© KeMsoft20041 Menzies High School AS Chemistry © KeMsoft20042 AS Module 1 Atomic Structure Fundamental particles be able to describe the properties.

© 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

© KeMsoft2004 4

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

© KeMsoft2004 7


1

2

3

4


pp

SS

GaGa GeGe AsAs BrBr KrKr

BB CC NN OO FF NeNe


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

© KeMsoft2004 8


1

2

3

4


pp

SS

GaGa GeGe AsAs BrBr KrKr

FF NeNe


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

© KeMsoft2004 9

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

© KeMsoft2004 10


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


0

500

1000

1500

2000

2500

0 5 10 15 20 25 30


Proton number

Ion

isat

ion

en

erg

y kJ

/mo

l

P3

Proton number

© KeMsoft2004 12

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


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.


• 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.

© KeMsoft2004 13

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


0

500

1000

1500

2000

2500

0 5 10 15 20 25 30


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.


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)

© KeMsoft2004 14

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


[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


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.


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.

© KeMsoft2004 15

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.


1s2s2p3s

12p

1s2s2p3s

20p

3p4s

1s2s2p3s

38p

3p4s3d

5s3p

1000

1s2s

4p

Be SrSrCaCaMgMg

© KeMsoft2004 16

ELECTRON BEING REMOVED

LO

G1

0(I

ON

ISA

TIO

N E

ER

GY

/kJm

ol)

Ca: 1s22s22p63s23p64s2Ca: 4s23p63s22p62s21s2

© KeMsoft2004 17

ELECTRON BEING REMOVED

LO

G1

0(I

ON

ISA

TIO

N E

ER

GY

/kJm

ol)

Ca: 4s23p63s22p62s21s2

© KeMsoft2004 18

© KeMsoft20041 Menzies High School AS Chemistry © KeMsoft20042 AS Module 1 Atomic Structure Fundamental particles be able to describe the properties.

Documents

p slide

terms of levels s

d slide

d distance

d blocks

size of ionisation energy

kemsoft20045 ionisation

ionisation energies