Concept of ionization energy

1.
The concept of ionization energy

The energy required to make 1 mol of the gaseous atom M in the ground state lose one electron to form the gaseous ion M+ is called the element's first ionization energy (also known as the ionization potential), which is represented by I1
.

M (G) → M ⁺ (G) + E ^-△ H = the I _.
1

The unit of ionization energy is kJ·mol-1 (or eV)
.

The energy required when 1 mol of gaseous ion M ⁺ loses one electron to form gaseous ion M ²⁺ is called the element’s second ionization energy, which is represented by I2.
Similarly, the third and fourth ionization energies can be defined
.

The ionization energy of the same element has the following law

I ₁ <I ₂ <I ₃ <I ₄ <…

2.
The changing law of the first ionization energy

The magnitude of the first ionization energy mainly depends on the nuclear charge, the radius of the atom, and the electron layer structure of the atom
.

Generally speaking, for elements of the same period, the first ionization energy gradually increases.
The reason is that as the number of nuclear charges increases, the radius gradually decreases, and the attraction of the nucleus to the outer electrons increases, so it is not easy to lose electrons
.

For the elements of the same group, the first ionization energy from top to bottom gradually decreases.

1) The change law of the first ionization energy of the main group elements

The first ionization energies of the main group elements in the same period change regularly, and the ionization energies increase greatly as the number of nuclear charges increases, as shown in Table 5-8
.

But there are two abnormalities

The electron configuration of the valence layer of B and Al is ns ² np ¹ , and an electron that loses the np orbital reaches the ns ² stable structure, so it is easier to lose an electron
.

The electron configuration of the valence layer of O and S is ns ² np ⁴ , which is easy to lose an electron of the np orbital to make the p orbital reach a stable structure half-filled with np ³ ; and the electron configuration of the valence layer of N and P is ns ² np ³ , The p orbital is a half-filled stable structure, and it is more difficult to lose an electron

Table 5-8 The first ionization energy of some main group elements

For the main group elements of the same group, the first ionization energy from top to bottom decreases, and the decrease is relatively large, as shown in Table 5-8
.

As the radius of the atom increases, the attraction of the nucleus to the electrons weakens, making it easier to lose electrons

2) The changing law of the first ionization energy of subgroup elements

In the same period, the total change trend of the first ionization energy of the elements in the same period is that the number of nuclear charges increases, but the increase is small and the change regularity is poor, as shown in Table 5-9
.

Among the sub-group elements of the same group (Table 5-9), only group IIIB elements gradually decrease the first ionization energy from top to bottom
.

Among other subgroup elements, the first ionization energy of the fifth period element is basically smaller than that of the fourth period element.
The reason is that the atomic radius of the fifth period element is significantly larger than that of the fourth period element; the first ionization energy of the fifth period element is less than For the sixth period element, the shrinkage of the steel system causes the atomic radius of the sixth period element to be similar to that of the fifth period element of the same family, but the nuclear charge of the sixth period element is greater than the nuclear charge of the fifth period element of the same family

Table 5-9 First ionization energies of some subgroup elements

The ionization energies of the subgroup elements have a small variation range and poor regularity.

This is because the newly added electrons fill the (n-1)d orbital and the ns and (n-1)d orbital energies are relatively close

Related link: The concept of atomic radius