Modern periodic law says that the properties of elements are the Periodic function of their atomic number.Īccording to the modern periodic law given by Henry Moseley, the elements should be arranged in the table on the basis of their ATOMIC NUMBER.Īfter arranging all the elements based on atomic number, the modern periodic table came into existence.Mandeleev law says that the properties of elements are the functions of their atomic mass.Henry Moseley arranged the elements according to the increasing atomic number.Mendeleev arranged the elements according to the increasing atomic mass.This law is exactly similar to the Mendeleev law, but the only difference is Modern Periodic Law was given by Henry Moseley in 1913. The properties of the elements are the Periodic function of their ATOMIC NUMBERS. Yes, all the elements in modern periodic table are arranged on the basis of their ATOMIC NUMBER. We have seen in previous section that Dobereiner’s law, Newland’s law as well as Mendeleev law were based on the arrangements of elements according to their increasing atomic masses.īut the only difference in modern periodic law is I have also discussed the merits and demerits of the Mendeleev periodic table. I know this seems a little difficult for you, so you can refer to this detailed guide on “ Mendeleev periodic table” where I have explained all these things with proper images for your better understanding. So there were some empty blocks seen on the Mendeleev periodic table. Now look, while arranging the elements according to atomic masses, Mendeleev found that the properties of few elements were not matching with any of the previous ones, so he didn’t place such elements in that particular column. Why are some blocks empty in the above Mendeleev periodic table? That’s why Mendeleev placed those elements in the same block. The short answer: Those elements show similarly in their properties. Have you noticed that many blocks have more than one element in Mendeleev periodic table? Why? There are a total 8 vertical columns in the Mendeleev periodic table, which are known as groups.Īnd there are 7 horizontal rows, which are known as periods. Since the effective nuclear charge also increases from left to right, then the attraction between the protons and electrons are greater therefore a higher ionization energy is required to remove the electron.This table is known as the Mendeleev periodic table of elements. If the orbitals are fully filled or half filled then it will take more energy to remove an electron from them. This is the general trend but there are many exceptions based on how the orbitals are filled. Both increase from left to right and decrease going from top to bottom. Ionization energy and electronegativity have the same trend. The more protons there are means that they attract the electrons more, thus making the atomic radius smaller. Atomic radius decreases going across the periodic table because the effective nuclear charge increases. How do they relate to shielding effect and number of electrons or protons?Ītomic radius increases going down the periodic table because a valence electron is added into a new energy level and the core electrons repel each other (shielding effect) which contribute to the atomic radius increasing. Kristen Kim 1I wrote:Can someone explain the reasons behind the trends we see in the periodic table? decreases.Īcross a period, effective nuclear charge increases and valence electrons are more strongly attracted to the increasingly positive nucleus so it is harder to remove a valence electron from the atom. Down a group, valence electrons are further away from the nucleus and less tightly bound hence less energy is required to remove a valence electron from the atom and first I.E. First ionization energy generally increases across a period and decreases down a group. Shielding effect remains relatively the same across a period because electrons are added to the same shell while nuclear charge increases. So the atom becomes more compact and the atomic radius decreases. Down a group, valence electrons are in shells that are further away from the nucleus and hence atomic radius increases down the group.Īcross a period there is a decrease because effective nuclear charge increases and valence electrons are more strongly attracted to the nucleus. Atomic radius generally increases down a group and decreases across a period.

Valence electron trend periodic table