Name: Nomenclature of Elements With Atomic Numbers > 100
Uploaded: 2019-07-19
Duration: 16 min 52 s
Description: Elements with atomic number greater than 100 have been named after famous scientists, although the universally accepted names are the names derived from IUPA...

Question

What is long form of periodic table? How do the properties of elements vary in groups and periods of the periodic table?

Accepted Answer

In the long form of periodic table the elements are arranged in the order of increasing atomic number. This table has seven horizontal rows called periods and eighteen vertical columns known as groups.

Periodic trends vary with respect to atomic and ionic radii, ionization enthalpy, electron gain enthalpy and electronegativity.

1. Atomic radius- It is the distance from the centre of nucleus to the outermost shell of an atom. On moving across a period electrons are being added to same shell and therefore, atomic radius decreases. Down the group the atomic radius increases regularly with atomic number. For alkali metals and halogens, as we descend the groups, the principal quantum number (n) increases and the valence electrons are farther from the nucleus. This happens because the inner energy levels are filled with electrons, which serve to shield the outer electrons from the pull of the nucleus. Consequently, the size of the atom increases as reflected in the atomic radii.

2. Ionic radii- It is the effective distance from the nucleus of an ion up to the point where its influence over the electron cloud ceases. A cation is smaller than the parent atom and anion is larger than parent atom. The number of electrons in a cation is always less than the number of protons and effective nuclear charge increases.

3. Atomic volume- It is the volume occupied by one gram atom of the element in solid state. Atom volume increases on moving down the group due to increase in number of shells. Along a period it decreases first, becomes minimum in the middle and then increases.

4. Ionization energy- It represents the energy required to remove an electron from an isolated gaseous atom in its ground state. When we move across the second period, successive electrons are added to orbitals in the same principal quantum level and the shielding of the nuclear charge by the inner core of electrons does not increase very much to compensate for the increased attraction of the electron to the nucleus. Thus, across a period, increasing nuclear charge outweighs the shielding. Consequently, the outermost electrons are held more and more tightly and the ionization enthalpy increases across a period. As we go down a group, the outermost electron being increasingly farther from the nucleus, there is an increased shielding of the nuclear charge by the electrons in the inner levels. In this case, increase in shielding outweighs the increasing nuclear charge and the removal of the valence electron requires less energy down a group.

5. Electron affinity- When an electron is added to a neutral gaseous atom to convert it into a negative ion, the enthalpy change accompanying the process is defined as the Electron affinity or electron gain enthalpy. Electron gain enthalpy becomes more negative with increase in the atomic number across a period. The effective nuclear charge increases from left to right across a period and consequently it will be easier to add an electron to a smaller atom since the added electron on an average would be closer to the positively charged nucleus while down the group electron affinity decreases as atomic size increases.

6. Electronegativity- A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself is called electronegativity. The attraction between the outer (or valence electrons and the nucleus increases as the atomic radius decreases in a period. The electronegativity also increases. On the same account electronegativity values decrease with the increase in atomic radii down a group. The trend is similar to that of ionization enthalpy.

What is long form of periodic table? How do the properties of elements vary in groups and periods of the periodic table?

Important Questions on Classification of Elements and Periodicity in Properties

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