Question

what happens to the effective nuclear charge along the period...??​

Answer 1

along the period effective nuclear charge increases

Answer 2

An electron in an atom feels two forces. One comes from the nucleus, where positively charged protons attract the negatively charged electrons. The second force comes from the other electrons, which repel each other because of their like charges. Effective nuclear charge is one way of expressing this balance between the attractive and repulsive forces of electrons when we think about the outermost valence electrons in an atom. (Figure 4-10)

(Figure 4-10)

To calculate effective nuclear charge, we have to take the total number of electrons into account. Electrons in outer energy shells feel a weaker pull from the nucleus than the inner electrons because the inner electrons "shield" some of the positive force coming from the protons in the nucleus. This means that the outermost electrons feel the weakest pull from the nucleus, and the inner electrons feel the most pull. We can calculate a numerical value for effective nuclear charge (Zeff) by subtracting the number of shielding, or inner, electrons from the atomic number. From left to right on the periodic table, Zeff increases because the number of shielding electrons within each row stays constant while the number of protons increases. Zeff is one of the factors in the size of an atom. If an atom has a strong pull on its outer electrons, the atom as a whole will be smaller.

Despite knowing Zeff, it is very difficult to determine the size of an atom, which is the size of the electron cloud around the nucleus of an atom. But because we can never know the exact location of an electron, we cannot actually specify the size of an atom. One way to get around this problem is to assume that the atom is a perfect sphere. We can then determine an atomic radius by measuring the nucleus to the edge of the spherical cloud of electrons. There are a variety of experimental and theoretical methods to determine or calculate the atomic radius for an element. Using these radii, going from left to right across the periodic table, the atomic radius decreases because effective nuclear charge increases. (Figure 4-11)

Another determinant of atomic size is electron shells. Each row on the periodic table starts a new shell for the electrons. Each subsequent shell is much farther from the nucleus, so atomic radius increases down a column on the periodic table.