Note on Radicals and Inert Gases

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Radicals

A radical is an atom or a group of atoms of different elements having positive or negative charge and acts as a single unit throughout the chemical reactions. They do not exist freely.

On the basis of electric properties, radicals can be classified into:

  • Electro-positive radicals: The radicals which have the capacity of losing electrons and carry positive charge are called electropositive radicals. E.g. Ca++, Na+ etc.
  • Electro-negative radicals: The radicals, which have the capacity of gaining electrons and carry negative charge are called electronegative radicals. E.g. O--, HCO3- etc.

Inert gases

The elements fall into the zero group of the periodic table are inert gases or noble gases. They are helium, neon, argon, krypton, xenon and radon. These elements are chemically inert because of their stable electronic configuration. Among all of them, only helium contains 2 electrons in their valence shell while the remaining contains 8 electrons in their valence shell. Those elements which have 8 electrons in their valence shell and do not take part in a chemical reaction are called inert gases. The given table shows the electronic configuration of inert gases,

Duplet and duplet rule

The arrangement of two electrons in the K-shell is said to be duplet. It is chemically inert because it has a complete number of electrons in its K-shell. Helium is a duplet as it has two electrons in K- shells. Hydrogen, Lithium, Beryllium and Boron also attains a stable electronic configuration similar to that of a helium atom. It is called duplet rule. The tendency of an atom with single shell to attain two electrons in its K- shell is called duplet rule.

Octet and octet rule

Except helium, the other inert gases have 8 electrons in their valence shell. Such arrange of a stable group of 8 electrons in their valence shell is said to be octet. Some atom of elements make 8 electrons in their valenceshell by gaining, losing or sharing electrons between the combining atoms during the formation of a molecule is called octet rule.

  • The combining capacity of elements or the radicals with the other elements or radicals to form molecule of an element or compound is called valency.
  • A radical is an atom or a group of atoms of different elements having positive or negative charge and acts as single unit throughout the chemical reactions.
  • The arrangement of two electrons in the K-shell is said to be duplet.
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Very Short Questions

The combining capacity of elements or the radicals with the other elements or radicals to form a molecule of an element or a compound is called valency. Numbers such as 1, 2, 3, 4, 5 and 6 represents the valency.

Elements Valency
Na (Sodium) 1
Zn (Zinc) 2
K (Potassium) 1
Cl (Chlorine) 1
Al (Aluminum) 3
Fe (Ferrum) 2 Or 3

A radical is an atom or a group of atoms of different elements having positive or negative charge and acts as single unit throughout the chemical reactions. E.g.: Ca++, O--etc.

The radicals, which have the capacity of losing electrons and carry positive charge, are called electropositive radicals. E.g.: Ca++, Mg++, Na+, etc.

Radicals act as a charged atom and are highly unstable. So, to be a stable it wants to gain or lose the electrons. So, they contain charge.

The radicals, which have the capacity of gaining electrons and carry negative charge, are called electronegative radicals. They are also called acidic radicals or non-metalic radicals, e.g.
O-- valency (2)
NO3- valency (1)
CO3-- valency (2)
HCO3- valency (1)

The compounds which are formed by sharing electrons between two or more atoms and contain covalent bonding are called covalent compounds. E.g.:
CH4 (Methane), H2O (water) etc

The chemical bond formed by the transfer of electrons from valance shell of one atom to valance shell of another atom is called electrovalent bond and the valency is electrovalency. MgCl2, CaO, Na2O, AlCl3 are some example of compounds formed by electrovalent bond.

The covalent bond is the bond formed by sharing of a pair of electrons between two atoms each contributing equal number of electrovalent electron pair. E.g.: H2, O2, CH4, CO2, etc.

The valency of sodium is 1.
The valency of sodium is 1 because it loses 1 electron at the time chemical reaction to be stable.
The valency of argon is zero.
In the valence shell of Argon, there are eight electrons. That means it is stable by octate rule. That's why it neither gains electron nor loose electron. So, it has zero valency.

Symbolic representation of one molecule of a substance is called molecular formula. E.g. H2 denotes one molecule of hydrogen.

In Nacl the valency of sodium (Na) is 1.
In MgCl the valency of Magnesium (Mg) is 2.
In CCl4 the valency of Carbon is 4.
In AlCl3 the valency of Aluminum is 3.

The state of having two electrons in the K shell of an atom is duplet state. E.g.Helium.

The arrangement of 8 electrons in the valance shell of an atom is called octet state. E.g. Neon (Ne).

Those elements which have 8 electrons in their valance shell and are kept in the zero group of periodic table are noble gases. Their valency is zero because they are stable and do not take part in chemical combination.

If the elements have more than one valency, then it is said to be variable valency.
For e.g.: Cuprous (Cu) has 1 valency
Cupric (Cu) has 2 valency.

Radicals Valency
Nitrate → 1
Chloride → 1
Silicate → 2
Sulphate → 2
Carbonate → 2

  • The valency of element 'B' is 2. This is because it required or shares two electrons at the time of chemical combination. Because there are six electrons in its valence shell, so for the octet it requires two electrons.
  • When element 'A' and 'B' combines, sulphur dioxide (SO2) is formed. Covalent bond is formed in between them.

In MgCl2, valency of Cl is 1 and valency of Mg is 2.
Electrolyte: A compound which conducts electricity in its solution is electrolyte. For e.g.: NaCl solution, HCl solution etc.

Molecular formula is the short form of a molecule which is represented by the symbol of elements present in the molecules.
The molecular formula can be of an element or a compound. For example: H2, O2, N2 etc are the molecular formula of elements. Similarly, CO2, H2O, NH3 etc are the molecular formula of the compounds.
Significance of molecular formula:

  • It represents name of the substance.
  • It helps to know name and number of atoms of all the elements present in the molecule.
  • It helps to find out molecular weight of a molecule.
  • It helps to write chemical equation.
  • It represents one molecule of the substance.
  • It helps to know the valency of elements present in the molecule.

In XCl5, 1 atom of 'X' combines with 5 atoms of 'Cl'. So, the valency of 'X' in XCl5 is 5. Here, the valency of 'X' is found out by comparing it with the number of chlorine.

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  • What is the molecular formula of the compound formed by chemical combination of hydrogen and oxygen in the proportion of 1:2 respectively?

    H2O
    H2O2
    OH
    H3O
  • What is the valence of lead in plumbic chloride (lead can have variable valency of 2 or 4)?

    2
    1
    4
    3
  • Which element does not have variable valency?

    Tin
    Magnesium
    Sulphur
    Copper
  • Which is false statement?

    In C2H2 the valency of carbon is 4
    In CO the valency of carbon is 4
    In C2H4 the valency of carbon is 4
    Noble gases don't participate in chemical reaction because they lack valence electrons
  • What are the electropositive and electronegative radicals of H3PO4?

    H+3 and PO4-3
    3H+ and PO-4
    3H+ and PO4-1
    H+ and PO4-3
  • Which is false statement?

    Electropositive radicals are acidic while electronegative radicals are basic
    In electropositive radical number of proton is greater while in electronegative radical the number of electrons is greater
    When an ionic compound breaks it forms one electronegative radical and one electropositive radical
    The number of + or charge on a radical indicates it's valency
  • Which is false about inert gases?

    They are inert because they have valency of 8
    There are total of 6 inert gases in the periodic table till date
    They can combine with other elements under suitable condition of temperature, pressure and catalyst
    They all have 8 electron in their valence shell
  • Which element doesn't follow duplet rule?

    Carbon
    Beryllium
    Hydrogen
    Lithium
  • Which atom is in octate state?

    O
    Ne
    N
    C
  • Which element follow octate rule?

    Beryllium
    Hydrogen
    Carbon
    Lithium
  • Caesium is an element with atomic no 55 and lies next to the inert gas Xenon whose atomic no is 54. What must Caesium do to gain octate state?

    Gain one electron
    Gain two electron
    Lose one electron
    Lose two electron
  • Which is not a chemical bond?

    Carbon bond
    Covalent bond
    Electrovalent bond
    Coordinate bond
  • Which is not a characteristic of electrovalent compounds?

    Current can flow through NaCl power since it can be decomposed into ions
    They can be decomposed into cations and anions on heating
    They have high melting point
    They are formed between a metal and non-metal
  • What is false about Magnesium Chloride?

    It gives magnesium cation and chlorine anion
    it is formed between the metal magnesium and the nonmetal chlorine
    It is formed by sharing of two electrons between magnesium and chlorine
    It is electrovalent compound
  • Which is not a characteristic of covalent compounds?

    They have fixed geometrical shape
    They decompose into neutral non-metal atoms
    They dissolve in organic solvent
    They are weaker than organic compounds
  • Formation of Methane CH occurs when

    One Carbon is surrounded by four hydrogen atoms
    One carbon atom shares one electron with each four hydrogen atoms
    Hydrogen atom accepts four electrons from carbon atom
    One Carbon atom shares four electrons with each four hydrogen atoms
  • What is molecular weight of Na2(CO(Given : N=23,C=12,O=16)?

    108
    105
    106
    107
  • What is molecular formula of Aluminum Nitride?

    Al(NO3)3
    Al(NO2)3
    AlN
    AlN3
  • What is molecular formula of Phosphorus pent oxide?

    P2O5
    PO5
    P5O
    PO5
  • KclO3 decomposes into

    KCl+ and O3-
    K+ and ClO3-
    K+ and ClO-3
    KCl+ and O-3
  • What information is not provided by molecular formula?

    Represents percentage composition of each element forming the compound
    Calculate molecular weight
    Structure of the compound
    Shows actual number of atoms of each element forming the compound
  • Which is correct according to rules to write symbols?

    c.m
    10kgs
    M J
    N m
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nabin sodari

why helium has valency 2


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