ICSE Class 9 Chemistry Chapter 09 Study of the First Element Hydrogen

Chapter 9

Study of the First Element - Hydrogen

Latest Syllabus - Scope of Syllabus - Study of the First Element -Hydrogen

Position of the non-metal (Hydrogen) in the periodic table and general group characteristics with reference to valency electrons, burning, ion formation applied to the above mentioned element.

i) Hydrogen from water (ii) hydrogen from dilute acids (iii) hydrogen from alkalis.

Hydrogen from water: Cold water and metals; hot water and metals; steam and metals; steam and non-metals. Application of activity series for the above mentioned preparations.

Displacement of hydrogen from the sulphuric acid or hydrochloric acid by zinc or iron [no reaction with copper].

Displacement of hydrogen from alkalis [NaOH, KOH] by Zn, Al - unique nature of these elements.

ii) The preparation and collection of hydrogen by a standard laboratory method other than electrolysis.

In the laboratory preparation, the reason for using zinc, the impurities in the gas, their removal and the precautions in the collection of the gas must be mentioned. Industrial manufacture of hydrogen by Bosch process with main reactions and conditions; separation of CO2 and CO from it.

A. Position of the Non-Metal - Hydrogen in the Periodic Table

Elements of Group 1 [IA] - alkali metals

Lithium [Li], Sodium [Na], Potassium [K], Rubidium [Rb].

Elements of Group 17 [VIIA] - halogens

Fluorine [F], Chlorine [Cl], Bromine [Br], Iodine [I].

Position of Hydrogen - In the Periodic Table

Atomic number of hydrogen = one; Number of valence electrons = one

1st element of the periodic table placed in Group 1 [IA] [period - 1] of the periodic table.

Dual Nature of Hydrogen

Hydrogen has the simplest electronic configuration of 'one' and hence:

Either loses one electron behaving like electropositive alkali metals [group 1 (IA)]

e.g. H - 1e- \(\to\) H\(^{1+}\), Li - 1e- \(\to\) Li\(^{1+}\), Na - 1e- \(\to\) Na\(^{1+}\).

Gains one electron behaving like electronegative halogens [group 17 (VIIA)]

e.g. H + 1e- \(\to\) H\(^{1-}\), F + 1e- \(\to\) F\(^{1-}\), Cl + 1e- \(\to\) Cl\(^{1-}\).

Resultant Position of Hydrogen

Hydrogen thus show similarities with:

Alkali metals of group 1 [IA] and Halogens of group 17 [VIIA]

and is placed above Lithium [Li] in group 1 [IA] or above Fluorine [F] in group 17 [VIIA]. [Thompson had assigned a separate position to hydrogen on top of the periodic table which does not disturb the periodic law or the symmetry of the table].

Teacher's Note

Hydrogen's unique position in the periodic table mirrors how water itself is essential to all life on Earth, making it the most fundamental element in chemistry.

B. General Group Characteristics - First Element Hydrogen

Similarity of Hydrogen With - Alkali Metals - [Group 1 (IA)]

Similarity of Hydrogen With - Halogens - [Group 17 (VIIA)]

Teacher's Note

Just as hydrogen bonds with other elements to form compounds like water and salt, hydrogen atoms in your body continuously bond with oxygen and carbon to form the proteins and sugars that sustain life.

C. Discovery and Occurrence - Of Hydrogen

Discovery

Hydrogen was initially called 'inflammable gas'.

Robert Boyle - in 1672 - established the elementary character of hydrogen.

Henry Cavendish - in 1776 - first prepared hydrogen in the pure state and also described its properties and recognized it as an element. He found that the gas was inflammable and that it burnt in air to produce water.

Lavoisier - in 1783 - established its name 'hydrogen' meaning 'water producer' [Greek word Hydro = water, gen = producer].

Occurrence

In the Free State

Hydrogen stands ninth in abundance [by mass] - among the elements present in the earth's crust. It makes up approximately 1% of the earth's crust.

Hydrogen is seldom found in the free state on the planet earth.

It exists upto 0.01% in the earth's atmosphere.

It is also found in minute traces, in volcanic gases and to a higher extent around the sun and the stars.

In the Combined State

Hydrogen is distributed in combination with other elements in the combined state.

It occurs in the combined state:

In plant and animal tissues - which are made of compounds of hydrogen along with carbon, oxygen and nitrogen.

In water - about one ninth by mass of water is hydrogen.

As a constituent of different substances - i.e. acids, alkalis, petroleum products and organic substances. Combined with carbon, hydrogen is found in -

a] natural gas, b] kerosene, c] gasoline, d] petroleum products

It is a constituent of most organic substances including -

a] proteins, b] carbohydrates, c] fats which are essential for all living matter.

Teacher's Note

Hydrogen's presence in water and organic molecules explains why hydrogen-rich compounds are found everywhere from the air we breathe to the food we eat.

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