T2- s Block LP1 + LP2

Question 1

What are alkali metals?

Answer 1

Group 1 elements

Question 2

What are relativistic effects?

Answer 2

As the element gets heavier, those electrons going around approach the speed of light. This makes them heavier, and their increased mass perturbs the energy levels that apply to electronic transitions, and actually it moves it into the visible region.

Question 3

Using flame test, what colour is lithium?

Answer 3

Crimson

Question 4

Using flame test, what colour is sodium?

Answer 4

Yellow

Question 5

Using flame test, what colour is potassium?

Answer 5

Red to violet

Question 6

Using flame test, what colour is rubidium?

Answer 6

Violet

Question 7

Using flame test, what colour is caesium?

Answer 7

Blue

Question 8

Why flame tests give colours?

Answer 8

Alkali metals give electronic transitions in the flames which fall in the visible part of the spectrum.

Question 9

For what you can use flame test?

Answer 9

To identify alkali metals and intensity can be measures quantitatively using a flame photometer.

Question 10

What are chemical properties for alkali metals?

Answer 10

Low first ionisation energym very reactive, going down the group atomic radius increases that leads to increase in ionisation energy forming M⁺ ions more readily doen group.

Question 11

Describe alkali metal reaction with water.

Answer 11

Reaction is very exothermic and increases in violence from the lightest to the heaviest elements in the group.

Question 12

Why alkali metals must be stored under hydrocarbon oil?

Answer 12

To prevent reaction with atmospheric oxygen. Li, Na and K can be handled in air for short periods, Rb and Cs must be handied under an inert atmosphere at all times.

Question 13

Why Li⁺ can exhibit a high degree of covalent character?

Answer 13

Because it has a very high charge density on a very small cation. So it can distort the electron clouds of anion towards itself, crating greater covalent bonding.

Question 14

Why alkali metals exept Li form ionic compounds?

Answer 14

They are heavier, they are not very polarising.

Question 15

Why metallic bonding is weak for alkali metals?

Answer 15

Becaus ethey have only one electron in valence shells which contributes to molecular orbital band.

Question 16

What are azides?

Answer 16

Compound with present N₃

Question 17

For what hydrides are used in reactions?

Answer 17

They react vigously with water.

NaH +H₂O —> NaOH +H₂

Used as reagents for the synthesis of othe compounds.

4LiH +SiCl₄ —-> SiH₄ + 4LiCl

Usefull as non-nucleophilic bases and reductants.

NaH + NH₃—> NaNH₂ +H₂

Question 18

What are halides?

Answer 18

Inorganic compounds with formula MX. Colourless crystalline solids, with high melting temperature. All of the halides (exept LiF) soluble in water to give ionic solutions.

Question 20

When generally solubility is the highest?

Answer 20

When there is large difference in radius between the cation and the anion.

Question 21

What is formed when Li reacts with O?

Answer 21

Lithium oxide

Question 22

What is formed when Na reacts with O?

Answer 22

Sodium peroxide

Question 23

What is formed when K reacts with O?

Answer 23

Potassium superoxide, O₂^-

Question 24

What is Kapustinskii equation for lattice energy?

Answer 24

Question 25

Why M₂O₂ and MO₂ have tendency to decompose?

Answer 25

It is linked to Kapustinskii equation. O^2- smaller than O₂^2- or O₂^- so the lattice energy of the oxyde is larger.

Question 26

Why lower down the alkali group oxides less tend to decompose?

Answer 26

It is linked to Kapustinskii equation. The larger the radius the lower the lattice energy the lower tendency to decompose.

Question 27

How ozonides (MO₃) formed?

Answer 27

By burning M, or heating M₂O₂ or MO₂ with ozone. It is very unstable.