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
If ORANGE Bromine water is added to COLOURLESS potassium chloride solution, what would be observed?
No observable reaction
If BROWN iodine solution is added to COLOURLESS potassium chloride solution, what would be observed?
No observable reaction
If COLOURLESS Chlorine water is added to COLOURLESS potassium bromide solution, what would be observed?
Orange solution of Br2 formed
REACTION:
Cl2 + 2Br- —> 2Cl- + Br2
The Chlorine is more reactive- displaced the bromine
If ORANGE Bromine water is added to COLOURLESS potassium bromide solution, what would be observed?
No observable reaction
If BROWN Iodine solution is added to COLOURLESS potassium bromide solution, what would be observed?
No observable reaction
If COLOURLESS Chlorine water is added to COLOURLESS potassium Iodide solution, what would be observed?
Brown solution of I2 formed
REACTION:
Cl2 + 2I- —> 2Cl- + I2
The Chlorine is more reactive-displaced the iodine
If ORANGE Bromine water is added to COLOURLESS potassium Iodide solution, what would be observed?
Brown solution of I2 formed
REACTION:
Br2 + 2I- —> 2Br- + I2
If BROWN Iodine solution is added to COLOURLESS potassium Iodide solution, what would be observed?
No observable reaction
State the physical properties of group 8
- The noble gases are colorless gases at room temperature
- Have very low melting and boiling points, which increase down the group
- The densities of the noble gases increase down the group
