Periodic Table Flashcards
1
Q
How is the periodic table arranged?
A
- by increasing atomic number
- in periods showing repeating trends in physical and chemical properties
- in groups having similar chemical properties
2
Q
Explain the classification of the ‘blocks’ in periodic table
A
- the s-block has an outer shell arrangement of s1 or s2
- It includes group one and group two on the periodic table
- the p-block elements have an outer shell electron configuration of s2p1 to s2p6
- it includes group 3 - 8
- the d-block elements have electron configurations in which d sub-shells are being filled
- it includes all of the transition metals
3
Q
How does the reactivity change down group 2?
A
- As you go down the group, the ionisation energies decrease. This is due to the increasing atomic radius and shielding effect.
- When Group 2 elements react they lose electrons, forming positive ions. The easier it is to lose electrons, the more reactive the element, so reactivity increases across the group
4
Q
How do group 2 elements react with water and oxygen?
A
- They react with water to produce hydroxides
M (s) + 2H20 (l) -> M(OH)2 (aq) + H2 (g) - They burn in oxygen to form oxides. Group 2 metals form solid white oxides.
2M (s) + O2 (g) -> 2MO (s) - They react with dilute hydrochloric acid to produce a salt and a hydrogen
M (s) + 2HCl (aq) -> MCl (aq) + H2 (g)
5
Q
Are Group 2 oxides and hydroxides basic or acidic?
A
- The oxides of the Group 2 metals react readily with water to form metal hydroxides, which dissolve. The hydroxide ions make these solutions strongly alkaline.
- Magnesium oxide is an exception - it only reacts slowly and the hydroxide isn’t very soluble.
- The oxides form more strongly alkaline solutions as you go down the group, because the hydroxides get more soluble.
6
Q
How are Group 2 compounds useful?
A
- Because they are bases, they are often used to neutralise acidity
- Calcium hydroxide is used in agriculture to neutralise acidic soils.
- Magnesium hydroxide and calcium carbonate are used in some indigestion tablets as antacids
- The ionic equation for neutralisation is :
H+ (aq) + OH- (aq) -> H20 (l)
7
Q
What are halogens?
A
- Halogens are the highly reactive non-metals of group 7
- The halogens exist as diatomic molecules
8
Q
How do the physical properties of the halogens change down the group?
A
- Their boiling and melting points increase down the group. This is due to the increasing strength of the London forces as the size and relative mass of the atoms increases
- This is shown by how the physical state from chlorine gas at the top of the periodic table to iodine solid at the bottom of the periodic table. Volatility decreases down the group
- The colour gets darker down the group
9
Q
How does the reactivity change down the group for halogens?
A
- Halogen atoms react by gaining an electron in their outer shells to form 1- ions.
- As you go down the group, the atomic radii increase so the outer electrons are further from the nucleus. The outer electrons are also shielded more from the attraction of the positive nucleus because there are more inner electrons. This makes it harder for larger atoms to attract the electron needed to form an ion so larger atoms are less reactive.
- Another way of saying this is that halogens get less oxidising down the group as they are oxidising agents and are themselves reduced.
10
Q
What are the colour changes seen when displacement reactions of halogens take place with chlorine?
A
- KCl (aq), KBr (aq), and KI (aq) are colourless
- Chlorine water is colourless
- When chlorine water reacts with KBr in an aqueous solution it becomes yellow and when it is in an organic solution it becomes orange.
- When chlorine water reacts with KI in an aqueous solution it becomes orange/brown and when it is in an organic solution it becomes purple.
- The organic solution could be hexane
11
Q
What are the colour changes seen when displacement reactions of halogens take place with bromine?
A
- KCl (aq), KBr (aq), and KI (aq) are colourless
- Bromine water is yellow
- When bromine water reacts with KCl no reaction takes place
- When bromine water reacts with KI in an aqueous solution it becomes orange/brown and when it is in an organic solution it becomes purple.
- The organic solution could be hexane
12
Q
What are the colour changes seen when displacement reactions of halogens take place with Iodine?
A
- There is no reaction as iodine as less reactive than all of the halogens except Ast
13
Q
How do you test for halides?
A
- First add dilute nitric acid to remove ions (especially carbonate ions which would also form a white precipitate and give a false positive)
- Then add silver nitrate solution
- The colour of the precipitate will identify the halide
- Chloride forms a white precipitate, bromide forms a cream precipitate and iodide forms a yellow precipitate.
- If the colour is not clear then you can test the ions by attempting to dissolve them in ammonia solution.
- Chloride will dissolve in weak ammonia solution, bromide will dissolve in concentrated ammonia solution and iodide won’t dissolve.
14
Q
What is disproportionation?
A
- When something is simultaneously oxidised and reduced
15
Q
How do halogens undergo disproportionation with alkalis?
A
EXAMPLE
X2 + 2NaOH -> NaXO + NaX + H2O
ionic X2 + 2OH -> XO + X + H2O
oxidation
number 0 +1 -1
of X
X has therefore been both oxidised and reduced
