03.03 Periodic Trends: First Five Ionization Energies—Text Version

The tables below shows the first five ionization energies for several elements. Look at each one carefully.

	Period One		Period Two
	H	He	Li	Be	B	C	N	O	F	Ne
First	1212	2372	520	900	801	1086	1402	1314	1681	2081
Second		5250	7298	1757	2427	2856	2856	3388	3374	3952
Third			11815	14849	3660	4578	4578	5300	6050	6122
Fourth				21007	25026	6223	7475	7469	8408	9370
Fifth					32827	37830	9445	10990	11023	12178

	Period Three
	Na	Mg	Al	Si	P	S	Cl	Ar
First	496	738	578	787	1012	1000	1251	1521
Second	4562	1451	1817	1577	1903	2251	2297	2666
Third	6912	7733	2745	3232	2912	3361	3822	3931
Fourth	9544	10540	11578	4356	4957	4564	5158	5771
Fifth	13353	13628	14831	16091	6274	7031	6540	7238

The table above shows the first five ionization energies for several elements. Look at each one carefully. Do you notice a trend that is the same for each element?

Look at the ionization energy values for each element again. Each element in Period 2 has one difference in its ionization energies that is greater than all of the others. For lithium (Li), the greatest difference, or jump, in its ionization energy values occurs between the first and second ionization, whereas beryllium (Be) has the greatest difference between its second and third ionizations.

Using what you know about each of these elements, can you explain this trend?

In each case, the largest difference between successive ionization energy values occurs when the valence has been emptied and an electron from a lower energy level is now being removed. Lithium is an alkali metal in Group 1, so it has one valence electron in its second energy level. The first ionization energy of lithium was used to remove its only valence electron. The second ionization energy of lithium is the amount of energy required to remove an electron from its inner energy level, the first energy level. Because the first energy level is closer to the nucleus and its electrons experience less shielding, those electrons have a greater effective nuclear charge and will require more energy to be removed. Whenever an energy level has been emptied, the next ionization energy will be much higher because an electron is being removed from a lower energy level that is closer to the nucleus.

	Period One		Periods Two
	H	He	Li	Be	B	C
First	1212	2372	520	900	801	1086
Second		5250	7298	1757	2427	2856
Third			11815	14849	3660	4578
Fourth				21007	25026	6223
Fifth					32827	37830

	Period Three
	Na	Mg	Al	Si
First	496	738	578	787
Second	4562	1451	1817	1577
Third	6912	7733	2745	3232
Fourth	9544	10540	11578	4356
Fifth	13353	13628	14831	16091