Effective Nuclear Charge of Potassium: What It Consists of (With Examples)

The effective nuclear potassium load is +1. The effective nuclear charge is the total positive charge perceived by an electron that belongs to an atom with more than one electron. The term"effective"describes the shielding effect exerted by electrons near the nucleus, from its negative charge, to protect electrons from higher orbitals.

This property has a direct relationship with other characteristics of the elements, such as their atomic dimensions or their disposition to form ions. In this way, the notion of effective nuclear charge provides a greater understanding of the consequences of the protection present in the periodic properties of the elements.

In addition, in the atoms that have more than one electron - that is, in the polyelectronic atoms - the existence of the shielding of the electrons produces a decrease in the electrostatic attraction forces existing between the protons (positively charged particles) of the nucleus of the atom and the electrons in outer levels.

In contrast, the force with which electrons repel in atoms considered polyelectronics counteract the effects of the attractive forces exerted by the nucleus on these particles with opposite charge.

What is the effective nuclear charge?

When it is an atom that has only one electron (hydrogen type), this single electron perceives the net positive charge of the nucleus. On the contrary, when an atom has more than one electron, the attraction of all the external electrons towards the nucleus is experienced and, simultaneously, the repulsion between these electrons.

In general, it is said that the larger the effective nuclear charge of an element, the greater the attractive forces between the electrons and the nucleus.

In the same way, the larger this effect is, the lower is the energy belonging to the orbital where these outer electrons are located.

For most of the elements of the main group (also called representative elements) this property increases from left to right, but decreases from top to bottom in the periodic table.

To calculate the value of the effective nuclear charge of an electron ( Z _eff or Z *) the following equation proposed by Slater is used:

Z * = Z - S

Z * refers to the effective nuclear charge.
Z is the number of protons present in the nucleus of the atom (or the atomic number).
S is the average number of electrons that are between the nucleus and the electron that is being studied (number of electrons that are not valence).

Effective nuclear potassium load

Potassium is an alkali metal belonging to the first group of the periodic table. It has a low ionization energy, so it has an enormous facility to lose the only electron present in its outer layer. In addition, it has 19 electrons around its nucleus, so its atomic number (Z) is 19.

This implies that, having 19 protons in its nucleus, its nuclear charge is +19. As we speak of a neutral atom, this means that it has the same number of protons and electrons (19).

In this order of ideas, we have that the effective nuclear charge of potassium is calculated by an arithmetic operation, by subtracting the number of internal electrons from its nuclear charge as expressed below:

(+19 - 2 - 8 - 8 = +1)

In other words, the valence electron is protected by 2 electrons from the first level (closest to the nucleus), 8 electrons from the second level and 8 electrons from the third and penultimate level; that is, these 18 electrons exert a shielding effect that protects the last electron from the forces exerted by the nucleus on it.

As can be seen, the value of the effective nuclear charge of an element can be established by its oxidation number. It should be noted that for a specific electron (at any energy level), the calculation of the effective nuclear load is different.

Explained examples of effective nuclear potassium loading

Below are two examples to calculate the effective nuclear charge perceived by a valence electron determined in a potassium atom.

- First, its electronic configuration is expressed in the following order: (1 s ) (2 s , 2 p ) (3 s , 3 p ) (3 d ) (4 s , 4 p ) (4 d ) (4 F ) (5 s , 5 p ), and so on.

- No electron to the right of the group (n s , n p ) contributes to the calculation.

- Each electron in the group (n s , n p ) contributes 0.35. Each electron of the level (n-1) contributes 0.85.

- Each electron of level (n-2) or lower contributes 1.00.

- When the protected electron is in a group (n d ) or (n F ), each electron of a group to the left of the group (n d ) or (n F ) contributes 1.00.

Thus, the calculation begins:

First example

In the case that the only electron of the outermost layer of the atom is in the orbital 4 s , you can determine your effective nuclear charge as follows

(1 s ² ) (2 s ² 2 p ⁵ ) (3 s ² 3 p ⁶ ) (3 d ⁶ ) (4 s ¹ )

The average of electrons not belonging to the most external level is then calculated:

S = (8 x (0.85)) + (10 x 1.00)) = 16.80

Having the value of S, we proceed to calculate Z *:

Z * = 19.00 - 16.80 = 2.20

Second example

In this second case the only valence electron is found in the orbital 4 s. You can determine your effective nuclear charge in the same way

(1 s ² ) (2 s ² 2 p ⁶ ) (3 s ² 3 p ⁶ ) (3 d ¹ )

Again, the average of non-valence electrons is calculated:

S = (18 x (1,00)) = 18.00

Finally, with the value of S, Z * can be calculated:

Z * = 19.00 - 18.00 = 1.00

conclusion

Making a comparison of the previous results, it can be seen that the electron present in the orbital 4 s it is attracted to the nucleus of the atom by forces greater than those that attract the electron that is located in the orbital 3 d . Therefore, the electron in the orbital 4 s It has a lower energy than the orbital 3 d .

Thus, it is concluded that an electron can be located in the orbital 4 s in its ground state, while in the orbital 3 d He is in an excited state.

References

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