The Periodic Table:  searching for order

History of the Periodic table:

Aristotle The 4 elements
Antoine - Laurent de Lavoisier The list of elements
Jons Jakob Berzelius Symbols and Atomic weights
Johan Wolfgang Dobereiner Law of Triads
Alexandre-Emile Beguyer de Chancoutois Spiral cylinder / aligning similar elements
John Newlands Law of Ocataves
Dmitri Mendeleev Atomic masses / Periodic law
Henry Moseley Atomic number
Glenn Seaborg Transuranic elements 94 - 102

 

 

The Periodic table:  Mendeleev and beyond

 

Periodic Table

Dobereiner – Law of Triads:-

Element

RAM

Properties with water

Lithium

6.9

Fizzes gently – hydrogen given off

Sodium

23

Fizzes – hydrogen given off

Potassium

39.1

Fizzes violently – hydrogen given off

Newlands – Law of Octaves:-

Na Mg Al Si P S Cl Ar K

 

Mendeleev’s Periodic Table

Mendeleev's Prediction

Observed Properties

Atomic mass = 72

Atomic mass = 72.6

Density = 5.5gcm-1

Density = 5.35gcm-1

Light grey colour

Silvery grey colour

Will combine with 2 atoms of oxygen to form a white powder (the oxide) with a high melting point.

Combines with 2 atoms of oxygen to form a white powder (the oxide) with a melting point above 1000oC

Oxide density = 4.7gcm-3

Oxide density = 4.2gcm-3

Will combine with 4 atoms of chlorine to form a chloride with a boiling point less than 100oC.

Will combine with 4 atoms of chlorine to form a chloride with a boiling point less than 100oC.

Chloride density = 1.9gcm-3

Chloride density = 1.8gcm-3

Henry Moseley

SEE SOME OLD PERIODIC TABLES

 

Questions P79  1 - 2  /  P81  1 - 2

 

 

The modern Periodic Table

Groups:

Periods:

Periodicity:

                           Is a regular periodic variation of properties of elements with atomic number and the position in the Periodic Table

 

                    Across a Period:        Metal  à  Non - metal

                    Down Group 4:           Non - Metal    à Metal

 

Variation in electron structure:

Li Be B C N O F Ne
[He]2s1 [He]2s2 [He]2s22p1 [He]2s22p2 [He]2s22p3 [He]2s22p4 [He]2s22p5 [He]2s22p6
Na Mg Al Si P S Cl Ar
[Ne]3s1 [Ne]3s2 [Ne]3s23p1 [Ne]3s23p2 [Ne]3s23p3 [Ne]3s23p4 [Ne]3s23p5 [Ne]3s23p6

Gp1 reactions

Questions 1-2 P83

 

Periodicity:  Ionisation energies and atomic radii

 

A)  Trends across a period:

 

1)  Periodic Patterns:  Atomic radii

 

2)  Periodic Patterns:  First ionisation energies

 

Recap – Factors affecting ionisation energies (from 1.2.1, P40)

 

1)     The distance of the electron from the nucleus

2)     Size of the positive nuclear charge

3)     The ‘shielding’ effect by full inner shells

 

Explanation:

Start with atomic radii:

Then include what effect that has on removing an electron:

B)  Trends down a Group:

1)  Down a Group:  Atomic radii increases:

 

  • As you go down a group, the nuclear charge increases.

  • There are more electron shells which increases shielding between nucleus and outer electron shell.

  • As there are more electron shells, the distance between nucleus and outer shell increases.

  • This means that attraction between the nucleus and outer electrons decreases.

  • Distance and shielding are the most important factors.

 

 

2)  Down a Group:  First ionisation energies decreases:

Explanation:

Start with atomic radii:

Then include what effect that has on removing an electron:

Questions 1 - 2  P85

 

Periodicity:  Boiling points

General trends:

Explanation:

                                Metals  à  Non - metals

                                Solid  à  Gas

                                Metallic  à  Giant Molecular  à  Molecular  à  Atomic

Metallic bonding - Gp 1 - 3

Review it

 

Giant covalent structures - Gp 4

Review it

Carbon - Diamond Carbon - Graphite Silicon

 

Molecular / Atomic - Groups 5 - 0:

Review it

Summary:
Period 2 Li Be B C N2 O2 F2 He
Period 3 Na Mg Al Si P4 S8 Cl2 Ar
Structure Giant metallic Giant covalent Simple molecular / atomic structures
Forces Strong forces between positive ions and negative delocalised electrons Strong forces (bonds) between atoms weak forces between molecules / atoms
Bonding Metallic bonding Covalent bonding Van Der Waals'

Periodicity

Questions 1 - 2  P 87  /  1 - 3 P97  /  1 - 3  P98