AS Chemistry The Periodic Table. THE PERIODIC TABLE occur in the same vertical columns (GROUPS). =...

AS Chemistry

The Periodic Table

THE PERIODIC TABLE

occur in the same vertical columns (GROUPS).

= the elements arranged in rows (PERIODS)

such that chemically similar elements

in order of increasing atomic number (Z)

Period 1

Period 2

Period 3

Period 4

Period 5

Period 6

Period 7

Gro

up

1

Gro

up

2

Gro

up

3

Gro

up

4G

rou

p 5

Gro

up

6G

rou

p 7

Gro

up

0

s-blo

ck

d-block

p-block

Group VII

GROUP

Group number = number of electrons in highest occupied energy level

e.g. Group I the alkali metals

the halogens

eg Na[2,8,1] =

eg F[2,7] =

= elements within the same vertical column

Chemical and physical properties are similar within a group

AS Chemistry

MgMg

CaCa

SrSr

BaBa

?Trends in Physical Properties of Group 2 Metals

INCREASES as EXTRA e- SHELLS ADDED which are INCREASINGLY SHIELDED from the nucleus.

even though more p+ are present.

This causes a WEAKER attractive force and consequently, a lowering of ionisation energy

DECREASES because the outer e- is more distant and more shielded from attracting nuclear protons,

M (g) M+(g) + e-

attractions between 2+ cations and the 2 delocalised electrons per atom become WEAKER.

DECREASE A s metallic bonding gets WEAKER because radius and mass of the 2+ ions INCREASE

Mg unusual because atoms DO NOT pack together as well as others

attractions between 2+ cations and the 2 delocalised electrons per atom become WEAKER.

DECREASE A s metallic bonding gets WEAKER because radius and sheilding of the 2+ ions INCREASE

Mg unusual because atoms DO NOT pack together as well as others

PERIOD

Chemical and physical properties change from extremes across any period.

e.g. Period 3

Sodium = a reactive metallic solid

Argon = an unreactive, non- metallic gas

eg Si (Z=14)

Period number = number of shells

2,8,4 Period 3 and Group 4

= elements within the same horizontal row

Atomic Radii Across Period 3

0

0.05

0.1

0.15

0.2

0.25

10 11 12 13 14 15 16 17 18

Atomic Number (Z)

Ato

mic

Radiu

s / n

m

Outer e- in same energy level (distance & shielding similar)

but attracted more strongly as no. of nuclear protons increases

Atomic radius DECREASES across period 3.

MELTING POINTMELTING POINT


Na Mg Al Si P S Cl Ar

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Boiling and melting points are a measure of the energy required toseparate the particles in a substance. Bond type is significant.

PeriodsA general increase then a decrease

Kelvin SODIUM MAGNESIUM



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PeriodsA general increase then a decrease

Metals Na-AlMelting point increases due to the increasing strength of metallic bonding caused by ...

the larger number of electrons contributing to the “cloud”

larger charge and smaller size of ions gives rise to a larger charge density.

Kelvin

The electron cloud in magnesium is denser than in sodium so more energy is required to separate the ‘ions’

SODIUM MAGNESIUM



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Non-metals Si-Ar

SILICON Large increase in melting point as it has a giant molecular structure like diamond

A lot of energy is required to break the many covalent bonds holding the atoms together.

Kelvin



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P, S, Cl, ArVery much lower melting points as they are simple covalent molecules

Melting point depends on the weak intermolecular van der Waals’ forces.

The larger the molecule the greaterthe van der Waals’ forces

P4 S8 Cl2

relative mass 124 256 71

melting point 44°C 119°C -101°C

Kelvin



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PHOSPHORUS

can exist is several allotropic forms. In the most common, red phosphorus, each molecule exists in a tetrahedral structure. The atoms are joined by covalent bonds within the molecule

formula P4

relative mass 124melting point 44°C

Melting point drops dramatically as intermolecular attractions are now due to weak van der Waals’ forces.

Kelvin



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SULPHUR

can exist is several allotropic forms. Sulphur usually exists in a puckered eight membered ring structure. The atoms are joined by covalent bonds within the molecule

formula S8

relative mass 256melting point 119°C

Melting point rises slightly as the molecule is bigger so has slightly stronger van der Waals’ forces.

Kelvin



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CHLORINE

Exists as a linear diatomic molecule.

The atoms are joined by covalent bonds within the molecule

formula Cl2

relative mass 71melting point -101°C

Melting point falls slightly as the molecule is smaller so has slightly lower van der Waals’ forces.

Kelvin




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ARGON

Exists as a monatomic species.

formula Arrelative mass 40melting point -189 °C

Melting point falls.

Kelvin

MELTING POINT TREND - NON METALSMELTING POINT TREND - NON METALS

P4 S8 Cl2 Ar

relative mass 124 256 71 40melting point / K 317 392 172 84


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Boiling points tend to be a better measure and show better trends because solids can be affected by the crystal structure as well as the type of bonding.

As is expected, the boiling points are higher than the melting points.

Kelvin

BOILING POINTBOILING POINT



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Note the trend from Al – Si varies slightly when we consider the mpt trend and the bpt trend. The mpt increases from Al – Si but the bpt decreases.

The is because when Silicon melts many of its covalent bonds are broken so to vaporize molten silicon does not require as much energy as to vaporize molten Aluminium

Kelvin

BOILING POINTBOILING POINT


Giant

Giant

Simple

Metallic

Covalent

Covalant

AS Chemistry The Periodic Table. THE PERIODIC TABLE occur in the same vertical columns (GROUPS). =...

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Transcript of AS Chemistry The Periodic Table. THE PERIODIC TABLE occur in the same vertical columns (GROUPS). =...