CHEM C4

Position of periodic table

Period, group

Elements that are in period are determine by

Number of shells filled with e-

Elements that are in group are determined by

Valence e-

Characteristics of G18 elements

Monoatomic gas

8 valence e- → octet / 2 valence e- → duplet (if only 1 shell)= STABLE

Known as nobel gas

Chemically inert / unreactive

Why are G18 elements chemically inert / unreative?

Achieve stable duplet / octet e- arrangements

Cannot accept, donate or share e-

Trend of G18

When going down G18, the size of the atomic radius of elements increases because the number of e- and the number of shells containing e- increases

Characteristics of G1 elements

Known as alkali metals

Placed in 1st column

Must have 1 valence e- → to achieve stable octet / duplet : lose 1 e- = form +1 ion

Atomic radius increases due to more shells filled with e-

MP and BP decreases

Soft metals

Low density

Grey shiny surface at R.T

G1 elements : low MP and BP compared to other metal

E.g : Li, Na, K

TREND : MP and BP of G1 elements decreases when going down the group

Why?

This is due to the increase of atomic size of the elements down the grp

This will weaken the attraction force between the atoms

Therefore, less heat energy is required to overcome the attraction force between the atoms

Chemical properties / chemical reactions of G1

G1 + H2O → alkali + H2

G1 + O2 → metal oxide

G1 + Cl2 → metal chloride

Reactivity increases in G1, WHY?

Due to easier for G1 atom to donate it’s valence e-

This is because the number of shells filled with e- increases when going down G1

How can G1 elements achieve stable duplet / octet e- arrangement?

Based on how easy to lose 1 e-

If it’s easier to lose 1 e-, what does it mean?

Elements are more reactive

Formula for alkali metals + H2O → alkaline OH + H2

2() + 2H2O → 2()OH + H2

Formula for alkali metal + O2 → metal oxide

4() + O2 → 2()2O

Formula for metal oxide + H2O → alkaline solution

()2O + H2O → 2()OH

Formula for alkali metal + Cl2 → metal chloride

2() + Cl2 → 2()Cl

Characteristics of G17

Known as halogens

Exists as diatomic molecule

E.g : F2, Cl2, Br2, I2, Al2

Physical state and colour at R.T

Cl2 : gas & pale greenish yellow (g&l)

Br2 : liquid & brown (l&g), yellow (diluted)

I2 : solid & black (s&l), purple (g)

Reactions of G17 (halogen) - water

Cl2 + H2O ←→ HCl + HOCl

Br2 + H2O ←→ HBr + HOBr

I2 + H2O ←→ HI + HOI

Examples of bleaching agents

HOCl (hypochlorous) , HOBr (hypobromus)

Examples of non-bleaching agent

HOI (hypoiodous)

Reactions of G17 - metals

2Fe + 3Br → 2FeBr3

2Fe + 3Cl2 → 2FeCl3

2Fe + 3I2 → 2FeI3

Cl2, Br2, I2 molecules are known as

Halogens

Cl-, Br-, I- ions are known as

Halide

G17- reactive, WHY?

valence e- is closer : easier to gain e-, more reactive

explain the position of magnesium in the periodic table of elements

Electron arrangement of Mg is 2.8.2

Mg will be in g2 because it’s valence electron is 2

Mg will be in period 3 because of the number of shells occupied with electrons in Mg is 3

Argon gas is chemically unreactive, WHY?

Argon atom cannot accept, donate or share electrons

Argon have achieve stable octet electron arrangement

Physical properties of G18 elements

Insoluble in water

Colourless gas

Low MP and BP

Poor heat conductors

Do not conduct electricity

State the changes in MP and BP when going down G18 elements and explain

MP and BP increases

The atomic size of elements becomes bigger going down the group, resulting in a stronger FOA between the atom

Thus, more heat energy is required to overcome the force

Physical properties of G1 elements

Low density

Soft metals

Conducts electricity

Good heat conductors

Grey shiny surface at R.T

Low MP and BP

The MP and BP decreases on G1 elements, explain

This is due to the increase of atomic size of the elements down the group

This will weaken the attraction force between the atoms

Therefore, less heat energy is required to overcome the attraction force between the atoms

Observation for a piece of lithium is dropped into a basin of water

Lithium moves slowly on the surface of water with a slow/soft ‘hiss’ sound

Red litmus paper turns blue (due to LiOH)

Observation for a piece of sodium is dropped into a basin of water

Sodium moves rapidly on the surface of the water with a loud ‘hiss’ sound

Red litmus paper turns blue

Observation for a piece of potassium is dropped into a basin of water

Potassium moves very rapidly on the surface of water with a ‘pop’ sound

Red litmus paper turns blue

Observation for a piece of lithium is heated until it burns and put into a gas jar containing oxygen, the product is then dissolved in water

Lithium burns slowly with a red flame

A white solid is formed

Red litmus paper turns blue

Observation for a piece of sodium is heated until it burns and put into a gas jar containing oxygen, the product is then dissolved in water

Sodium burns vigorously with a yellow flame

A white solid is formed

Red litmus paper turns blue

Observation for a piece of potassium is heated until it burns and put into a gas jar containing oxygen, the product is then dissolved in water

Potassium burns vigorously within a reddish-purple/lilac flame

A white solid is formed

Red litmus paper turns blue

Why do alkali metals have similar chemical properties

Because G1 elements have 1 electron in the valence shell

Compare the reactivity between sodium and potassium, explain why

Potassium is more reactive than sodium

The atomic size of potassium is larger than sodium

Therefore, resulting in a weaker FOA between the nucleus and the valence electrons in potassium compare to sodium

Hence, it is easier for potassium atom to release its valence electron

State the changes in atomic size of element when going down G17 elements, explain why

Going down G17 atomic size increases

Because the number of shells occupied with electrons increases

The MP and BP of the elements increase when going down G17, explain why

The molecular size of elements causing the Van der Waales / intermolecular FOA between the molecules to become stronger

Thus more heat energy is required to overcome the force

Observation for chlorine dissolved in water

Blue litmus paper turns red and then white

Observation for bromine is dissolved in water

Blue litmus paper turns red and white

Observation for iodine is dissolved in water

Blue litmus paper turns red

Observation when chlorine is dissolved in sodium hydroxide solution

A colourless solution is produced

Observation for bromine is dissolved in sodium hydroxide solution

A colourless solution is produced

Observation for iodine is dissolved in sodium hydroxide solution

A colourless solution is produced

Observation for chlorine is flowed through hot iron wool

Iron wool burns vigorously with a bright flame

A brown solid is formed

Observation when bromine is flowed through hot iron wool

Iron wool flows brightly and rapidly

A brown solid is formed

Observation for iodine is flowed through hot iron wool

Iron wool glows slowly

A brown solid is formed

Compare the reactivity between chlorine and bromine, explain why

Chlorine is more reactive than bromine

The atomic size of chlorine is smaller than bromine, resulting in a stronger FOA between the nucleus and the electrons to fill up the valence shell

Thus, making it easier for chlorine atom to pull an electron

Properties of oxide for Na and Mg

Basic oxide

Properties of oxide for Al

Amphoteric oxide

Properties of oxide for Si, P, S and Cl

Acidic oxide

Meaning of amphoteric

Can react with both acid and alkali

Going across the period from L to R, explain the change in atomic size

The proton number increases

Hence, the attraction force between the nucleus and the valence electrons is stronger

This causes the atomic size to decreases moving across P3 from L to R

The electronegativity of the elements increases when going across the period from L to R, explain why

As proton number increases, the FOA between nucleus and the valence electrons increases

The atom has a higher tendency to attract electrons

Hence, the electronegativity increases

Meaning of electronegativity

Ability for an atom to accept e-

Transition elements are placed in

Group 3 to group 12

Properties of transition elements

Solid with shiny surfaces

Very hard compared to metals in G1 and 2

High densities

High MP and BP

Transition elements have a special characteristic unknown to other metals, what is it?

Transition elements can function as a catalyst to increase the rate of reaction without undergoing chemical changes at the end of the reaction

Able to form coloured ions or compounds

Have more than 1 oxidation number

Can form complex ions

Uses of transition elements as a catalyst in industry

Iron - production of ammonia (haber process)

Platinum - production of nitric acid (ostwald process)

Vanadium oxide - production of sulphuric acid (contact process)

Nickel/platinum - production of margarine (hydrogenation process)

Uses of transition elements apart from catalyst

Manganese - stained glass windows

Iron - build bridges

Titanium - paint

Examples of transition elements

chromium (Cr), manganese (Mn), iron (Fe), copper (Cu)