Group chemistry Flashcards
State the physical properties of the alkali metals (Group 1)
- shiny metallic solids at room temperature
- Melting and boiling points are low for metals, and decrease down the group
- Densities are low, and generally increase down the group
- They are soft and become softer down the group
- They are good conductors of heat and electricity
Explain why the melting/ boiling points of the alkali metals decrease as you go down the group
- Each element wants to lose 1 electron to become stable
- As you go down the group, the distance between the delocalised electron and the +1 ion core within the metallic solid will increase as the ions get larger
- The attraction b/t the electrons and the ions will decrease
- leads to decrease in metallic bond strength
- resulting in lower mp/bp’s
Explain why the density of the alkali metals increases as you go down the group
- As you go down the group
- the masses of the individual ion cores within the metallic solids increase
- as there are more electrons/ energy levels
- which leads to an increased density
Explain why the alkali metals become softer as you go down the group
- As you go down the group, the distance between the delocalised electron and the +1 ion core within the metallic solid will increase as the ions get larger
- The attraction b/t the electrons and the ions will decrease
- leads to weaker metallic bond strength
- making it easier to cut/ softer
State 4 chemical properties of Group 1
- The alkali metals are very reactive- have to be stored in oil to prevent them from reacting with oxygen and water in the air
- When freshly cut and exposed to the air, the shiny metals will quickly react with oxygen and tarnish, forming metal oxide
- The alkali metals react with non-metals to form ionic compounds
- As you go down the group, the elements become more reactive
State the observations when the alkali metals react with water
- When Li, Na and K are added to cold water, they visibly react
- Li, Na and K float on water, moving around on the surface and fizzing
- Hydrogen gas is produced, which burns with a “squeaky pop” sound when ignited
- K reacts so exothermically that the hydrogen produced spontaneously ignites and burns with a lilac flame
- A soluble metal hydroxide is also formed, so the resultant solution will be alkaline and have a high pH, which would turn universal indicator blue/ purple.
State the general equation for the reaction between the alkali metals and water
2M(s) + 2H2O(l) —> 2MOH(aq) + H2(g)
M: alkali metal
State the general equation for the reaction between the alkali metals and oxygen
2M(s) + O2(g) —> M2O(s)
M: alkali metal
Explain the trend in reactivity in the alkali metals
- As you go down the group, the reactivity increases
- As you go down, the number of electrons increase
- the atomic radii increases
- The distance b/t the outermost electron and the nucleus increases
- The attraction between the outermost electron and the nucleus decreases
- Less energy is required to remove an electron
State the physical properties of Group 7
- The halogens are all non-metals with coloured vapours
- Low melting and boiling point, which increase down the group
- Poor conductors of heat and electricity
- Exist as diatomic molecules
Give the colour and state of the halogens at room temperature
- Fluorine is a pale yellow GAS
- Chlorine is a yellow-green GAS
- Bromine is a red-brown volatile LIQUID, with an orange VAPOUR
- Iodine is a grey shiny SOLID (when heated gives a purple VAPOUR)
Explain the trend in reactivity in the halogens
- As you go down the group the number of electrons increases
- The No. of shells increases
- The distance between the positively charged nucleus and the outermost electron increases
- The attraction between the nucleus and the outermost electron decreases
- More difficult to gain an electron
- reactivity decreases
How do alkali metals and the halogens interact?
The halogens react vigorously with heated alkali metals o form metal halide salts
E.g, 2K(s) + Br2(g) —> 2KBr(s)
How do displacement reactions occur between halogens?
A more reactive halogen will displace a less reactive halogen from solutions of its salts
If COLOURLESS Chlorine water is added to COLOURLESS potassium chloride solution, what would be observed?
No observable reaction
