Answer:<em> Berylium (Be)</em>
Step-by-step explanation:
The <em>first ionisation energy</em> is the energy required to remove one mole of the outermost electrons from one mole of gaseous atoms.
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<em> Second, third, and fourth ionisation</em> energies are the energies required to remove the succesive mole of electrons of the same atoms
Successive ionisation energies are larger because, <em>once you have removed the first electron you get a positive ion</em>. Removing an electron (which is a negative charge) from a positive ion is more difficult than removing it from the neutral atom. And removing an electron from an ion with 2⁺ or 3⁺ charges is increasingly difficult.
When you find a large jump from one inoization energy to the succesive one you can predict that you are removing an electron from a closer to the nucleus orbital.
Berylium has atomic number 4. So, the number of electrons of the neutral atom is also 4. Hence, the electron configuration of beryllium is 1s² 2s².
From the given data, <em>the first four ionization energies in kJ/mol are 900, 1757, 14,849, and 21,007</em>.
From that you can calculate the following changes in the ionization energies:
- From first to second: 1,757 kJ/mol - 900 kJ/mol = 857 kJ/mol
- From second to third: 14,849 kJ/mol - 1,757kJ/mol = 13,092 kJ/mol
- From third to fourth: 21,007 kJ/mol - 14,849 kJ/mol = 6,158 kJ/mol
And now you can see that there is a larger jump in the energy, a greater change, required to remove the third electron.
That is explained because the first and second electron are removed from the orbital 2s while the third electron has to be removed from the orbital 1s which is closer to the nucleus. This third electron is more strongly attracted by the nucleus and substantially more energy is required to accomplish this work.
