Chapter 8 Reactivity Trends Flashcards
What type of agents are group 2 elements ?
Reducing agents
- X—> X2+ +2e-
What three redox reactions do they undergo?
What are products
- with oxygen : gives you magnesium OXIDE
- with water : gives you magensium HYDROXIDE and HYDROGEN
- with dilute acids : gives SALT AND HYRDROGEN
Specific reaction of magensium with oxygen? (What observations?)
Burns with a brilliant white light
2) What is the trend of reactivity in general for the group 2 and how does work in water
It increases lower you go
- doesnt react with berrilium
- slowly with magnesium
- VIGOUROUS THE MORE YOU GO DOWN
In a redox reaction with water how does redox (in terms of numbers) work?
Hydrogen will reduce but some stay the same, others increase and thus oxidise
Why are group two elements more reactive down they go?
Why even thiugh other energy changes happen
What does this make them?
- to become 2+ ions from gaseous form requires the input of TWO IONISATION ENERGIES
- inionsstion energy lowers lower you go due to INCREASED SHIELDING and increased atomic radius, which both lower the overall nuclear attraction (and thus energy)
- EVEN THOUGH other energy changes take place when react the first /second ionisation male up most of the energy input
== this means they are stronger REDUCING AGENTS lower you go
In reaction of group 2 with water to make alkaline solution, what is the trend the lower you go?
Alkalinity + solubility increases
Why is grouo 2 more solubke / alklaine lower you go
Essentially last point
- The attraction between higher up metals is greater with the hydroxide ion (due to less shielding and less radius).
- as a result higher up there are less OH- ions aqeuos in the soltuion (more are still combined with the metal ).
- thus less alklaine higher and also less solible
Barium more alklaine and solible then magnesium due to HIGHER OH-(aq) CONCENTRATION!
How can the group 2 compounds be used as bases (3 different ones)?
A hydroxide
An oxide
A carbonate
How can group 2 compounds be used in agriculture (which compound)+ ionic equation
Calcium hydroxide Ca(OH)2 is added the acidic fields as LIME to increase pH of soil - white powder , neutrilises acid to water
Ca(OH)2 + 2H+—> H2O+ Ca2+
How can group 2 compounds be used in medicine?
Used as antacids fo neutrilse acid in stomach to cure acid indigestion
- these are either magnesium or calcium carbonates
- or magensium hydoxide which is suspended in water (slightly soluble ) as milk of magnesia
Reactions are :
Mg(Co3) + 2HCl—> MgCl2 + H2O + Co2
Mg(OH)2 + 2HCl—>MgCl2 + 2H2O
Why is milk of magnesia useful?
As it is only slightly soluble ots soluble enough to get to stomach but all that doesnt react can pass through your system as not soluble enough
Physical properties of group 2
How does boiling + melting change
- light
- compounds white or colourless
- high melting boiling but lower you go decrease
Finally what happens to groupn2 hydroxides when you hest
As only slightly soluble they become saturated and form a precipate like Ca(OH)2 lime
What do the halogens exist as lower down you go
Diatomic molecules, as gas and then solids as simole molecular
What is the trend in boiling point and why
Lower down you go = INCREASE
- this because the greater number of electrons cause greater and stronger number of london forced between and thus more energy needed to overcome so boiling point is higher