Standard 10 Chapter Periodic Table

Gurudatta K Wagh

Dobereiner's Triads

Triads Groups of three elements which showed similar properties

Atomic mass of the middle element is approximately the mean of the atomic masses of other two elements

Element Atomic massLi 6.9Na 23K 39

Standard 10 Chapter Periodic Table

In the triad of Li, Na and K the atomic mass of Na (23) is the mean of the atomic masses of Li and K6.9 + 39 = 45.9 ÷ 2 = 22.95

Johann Wolfgang Dobereiner

Element Atomic massLi 6.9Na 23K 39Ca 40.1Sr 87.6Ba 137.3Cl 35.5Br 79.9I 126.9S 32Se 79Te 128

Features

Only a few triads could be identified

System of triads could not continue

Newland’s OctavesFifty-six elements were discoveredNewlands arranged them in the increasing order of their atomic massesEvery eighth element had properties similar to the firstCompared them with the octaves in music

John Alexander Reina Newlands

Seven musical notesIndiansa, re, ga, ma, pa, da, niWesterndo, re, mi, fa, so, la, ti

Features

Out of the 56 elements, elements up to Ca could be arranged

After Ca every eighth element did not possess properties similar to the first

To fit the existing elements two elements were placed in the same position which differed in their properties

Inert (noble) gases were not included because they were not discovered

Dmitri Ivanovich Mendeleev

Mendeleev’s Periodic Table

Examined the relationship between the atomic masses of elements and their physical and chemical properties

Chemical properties Concentrated on the compounds formed by the elements with oxygen and hydrogen as they were very reactive

Believed that atomic mass was the most fundamental property in classifying the elements

Arranged elements in the increasing order of their atomic masses in horizontal rows till he came actoss an element which had properties similar to the first

He placed this element below the first element and thus started the second row of elements

Created the first periodic table containing 63 elements known

Mendeleev’s Periodic Table The tabular arrangement of the elements based on the periodic law

Mendeleev’s Periodic LawThe physical and chemical properties of elements are a periodic function of their atomic masses

Features

Periods Horizontal rows, numbered 1 to 7Properties of elements in a period show regular gradation from left to right

GroupsVertical columns, numbered I to VIII. I to VII are further divided into A and B subgroups

Demerits

H resembles alkali metals and halogens. No fixed position could be given to H

Isotopes of same elements have different atomic masses. Each of them should be given a different position. As isotopes are chemically similar, they were given same position

Co with higher atomic mass (58.93) is placed before Ni (58.71)

Mn is placed with halogens which totally differ in the properties

Merits

Successful classification of all known elementsSome vacant/ blank spaces were left for elements yet to be discovered

Mendeleev predicted properties of these elements even before they were discovered

Later they were found to be correct

Noble gases were discovered later and placed in the table without disturbing the positions of other elements

Modern Periodic Table

Atomic number is the most fundamental property of an element and not its atomic mass – Henry MoseleyHenry

Gwyn Jeffreys Moseley

Atomic number (Z) = number of protons in the nucleus of the atom

Also represents number of electrons in the outer shell

Mendeleev’s Periodic Law was modified into Modern Periodic Law

The chemical and physical properties of elements are a periodic function of their atomic numbers

Modern Periodic Table = Long Form of Modern Periodic Table

Not much different from Mendeleev’s Periodic Table

Discovery and Assignment of Elements with Atomic Numbers 113, 115, 117 and 118

IUPAC announces the verification of the discoveries of four new chemical elements: The 7th period of the periodic table of elements is complete.Update 21 Jan 2016: Technical Reports available

The fourth IUPAC/IUPAP Joint Working Party (JWP) on the priority of claims to the discovery of new elements has reviewed the relevant literature for elements 113, 115, 117, and 118 and has determined that the claims for discovery of these elements have been fulfilled, in accordance with the criteria for the discovery of elements of the IUPAP/IUPAC Transfermium Working Group (TWG) 1991 discovery criteria. These elements complete the 7th row of the periodic table of the elements, and the discoverers from Japan, Russia and the USA will now be invited to suggest permanent names and symbols. The new elements and assigned priorities of discovery are as follows:Element 113 (temporary working name and symbol: ununtrium, Uut)Elements 115, 117, and 118 (temporary working names and symbols: ununpentium, Uup; ununseptium, Uus; and ununoctium, Uuo)http://www.iupac.org/news/news-detail/article/discovery-and-assignment-of-elements-with-atomic-numbers-113-115-117-and-118.html

Position of elements in the Modern Periodic Table

Periods (number of shells)

Horizontal rows, Seven, numbered 1-7

Elements in the same period have same number of shells which is equal to the period number. E.g. Period 7 has 7 Shells

In each period a new shell starts filling up

Period no.

Size Elements

1 shortest 22 short 83 short 84 long 185 long 186 longest 327 incomplete see box*IUPAC announces the verification of the discoveries of four new chemical elements: The 7th period of the periodic table of elements is complete.Update 21 Jan 2016: Technical Reports availablehttp://www.iupac.org/news/news-detail/article/discovery-and-assignment-of-elements-with-atomic-numbers-113-115-117-and-118.html

*Temporary working names and symbols113 ununtrium, Uut115 ununpentium, Uup117 ununseptium, Uus 118 ununoctium, Uuo

Groups (number of valence electrons)

Vertical columns, Eighteen, numbered 1-18

Elements in the same group have •same number of valence electrons/ same outer electronic configuration, •show same chemical properties

Group 1, alkali metalsGroup 2, alkaline earth metalsGroup 17, halogensGroup 18, inert/ noble gases

Metals – left hand side

Non-metals – right hand side

Normal elements – Groups 1, 2 and Groups 13-17. One outermost shell incomplete

Transition elements – Groups 3-12. Two outermost shells incomplete

Inert gases – Outermost shell contains 8 electrons

Group no. 1 2 3-4-5-6-7-8-9-10-11-12

13-14-15-16

17 18

Type Alkali metals

Alkaline earth metals

Transition elements

Non-metals, metalloids, metals

Halogens Inert or noble gases

Normal elements Normal elements

Inner transition – at the bottom, contain two series, viz. lanthanides, actinides

Lanthanides (Ce – Lu) – 14 elements, atomic numbers 58-71. Placed along with La (57), Group 3, Period 6. Close resemblance in properties to La

Actinides (Th – Lr) – 14 elements, atomic numbers 90-103. Placed along with Ac (89), Group 3, Period 7. Close resemblance in properties to Ac

Group 3Period 6 Lanthanides 14 elementsPeriod 7 Actinides 14 elements

Classification of elements as per electronic configuration

Four blocks s, p, d, f

s-block Metals, Groups 1, 2. 1 or 2 electrons in outermost shell, normal elements

p-block Metals, non-metals, metalloids, Groups 13-18. 3-8 electrons in outermost shell, normal elements except Group 18

d-block Transition elements/ metals, Groups 3-12. Two outermost shells incomplete

f-block Inner transition elements/ metals, at the bottom, lanthanides, actinides

Group/s 1-2 3-12 13-18 3Block s

MetalsdTransition elements/ metals

pMetals,Non-metals,metalloids

fInner transition elements/ metalsLanthanides (Period 6)Actinides (Period 7)

Electrons in outermost shell

1, 2 2 outermost shells incomplete

3-8 2 outermost shells incomplete

Merits

Modern Periodic Table (atomic number) versus Mendeleev’s Periodic Table (atomic mass)

All isotopes of the same elements have different masses but same atomic number and occupy the same position

Anomaly regarding Co (27) and Ni (28) disappears

Classification of elements into blocks based on their electronic configuration

Periodic properties

Properties show gradual variation in a group and in a period

Properties repeat after a certain interval of atomic number

ValencyNumber of valence electrons in the outermost shell

In a group all the elements have the same valency

Increases from 1 to 4 for the periods 2, 3 and decreases from 4 to 0 left to right

Atomic size

Determined using atomic radius

Atomic radius is the distance between the centre of atom and the outermost shell

Atomic radius decreases from left to right in a period because electrons are added to same shell and experience greater pull from the nucleus

Atomic radius increases from top to bottom in a group because new shells are added, thereby pushing outermost electrons farther from the nucleus

Atomic radius

Period

Atomic radiusdecreases from left to right

O o o

electrons are added to the same shell and experience greater pull from the nucleus

Group O

OO

Atomic radius increases from top to bottom new shells are added, thereby pushing outermost electrons farther from the nucleus

Metallic and non-metallic properties

Metals – tendency to lose electrons, electropositive

Non-metals – tendency to accept/ share electrons, electronegative

Because atomic size decreases and electrons are not easily released•Metallic character – decreases left to right in a period•Non-metallic character – increases left to right in a period

In the group, on the right side, lower members are non-metals and higher members are metals

Because atomic size increases and valence electrons can be easily removed•In a group, metallic character increases and non-metallic character decreases from top to bottom•Group 14 First element is C, non-metal, next two Si and Ge are metalloids, Sn and Pb are metals

A zig-zag line separates metals from non-metals

Borderline elements B, Si, Ge, As, Te, Po show intermediate properties – metalloids/ semi-metals

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