8 Reactivity trends Flashcards
(36 cards)
What are the elements in group 2 called? (1 mark)
Alkaline Earth metals
What is similar (in terms of electron configuration) about the elements in group 2? (1 mark)
All have 2 electrons in an outer āsā orbital.
Does the atomic radius increase or decrease as you go down group 2? (1 mark)
Increase
Describe and explain the trend in ionisation energies in group 2. (4 marks)
Outer electrons are less tightly held my nucleus as go down group,
due to extra shielding from filled shells
and increased repulsion between electrons.
This means less energy is needed to remove outer electrons,
so ionisation energies decrease.
Describe and explain the trend in melting points in group 2. (4 marks)
Outer electrons are less tightly held my nucleus as go down group,
due to extra shielding from filled shells
and increased repulsion between electrons.
This means less energy is required to break bonds,
so melting points decrease.
How do group 2 metals react with oxygen? ( 2marks)
Forms a metal oxide with the general formula MO.
How do group 2 metals react with water? (3 marks)
Forms an alkaline hydroxide, with general formula M(OH)2, and hydrogen gas.
How do group 2 metals react with dilute acids? (2 marks)
Redox reaction
Forms a salt + hydrogen gas
How do group 2 oxides react with water? (2 marks)
release OH- ions
Form alkaline solutions of the metal hydroxide
What is the trend in solubility of the hydroxides in group 2? (3 marks)
Increases as go down group
The resulting solutions contain more OH- ions,
and are more alkaline.
What is one use of the group 2 compounds in agriculture? (2 marks)
Calcium hydroxide is added to fields as lime by farmers, to increase the pH of acidic soils.
State two uses of group 2 compounds in medicine. (2 marks)
Antiacids- treat indigestion
BaSO4 used in a barium meal (because absorbs xrays well)
What are the elements in group 7 called? (1 mark)
The halogens
What is the electron configuration of an element in group 7? (1 mark)
All have 7 electrons in their outer shell.
Describe (colour and state) he first 4 elements in group 7, at RTP. (8 marks)
F- pale yellow/green gas
Cl- yellow-green gas
Br- red-brown liquid
I- shiny grey solid/ purple vapour
What is the trend in boiling points in group 7, and why? (4 marks)
As go down group, the atoms have more electrons, so there are stronger induced dipole-dipole interactions, which means more energy is required to overcome them, this means the boiling point increases.
What is the trend in atomic radius in group 7, why? (2 marks)
Increase as go down group, because there are more electron shells (more shielding).
What is the trend in electronegativity in group 7, why? (2 marks)
Decrease as go down group, because the attraction of the nucleus to the valent electrons decreases (due to larger atomic radius).
What is the chemical test for halide ions? (2 marks)
Add nitric acid + silver nitrate
Positive results:
Cl- white
Br- cream
I- yellow
After using nitric acid and silver to test for halides, how do we further distinguish them? (3 marks)
Add dilute NH3:
AgCl dissolves
Add concentrated NH3:
AgBr dissolves
AgI is insoluble in both
What can be added to halide displacement reactions to make the colour change more obvious? (1 mark)
An organic solvent ( like hexane)
What is the common name sodium chlorate? (1 mark)
Bleach
What is disproportionation? (1 mark)
Redox reaction where the same element is both oxidised and reduced.
What are the benefits and risks of using chlorine to treat water? (3 marks)
Benefits:
Kills bacteria
Risks:
Can irritate respiratory system
Cl can react with hydrocarbons in water to create chlorinated hydrocarbons (many of these are carcinogenic).
