basic chemistry

Trends in physical properties of elements in period 3 – Digital Kemistry

Trend in Physical properties of Period 3 elements:

Electronic configuration:

The 3rd shell starts from sodium and completes at argon.

11Na        →           1s2, 2s2, 2p6, 3s1                             = [Ne], 3s1

12Mg       →            1s2, 2s2, 2p6, 3s2                   = [Ne], 3s2

13Al         →           1s2, 2s2, 2p6, 3s2, 3p1                  = [Ne], 3s2, 3p1

14Si          →            1s2, 2s2, 2p6, 3s2, 3p2            = [Ne], 3s2, 3p2

15P           →           1s2, 2s2, 2p6, 3s2, 3p3            = [Ne], 3s2, 3p3

16S           →           1s2, 2s2, 2p6, 3s2, 3p4                  = [Ne], 3s2, 3p4

17Cl         →            1s2, 2s2, 2p6, 3s2, 3p5           = [Ne], 3s2, 3p5

18Ar         →            1s2, 2s2, 2p6, 3s2, 3p6            = [Ne], 3s2, 3p6

Trend in atomic radii:

Generally atomic radii decrease in a period from left to right across the period due to increasing nuclear charge.

For Na, Mg and Al metallic radii are considered. For Si, P, S, and Cl covalent radii are considered while for Argon van der waal radius is taken into consideration. Metallic radii and covalent radii are comparable while van der waal is not comparable to them. Van der waal radius is bigger than metallic and covalent radius.

 Ionization energy:

The energy required to remove the most loosely bound electron from an isolated atom (gaseous atom) or gaseous ion to make cation is called Ionization Potential or Ionization Energy.”

Ionization energy is an endothermic process in which energy is absorbed so sign for this energy is +ve. This energy is required to overcome the force of attraction of nucleus on the electron. After removal of first electron hold of nucleus on remaining electrons increases so Second I.P is greater than First I.P because more energy is required to remove the second electron and so on.

                                e.g (i)      Na           →            Na+        +      e-          (I.E)1 = +496 kJ/mol

                                                (2,8,1)                    (2,8)

                                e.g (ii)     Mg          →            Mg+        +       e-           (I.E)1 = +738 kJ/mol

                                                (2,8,2)                    (2,8,1)

                                                Mg+        →            Mg2+     +         e-            (I.E)2 = +1451 kJ/mol

                                                (2,8,1)                    (2,8)

By I.E values we can determine number of valence electrons and valency of an atom. e.g.

                1st I.E                      2nd I.E                     3rd I.E                     4th I.E

Li            520                         7,298                      11,815                   –

Be           899                         1,757                      14,848                   21,006

In case of Li there is a sudden jump in value of its 2nd I.E which means this is electron of its inner shell so its valence shell has only one electron and thus its valency is one.

In case of Be there is a sudden jump in value of its 3rd  I.E which means this is electron of its inner shell so its valence shell has two electrons and thus its valency is two.

Factors affecting I.E or I.P:

(i)            Nuclear Charge:   With increase in nuclear charge, hold of nucleus increases on electrons so more energy will be required to remove electrons. Thus more is the nuclear charge more will be the I.E and vice versa.

(ii)           Atomic Size:         Smaller is the size of atom, more will be the hold of nucleus on electrons so more energy will be required to remove electrons. Thus smaller is the atomic size more will be the I.E and vice versa.

                                                                I.E α 1/r2

(iii)          Shielding Effect:  Greater the shielding effect of lower shells less will be the hold of nucleus on electrons of outer shell so low will be the I.E and vice versa.

(iv)          Penetration Effect:              Fraction of time which the electrons of outer orbitals spend near nucleus is called penetration effect. The order of this effect and thus I.E is

                                                                s > p > d > f

(v)           Electronic Configuration: Completely filled and half filled orbitals are more stable and thus their electrons are difficult to remove so their I.E is high. Thus elements of Groups 1A, IIA and VIIIA have extra ordinary high I.E.

Trend of 1st ionization energy in Periodic Table:

                Generally I.E increases in a period from left to right due to decreasing atomic size and increasing nuclear charge. But anomalies are observed at group IIA and VA they have extra ordinary high I.E. This is due to the reason that they have completely filled or half filled outer orbitals which are more stable and thus their electrons are difficult to remove so their I.E are high. Group II-A has outer completely filled s-orbital while group V-A has outer half filled p-orbital so they have extraordinary high ionization energies.

e.g. trend of Ionization Energy in 2nd and 3rd period is:

Groups                                 IA           IIA          IIIA        IVA        VA          VIA        VIIA       VIIIA

Elements of period II          Li            Be           B         C             N         O             F              Ne

Ionization Energy (kJ)        520         900         801       1086     1402      1314       1681      2081        

Elements of period III        Na           Mg          Al            Si             P              S              Cl            Ar

Ionization Energy (kJ)        496         738         578         786         1012       1000       1251       1521

                On other hand in a group I.E decrease from top to bottom due to increasing atomic size.

Electron Affinity:

The energy released or absorbed when an electron is added to a gaseous atom or gaseous ion is called electron affinity.”

e.g. (i)                                     Cl + e → Cl         ∆H E.A = -349 kJ/mol

e.g. (ii)                                    O + e → O           ∆H E.A(1) = -141 kJ/mol

                                                O + e → O2         ∆H E.A(2) = +844 kJ/mol

Trend of Electron Affinity:

Elements of period III        Na           Mg          Al            Si             P              S             Cl            Ar  Electron affinity                 -53          230         -50          -120        -74          -200        -349         35

Generally electron affinities increase across the period (from left to right). However group II-A elements due to their complete s-orbital have positive values for their first electron affinities. Similarly group VIII-A elements also have positive values for their first electron affinities due to complete p-orbital.

Second electron affinities are positive for all elements.

Electronegativity:

The tendency of an atom to attract shared pair of electrons is called electronegativity.”

Trend in electronegativity:

                Electronegativity increases across the period (from left to right) due to increasing nuclear charge and decreasing atomic size.

Elements of period III        Na           Mg          Al            Si             P              S              Cl            Ar

Electronegativity                 0.93        1.31        1.81        2.02         2.19        2.58        3.16         –

As Argon does not form covalent bonds hence it cannot be assigned electronegativity value.

Electrical Conductivity:

The ability of a substance to conduct electricity is called electrical conductivity.”

Metals possess free electrons (valence shell electrons) so they conduct electricity but non metal cannot conduct electricity as they do not possess free electrons. However carbon (graphite) has free p-electrons so it also conduct electricity.

Trend in electrical conductivity:

                Electrical conductivity increases from sodium to aluminum. Silicon is semi conductor. From Phosphorus to Argon are non metals and non conductors.

     Elements of period III        Na           Mg          Al            Si             P              S              Cl            Ar

      Electrical conductivity        0.26        0.42        1.00         0.10        0              0              0             0  

Melting and Boiling Points:

The temperature at which solid and liquid exist in equilibrium is called melting point.”

The temperature at which vapour pressure of liquid becomes equal to atmospheric or external pressure is called boiling point.”

Trend in Melting and Boiling Points:

The melting and boiling points increases across the period (from left to right) up to middle and then decreases.

Elements of period III        Na           Mg          Al            Si             P              S              Cl            Ar Melting Point (K)               371         922         933        1683       317          392         172          84

Boiling Point (K)                1156       1380       2740       2628       553          718         238          87

Also Read !!

Trends in the chemical properties of period 3 elements

Electron affinity trends

Ionization Energy Trends

Electronegativity – Definition, Periodic Trends ,Examples , Importance ,Electronegativity Difference

Ionic Bond

Covalent Bond

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