Electropositivity indicates the tendency for the nucleus of the atom of a chemical element to move away from its electrons in the valence shell when forming a compound. It is, therefore, the opposite of electronegativity, which refers to the atom's tendency to attract the shared electrons in a bond.
For example, sodium oxide is a compound formed by the bond between two atoms of sodium and one of oxygen (Na2O). If these bonds were broken, oxygen would attract the electrons shared in the bond to itself more easily, as it is the most electronegative. Sodium has a greater tendency to lose electrons, which means it is more electropositive.
Electropositivity is also called metallic character, as metals have a greater tendency to lose electrons from the valence layer when placed in contact with electronegative elements.
Like electronegativity, electropositivity is a periodic property, that is, it is a property of chemical elements that varies at regular periods with the increase or decrease of the atomic number along the Table Periodic.
Electropositivity increases with increasing atomic radius, that is, in the Periodic Table, electropositivity increases from right to left and from top to bottom:
In the same family of the Periodic Table, that is, in the same column, electropositivity increases from top to bottom, because in this meaning the periods increase, which means that the electronic layers increase and the electrons in the valence layer (layer outermost) they get further away from the nucleus, so the attraction between them is less and less, that is, the electropositivity is increasingly bigger.
For example, considering the elements of family 17 or VII A, we have that the increasing sense of their electropositivity is: F < Cl < Br < I < At.
Now, when we consider the elements in the same period, which is the same horizontal line, we see that electropositivity decreases from left to right, because in that sense they all have the same amount of electron shells, but with each family that increases, the amount of electrons in the valence shell increases and, with that, the attraction for the nucleus is bigger.
For example, considering all the elements of the second period of the Periodic Table, we have that the increasing sense of its electropositivity is given by: Ne < F < O < N < C < B < Be < Li.
If you look at the location of sodium (Na) and oxygen (O) in the Table, you will actually see that sodium is more electropositive.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/eletropositividade.htm
