As one goes across the period, the ionization energy increases. There are several chemical methods for estimating the percentage of an element present in a sample; these, however, require a detailed knowledge of the chemistry of the element in question (see analysis). The loss of a beta particle, or electron, from the nucleus increases the atomic number by one unit; the loss of an alpha particle, or helium nucleus (two protons and two neutrons), decreases the atomic number by two units; and the process of electron capture, in which an electron from an inner shell is drawn into the nucleus, corresponds to a decrease of atomic number by one unit. The atomic radius is the distance between the atomic nucleus and outermost stable electron orbital of an atom which is at equilibrium. It consists of 18 vertical columns and 7 horizontal rows. The metallic properties increase down the group as the nuclear charge decreases down the group. Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. Elements with atomic numbers greater than 92, the so-called transuranium elements, have been synthetically prepared and are all radioactive. The table is the arrangement of elements in increasing order of their atomic numbers. The modern periodic table is the present form of the periodic table.

This is a characteristic feature of nonmetals as they gain electrons to become anions.

An atom such as fluorine, with seven electrons in its outer shell, can combine with a similar atom by sharing a pair of electrons with it; each atom thus achieves the noble-gas configuration by having three unshared pairs and one shared electron pair in its valence shell. Across a period, the electron affinity increase as nuclear charge increases.

Unlike other groups, noble gasses are unreactive and have very low electronegativity or electron affinity.

But as one goes down the group, the ionization energy decreases down the group. An element exhibits its own characteristic spectrum whether it exists in the free state, in a mixture, or in chemical combination with other elements.

The periodic table is the tabular arrangement of all the chemical elements on the basis of their respective atomic numbers. Lower the nuclear charge lower is the force of attraction between the nucleus and valence electrons, thus low ionization energy.

The reason behind this is, down the group the valence electrons go farther away from the nucleus, thus the nuclear charge decreases. Pro Lite, Vedantu This is what is meant by periodicity or periodic table … The reason being, new shells are being added and thus the nuclear charge decreases. As well as being numbered, some of these groups have names—for example, alkali metals (the first column of elements), alkaline earth metals (the second column of elements), halogens (the next-to-last column of elements), and noble gases (the last column of elements).