Classification of elements and periodicity in properties  

What is Classification of elements and periodicity in properties

  • The periodic table is the table of the elements that are found on the earth. Initially, this table was given by a Russian chemist Dmitri Mendeleev in 1869.

  • Some periodic tables existed before but Mendeleev’s periodic table was considered as:

(i) Atomic weight is the fundamental property of elements.

(ii) The physical and chemical properties of elements are a periodic function of their atomic weight.

  • Then in 1972, Moseley proposed the Modern periodic law, which says “the physical and chemical properties of the elements are periodic functions of their atomic numbers”.

Then finally, came the Long form of periodic table. This was based on Bohr-Bury concept of electronic configuration. This table has 7 periods and 18 groups. The elements existed in the table can be classified on the basis of their electronic configuration such as s-block, p-bock, d-block, and f-block elements. Hydrogen with one electron occupies a special position in the periodic table

 

Classification of Elements and Periodicity in Properties

Fig. 1: A Long form of Periodic Table

 

Most of the elements in the periodic table are metals. These metals exist at the left side of the periodic table. Some of the elements in the table are non-metals and they are less than 20 in number and they exist on the right side of the table. Some of the elements that exist on the border of the metals and non-metals are known as metalloids. Their properties are similar to metals as well as to non-metals.

 

Topics:

(i) Atomic Radii, and its trend in periods and groups

(ii) Ionic Radius, isoelectronic species

(iii) Ionization Enthalpy and factors affecting ionization enthalpy

(iv) Electron Gain Enthalpy and Electron Affinity

(v) Electronegativity and Electropositivity

(vi) Acids, Bases and Amphoteric Nature

(vi) Acidic Nature of Non-Metals Hydrides and Oxyacids

 

Overview of the Chapter

 

In this chapter, there are various important topics that you must understand completely:

(i) Atomic Radius:

  • This is basically the size of any atom. Within a given period, the atomic radius decreases from left to right because of an increase in nuclear charge in the same shell.

  • In the group, the atomic radius increases from top to bottom due to the increase in the number of shells.

 

Table 1: Atomic radii (in pm) across the periods and groups

Period/Group

IA

IIA

IIIA

IVA

VA

VIA

VIIA

2

Li(152)

Be(111)

B(88)

C(77)

N(74)

O(66)

F(64)

3

Na(186)

Mg(160)

Al(143)

Si(117)

P(110)

S(104)

Cl(99)

 

(ii) Ionization Enthalpy:

  • It is defined as the amount of energy required for the electron to come out of the atom. It is expressed in kJ/mol.

  • It increases in the period from left to right due to the increased nuclear charge and decreases down the group because of the distance of the electron from nucleus increases.

 

Table 2: Trend of ionization energy (kJ/mol) in second period

Period/Group

IA

IIA

IIIA

IVA

VA

VIA

VIIA

VIIIA

2

Li(520)

Be(899)

B(801)

C(1086)

N(1402)

O(1314)

F(1681)

Ne(2080)

 

Trend of ionization energy (kJ/mol) down the group 1

(iii) Electron gain enthalpy and electronegativity:

  • Electron gain enthalpy is defined as the amount of energy released when a new outside electron enters into an atom. It can be positive or negative that completely depends upon the nature of the element.

Fig. 3: Representation of Electron gain enthalpy

 

  • Electronegativity is defined as the ability of an atom to attract the electrons towards itself. It is not a measurable quantity, but according to the Pauling scale, fluorine has given the arbitrary value of 4, and rest other elements are measured on the basis of this.

 

Table 3: Electronegativity values according to the Pauling scale across periods 2 and 3.

Period/Group

IA

IIA

IIIA

IVA

VA

VIA

VIIA

2

Li(1.0)

Be(1.5)

B(2.0)

C(2.5)

N(3.0)

O(3.5)

F(4.0)

3

Na(0.9)

Mg(1.2)

Al(1.5)

Si(1.8)

P(2.1)

S(2.5)

Cl(3.0)

 

(iv) Acidic nature of Hydrides and Oxyacids:

  • Acidic nature of non-metal hydrides increases down the group.

H-F < H-Cl < H-Br < H-I
Classification of Elements and Periodicity in Properties

  • Acidic nature of oxyacids increases from left to right as follows:

    H3BO3 < H2CO3 < HNO3

Classification of Elements and Periodicity in Properties

 

    General trend of properties of the elements

Fig. 4: General trend of properties of the elements

 

How to prepare for the Periodic Table and its Elements?

  • This chapter is the part of Inorganic chemistry. It is completely theory based. You are not supposed to memorize any formula and numerical practice for getting the good hold on this chapter.

  • First, you must have the complete knowledge of Atomic Structure chapter. For this, you must go through chapter 3 of the NCERT book 11th class part 1 thoroughly.

  • You must deeply observe that how and why the properties of elements like atomic radius, ionization enthalpy, electron gain enthalpy, etc. are following some general trends.

  • In these properties, there are also some exceptional cases which exist that you must understand, for example, why oxygen atom has bigger size than nitrogen atom or why electron gain enthalpy of chlorine is more than fluorine.

 

Prescribed Books

For this chapter first, you need to finish the theory thoroughly from chapter 3, class 11th NCERT book and then simultaneously solve the examples and questions given in the book. Apart from this, if you want to prepare for the advanced level for competitive exams like JEE and NEET, you must choose to read the book - O.P. Tandon. Meanwhile, in the preparation, you must continuously write the mock tests for the depth of knowledge. Our platform will help you to provide with the variety of questions for deeper knowledge with the help of videos, articles and mock tests.

Topics from Classification of elements and periodicity in properties

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  • s, p, d and f block elements ( JEE Main ) (130 concepts)
  • periodic trends in properties of elements atomic and ionic radii ( JEE Main ) (215 concepts)
  • ionization enthalpy ( JEE Main ) (95 concepts)
  • electron gain enthalpy ( JEE Main ) (40 concepts)
  • valency, oxidation states and chemical reactivity. ( JEE Main ) (50 concepts)
  • Genesis of periodic classification ( JEE Main ) (1 concepts)
  • Modern periodic law and the present form of the periodic table ( JEE Main ) (3 concepts)
  • Nomenclature of elements with atomic numbers >100 ( JEE Main ) (1 concepts)
  • Electronic configurations and types of elements:s-, p-, d-, f-, blocks ( JEE Main ) (5 concepts)
  • Periodic trends in properties of elements ( JEE Main ) (8 concepts)
  • Smart tips: Classification of Elements and Periodic Table ( JEE Main ) (1 concepts)

Important Books for Classification of elements and periodicity in properties

  • Classification of elements and periodicity in properties Book
  • Classification of elements and periodicity in properties Book
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