Why does metallic character decrease across a period?

Metallic character decreases across a period because the atomic radius decreases and nuclear charge increases, reducing the tendency to lose electrons.

In the periodic table, as you move from left to right across a period, the atomic number increases. This means there are more protons in the nucleus, increasing the nuclear charge. At the same time, the atomic radius, or the distance from the nucleus to the outermost electron shell, decreases. This is due to the increased nuclear charge pulling the electrons closer to the nucleus.

The metallic character of an element is determined by its ability to lose electrons and form positive ions, a process known as oxidation. Metals tend to have low ionisation energies, meaning they can easily lose electrons. However, as the atomic radius decreases and the nuclear charge increases across a period, the electrons are held more tightly by the nucleus. This makes it harder for the atom to lose electrons, thus reducing its metallic character.

Furthermore, the increase in nuclear charge also leads to an increase in electronegativity, which is the ability of an atom to attract shared electrons in a chemical bond. Non-metals, which are found on the right side of the periodic table, tend to have high electronegativities as they are more likely to gain electrons to achieve a stable electron configuration. This is the opposite of the metallic character, which involves the loss of electrons.

Therefore, the combination of decreasing atomic radius and increasing nuclear charge as you move across a period in the periodic table results in a decrease in metallic character. This is because these changes make it more difficult for an atom to lose electrons, which is a key characteristic of metals.