GROUP-1 and 2 - PART-A -PHYSICAL PROPERTIES -

       GROUP- I  AND II

PHYSICAL PROPERIES 

 

    Topics:

• Introduction
• Abundance of elements on earth
• Electronic configuration
• Atomic radius 
• Ionic radius 
• Ionization Enthalpy
• Hydration enthalpy 
•  Electronegativity 
• Melting Point

a. INTRODUCTION:

·       The elements in which their last electron enters into the sub shell “S” (first sub shell) of any shell (K, L, M, N…) in the atom is called as S BLOCK ELEMENT.

·       The Maximum number of electrons in the sub shell “S” can be occupied by only 2 electron. 

·       Hence this block is classified into two Group in periodic table.

¨     Group -1  (Alkali Metals)

¨     Group- 2 ( Alkaline Earth Metals)

	1	2
1	H
2	Li	B
3	Na	Mg
4	K	Ca
5	Rb	Sr
6	Cs	Ba
7	Fr	Ra

 

 

 

ALKALI  METAL : ·         The first group of  S-block is known as Alkali metal .  ·         The word “ALKALI” derived from the word  “AL- QUALIY” meaning the Plant  ashes  referring to the original sources of alkaline substance. ·         This group consist of 6 elements, v  Lithium v  Sodium v  Potassium v  Rubidium v  Caesium v  Francium   GENERAL CHARECTERISTIC OF ALKALI METAL:         ·     Highly reactivity       ·         Found in nature as a compound, ü  Rb and Cs associated minute quantity with minerals of other alkali metal ü  Fr is highly radioactive and doesn’t exits appreciably in nature (longest lived isotopes has a half-life of only 21minutes)

ALKALINE EARTH METAL           The second group of the periodic table is known ALKALINE EARTH MEATAL.        This group contains 6 elements. v  Beryllium v  Magnesium v  Calcium v  Strontium v  Barium v Radium   GENERAL CHARECTERISTIC OF ALKALI METAL:   ·        Harder than alkali metals

 

 

 

 

               

ABUNDANCE OF ELEMENT:

    The percentage of element found on EARTH crust.

ALKALI  METAL :   SL.NO            ELEMENT   ABUNDANCE IN EARTH CRUST (%)   MINERAL SOURCES   1.   LITHIUM   0.0018   SPODUMENE   2.   SODIUM   2.27   ROCK SALT   3.   POTASSIUM   1.84   SYLVITE   4.   RUBIDIUM   0.0078   No convenient  sources ( Obtained as by product of lithium processing)   5.   CESIUM   0.00026   6.   FRANCIUM

ALKALINE EARTH METAL       SL.NO   ELEMENT   ABUNDANC IN EARTH CRUST (%)   MINERAL SOURCES   1.   BERYLLIUM     BERYL      2.   MAGNESIUM     CARNALLITE   3.   CALCIUM     FLUORAPATITE   4.   STRONTIUM     CELESTITE   5.   BARIUM     BARYTES   6.   RADIUM

 

 

 

1.4.1.a ELECTRONIC CONFIGURATION:

 

The electronic configuration of an atom is the representation of the arrangement of the electrons distributed among the orbital shell and subshell.

ALKALI  METAL :            v The general electronic configuration  of this group is                                                     Ns1     Element Electron Distrib -ution Electronic  configuration Short cut Representa -tion   Li   3   1s2 2s1   2He[2s1]   Na   11   1s2 2s22p63s1   10Ne[3s1]   K   19   1s2 2s22p63s3p64s1   18Ar[4s1]   Rb   37   1s22s22p63s3p63d104s2 4p65s1     36Kr[5s1]   Cs   55   1s22s22p63s3p63d104s2 4p64d105s25p6    6s1     54Xe[6s1]   Fr   87   1s22s22p63s3p63d104s24p6 4d105s25p65d106s26p67s1       86Rn[7s1]

ALKALINE EARTH METAL     v The general electronic configuration  of this group is                             Ns2.     Element Electron Distrib -ution Electronic configuration Short cut Representa -tion   Be   4   1s2 2s2   2He[2s2]   Mg   12   1s2 2s22p63s2   10Ne[3s2]   Ca   20   1s2 2s22p63s3p64s2   18Ar[4s2]   Sr   38   1s22s22p63s3p63d104s2 4p65s2     36Kr[5s2]   Ba   56   1s22s22p63s3p63d104s2 4p64d105s2    5p66s2     54Xe[6s2]   Ra   88   1s22s22p63s3p63d104s2 4p64d105s25p65d106s2 6p67s2     86Rn[7s2]

1.4.1.b .ATOMIC RADIUS / METALIC RADIUS :  

                      The atomic radius is defined as one-half the distance between the nuclei of the identical atoms that are bonded together.

Ø The distance from the centre of an atom’s nucleus to it’s outermost electron.

Ø Each row on the periodic table adds a “new shell” or “ energy level to the atom”

Ø Atomic size is determined by how closely an atom lies to a neighboring atom.

As we move down the group ,the atomic radius increases because the electron enters into new shell.

ALKALI  METAL :   Element   No.of electrons   Size of atomic radius          (A0)   Li   3   1.52   Na   11     1.86   K   19   2.27   Rb   37   2.48   Cs   55   2.65   Fr   87

ALKALINE EARTH METAL   Element   No.of electrons   Size of atomic radius          (A0)   Be   4   1.12   Mg   12     1.60   Ca   20   1.97   Sr   38   2.15   Ba   56   2.22   Ra     88

1.4.1.c. IONIC RADIUS:

v The ionic radii correspond to the radii of ions in ionic crystal.

v The radius of an atom forming an ionic bond or ion. Element’s share  the distance between their neighbouring ions in an ionic solid.

§  Cation are smaller then their parent ion

§  Anions are larger their parent’s ion.

v When an atom loss electron, they always become smaller.

v  When an atom gain an electron ,they always become bigger .

ALKALI  METAL :       Element   Size of ionic radius          (A0)   Li   0.76   Na   1.02   K   1.38   Rb   1.52   Cs   1.67   Fr

ALKALINE EARTH METAL       Element   Size of ionic radius          (A0)   Be   0.27(0.31)   Mg   0.72   Ca   1.00   Sr   1.18   Ba   1.35   Ra

 

NOTES: *        The atomic and ionic radii of alkaline earth metals are smaller than the corresponding members of the alkali metals. *        This is due to the fact of group 2 element having a higher nuclear charge that allows the electrons to be attracted more strongly toward the nucleus

1.4.1.d. IONISATION ENTHALPY:

v  Ionization enthalpy of an element can be defined as the amount of energy required to remove an electron from an isolated gaseous atom in its gaseous state

v  Ionization enthalpy depends on the following factors:

•   Penetration effect
• Shielding effect
• Electronic configuration
• Atomic size
• Nuclear charge

v  The Ionization Enthalpy is a quantitative measure of an element's tendency to lose electrons

ALKALI  METAL :               *       The ionization enthalpies of the alkali metals are considerably low and decrease down the group from Li to Cs.        * *         This is because the effect of increasing size outweighs the increasing nuclear charge, and the outermost electron is very well screened from the nuclear charge.           *    The second ionisation enthalpies of alkali  metal are very high     Element   First Ionisation [KJ mol-1] Second Ionisation [KJ mol-1]   Li   520     Na   496     K   419     Rb   403     Cs   376     Fr   -375

ALKALINE EARTH METAL            *   The alkaline earth metals have low ionization enthalpies due to fairly large size of the atoms.         * The atomic size increases down the group, their ionization enthalpy decreases        * The first ionisation enthalpies of the alkaline earth metals are higher than those of the corresponding Group 1 metals        * The second ionisation enthalpies of the alkaline earth metals are smaller than those of   corresponding alkali metals       Element   First Ionisation [KJ mol-1] Second Ionisation [KJ mol-1]   Be   899   1757   Mg   737   1450   Ca   590   1145   Sr   549   1064   Ba   503   965   Ra   509   979

1.4.1.e HYDRATION ENTHALPY

v  The enthalpy of hydration is described as the amount of energy released on dilution of one mole of gaseous ions.

v  It can be considered as enthalpy of solvation with solvent being water

v  It is also known as a hydration energy.

v  It’s values are negative.

v  The ionisation energy decrease down the group.

v  The hydration enthalpies decreases with increasing ionic sizes.

ALKALI  METAL :   *    Hydration enthalpy is the energy released when new bonds are formed between ions and water molecules.    *     Li+ > Na+  > K+  > Rb+  > Cs+   Element Hydration Energy [KJ mol-1]   Li   -506   Na   -406   K   -330   Rb   -310   Cs   -276   Fr

ALKALINE EARTH METAL This group are more extensively hydrated than those of alkali meatal. *       Because the ions of this group is larger then the group 1 *       Be2+ > Mg2+  > Ca2+  > Sr2+  > Ba2+   Element Hydration Energy [KJ mol-1]   Be   -2494   Mg   -1921   Ca   -1577   Sr   -1443   Ba   -1305   Ra

1.4.1.f  ELECTRONEGATIVITY:

v  The tendency of an atom in a molecule to attract the shared pair of electron toward itself is known as electronegativity.

v  It is a dimensional property because I is only a tendency

v  It is basically indicates the net result of the tendency of atoms in different to attract the bond-forming electron pairs.

ALKALI  METAL :   *        Cesium is the least electronegativity element     Element   Electronegativity value        [Pauling scale]   Li   1.0   Na   0.9   K   0.8   Rb   0.8   Cs   0.7   Fr

ALKALINE EARTH METAL         Element   Electronegativity Value        [Pauling scale]   Be   1.6   Mg   1.2   Ca   1.0   Sr   1.0   Ba   0.9   Ra

1.4.1.g. MELTING POINT:

ALKALI  METAL :   Element   Melting Point   Li   180.5o C   Na   97.7o C   K   63.4o C   Rb   39.5O C   Cs   28.4o C   Fr   27.0o C

ALKALINE EARTH METAL     Element   Melting Point   Be   1278O C   Mg   650O C   Ca   839O C   Sr   764O C   Ba   725O C   Ra   700O C

1.4.1.h. REACTIVITY

                     The reactivity of the group metal increase down the group.

Because the outer electron gets further from the Nucleus and Become easier to remove.

     

ALKALI  METAL :             * Highly reactivity

ALKALINE EARTH METAL         *     Less reactivity

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