Group 1: Alkali Metals
GROUP 1: Alkali Metals Physical Properties
- They are highly reactive
- Reactivity increases down the group – because tendency to loose one electron increases down the group due to increase increase in size and decrease in nuclear charge
- They loose one electron and form +1 Ions.
- They are stored in kerosene or oil to prevent them reacting from air and water
- They are soft, silvery and shinny.
- They look dull in air as they react with oxygen and form oxide which coats their surface
- Lithium is less reactive and francium is highly reactive.
- They have low melting and boiling point and the melting and boiling point decreases down the group.
Group 1: Alkali Metals Chemical Properties
REACTION WITH WATER
Reacts with water to metal hydroxide
2M + H2O 2MOH + H2
Metal hydroxide are alkali therefore the pH increases. Reactivity increases down the group so potassium reacts violently
Fizzing is produced due to the formation of hydrogen.
Eg – 2Li(s) + H2O(l) 2LiOH(aq) + H2(g)
Reaction with Oxygen
Reacts with oxygen to form a metal oxide
2M + O2 M2O
Metals go dull in air due to this reaction
4Li(s) + 4O2(g) 2Li2O(s)
Reaction with Halogens
React with halogens to form metal Halides
2M +X2 2MX [X= F, Cl, Br, I]
Metal Halides are while solids but dissolve in water to form colourless solutions.
2Li(s) + F2(g) 2LiF(s)
| LITHIUM | SODIUM | POTASSIUM |
2Li(s) + 2H2O (l) 2LiOH(aq) + H2(g)
| 2Na(s) + 2H2O (l) 2NaOH(aq) + H2(g)
| 2K(s) + H2O (l) KOH(aq) + H2(g)
|
| Floats in water due to less denisty than water | Floats in water due to less density than water | Floats in water due to less density than water |
| Fizzes due to the formation of hydrogen gas. | Fizzes due to the formation of hydrogen gas. | Fizzes due to the formation of hydrogen gas. |
| Shape is retained while reacting and gets smaller. | It melts into a call while reacting. | Melts into a ball, catches fire and produces a lilac flame. |
WHY REACTIVITY OF GROUP 1 INCREASES DOWN THE GROUP ?
The Reactivity of Group 1 increases down the group as the tendency to loose an electron increases down the group. – React by loosing an electron
FACTORS AFFECTING TENDENCY TO LOOSE AN ELECTRON
- To loose an electron small nuclear charge greater size of atom and greater shielding is required
- Nuclear charge – Great the size of the atom, the outer electron becomes further away from the nucleus decreasing the nuclear charge
- Shielding – More the number of inner electrons due to increases in number of shell greater will be the shielding of the outer electron from the nuclear charge
- Size of the atoms – Greater the size of the atom, the outer electron will become further away from the nucleus resulting in decreases in nuclear charge
- Down the group the atom size increases due to increase in number of electron shells. This results in the outer electron being further away from the nucleus.
- As the outer electron becomes further away from the nucleus the nuclear charge decreases. Increase in number of shells also increases the shielding and shields the outer electron from the nuclear charge.
- Therefore, the tendency of atom to loose an electron increases down the grou resulting in increase in reactivity down the group.