Trends in Period 3 Elements

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Chem Factsheet

January 2001

Number 12

Periodicity - Trends in Period 3
To succeed in this topic you need to:• understand the work in Factsheet 1 on Atomic Structure • understand the work in Factsheet 6 on structure of elements and compounds, including how bonding relates to physical properties. • be able to use the periodic table to locate the positions of elements.

The Periodic Table
In the periodic table, elements are placed in order of increasing atomic number (fig 1.)
The horizontal rows of elements are called periods
The vertical columns of elements are called groups

After working through this Factsheet you will:• understand the format of the PeriodicTtable. • understand the term periodicity.
• understand trends in melting point, boiling, electrical conductivity, ionisation energy, atomic radius and electronegativity across the third period.

Modern periodic law states the properties of elements are a periodic function of their atomic numbers. This means that their properties repeat regularly, so that elements in the same group tend to show similar chemical and physical properties.

You need to know the names of the following groups:

Exam Hint: Examination questions across the syllabus will
require you to understand the format of the periodic table. Specific questions are often set on describing and explaining the trends in physical and chemical properties down groups and across the third period. Understanding these trends, and the reasons behind them, will also make much of the rest of Chemistry easier to remember.

Group Number
I
II
VII
0

Group Name
Alkali Metals
Alkaline Earth Metals
Halogens
Noble Gases

Fig 1. The Periodic Table

1

2

3

4

5

6

7

0

Key
1

1

2
Atomic
Number

H
1
3

Be

11

3

Li

Symbol

4

7

2

He
4
5

6

7

8

9

10

B

C

N

O

F

Ne

9

11

12

14

16

19

20

12

13

14

15

16

17

18

Relative
Atomic Mass

Na

Mg

Al

Si

P

S

Cl

Ar

23

24

27

28

31

32

35.5

40

19

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

40

45

48

51

52

55

56

59

59

63.5

65.4

70

73

75

79

80

84

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te
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