Chapter 8 - Reactivity Trends Flashcards
What is the reactivity down group 2? How does it compare to the reactivity of group 1?
Reactivity increases:
- easier to lose 2 outer electrons due to increasing atomic radius and more electron shielding = more reactive
Same as group 1
What is an oxidising agent?
Reactivity increases:
- easier to lose 2 outer electrons due to increasing atomic radius and more electron shielding = more reactive
Same as group 1
What is a reducing agent?
Causes another species to be reduced (it itself gets oxidised)
Are group 2 elements reducing agent or oxidising agent?
They lose 2 electrons so are oxidised = reducing agents
Why do melting points decrease down group 2?
- atomic radius increases down the group = weaker forces of attraction between the positive ions and delocalised electrons
- requires less energy to break = decreasing melting points
Which element’s melting point is an exception?
Magnesium as it’s lower than expected
Which redox reactions do group 2 elements occur in?
Metal + oxygen -> metal oxide
Metal + water -> metal hydroxide + hydrogen
Metal + acid -> salt + hydrogen
How can you check if something is a redox reaction?
Check the oxidisation numbers
See if one element is oxidised and one is reduced
What happens when oxides of group 2 elements react with water?
Hydroxide ions are released and form alkaline solutions of the metal hydroxides
Group 2 hydroxides are only slightly soluble in water
What is the trend in solubility down group 2?
Increases down the group as more hydroxide ions are released which makes the solution more alkaline
What group are the halogens?
Group 17
What is the trend in reactivity down group 17?
Decreases down the group:
- group it react by gaining an electron
- as atomic radius & electron shielding increase down the group, nuclear attraction to outer electrons decreases which makes it less easy to gain/pull electrons
What intermolecular forces do halogen molecules ( F2, H2, CI2) have?
Only London forces (electro-negativities cancel so cannot have permanent dipole- dipole interactions)
What is the trend in mp/bp for halogens down the group? Why this trend?
MP/ BP increases down the group:
- more electrons down the group so stronger London forces
- require more energy to overcome the stronger forces = higher mp/bp
What are the physical appearances and states of the halogens?
Fluorine: pale yellow gas
Chlorine: pale green gas
Bromine: red-brown liquid
Iodine: shiny grey-black solid
Astatine: never been seen
What are the 2 uses of group 2 compounds?
- In agriculture - lime water (calcium hydroxide) added to fields to neutralise the acid in the soil/increase the pH of acidic soils
- In medicine - magnesium hydroxide or calcium carbonate used in antiacid medication to neutralise excess stomach acid / treating acid indigestion
What is the acid + base reaction?
ACID + BASE -> SALT + WATER
What happens when universal indicator is added to HClO (hypochlorous acid)?
First turns red as it’s an acid then the colour disappears as bleaching action takes action
Why is chlorine added to water?
Used as a disinfectant for drinking water
Hypochlorous acid (HClO) produced kills bacteria and acts as a weak bleach
What happens if chlorine reacts with NaOH?
Much more chlorine dissolved than when in water as it is less soluble in water
What are chlorine reacting with water & chlorine reacting in with cold, dilute aqueous sodium hydroxide examples of?
Disproportionation reactions (chlorine)
What are the risks of chlorine use?
- toxic gas
- respiratory irritant in small concentrations
- fatal in large concentrations
- if it reacts with hydrocarbons, chlorinated hydrocarbons form which are suspected carcinogens
What colours do Cl2, Br2, I2 form in water and cyclohexane?
Cl2 - pale green in both
Br2 - orange in both
I2 - brown in water, violet in cyclohexane
What is the test for carbonate ions?
- add nitric acid
- effervescence will be observed as gas is produced
- to prove it is CO2 (from the carbonate ions) bubble it through limewater (Ca(OH)2) which will turn cloudy
