ICSE Class 10 Chemistry Chapter 01 Periodic Table Periodic Properties and Variations of Properties

Periodic Table, Periodic Properties and Variations of Properties

Syllabus

Periodic properties and variations of properties - Physical and Chemical

(i) Periodic properties and their variations in groups and periods. Definitions of following periodic properties and trends in these properties in groups and periods should be studied:

Atomic size, Metallic character, Non-metallic character, Ionisation potential, Electron affinity, Electronegativity

(ii) Periodicity on the basis of atomic number for elements. Relation between atomic number for light elements (proton number) and atomic mass for light elements; the modern periodic table up to period 3 (students to be exposed to the complete modern periodic table but no questions will be asked on elements beyond period 3 - Argon); periodicity and other related properties to be described in terms of shells (not orbitals); special reference to the alkali metals and halogen groups.

Note: According to the recommendation of International Union of Pure and Applied Chemistry (IUPAC), the groups are numbered from 1 to 18 replacing the older notation of groups IA ... VIIA, VIII, IB ... VIIIB and O. However, for the examination both notations will be accepted.

1.1 Introduction

Elements are pure substances made up of one type of atoms. They are the basic units of all types of matter. In order to study elements in an organised manner, they need to be classified.

You have studied in class IX contribution of Dobereiner, Newland and Mendeleev to the classification of elements.

Dobereiner, grouped the elements in three (triads).

Newland, observed that when elements are arranged in increasing order of their atomic mass, every eighth element beginning from any element resembles the first element in its physical and chemical properties.

Dmitri Mendeleev, a Russian chemist gave the first periodic table of elements base on his law which states that "the properties of elements are the periodic functions of their atomic masses". This arrangement enabled Mendeleev to place 63 elements known that time in vertical columns (groups), and in horizontal rows (periods). He predicted the existence of those elements which were yet to be discovered. But this method could not explain the positions of certain elements, the rare earth metals and the isotopes. These defects were removed when Henry Moseley put forward the modern periodic table. He stated that "the physical and chemical properties of elements are the periodic functions of their atomic number".

Later on Niel Bohr gave the extended form of the table known as long form of the modern periodic table given on page 2.

A tabular arrangement of elements in groups (vertical columns) and periods (horizontal rows) highlighting the regular trends in properties of elements is called a Periodic Table.

1.2 Salient Features of The Modern Periodic Table (See Page 2)

Groups

The modern periodic table has eighteen vertical columns. They are known as groups, arranged from left to right in the order.

Group 1:

These elements are known as Alkali metals as they form strong alkalis with water.

Group 2:

Alkaline earth metals - They form weaker alkalis as compared to group1 elements.

Groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 are known as the transition elements.

They have their two outermost shells incomplete.

Group 13:

Boron family - Boron is the first member of the group.

Group 14:

Carbon family.

Group 15:

Nitrogen family.

Group 16:

Oxygen family also known as chalcogens meaning ore forming.

Group 17:

These elements form salts and so known as Halogen (meaning - salt former).

Group 18:

(Zero group) - Elements of this group are called the noble gases or inert gases.

These elements have their outermost orbit complete. Due to stable electronic configuration they hardly react with other elements.

Note: The elements of groups 1, 2, 13, 14, 15, 16 and 17 are known as the main group elements or representative elements or normal elements.

The outermost shell of all the elements of these groups are incomplete.

Periods

There are seven horizontal rows in the modern periodic table. They are known as periods (see table given below).

The number of shells present in an atom determines its period. For example:

Elements of period one have one shell, elements of period two have two shells, and that of period three have three shells and so on.

Note: Lanthanides Group 3 of the sixth period and actinides Group 3 of the seventh period have similar properties because they belong to the same Group 3. They are shown at the bottom of the periodic table because they are large in number, and if shown in the main body of the table will distort its shape.

The third period elements, Na, Mg, Al, Si, P, S and Cl, summarise the properties of their respective groups and are called typical elements.

A period is determined by the number of shells and a group is determined by the number of electrons present in the outermost shell. For example: Sodium has atomic number 11 and its electronic configuration is 2, 8, 1. It has three orbits (shells) and has one electron in the outermost orbit hence it is placed in third period and group 1. Similarly, calcium, atomic number 20, electronic configuration 2, 8, 8, 2 is placed in fourth period and group 2.

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