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9 Class- Periodic Table of Elements

Periodic Table of Elements

More than 115 elements have been discovered which need to be arranged systematically, first elements were classified as metals and non metals.

History of classification of elements

1.     Prout’s Hypothesis – 1815
2.     Dobereiner’s Triads – 1829
3.     Newland’s Law of Octaves – 1863
4.     Lother Meyer Curves – 1869
5.     Mendeleev’s Periodic Table – 1869
6.     Modern Periodic Laws of Moseley -1913
7.     Modern Periodic Table ( of 18 columns ) 

 Prout’s Hypothesis

                                    According to this hypothesis atomic mass of elements is multiple of mass of hydrogen atom. So elements are related to each other on the basis of their atomic masses. It fails due to the reason that some elements do not have atomic mass in whole no. (Like chlorine have atomic mass of 35.5).

Dobereiner’s Triads

                                    According to Dobereiner’s triads elements arranged in the group of three elements so that atomic mass of central element is appropriate mean of 1st and 3rd element. These groups of three elements are known as Dobereiner’s triads.
Example-
Element                                                           
 Li                Na                  K
Atomic Mass                                              
7                 23                  39
Mean of Atomic Masses of 1st and 3rd elements  is (7+39)/2  =   46/2   =  23
Drawback of Dobereiner’s triads : All elements are not arranged in triads.

Newland’s Law of Octaves

According to Newland’s Law of Octaves elements arranged in the group of 8 elements and every 8th element is similar to the 1st element.
Li         Be         B        C          N         O           F
Na        Mg       Al        Si         P          S          Cl 

Drawback of Newland’s Law of Octaves :

Heavy elements do not follow this law, inert gases disturb the order of octave.

Lother Meyer Curves

                                       In 1869, Lother Meyer derived following conclusion by obtaining information from graph between the atomic weight at x-axis and atomic volume at y-axis.
1.     Elements which have similar properties found on the same position on the graph curves.
2.     All alkali metals like Li, Na, K, Rb, Cs, and Fr found at highest peak of curve.
3.     Halogens like F, Cl, Br and I are found on ascending portion of curve.
4.     Alkaline earth metals like Mg, Ca, Sr, Ba and Ra are found on descending portion of curve.
5.     Elements which do not melt easily like Be, B, C, Al, Si, Cu etc. are found at lowest point of curve.

On the basis of above conclusions Lother Meyer give periodic Law:
                                                                                                  According to Lother Meyer periodic law – “Atomic volume of elements are periodic function of their atomic weights”.

Periodic Table

                        To classify elements a chart is prepared in which elements are arranged in rows and columns. These elements are arranged in table in such a way that the elements with similar properties are repeat after some intervals; also elements with similar properties are put in same column below one another. In periodic table vertical columns are called group while horizontal rows are called periods. In periodic table this repetition of properties in regular interval is known as periodicity. Read below chemistry notes of periodic table like Mendeleev periodic table, Mosley periodic table, Modern periodic table etc.

Mendeleev’s Periodic Table

                                                In Mendeleev’s Periodic Table, Mendeleev classify elements according to their atomic masses and arranged these elements in table according to their increasing order of atomic masses.

Mendeleev’s Periodic Law

                                                According to Mendeleev’s Periodic Law – “Physical and chemical properties of elements are periodic function of their atomic masses”.
Mendeleev’s Periodic Table contains seven horizontal rows known as periods and nine vertical columns known as groups.

Groups of Mendeleev’s Periodic Table

1.     In original Mendeleev’s Periodic Table only 8 groups present because Zero group contains noble gases is added later after discovery of noble gases.
2.     So, total vertical column is 9 including group 1 to 8 and Zero group.
3.     Group 1 to 7 are divided into two subgroups (A and B) each.
4.     In eighth group, three elements found together in each period (from fourth period onward) known as transition triplet.

Periods of Mendeleev’s Periodic Table

1.     Mendeleev’s Periodic Table has seven periods.
2.     First period is known as very short period because contain only two elements.
3.     Second and Third period is known as short period because contain only 8 elements each.
4.     Fourth and Fifth period is known as long period because contain 18 elements each.
5.     Sixth period is known as very long period because contain 32 elements each, 18 elements in table and remaining 14 elements called Lanthanides (from atomic no. 58 to 71)
6.     Seventh period is known as incomplete period because it contains only 24 elements and some places are left vacant for elements as they are not known yet. 10 elements in the table and remaining 14 elements called Actinides (from atomic no. 90 to 103) placed outside at bottom of periodic table.

Demerits of Mendeleev’s Periodic Table

These below points are some Demerits of Mendeleev’s Periodic Table
1.     Position of Hydrogen: Hydrogen is placed in 1st as well as in 7th group because its properties are similar to both groups, which is not explained well.
2.     Elements which have similar properties are placed apart in different groups.
Example: Copper and Mercury with similar properties placed in group first and second.
3.     Elements with different properties are placed in one group.
Example: Coin metals like Li, Na, K, Rb, Cs.
4.     Atomic weights are not kept in serial order.
Example: Argon with higher atomic weight 39.948 is placed before potassium, which have lower atomic weight of 39.102
5.     Position of isotope is not proper because all isotopes of elements are placed in one group though the atomic weights of isotopes are different.
6.      Eighth group elements position is not appropriate because elements put in triplet form.
7.     Rare earth elements (Lanthanides and Actinides) position is not proper so they placed outside at bottom of periodic table.

Modern Periodic Law and Modern Periodic Table

                                                                                   Moseley in 1913, after doing many experiments comes to a conclusion that the elements should be arranged as per their atomic no. and not according to atomic masses. As atomic no. is fundamental property of all elements of periodic table. So Mosley gives a new law which is called is Modern Periodic Law.

Modern Periodic Law

                                         According to Modern Periodic Law- “Physical and Chemical properties of elements are periodic function of their atomic numbers”.

Long Form of Periodic Table

                                                     Bohr Bury invented new periodic table, which is called as Long Form of Periodic Table. This Long Form of Periodic Table is also known as Modern Periodic Table.

Special features of Modern or Long Form of Periodic Table

These below are Special features of Modern or Long Form of Periodic Table
1.     18 vertical columns known as groups.
2.     Horizontal rows known as periods.
3.     Light metals – These are elements of periodic table of group 1 and 2.
4.     Heavy metals or Transition metals - These are elements of periodic table of group 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.
5.     Non-Metals – These are elements of periodic table of group 13, 14, 15, 16 and 17.
6.     Zero group – These are elements of periodic table of group 18.

Properties of periods

1.     All periods start with alkali metal and end with noble gases.
2.     If we see table, it is very clear that from 1st to 7th period there is an addition of one shell in the each period like n=1,2,3,4,5………………

Properties of groups

1.     In any group, outermost shell electron are known as valance electrons and these electrons are same so main properties of elements of group is similar.
2.     Elements are divided into four blocks, which is s, p, d, f   according to valance electrons.
3.     s-block elements – elements of 1 and 2 group.
4.     p-block elements – elements of 13 to 18 group.
5.     d-block elements – elements of 3 to 12 group.
6.     f-block elements – elements of the Lanthanide and Actinide series.
7.     Representative Elements – elements of s-block and p-block collectively called as Representative elements also known as Normal elements or Typical elements.
8.     Transition Elements – elements of d-block.
9.     Inner Transition Elements – elements of f-block, also known as Rare Earth Elements.
10.                         Alkali Metals – elements of 1st group.
11.                         Alkaline Earth Metals – elements of 2nd group.

Solution for the demerits of Mendeleev’s Periodic Table in the Long Form of Periodic Table (or Modern Periodic Table)

1.     Mendeleev’s Periodic Table contains some heavy elements placed before lighter elements, this problem is solved automatically in Modern Periodic Table
2.     All isotopes of an element have same atomic number so no need to place them separate.
3.     All inert gases (or noble gases) got their appropriate place in zero group (or 18th group).
4.     Mendeleev’s Periodic Table have problem with 8th group but it is resolved in Modern Periodic Table as it is divided into three groups.

Drawback of Modern Periodic Table

1.     Position of Hydrogen is still not clear in Modern Periodic Table.
2.     Position of f-block elements (Lanthanides and Actinides) is not proper as these placed at bottom, separately from periodic table that is impractical.

Periodic Properties of the Elements


Periodic properties are the properties of the elements which depend on their electronic configuration and these properties changes on moving down in the group and on moving left to right in the period of the periodic table. Some periodic properties are atomic size, electron affinity, ionization energy, metallic and non metallic properties etc. are the main periodic properties.

Atomic Size


                        Size of any atom is explained with the help of atomic radius.

Atomic Radius


                        The distance between outermost shell electrons and centre of nucleus of isolated atom is called atomic radius.

There are two hypotheses for the calculation of atomic radius i.e.

1.     Van der Waals Radii


It is the one half of the distance between the two adjacent atoms nuclei centres, is known as Van der Waals radii.

Van der Waals radii is calculated as follows, first calculate the distance from the centre of nuclei of one atom to centre of nuclei of another adjacent atom in solid state of same substance. Then divide this distance by two. Van der Waals distance is represented by Angstrom A.

Where, 1 A = 10-8 cm.

2.     Covalent Radii


It is the one half of the distance between the diatomic molecule nuclei centres, is known as Covalent Radii.

Covalent radii is calculated as follows, first calculate the distance from the centre of nuclei of one atom to centre of nuclei of another atom in diatomic molecule containing covalent single bond. Then divide this distance by two.

  Isolated Atom


                        Isolated atom is an absolutely alone single atom.

  Periodicity in Atomic Size


  In Period: On moving left to right in any period atomic size decreases because atomic radii decreases, As electrons are attracted towards nucleus due to increasing nuclear charge.

  In Group: On moving down in any group atomic size increases because atomic radii increase, as more electrons shells added.

  An ionic radius of cation is smaller than its normal atom while that of anion is larger than its normal atom.

  Cations are formed by loss of electron or electrons and carry positive charge.

  Anions are formed by gain of electron or electrons and carry negative charge.

  Ionization Energy


                                    The energy required for the removal of one electron from the isolated atom in gaseous state is called ionization energy.

  Ionization Energy is represented by I.E.

  Ionization Energy is expressed in Electron Volts per Atom or Kilo Joules per Mole or Kilo Calorie per Mole. Ionization Energy is also known as Ionization Potential.

  Equation for I.E.

  Atom (g) + Ionization Energy (I.E.) ---à Cation + Electron (e-

  Removal of further electron from cation is difficult so value of Ionization Energy kept on increasing.

  I.E.1 < I.E.2 < I.E.3 < I.E.4 …………………………………..

  Periodicity in I.E. (Ionisation Energy)


  In Period: On moving left to right in any period ionization energy increases because nuclear charge increases with the increasing atomic number, so more energy required to remove electron. Therefore value of I.E. increases on moving left to right in any period.

  In Group: On moving down in any group ionisation energy decreases because atomic size increase, as more electrons shells added.

  Electron Affinity


                                    The amount of energy release as a result of addition of electron in any atom in gaseous state to form anion is known as Electron Affinity.

  Electron Affinity is represented by E.A.

  Electron Affinity is expressed in Electron Volts per Mole or Kilo Joule per Mole

  Values of all electron affinity are negative except first Electron Affinity which is positive.

  Periodicity in E.A. (Electron Affinity)


  In Period: On moving left to right in any period the value of Electron Affinity increases because atomic size decreases so amount of energy released is more.

  In Group: On moving down in any group the value of Electron Affinity decreases with some irregularities.

  Metallic and Non-Metallic characters


 In Period: On moving left to right in any period Metallic character decreases and Non Metallic character increases.

  In Group: On moving down in any group Metallic character increases and Non Metallic character decreases.

  In Periodic Table: Metallic elements are found on left hand side and Non Metallic elements are found on right hand side.

  Metalloids


                  The elements which are neither metals nor non metals are known as metalloids.

  Example of Metalloids: B, Si, As, Te etc.
Periodic table of elements

9 Class- Chemical Bonding and Reactions

Chemical Bonding and Reactions

Chemical Bonding

                             Molecule forms by the combination of two atoms of elements, the attraction force operate between atoms is known as Chemical Bonding. Chemical bonds are formed due to presence of valence electrons in atoms which present in outermost shell of atom.
Question: Why chemical bonds are formed between atoms?
Answer: Chemical bonds are formed between atoms to achieve stable state like inert or noble gases.
Atoms achieve stable state of nearest inert gas with complete octet in two ways:
1.     By exchanging electron with any other atom.
2.     By sharing electron with any other atom.

Types of Chemical Bonds

  • 1.     Electrovalent Bond or Ionic bond

  • 2.     Covalent Bond

Electrovalent Bond
Electrovalent Bond is also known as Ionic Bond because compound formed is ionic in nature having polarity. In electrovalent bond one atom loose electron to form positive ion called cation and another which gain electron to form negative ion called anion. This type of bond is known as Electrovalent Bond or Ionic Bond.
Example: NaCl
        Na                    -------->          Na+ +e-
        Cl  +  e-            -------->          Cl-
        Na+  +  Cl-       -------->          NaCl

Electrovalent Compound

                             The compounds which contain ionic or electrovalent bonds are known as Electrovalent or Ionic Compounds. Mainly electrovalent compounds are formed due to reaction between highly electropositive and highly electronegative atoms.

Characteristics of Electrovalent Compounds

1.     Crystal Structure:

                              In solid state of electrovalent compounds anions and cations are arranged in regular manner called as crystal, In which anions surrounded by definite number of cations and cations surrounded by definite number of anions.

2.     Physical Nature:

       Ionic or electrovalent compounds are generally hard and their hardness increases with increasing ionic charge and decreasing distance between ions.

3.     Solubility:

Positive ion of ionic compound attach with negative part of polar solvent and negative ion of ionic compound attach with positive part of polar solvent, so ionic or electrovalent compounds are soluble in polar solvents like water and insoluble in non polar solvents like benzene, ether, alcohol.

4.     Melting Point and Boiling Point:

Electrovalent or ionic compounds have high Melting and boiling points because they need large amount of energy to break strong ionic bonds.

5.     Electrical Conductivity:

                                    In molten and solution forms electrovalent compounds conduct electricity because ions flows in molten and solution forms.

Covalent Compound

Covalent bonds are the bonds which are formed due to the equal sharing of electrons between two atoms.  These chemistry notes are provided by Chemistry Notes Info Organization www.ChemistryNotesInfo.com , This type of bonds (i.e. covalent bonds) is formed in atoms which carry four or more than four electrons in outermost shell, generally sharing of electrons happen in two ways –
1.     Equal Sharing – Covalent Bond
2.     One Side Sharing – Coordinate Bond

Covalent Compounds

                                   Compound which are formed as a result of covalent bonding and containing covalent bonds are known as Covalent Compounds.
Example: Hydrogen, Chlorine, Oxygen, Water, Ethanol etc.

Types of Covalent Bonds

Covalent Bonds are of three types which are as follows-

1.     Single Covalent Bonds

2.   Double Covalent Bonds

3.     Triple Covalent Bonds

Single Covalent Bonds

                                      Bonds which are formed due to sharing of single pair of electrons between two atoms are called single covalent bond. It is represented by single line (-)
Example: Formation of H2 molecule, Formation of Cl2 molecule.

i.                   Formation of Hydrogen (H2) molecule:

                                                         In the outermost shell of hydrogen atom, it have single electron, which it share with another hydrogen atom to acquire inert configuration of helium so single bond is formed between these two hydrogen atoms and this single covalent bond is represented by single line (-)

ii.                 Formation of Chlorine Molecule (Cl2) :

In the outermost shell of chlorine atom, it have seven electrons, it share its one valence electron with another chlorine atom to form chlorine molecule by single covalent bond.

Double Covalent Bonds

                                      Bonds which are formed due to sharing of double pair of electrons between two atoms are called double covalent bond. It is represented by double line (=)
Example: Formation of O2 molecule.

i.                   Formation of Oxygen (O2) molecule:

                                                          In the outermost shell of oxygen atom, it have six electrons, it share its two valence electrons with another oxygen atom to form oxygen molecule by double covalent bond.

Triple Covalent Bonds

                                      Bonds which are formed due to sharing of triple pair of electrons between two atoms are called triple covalent bond. It is represented by triple lines
Example: Formation of N2 molecule.

i.                   Formation of Nitrogen (N2) molecule:

                                                          In the outermost shell of nitrogen atom, it have five electrons, it share its three valence electrons with another nitrogen atom to form nitrogen molecule by triple covalent bond.

Characteristics of covalent compounds

1.     Crystal Structure:

                              Crystal structure of covalent compounds is formed from atoms or molecules. Crystal of covalent compounds are divided in three parts as –
i.                   These are crystals of covalent compounds whose molecule are very small and these molecules are held together by vander waals forces.
Example: Sulphur, Iodine.
ii.                 These are crystals of covalent compounds whose molecule are very large due to combination of every atom with other atom by covalent bonds.
Example:  Diamond, Silica.
iii.              These are crystals of covalent compounds whose have separate layers.
Example: Graphite.

2.     Physical Nature:

      Due to weaker force of attraction between the molecules of the covalent compounds, maximum covalent compounds are gases or liquids but some covalent compounds exist as solid like Urea, Sugar, Glucose, and Naphthalene.

3.     Solubility:

                Covalent compounds are not soluble in polar solvents like water but are soluble in non-polar solvent like alcohol, ether, carbon tetra chloride.

4.     Melting Point and Boiling Point ( MP and BP) :

                Melting and boiling points of covalent compounds are very low because very less energy is required to overcome the weak force of attraction between the neutral molecules in the covalent compound. But Diamond and Graphite are exception because they have very high melting and boiling points.

5.     Conductivity:

                   Covalent compounds do not have ions so they do not conduct electricity but some polar covalent compounds conduct very less electricity.

Polar Covalent Bond

                                    In the covalent compound if one is the more is more electronegative than other atom, then shared pair of electrons is attracted towards more electronegative atom so it acquire or obtain some partial negative charge which is represented by delta negative (d-) and other atom acquire some partial positive charge which is represented by delta positive (d+) therefore polar bond is form, which is known as Polar covalent bond.
Example : Hydrogen Chloride Molecule.
In HCl molecule, Chlorine is more electronegative than Hydrogen so chlorine acquires partial negative charge and hydrogen acquire partial positive charge.

Characteristics of Polar Covalent Compounds

i.                   Polar covalent compounds are approximately 80% covalent and 20% ionic so they so characteristics of both covalent and ionic (or electrovalent) compounds.
ii.                 In solution forms, polar covalent compounds are good conductor of electricity. Example: HCl
iii.              As compared to pure non-polar covalent compounds and electrovalent compounds, the melting point and boiling point of polar covalent compound are higher.

Chemical Reactions

Chemical Reaction is the reaction in which two or more than two substances react to form a new substance is known as Chemical Reaction. The substances which react may be ion or compound of element.
Reaction: Reactant reacts with each other to give product.
               Reactant   -------->  Product
Example of general chemical reactions from daily life is rusting of iron, formation of curd from milk etc.

Chemical Formula

                               Chemical Formula is simple representation of any compound by writing together the numbers and symbols of constituting elements forming that compound.
Example: H2O, CaCl2, AlCl3, Ca(OH)2

Chemical Formula for Ionic Compounds

                                                     As we know Ionic compound formed as a result of electron transfer between metal and non-metal atoms. When we have to write chemical formula for ionic compound then write metal atom symbol on left hand side and non-metal atom symbol on right hand side. Metal atom name remain same but ‘ide’ or ‘ate’ suffix is added to non-metal atom name.

Ionic compound formed by one metal atom and non-metal atoms.

Metal Atom
Non-Metal Atom
Name of Compound
Chemical Formula  of Compound
Name and Symbol
No.
Name and Symbol
No.
Calcium (Ca)
1
Oxygen (O)
1
Calcium Oxide
CaO
Magnesium (Mg)
1
Chlorine (Cl)
2
Magnesium Chloride
MgCl2
Aluminium (Al)
1
Chlorine (Cl)
3
Aluminium Chloride
AlCl3

    Chemical Formula for Covalent Compounds

                                                                        As we know covalent compound formed as a result of electron sharing and contains non-metal atoms. When we have to write chemical formula for covalent compound then relatively less electronegative non-metal atom symbol is written on left hand side and other witch is more electronegative is written  on right hand side. Name of non-metal atom which is written on left hand side is remain same but ‘ide’ suffix is added to non-metal atom name which is written on right hand side. 

Covalent compound formed by two  non-metal atoms.

Low Electronegative Non-Metal Atom
High Electronegative Non-Metal Atom
Chemical Name of Compound
Chemical Formula  of Compound
Name and Symbol
No.
Name and Symbol
No.
Carbon (C)
1
Oxygen (O)
1
Carbon Mono Oxide
CO
Carbon (C)
1
Oxygen (O)
2
Carbon Di Oxide
CO2
Phosphorus (P)
1
Chlorine (Cl)
3
Phosphorus Tri Chloride
PCl3
Phosphorus (P)
1
Chlorine (Cl)
5
Phosphorus Penta Chloride
PCl5
Nitrogen (N)
2
Oxygen (O)
5
Nitrogen Penta Oxide
N2O5

Formation of Compound

                                      We get chemical formula of molecule by writing valence of 1st atom in front of 2nd atom and valence of 2nd atom in front of 1st atom.
Example: valence of carbon is 4 and oxygen is 2, write 4 in front of O and 2 in front of C in subscripts as shown below.
C2O4
as we see, both valences are multiple of two so divide it by two to get CO2 formula.
Similarly,
           Na+ + CO3-2   ---> Na2CO3
          Al+3 + SO4-2  --->  Al2(SO4)3
          Mg+2 + N-3    --- Mg3N2

Simple Chemical Reaction

                                         Chemical reaction is represented by chemical equation in brief by taking help of symbol and formula of participating substances in reaction.

General Rule for writing Simple Chemical Reaction

   1.     Reactant are written on left hand side and if more than one reactant are present than write plus (+) sign between them.
   2.     Product are written on left hand side and if more than one product are present than write plus (+) sign between them.
   3.     Arrow sign is placed between reactants and products.
Example: Zn + H2SO4 ( Reactants)  -----> ZnSO4 + H2 (Products)
 4.     To get more information from the reaction write temperature, pressure, catalyst name above or below arrow sign. 
   5.     On the right side of the gaseous substances sign and on the left side of heavy substances which precipitate sign is placed.
   6.     Reactions which absorb heat are known as endothermic reactions and (+Q) heat sign is added on reactant side.
   7.     Reactions which produce heat are known as exothermic reactions and (+Q) heat sign is added on product side.
    8.     (Aq) is written for aqueous solution substances.

Balancing of Chemical Reactions

                                                    For balancing of chemical reaction the no. of atom on reactant side should be equal to no. of atom on product side, so that total mass of reactant is equal to total mass of product. You read these 9 class notes at www.ChemistryNotesInfo.com of ‘Chemistry Notes Info’ organization website.
H2 + O2   ----->   H2O   (Imbalance Equation)
2H2 + O2 ----->   2H2O   (Balance Equation)

Types of Chemical Reaction

  • ·        Addition Reaction

  • ·        Decomposition Reaction

  • ·        Substitution Reaction

  • ·        Oxidation and Reduction Reaction

1.     Addition Reaction

Reactions in which two or more than two substances reacts together to produce a new compound is known as Addition Reaction.
Example:-
2Mg + O2 ------> 2MgO

          2.     Decomposition Reaction

Reactions in which one compound get break into two or more than two simple compounds by breaking of chemical bonds, these chemical bonds get broken by heat, light or electricity.
Example:-
CaCO3 ------> CaO + CO2

          3.     Substitution Reaction

Reactions in which one element replaces another element to form a new compound is known as Substitution Reaction
Example:-
CuSO4 (Aq) + Zn (s) -----> ZnSO4 (Aq) + Cu (s)

          4.     Oxidation and Reduction Reaction

Oxidation and reduction reaction are described below on these two basis-
          Oxidation and Reduction Reaction based on oxygen and hydrogen-
·  Removal of hydrogen and addition of oxygen is known as oxidation reaction.
·  Removal of oxygen and addition of hydrogen is known as reduction reaction.
Oxidation and Reduction Reaction based on electron transfer-
·        Oxidation reactions are the reactions in which atom or ion looses electrons.
·         Reduction reactions are the reactions in which atom or ion gains electrons.
Oxidation and Reduction reactions occurs simultaneously because electron removed from one atom or radical is added to another atom or radical.
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