Periodic Classification of Elements

Periodic Table Elements

The modern periodic table is the long form of the periodic table elements and it is based on the electronic configuration of elements. It is also the most convenient and widely used periodic table. In the periodic table of elements, the horizontal rows are called periods and the vertical columns are called groups. There are eighteen groups and seven periods in the modern periodic table. In the periodic table elements of a group possess similar chemical properties. In each period a new electronic shield gets filled. The number of valance electrons increases from one to eight on moving from left to right in a period.

From left to right in a period atomic size, electropositive nature, metallic nature, basic nature of oxides all decreases, and electronegative nature, non-metallic nature, acidic nature of oxides all increases. Similarly, all the elements of a group of the periodic table have the same number of valance electrons hence have similar chemical properties. Reactivity of metals increases down the group.

Periodic table elements

                                                                                     Periodic table elements

Type of Elements

Depending upon the type of orbital receiving the valance electron the elements are classified into four blocks such as s-block, p-block, d-block, f-block. In s-block elements, valance electrons enter an s-orbital. Group-IA and group-IIA belong to this block in the periodic table. d-block elements are transition elements except for zinc, cadmium, mercury. The valance electrons enter in d orbitals for d-block elements. Group-IIIA to group-XIIA belongs to this group. In p-block elements, the valance electrons enter in p orbital and group-XIIIA to XVIIIA belongs to these elements. The f-block consists of two series of lanthanoids.

Periodic Properties

  1.  Atomic size: Atomic size of elements refers to the radius of the atom. On moving down the group the atomic size of elements  increases because as we go down the group a new shield is being added. But in a period from left to right it decreases. In a period from left to right nuclear charges increase hence it has the tendency to pull the electrons closer to the nucleus and reduces the size of the atom. So in a period, alkali metals are the largest and the halogens are the smallest. Noble gases are larger than halogens.
  2. Electronegativity: Electronegativity is the tendency of an atom in a molecule to attract the shared pair of electrons towards the centre. The electronegativity of an atom increases along a period from left to right and decreases on moving down a group. Fluorine has the highest electronegativity.
  3.  Valency: In the periodic table elements the valency increases from one to seven in period with respect to hydrogen but with respect to oxygen it first increases one to four and then decreases to zero. Valancy of sodium, potassium is one. For alkaline earth metals, valency is two and for aluminium, valency is three. For nitrogen, valency varies from -3 to +5.
  4.  Ionisation energy: Ionisation energy is a type of energy required to remove an electron from its ground state. Ionization energy increases along a period from left to right because the nuclear charge increases from left to right. But in group IIA elements have more ionization energy than group-IIIA elements.
  5.  Electron gain enthalpy: Electron gain enthalpy increases along the period from left to right and decreases on moving down the group. Chlorine has the highest electron gain enthalpy.
  6.  Metallic character: Metallic character of an element is the tendency of an element to form cation by the loss of one electron. The metallic character of an element decreases along a period from left to right and increases on moving down a group.
  7.  Non-metallic character: It is the tendency of an atom to form anion by gaining an electron, Non-metallic character increases on moving down the groups and decreases along a period from left to right.
  8. Density: The density of an element increases from left to right along a period as well as moving down a group. Gold has a higher density than mercury.
  9. Mendeleev’s periodic law:

According to Mendeleev all the physical and chemical properties of the elements are the periodic function of their atomic masses. Mendeleev arranges all the known elements in increasing order of atomic masses and named them periodic table elements. In Mendeleev’s periodic table total numbers of periods are seven and the total numbers of groups are nine. This periodic table has some defects as elements that are chemically similar are placed in the different groups. Copper, silver has no resemblance with alkali metals but they have been placed together.

Hydrogen has no specific place because it forms a positive ion in the case of HCL and also forms a negative ion in the case of NaH. So it was considered in group IA and also in group VIIA. According to Mendeleev’s law isotopes must be given different places in the periodic table since their atomic masses are different. But they don’t have separate places.

Modern Periodic Table

According to Moseley, all the physical and chemical properties of an element are the periodic function of its atomic numbers. In the modern periodic table, there is a total of seven periods and eighteen groups. In the periodic table elements, two horizontal rows contain fourteen elements each at the bottom. The first row contains fourteen elements from atomic number 58 to 71 and it is known as the lanthanides series. Elements in a period have the same number of orbit but in a group, it changes.

Periodic Table Elements

Copper: The symbol of copper is Cu and the atomic number is 29. The density of copper is 8.96. Copper is a soft but tough material. It is mixed with tin to form bronze.

Nickel: The symbol of nickel is Ni and the atomic number is 28. Nickel is located in the fourth period on the periodic table. It is useful in making coins and it is mixed with copper to form monel which is an alloy of copper and nickel.

Zinc: The symbol of zinc is Zn and the atomic number is 30. Zinc is in use to make zinc oxide and also as an additive to the rubbers.

Sodium: The symbol of sodium is Na and the atomic number is 11. It is an alkali metal and it has a very low melting point. Sodium reacts with water, ice, rapidly to form sodium hydroxide. It improves the structure of soaps, purification of molten metals. Sodium chloride is a common compound of sodium which widely in use in daily life and also as salt in fertilizers.

FAQs about Periodic Table Elements

Q.1 Write the total number of elements present in the periodic table.

Answer:  The total number of elements present in the periodic table is 118. Four new elements have been added to the periodic table and they are Nihonium, Moscovium, Tennesine, Oganesson.

Q.2: Write all the groups of metals according to the periodic table.

Answer: According to the periodic table most of the elements are metals. Alkali metals, alkaline earth metals, basic metals, transition metals, lanthanides, actinides all are the group of metals.

Q.3: What is the basic difference between the Mendeleev periodic table and the modern periodic table?

Answer: Mendeleev arranges the elements based on their atomic weight while in the modern periodic table all the elements are placed according to their increasing atomic numbers.

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One response to “Earlier Attempts at Classification of Elements”

  1. Kashif says:

    What about the Al Razi classification??

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