PERIODICPERIODIC TABLE TABLE

OF OF ELEMENTSELEMENTS

• The Periodic Table of elements is a The Periodic Table of elements is a form of classifying elements form of classifying elements systematically by placing elements systematically by placing elements with similar features in the same with similar features in the same group.group.

• The elements are arranged in the PT The elements are arranged in the PT in in ascendingascending order of their order of their proton proton numbernumber..

Historical Development of the Periodic Historical Development of the Periodic TableTableAntoine Lavoisier (1743-1794)Antoine Lavoisier (1743-1794)

• He was the first person to attempt to He was the first person to attempt to classify elements in the form of a classify elements in the form of a table.table.

• He classifed all elements into 4 He classifed all elements into 4 groups.groups.

• This classification failed as many This classification failed as many elements showing different chemical elements showing different chemical properties were classified together.properties were classified together.

J. W. Dobereiner (1780-1849)J. W. Dobereiner (1780-1849)• He introduced the He introduced the Triad Law Triad Law where where

he classified the elements with he classified the elements with similar properties in the same group.similar properties in the same group.

• Each group comprised only 3 Each group comprised only 3 elements, thus the name triad.elements, thus the name triad.

• The relative atomic mass of the The relative atomic mass of the second element in each triad was second element in each triad was equal to or almost equal to the equal to or almost equal to the average relative atomic mass of the average relative atomic mass of the other 2 elements.other 2 elements.

• This law failed too because it was This law failed too because it was limited to some elements only.limited to some elements only.

John Newlands (1838-1898)John Newlands (1838-1898)

• He proposed the Octave Law, which He proposed the Octave Law, which classified elements according to classified elements according to increasing relative atomic mass.increasing relative atomic mass.

• He grouped the elements under He grouped the elements under horizontal groups containing 7 horizontal groups containing 7 elements. The chemical and physical elements. The chemical and physical properties of each element were properties of each element were similar to the eight elements.similar to the eight elements.

• This law could be applied to the first This law could be applied to the first 17 elements only, thus it failed too.17 elements only, thus it failed too.

Lothar Meyer(1830-1895)Lothar Meyer(1830-1895)

• He successfully showed that the He successfully showed that the properties of elements varied properties of elements varied periodically by plotting the graph of periodically by plotting the graph of atomic volume against the atomic atomic volume against the atomic mass of each element.mass of each element.

• He found that elements occupying He found that elements occupying corresponding positions on the graph corresponding positions on the graph showed similar chemical properties. showed similar chemical properties.

Dmitri Mendeleev (1834-1907)Dmitri Mendeleev (1834-1907)

• He arranged according to increasing He arranged according to increasing atomic numbers in horizontal groups atomic numbers in horizontal groups called periods.called periods.

• According to his According to his Periodic LawPeriodic Law, the , the properties of elements varied properties of elements varied periodically. Elements with similar periodically. Elements with similar chemical properties were placed in chemical properties were placed in vertical rows called groups.vertical rows called groups.

• Mendeleev was more successful than Mendeleev was more successful than Newlands because:Newlands because:

a) he realised several elements were still a) he realised several elements were still undiscovered and so left empty spaces for undiscovered and so left empty spaces for them.them.

b) Elements like iron, cobalt and nickel b) Elements like iron, cobalt and nickel which had completely different properties which had completely different properties from the other elements were placed in a from the other elements were placed in a separate group.separate group.

• Mendeleev was able to predict the Mendeleev was able to predict the properties of the undiscovered elements, properties of the undiscovered elements, such as germanium which was only such as germanium which was only discovered years later. He also predicted discovered years later. He also predicted Iodine, Nickel, Cobalt and Tellurium.Iodine, Nickel, Cobalt and Tellurium.

Henry Moseley(1887-1915)Henry Moseley(1887-1915)

• He discovered the proton number of He discovered the proton number of elements by investigating the frequency of elements by investigating the frequency of X-rays produced by each element.X-rays produced by each element.

• He proposed that it was the proton number He proposed that it was the proton number that determined the position of elements in that determined the position of elements in the PT.the PT.

• He arranged the elements according to He arranged the elements according to ascending proton numbers.ascending proton numbers.

• Moseley also proved that Mendeleev’s Moseley also proved that Mendeleev’s prediction were correct especially regarding prediction were correct especially regarding the position of Nickel, Cobalt, Iodine and the position of Nickel, Cobalt, Iodine and Tellurium in the table.Tellurium in the table.

• Mosely’s contribution formed the base for Mosely’s contribution formed the base for the Modern Periodic Table.the Modern Periodic Table.

MODERN PERIODIC TABLEMODERN PERIODIC TABLE• This is arranged according to ascending This is arranged according to ascending

proton numbers of the elements.proton numbers of the elements.• There are 18 groups called Groups, which There are 18 groups called Groups, which

are named Group 1,2, 3…..18.are named Group 1,2, 3…..18.• Elements exhibiting similar chemical Elements exhibiting similar chemical

properties are placed in the same group.. properties are placed in the same group.. They physical properties change gradually They physical properties change gradually as we go down the group.as we go down the group.

• There are 7 horizontal rows called Periodic, There are 7 horizontal rows called Periodic, which are named Period 1, 2,3….7. The which are named Period 1, 2,3….7. The elements of each period are placed elements of each period are placed according to ascending proton number.saccording to ascending proton number.s

• Period 1 has only 2 elements, Periodic 2 and Period 1 has only 2 elements, Periodic 2 and 3 contains 8 elements, Period 4 and 5 have 3 contains 8 elements, Period 4 and 5 have 18 elements and are shown seperately as 18 elements and are shown seperately as the the LantanideLantanide and and Actinide Series.Actinide Series.

• Period 1, 2 and 3 are called short Periods. Period 1, 2 and 3 are called short Periods. Period 4 and 5 are called long periods.Period 4 and 5 are called long periods.

• Some of the Groups have special name:Some of the Groups have special name:

Eg: Group 1-Alkali metalsEg: Group 1-Alkali metals

• The elements in Groups 1, 2 and 13 and the The elements in Groups 1, 2 and 13 and the transition groups are metals, while elements transition groups are metals, while elements in Group 15-18 are non metals.Group 14 has in Group 15-18 are non metals.Group 14 has 2 non metals namely carbon and silicon.2 non metals namely carbon and silicon.

Electron ArrangementElectron Arrangement• The number of electrons in a neutral The number of electrons in a neutral

atom is equivalent to its number of atom is equivalent to its number of proton.proton.

• The electrons are arranged in The electrons are arranged in shells shells around the nucleus.around the nucleus.

• The maximum number of electrons The maximum number of electrons which can occupy each shell :which can occupy each shell :

1-2 electrons1-2 electrons

2-8 electrons2-8 electrons

3- 8 or 18 electrons3- 8 or 18 electrons

4-46 electrons4-46 electrons

All elements in a groupAll elements in a group

• Have the same valence electronsHave the same valence electrons

• Have the same chemical propertiesHave the same chemical properties

• Exhibit physical properties which Exhibit physical properties which change gradually down the group.change gradually down the group.

By knowing the By knowing the proton numberproton number of of an element, we can determine the an element, we can determine the group and Period it is placed in.group and Period it is placed in.

• An element W has a proton number of An element W has a proton number of 15. What group and Period does it 15. What group and Period does it occupy in the PT of elements?occupy in the PT of elements?

Number of protons= number of Number of protons= number of electrons=15electrons=15

The electron configuration= 2.8.5The electron configuration= 2.8.5

Group????Group????

Period????Period????

Group 18Group 18Elements:Elements:• Helium (He)Helium (He)• Neon (Ne)Neon (Ne)• Krypton (Kr)Krypton (Kr)• Xenon (Xe)Xenon (Xe)• Radon (Rn)Radon (Rn)

• They are called They are called noble or inert noble or inert gases. gases. They are single atoms and so They are single atoms and so are are monoatomicmonoatomic gases. gases.

Physical PropertiesPhysical Properties• The atomic size of the elements increase as The atomic size of the elements increase as

going down the group.This is because an going down the group.This is because an additional shell is added on each of the additional shell is added on each of the element.element.

• All noble gases cannot dissolve in water and All noble gases cannot dissolve in water and cannot conduct electricity and heat.cannot conduct electricity and heat.

• The m.p and b.p increase down the group as The m.p and b.p increase down the group as the atomic size or radius increases. The Van the atomic size or radius increases. The Van der Waals forces become stronger and more der Waals forces become stronger and more heat energy is needed to overcome these heat energy is needed to overcome these forces.forces.

• Density of elements increase as going down Density of elements increase as going down the group.This is because of the proton the group.This is because of the proton number increase when going down the group. number increase when going down the group. This causes an increase in atomic size.This causes an increase in atomic size.

Stability of Noble GasesStability of Noble Gases• Noble gases are not chemically reactive Noble gases are not chemically reactive

because they exist as monoatomic gases because they exist as monoatomic gases which cannot combine ionically or covalently which cannot combine ionically or covalently with any other element.with any other element.

• This is because their outermost shells are This is because their outermost shells are completely filled. He has the duplet (2 completely filled. He has the duplet (2 electrons) while the others have the octet( 8 electrons) while the others have the octet( 8 electrons) arrangement.electrons) arrangement.

• As their outermost shells are complete, As their outermost shells are complete, these atoms cannot accept, donate or share these atoms cannot accept, donate or share electrons with other elements.Thus, they are electrons with other elements.Thus, they are chemically not reactive or known as inert.chemically not reactive or known as inert.

Uses of Group 18 elementsUses of Group 18 elements• Helium- to fill air ships and weather Helium- to fill air ships and weather

ballons.ballons.

• Neon-to light up billboards on hotels, Neon-to light up billboards on hotels, building and airport runways.building and airport runways.

• Argon-used in filament bulb to Argon-used in filament bulb to prevent the burning of the tungsten prevent the burning of the tungsten filament.filament.

• Krypton- to fill high- speed flash bulb Krypton- to fill high- speed flash bulb in photographs.in photographs.

Group 1 elementsGroup 1 elements• Elements:Elements:

Lithium (Li)Lithium (Li)

Sodium (Na)Sodium (Na)

Potassium (K)Potassium (K)

Rubidium (Rb)Rubidium (Rb)

Caesium (Cs)Caesium (Cs)

Fransium (Fr)Fransium (Fr)

• Are known as Are known as alkali metalsalkali metals..

Pyhsical PropertiesPyhsical Properties• All group 1 elements are solid metal All group 1 elements are solid metal

which soft and shiny.which soft and shiny.

• They can conduct electricity and They can conduct electricity and heat.heat.

• They have high m.p and b.p.They have high m.p and b.p.

Changes in physical Changes in physical property down the property down the groupgroup

Brief explanationBrief explanation

Atomic radius or atomic size Atomic radius or atomic size of element increasesof element increases

Number of atomic shells in Number of atomic shells in increasesincreases

Melting and boiling point Melting and boiling point decreasedecrease

Atomic size increases causing Atomic size increases causing the metal bond between the metal bond between atoms to become weaker.atoms to become weaker.

Density increasesDensity increases Increase in atomic mass more Increase in atomic mass more than the increase in atomic than the increase in atomic radiusradius

Electropositivity increasesElectropositivity increases Tendency to donate electrons Tendency to donate electrons to form positive ions increasesto form positive ions increases

Chemical properties of Group 1 Chemical properties of Group 1 elementselements• All atoms of alkali metals have one All atoms of alkali metals have one

valence electrons which is one electron at valence electrons which is one electron at the outermost shell. They donate this 1 the outermost shell. They donate this 1 electron to attain gas noble stability. A electron to attain gas noble stability. A cation (positive ion) +1 is formed.cation (positive ion) +1 is formed.

• Reactivity of alkali metals increases when Reactivity of alkali metals increases when going down the group.going down the group.

• As atomic radius increases, the distance As atomic radius increases, the distance between valence electrons and nucleus between valence electrons and nucleus increases. There are weak force attraction increases. There are weak force attraction between nucleus and valence electrons.It between nucleus and valence electrons.It is easier to release the valence electron as is easier to release the valence electron as the atomic size inreases.the atomic size inreases.

A. Reaction of group 1 with waterA. Reaction of group 1 with water

• All group 1 elements reacts with All group 1 elements reacts with water.water.

• 2M + 2H2M + 2H₂O → 2MOH + H₂₂O → 2MOH + H₂

• Example: Example: 2Li + 2H2Li + 2H₂O → 2LiOH + ₂O → 2LiOH + H₂H₂

• Results????Results????

• Li-moves slowly on water surface. Li-moves slowly on water surface. Burns with red flame.Burns with red flame.

• Sodium- moves quickly on water Sodium- moves quickly on water surface. Burns with bright yellow surface. Burns with bright yellow flame.flame.

• Potassium- moves vigorously on Potassium- moves vigorously on water surface.Emits a brilliant purple water surface.Emits a brilliant purple flame.flame.

B. Reaction Group 1 with OxygenB. Reaction Group 1 with Oxygen

• 4M(s) + O4M(s) + O₂ 2M₂ 2M22O(s)O(s)

Eg: Eg: 4Li(s) + O4Li(s) + O₂ 2Li₂ 2Li22O(s)O(s)

C. Reaction Group 1 with ChlorineC. Reaction Group 1 with Chlorine• 2M(s) + Cl2M(s) + Cl22 2MCl(s) 2MCl(s)

Eg: 2Na(s) + ClEg: 2Na(s) + Cl22 2NaCl(s)2NaCl(s)