chem remed s.3.1 classification of elements

question no.1

d. (ClO4-)

2 (a) define the term first ionisation energy of an element

ionisation energy is the energy recquired to lose electrons in the outermost shell to form a positivve cation. From one mole of gaseous atom to form one mole of unipositive gaseous ion.

2 (b) Element C, with atomic number x, is in group 2 of periodic table. Justify this using all the information from Graph 1

In group 2 element C, the electron for the first ionisation energy is removed from a spin pair in an s sub-shell

For element D, a group 13 element, the electron for the first ionization energy is removed from a 3p sub-shell further away from the nucleus. The 3p sub-shell also experiences more shielding. That’s why there is a decrease in first ionisation energy when moving from element C to D.

Increase in nuclear charge accounts for the increasee from element E (np2) to element F (np3) in group 14.

ELement C can’t be in gorup 15 because there is a steady rise for the next elements D→E→F showinig the filling of a p sub-shell.

2(c ) Explain trend in first ionisation energy as shown in Graph 2

As you move down group 2 the first ionisation energies decrease.

As you descend the group the nuclear charge increases due to the

presence of additional protons, but the shielding effect

progressively increases due to the presence of an extra electron 3

shell as you move from one period to the next.

The effect of the extra protons is compensated for by the effect of

the extra electrons. The only factor left is the additional distance

between the outer electron and the nucleus. That lowers the first

ionisation energy.

2(d) State which period elemt C is in and explain you rreasoning

C is in period 3 since in period 2 the Group 2 element would have

the higher ionisation energy while in period 4 the Group 2 element

would have a lower ionisation energy. ✓

This can be accounted for by the progressively increasing 3

average distance the valence electron is from the nucleus. C

cannot be in the first period (He) as p-orbitals are being filled, ✓

it cannot be in the fourth period (Ca) as (x + 8) would not bring

you back to Group 2 again. ✓

2(e) outline the first ionisation energy of element G is lower than that of element F

There is a slight decrease from F to G due to the presence of a spin

pair in the p sub-shell for G. ✓

The resulting electron–electron repulsion is greater than the effects

of the increase in nuclear charge and reduces the ionisation energy

to form G+. ✓

3 (a) state the full electron configuraiton of a sodium atom.

1s^2 2s^2 2p^6 3s^1✓

3(b) outline why a sodium ion, Na+ is smaller than a fluoride ion, F-

Na+ is smaller than F- because Na is loosing electrons recquiring less radius compared to F- that’s gaining another electron, recquiring more radius in the electron shells.

3( c) Explain the decrease in atomic radius from sodium to chloorine

Increasing nuclear charge / effective nuclear charge; ✓

Electron shielding remains constant??

3 (d) State an equation including state symbols for the reaction of solid sodium with water

2Na(s) + 2H20(l) → 2NaOH9aq) + H2(g)

Suggest a value for the H of the solution formed in part (d)

above ph 7

pH 12-14

4 (a) write the complete electron electron configuration for the sodium atom

1s² 2s² 2p⁶ 3s¹

4(b) as IONS, SODIUM and OXYGEN have the same electron configuation as NEON. Predict with justification, which of the three species will have the smallest radius.

All three species have the electron configuration 1s2 2s2 2p6.

Sodium has the greatest number of protons so has a greater

attraction for the electrons. Therefore it has the smallest radius.

4( c) Identify, giving a reason which element in the list above has the most metallic character.

Rubidium has more metallic character; ✓

Rubidium has the largest atomic radius, therefore the weakest

attraction to its valence electrons ✓

5 (a) state and explain the sign (+ or m-) for ionisation energy amd electron affinity for the elements included above.

Ionisation energy is positive (+) values and electron affinities have negative (-) values.

removing an electron requires energy, making ionisation energies

an endothermic process energy is released when an electron is

gained, making electron affinity an exothermic process

5(b) explain the general increase in electron affinity across a period

The electron affinity values increase across a period; ✓

due to the increase in effective nuclear charge / in the number of

protons in the nucleus while the electrons are occupying the

same number of energy levels

Predict which elements, sodium or magnesium would have a more vigorous reaction with water and explain why.

Sodium would have a more vigorous reaction with water; ✓ due to

its smaller first ionisation energy

6. Explain why the first ionisation energy of magnesium is greater than that of sodium

The magnesium atom has a greater effective nuclear charge as it

has a higher number of protons in its nucleus, but the same

number of inner-shell electrons shielding its valence shell 3 electrons.

Consequently, the atomic radius is smaller and so there is a stronger

attraction for the electrons by the nucleus.

7. Lithium reacts with water. Deduce the equation for the reaction and state 2 observations that could be made during the reaction.

2Li(s) + 2H20(l) → 2LiOH(aq) + H2(g)

There will be effervescence or release of gas at the surface.

Bubbles of a colorless gas will be observed.

Lithium moves around the surface and is voncerted into a soluble product.

Heat and sound energy are released.

8. (a) The reaction between chlorine and potassium iodide

Cl2 + 2KI → I2 + 2KCL (aq)

Brown solution formed

8 (b) the reaction between silver ions and bromide ions

Ag+ + Br- → AgBr

8 ( c) Deduce whether or not each of the reactions in (b) is a redox reaction, giving a reason in each case.

THe reaction in (b) is not redox

There is no electron transfer / change in oxidation number.