PERIODIC TABLEPERIODIC TABLE

PeriodicityPeriodicity

Recurrence of similar properties of elements at a Recurrence of similar properties of elements at a regular intervals is called periodicity.regular intervals is called periodicity.Some of the properties that show periodic Some of the properties that show periodic variation are:variation are:

i. atomic radius & ionic radiii. atomic radius & ionic radii ii. Melting & boiling pointsii. Melting & boiling points iii. Electrical conductivityiii. Electrical conductivity iv. Enthalpy of vapourisationiv. Enthalpy of vapourisation v. Electronegativityv. Electronegativity vi. Ionisation energyvi. Ionisation energy

Atomic radiiAtomic radii

Atom is a sphere. Associated with an atom, there are 3 Atom is a sphere. Associated with an atom, there are 3 radii to be considered:radii to be considered:

atomic radius- distance from the centre of its nucleus to atomic radius- distance from the centre of its nucleus to the edge of the atom. Bigger the atomic radius the bigger the edge of the atom. Bigger the atomic radius the bigger the atomthe atom

Covalent radius- half distance between the nuclei of two Covalent radius- half distance between the nuclei of two atoms bonded by a covalent bond in the same moleculeatoms bonded by a covalent bond in the same molecule

Van der waals radius- half the distance between the Van der waals radius- half the distance between the nuclei of the two atoms of adjacent molecules.nuclei of the two atoms of adjacent molecules.Atomic radius is influenced by two factors:-Atomic radius is influenced by two factors:-

Nuclear charge per atomNuclear charge per atom Electron shielding effectElectron shielding effect

Nuclear charge per atomNuclear charge per atom

An increase in nuclear charge per atom An increase in nuclear charge per atom increase the binding force on the valence increase the binding force on the valence electron by the nucleus. As such, the electron by the nucleus. As such, the atomic radius is decreased.atomic radius is decreased.

Effective nuclear charge= Effective nuclear charge=

no. proton – inner shell electronno. proton – inner shell electron

Example: Magnesium; 1sExample: Magnesium; 1s22,2s,2s22, 2p, 2p66, 3s, 3s22

* * 12-10= +212-10= +2

Electron shielding effectElectron shielding effect

The electron shielding effect on valence electron The electron shielding effect on valence electron of the X atom of electronic configuration 2.8.1 is of the X atom of electronic configuration 2.8.1 is stronger than Y atom of electronic configuration stronger than Y atom of electronic configuration 2.1.2.1.This is due to the fact that the X atom has 2 This is due to the fact that the X atom has 2 inner shells with 10 electrons which are able to inner shells with 10 electrons which are able to provide a stronger shield to its valence electrons provide a stronger shield to its valence electrons compared to the Y atom which has only one compared to the Y atom which has only one inner shell with 2 electrons.inner shell with 2 electrons.Note: the effect of the electron shielding is Note: the effect of the electron shielding is opposite to the nuclear chargeopposite to the nuclear charge

Variation of atomic radiusVariation of atomic radiusacross period 2 & 3 from left to rightacross period 2 & 3 from left to right

Nuclear per charge increases because the Nuclear per charge increases because the proton number increases.proton number increases.The electron shielding effect of the inner shells The electron shielding effect of the inner shells remain constant because the number of inner remain constant because the number of inner shells are the same. The electrons are added to shells are the same. The electrons are added to the outer shells of atoms and not to the inner the outer shells of atoms and not to the inner shells.shells.Nuclear attraction on the valence electron of Nuclear attraction on the valence electron of atom increases causing the electron cloud to be atom increases causing the electron cloud to be pulled closer to the nucleus. pulled closer to the nucleus. Thus the atomic radius decreases.Thus the atomic radius decreases.

Variation of atomic radiusVariation of atomic radiusfor transition elementsfor transition elements

For transition elements, from left to right, the For transition elements, from left to right, the atomic radii are almost constant with no atomic radii are almost constant with no significant changes. significant changes. Nuclear per charge increases because the Nuclear per charge increases because the proton number increases.proton number increases.The electron shielding effect increases because The electron shielding effect increases because the electrons are added to the inner d-orbital.the electrons are added to the inner d-orbital.The increase in electron shielding effects offsets The increase in electron shielding effects offsets the increase in the nuclear charge.the increase in the nuclear charge.Overall the atomic radius does not show a Overall the atomic radius does not show a significant change.significant change.

Variation of atomic radiusVariation of atomic radiusdown the groupsdown the groups

As we go down the group the electrons per atom As we go down the group the electrons per atom increases, hence the number of electron shells increases, hence the number of electron shells increases.increases.This increases the number of inner electron This increases the number of inner electron shells, thus increase the electron shielding shells, thus increase the electron shielding effect.effect.This offsets the increase in nuclear charge per This offsets the increase in nuclear charge per atom due to increase in the number of protons.atom due to increase in the number of protons.Consequently the nuclear attraction on the Consequently the nuclear attraction on the valence electron weakens.valence electron weakens.The valence electron tend to move outwards and The valence electron tend to move outwards and increase the atomic radii.increase the atomic radii.

Ionic radiiIonic radii

When an atom loses one or more electrons to form When an atom loses one or more electrons to form cations the positive charge exceed the negative charge. cations the positive charge exceed the negative charge. Thus the electrons become closer.Thus the electrons become closer.Cation are smaller in size compare to the atom which Cation are smaller in size compare to the atom which they are formed.they are formed.Size of atom Na= 186pm & size of NaSize of atom Na= 186pm & size of Na++=99pm=99pmWhen an atom gain one or more electron to form anions When an atom gain one or more electron to form anions the nuclear charge remain constant but negative charge the nuclear charge remain constant but negative charge exceed the positive charge. In this case repulsion occurs exceed the positive charge. In this case repulsion occurs and the size of the anions increases.and the size of the anions increases.

Size of ClSize of Cl22 =99pmm but size of Cl =99pmm but size of Cl- - - Cl- Cl-- =181pm =181pm

isoelectronicisoelectronic

Ion that have equal number of electron in Ion that have equal number of electron in identical configuration.identical configuration.Example: NaExample: Na++ = 1s = 1s22,2s,2s22,2p,2p66

MgMg2+2+ = 1s = 1s22,2s,2s22,2p,2p66

MgMg2+ 2+ is smaller than Nais smaller than Na++ because its nuclear because its nuclear charge is largercharge is largerFor isoelectronic cations, the more positive the For isoelectronic cations, the more positive the ionic charge the more smaller the ionic radii.ionic charge the more smaller the ionic radii.For isoelectronic anions, the more negative the For isoelectronic anions, the more negative the charge, the larger the ionic radii.charge, the larger the ionic radii.

Ionisation energyIonisation energyQuantity of energy absorb to remove an Quantity of energy absorb to remove an electron.electron.

The variation of ionisation energy across the The variation of ionisation energy across the period is analysed between:period is analysed between:

A. The periods 2 and 3A. The periods 2 and 3

B. For transition elements (block d- elements)B. For transition elements (block d- elements)

C. down the groupsC. down the groups

Ionisation energy across the Ionisation energy across the periods 2 and 3 from left to rightperiods 2 and 3 from left to right

Ionisation energy increases because:-Ionisation energy increases because:- The nuclear charge per atom increasesThe nuclear charge per atom increases The atomic radius decreasesThe atomic radius decreases the distance between the nucleus and the the distance between the nucleus and the

valence electron shortens. Hence the valence valence electron shortens. Hence the valence electrons are closer to the nucleus.electrons are closer to the nucleus.

The nuclear attraction on the valence electron The nuclear attraction on the valence electron increases.increases.

The difficulty of removing the valence electron The difficulty of removing the valence electron increases. Thus, Ionisation energy increases. increases. Thus, Ionisation energy increases.

EXCEPTION 1:EXCEPTION 1:

Across the period 2, the ionisation energy of beryllium Across the period 2, the ionisation energy of beryllium which is on left is higher than boron which is on the right.which is on left is higher than boron which is on the right.

Be: 1sBe: 1s22,2s,2s2 2 B: 1sB: 1s22,2s,2s22,2p,2p11

Therefore the ionisation energy of B involves the Therefore the ionisation energy of B involves the removal of one valence electron from the 2premoval of one valence electron from the 2p1 1 while Be while Be involves the removal of 2 electrons. Removing an involves the removal of 2 electrons. Removing an electron from 2pelectron from 2p11 is easier compared to the 2s is easier compared to the 2s22 configuration.configuration.

This is because the energy level of 2p is higher than 2s. This is because the energy level of 2p is higher than 2s. The 2sThe 2s22 is more stable because the s orbital is is more stable because the s orbital is completely filled and its more closer to the nucleus than completely filled and its more closer to the nucleus than 2p orbital. Hence the valence electron of the 2s orbital 2p orbital. Hence the valence electron of the 2s orbital are more strongly bounded to the nucleus. are more strongly bounded to the nucleus.

EXCEPTION 2:EXCEPTION 2:

Across the period 2, the ionisation energy of Across the period 2, the ionisation energy of nitrogen which is on left is higher than oxygen nitrogen which is on left is higher than oxygen which is on right.which is on right.

This is because electronic configuration of N is This is because electronic configuration of N is 1s1s22,2s,2s22,2p,2p33 while that of oxygen is 1s while that of oxygen is 1s22,2s,2s22,2p,2p44. . The ionisation energy involves the removal of The ionisation energy involves the removal of valence electron from the 2pvalence electron from the 2p4 4 while nitrogen from while nitrogen from 2p2p33. Removing the electron from 2p. Removing the electron from 2p4 4 is easier is easier than 2pthan 2p33 because the p orbital of 2p because the p orbital of 2p3 3 are half are half filled orbitals which are more stable compare to filled orbitals which are more stable compare to 2p2p4 4 which have incomplete p orbitals.which have incomplete p orbitals.

Ionisation energy down the groupIonisation energy down the groupAs we go down the group, the ionisation energy As we go down the group, the ionisation energy decreases.decreases.This is because: This is because:

The number of electron shells increasesThe number of electron shells increases Hence the distance of the valence electrons from the Hence the distance of the valence electrons from the

nucleus increase sequentiallynucleus increase sequentially The increase in the number of inner electron shells, The increase in the number of inner electron shells,

cause electron shielding effect on the valence electron cause electron shielding effect on the valence electron increases.increases.

This factors decreases the force of attraction of the This factors decreases the force of attraction of the nucleus on the valence electronnucleus on the valence electron

This offsets the increasing nuclear charge per atomThis offsets the increasing nuclear charge per atom Hence the valence electron is donates easily.Hence the valence electron is donates easily. Consequently the ionisation energy decreases.Consequently the ionisation energy decreases.

Ionisation energy for block d Ionisation energy for block d elements or transition elementselements or transition elements

Involves the 1Involves the 1stst and 2 and 2ndnd ionisation energy (removal of 1 ionisation energy (removal of 1stst and 2 and 2ndnd valence electron from the orbitals). Copper and chromium have valence electron from the orbitals). Copper and chromium have higher ionisation energy from other block d elements.higher ionisation energy from other block d elements.

Example: copper = [Ar] 3dExample: copper = [Ar] 3d10104s4s11

chromium=[Ar] 3dchromium=[Ar] 3d55 4s 4s11

The 1The 1stst ionisation energy of both these elements involve the removal ionisation energy of both these elements involve the removal of valence electrons from the 4s orbital. The 2of valence electrons from the 4s orbital. The 2ndnd ionisation energy of ionisation energy of these elements involve the removal of valence electron from 3d these elements involve the removal of valence electron from 3d orbitals while for other block d elements , it is from 4s orbital. orbitals while for other block d elements , it is from 4s orbital. Furthermore the 3d orbital for copper is completely filled and Furthermore the 3d orbital for copper is completely filled and chromium is half-filled creating a more stable configuration. Hence chromium is half-filled creating a more stable configuration. Hence the 2the 2ndnd ionisation energy for these two elements is more higher than ionisation energy for these two elements is more higher than the 1the 1stst ionisation energy. ionisation energy.

Electronaffinity, EElectronaffinity, EAA

EEA A is the measurement of the energy change when an atom gains an electron

F(g) + e- → F- (g) ; EEA A = -328kJ/mol= -328kJ/mol

This is an exothermic process where it This is an exothermic process where it releases energy and given in negative releases energy and given in negative quantity.quantity.

ElectronegativityElectronegativity

Electronegativity is a measure of attraction of atom for Electronegativity is a measure of attraction of atom for electrons in a covalent bond. electrons in a covalent bond. When the force of attraction of the nucleus increases on When the force of attraction of the nucleus increases on valence electron the electronegativity increases.valence electron the electronegativity increases.Across the period from left to right the electronegativity Across the period from left to right the electronegativity increases. This is because the decrease in atomic radius increases. This is because the decrease in atomic radius increase the force of attraction of the nucleus on valence increase the force of attraction of the nucleus on valence electron.electron.However, as we go down any group the electronegativity However, as we go down any group the electronegativity decreases due to increasing in atomic radius down the decreases due to increasing in atomic radius down the group, decrease the force of attraction of the nucleus on group, decrease the force of attraction of the nucleus on valence electron.valence electron.

Metallic propertiesMetallic properties

Across the period the metallic properties Across the period the metallic properties become non-metallic properties. become non-metallic properties. This is because the atomic radius This is because the atomic radius decreases, the force of attraction of decreases, the force of attraction of nucleus on the valence electron increases,nucleus on the valence electron increases,Difficulty to loose electrons (non-metallic)Difficulty to loose electrons (non-metallic)Li, Be, B, C, N, O, F, Ne.Li, Be, B, C, N, O, F, Ne.Li and Be show prominent metallic Li and Be show prominent metallic property with electrical conductivity.property with electrical conductivity.

Boiling & Melting PointBoiling & Melting PointDepends on the strength of the intermolecular forces or Depends on the strength of the intermolecular forces or bonds that must be weeken or destroyed before melting bonds that must be weeken or destroyed before melting and boiling occurs.and boiling occurs.Across the period 3 from Li to Ne, the melting point & Across the period 3 from Li to Ne, the melting point & boiling point increases until it peaks at C and then boiling point increases until it peaks at C and then decreases sharply to N. decreases sharply to N. From N to Ne, the melting points & boiling points are From N to Ne, the melting points & boiling points are about the same.about the same.Metallic bond strength increases from Li to B causing the Metallic bond strength increases from Li to B causing the increase in melting & boiling points.increase in melting & boiling points.C is macromolecule with three dimensional giant C is macromolecule with three dimensional giant structure held by strong covalent bonds. structure held by strong covalent bonds. N to Ne are simple molecules held by weak Van Der N to Ne are simple molecules held by weak Van Der Waals forces.Waals forces.

Acid & Base CharacteristicsAcid & Base Characteristics

Across the period elements Na, Mg, Al, Si, Across the period elements Na, Mg, Al, Si, P, Cl & Ar, change from Base to acidic P, Cl & Ar, change from Base to acidic characteristics.characteristics.

Acid-Base Nature Of Element Acid-Base Nature Of Element OxidesOxides

LiLi22O react with water to form hydroxide which O react with water to form hydroxide which

exhibit a base character.exhibit a base character.

LiLi22O + HO + H22O O → 2Li→ 2Li++ + 2OH + 2OH--

An anhydride base become base when water is An anhydride base become base when water is added to itadded to it

NaNa22O & MgO yield base solution in water.O & MgO yield base solution in water.

ClCl22O, SOO, SO22, P, P44OO1010 – acidic solution – acidic solution

SiOSiO22 doesn’t dissolve in water but dissolve slightly doesn’t dissolve in water but dissolve slightly

in base solution to produce sillicates and form an in base solution to produce sillicates and form an acidic oxide.acidic oxide.

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