Explain why the first and second ionisation energies of strontium are less than those of calcium

Mokhions

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In their reactions, calcium and strontium each lose electrons to form ions with a 2 charge. The first and second ionisation energies of calcium and strontium are shown below. 1st ionisation energy
/ kJ mol–1 2nd ionisation energy
/ kJ mol–1 calcium 590 1145 strontium 550 1064

Explain why the first and second ionisation energies of strontium are less than those of calcium.

Pyruvic Acid

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(Original post by Mokhions) In their reactions, calcium and strontium each lose electrons to form ions with a 2 charge. The first and second ionisation energies of calcium and strontium are shown below. 1st ionisation energy
/ kJ mol–1 2nd ionisation energy
/ kJ mol–1 calcium 590 1145 strontium 550 1064

Explain why the first and second ionisation energies of strontium are less than those of calcium.

I don't really understand much about ionisation energies so if someone could explain these questions I'd be very grateful. a)why are the second ionisation energies of calcium and strontium greater than their first ionisation energies? (1 mark question)

b)Explain why the first and second ionisation energies of strontium are less than those of calcium. ( 3 mark question)

We get this question a lot. Give me a moment

I'll answer the first and then the second The second ionization energy for any element is greater than it's first ionization energy. You must be familiar with the definition of ionization energy and the factors affecting it. The second ionization energy is the energy required for one mole of unipositive gaseous ions to lose one mole of electrons resulting in one mole of dipositive ions. " More energy is required to remove an electron from a unipositive ion than from a atom because of the increased effective nuclear attraction as a result of the ion being positively charged and electron negatively charged. Therefore the second ionization energy is always higher than the first"

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The ionization energies depends on the ... 1 Effective Nuclear Charge - the more the greater will be the ionization energy 2 The atomic radius - the more the atomic radius the less the ionization energy 3 The shielding effect - the more the number of inner electrons the less the ionization electrons. Strontium and Calcium belong to the same group and therefore the net nuclear charge the outermost electron shell experiences is the same (+2). But strontium has a higher period number than calcium and therefore it's atomic radius and shielding effect is greater. Therefore it has a less ionization energy than calcium as the effective nuclear attraction experienced by the outermost election shell is greater in strontium than in calcium

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First ionisation energy is the amount of energy required to remove an electron from each atom in a mole of gaseous atoms, to form one mole of gaseous 1+ ions. Therefore you are actually removing one mole of electrons (this is 6 x1023 electrons). Basically, the idea is that when you remove an electron from a calcium atom, you remove an electron that is further away from the nucleus than the electron the next electron, which you'd remove for the 2nd ionisation energy of calcium. Recall that calcium and strontium are both group 2 metals. So they have 2 electrons in their outer shell. Basically: in this situation, second ionisation energy is higher than first ionisation energy because -

- 2 electrons in Ca are further away from the nucleus than the outer shell electron in the 1+ ion, because the former's electrons repel each other to an extent. When an electron is removed, the repulsive force is reduced, it's drawn slightly closer to the nucleus. So the atomic radius falls (well it's the ionic radius for Ca+)

basically, strontium is in a higher group, so the effect of electron shielding/screening is higher, and the atomic radius is larger. The factor of nuclear charge increasing is outweighed by these 2 factors.

(Original post by StUdEnTIGCSE) The ionization energies depends on the ... 1 Effective Nuclear Charge - the more the greater will be the ionization energy 2 The atomic radius - the more the atomic radius the less the ionization energy 3 The shielding effect - the more the number of inner electrons the less the ionization electrons.

Strontium and Calcium belong to the same group and therefore the net nuclear charge the outermost electron shell experiences is the same (+2). But strontium has a higher period number than calcium and therefore it's atomic radius and shielding effect is greater. Therefore it has a less ionization energy than calcium as the effective nuclear attraction experienced by the outermost election shell is greater in strontium than in calcium

(Original post by dippers)
do you mean it has more ionisation energy than calcium?

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