: Ar4s23d104p2
As: Ar4s23d104p3
Se: Ar4s23d104p4
Br: Ar4s23d104p5
Kr: Ar4s23d104p6
d
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I II III IV V VI VII O
1
2
3
4
Ionisation Energy - TrendsIonisation Energy - Trendss
pp
SS
GaGa GeGe AsAs BrBr KrKr
FF NeNe
AlAl SiSi PP ClCl ArAr
SeSeKK CaCa
LiLi BeBe
MgMg
HeHe
ScSc TiTi VV CrCr MnMn FeFe CoCo NiNi CuCu ZnZn
BaBa
SrSr
NaNa
HH
d
and in Period 3 (Na - Ar)
understand how ionisation energies in Group II (Be - Ba)
give evidence for electron give evidence for electron arrangement in levels and sub-arrangement in levels and sub-levelslevels
BB CC NN OO
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Ionisation Energy - TrendsIonisation Energy - Trends
• charge on the nucleus.charge on the nucleus.
Factors affecting the size of ionisation energy
the attraction between the nucleus and the outer electron
The greater will be the value of the 1st I.E.
• distance of the electron from the nucleus.distance of the electron from the nucleus.
• number of electrons between the outer electrons and the nucleus.number of electrons between the outer electrons and the nucleus.
The size of that attraction will be governed by:The size of that attraction will be governed by:
The more protons there are in the nucleus, the more positively charged The more protons there are in the nucleus, the more positively charged the nucleus is, and the more strongly electrons are attracted to it.the nucleus is, and the more strongly electrons are attracted to it.
Attraction falls off very rapidly with distance. An electron close to the Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away.nucleus will be much more strongly attracted than one further away.
If there are filled shells of electrons between the outer electron and the 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 nucleus they will ‘cut off’ some of the attractive force of the nucleus – this known as known as screeningscreening or or shielding.shielding.
The greatergreater
1s
2s
2p
3s
3p
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Ionisation Energy - TrendsIonisation 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...
a) The Period 3 elements, b) The group II elements
against their atomic numbers.
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
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Variation in 1st Ionisation Energy with Proton Number
Ion
isat
ion
en
erg
y kJ
/mo
l
P3
Ionisation Energy - TrendsIonisation Energy - Trends
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
Variation in 1st Ionisation Energy with Proton Number
Proton number
Ion
isat
ion
en
erg
y kJ
/mo
l
P3
Proton number
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0
200
11 12 13 14 15 16 17 18 19Proton number
1st I
on
isat
ion
en
erg
y kJ
/mo
l
400
600
800
1000
1200
1400
1600
400
Variation in ionisation energy across Period 3Variation in ionisation energy across Period 3
[Na Mg Al Si P S Cl Ar]
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
Variation in 1st Ionisation Energy with Proton Number
Proton number
Ion
isat
ion
en
erg
y kJ
/mo
l
P3
General trend: As the proton number increases, the 1st I.E. increases
Successive increase in nuclear charge (+ve) means the outer electrons become more strongly held and need more energy to remove them.
Ionisation Energy - TrendsIonisation Energy - Trends
• 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.
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0
200
11 12 13 14 15 16 17 18 19Proton number
1st I
on
isat
ion
en
erg
y kJ
/mo
l
400
600
800
1000
1200
1400
1600
400
Variation in ionisation energy across Period 3Variation in ionisation energy across Period 3
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
Variation in 1st Ionisation Energy with Proton Number
Proton number
Ion
isat
ion
en
erg
y kJ
/mo
l
P3
Ne3s2
Ne3s23px1
Two places where the general trend is not followed…
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.
Ionisation Energy - TrendsIonisation Energy - Trends
1s
2s
2p
3s
3p
1s
2s
2p
3s
3p
12p 13p
[Na /Li Mg/Be Al/B Si/C P/N S/O Cl/F Ar/Ne]
Explain why boron has a lower first ionisation energy than beryllium.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)
Explain why aluminium has a lower first ionisation energy than magnesium.
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)
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0
200
11 12 13 14 15 16 17 18 19Proton number
1st I
on
isat
ion
en
erg
y kJ
/mo
l
400
600
800
1000
1200
1400
1600
400
Variation in ionisation energy across Period 3Variation in ionisation energy across Period 3
[Na /Li Mg/Be Al/B Si/C P/N S/O Cl/F Ar/Ne]
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
Variation in 1st Ionisation Energy with Proton Number
Proton number
Ion
isat
ion
en
erg
y kJ
/mo
l
P3
Ne3s23px1py
1pz1
Ne3s23px2py
1pz1
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.
Ionisation Energy - TrendsIonisation Energy - Trends
1s
2s
2p
3s
3p
16p
Variation in ionisation energy across Period 3Variation in ionisation energy across Period 3Proton number
P3
Two places where the general trend is not followed…
1s
2s
2p
3s
3p
15p
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)
Explain why sulphur has a lower first ionisation energy than phosphorus.
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0
200
4 12 20 38 56Proton number
1st I
on
isat
ion
en
erg
y kJ
/mo
l
400
600
800
400
Variation in ionisation energy down Group IIVariation in ionisation energy down Group II
[Be Mg Ca Sr Ba]
General trend: As the proton
number increases, the 1st I.E. decreases
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.
Ionisation Energy - TrendsIonisation Energy - Trends
1s2s2p3s
12p
1s2s2p3s
20p
3p4s
1s2s2p3s
38p
3p4s3d
5s3p
1000
1s2s
4p
Be SrSrCaCaMgMg
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ELECTRON BEING REMOVED
LO
G1
0(I
ON
ISA
TIO
N E
ER
GY
/kJm
ol)
Ca: 1s22s22p63s23p64s2Ca: 4s23p63s22p62s21s2
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ELECTRON BEING REMOVED
LO
G1
0(I
ON
ISA
TIO
N E
ER
GY
/kJm
ol)
Ca: 4s23p63s22p62s21s2
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