Periodic Classification Of Elements Flashcards
In 1817, _______ a German chemist, suggested a method of grouping elements based on their relative atomic masses
Johann Wolfgang Dobereiner,
Dobereiner arranged the elements into groups containing three elements each. He called these groups as_____ ‘
triads’ (tri - three)
Dobereiner law
when the three elements in a triad are arranged in the ascending order of their atomic masses, the atomic mass of the middle element is nearly the same as average of atomic masses of other two elements
Dobereiner limitation
■Dobereiner could identify only three triads from the elements known at that time and all elements could not be classified in the form of triads.
The law was not applicable to elements having very low and very high atomic mass.
In 1866, ________ arranged 56 known elements in the increasing order of their atomic mass.
John Newlands
Newlands law of octaves
He observed that every eighth element had properties similar to those of the first element like the eighth note in an octave of music is similar to the first. This arrangement was known as law of octaves
Limitation of Newlands law of octaves
There are instances of two elements being fitted into the same slot, e.g. cobalt and nickel
Some elements, totally dissimilar in their properties, were fitted into the same group. (Arrangement of Co, Ni, Pd, Pt and Ir in the row of halogens)
The law of octaves was not valid for elements that had atomic masses higher than that of calcium.
Newlands’ table was restricted to only 56 elements and did not leave any room for new elements.
Discovery of inert gases (Neon. Argon….) at later stage made the 9th element similar to the first one. Eg: Neon between Fluorine and Sodium.
Find the pair of elements having similar properties by applying Newlands’ law of Octaves (Example: Mg & Ca):
Set I: F, Mg, C, O, B
Set II: Al, Si, S, Cl, Ca
F&Cl
C&Si
O& S
B&Al
In 1869, Russian chemist, _______ observed that the elements of similar properties repeat at regular intervals when the elements are arranged in the order of their atomic masses
Dmitri Mendeleev
Who proposed the law of periodicity
Dmitri mendeleev
the law of periodicity
the physical and chemical properties of elements are the periodic functions of their atomic masses”
Mendeleev arranged 56 elements known at that time according to his law of periodicity. This was best known as .
the short form of periodic table
Features of Mendeleev’s Periodic Table:
It has eight vertical columns called ‘groups’ and seven horizontal rows called ‘period’
Each group has two subgroups ‘A’ and ‘B’ All the elements appearing in a group were found to have similar properties.
For the first time, elements were comprehensively classified in such a way that elements of similar properties were placed in the same group.
It was noticed that certain elements could not be placed in their proper groups in this manner. The reason for this was wrongly determined atomic masses. Consequently those wrong atomic masses were corrected.
Eg: The atomic mass of beryllium was known to be 14. Mendeleev reassessed it as 9 and assigned beryllium a proper place.
Columns were left vacant for elements which were not known at that time and their properties also were predicted. This gave motivation to experiment in Chemistry
Limitation of mendeleev’s
Elements with large difference in properties were included in the same group. Eg: Hard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium (Na) and potassium (K).
No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), sodium (Na) and potassium (K).
The increasing order of atomic mass was not strictly followed throughout. Eg. Co & Ni, Te & I.
No place for isotopes in the periodic table
In 1913, the English Physicist ________ through his X-ray diffraction experiments, proved that the properties of elements depend on the atomic number and not on the atomic mass.
Henry Moseley
who prepared the modern periodic table by arranging elements in the increasing order of their atomic number.
Henry Moseley
This modern periodic table is the extension of the original Mendeleev’s periodic table and known as
long form of periodic table.
The physical and chemical properties of elements depend not only on the number of protons but also on _______ and their arrangements in atom
the number of electrons
the modern periodic law can be stated as follows:
The chemical and physical properties of elements are periodic functions of their atomic numbers”.
Based on the modern periodic law, the modern periodic table is derived.
Features of Modern Periodic Table
■All the elements are arranged in the increasing order of their atomic number.
The horizontal rows are called periods. There are seven periods in the periodic table.
The elements are placed in periods based on the number of shells in their atoms.
■Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
Based on the physical and chemical properties of elements, they are grouped into various families
The elements are placed in periods based on the _______ in their atoms.
number of shells
1st group
Alkali metal
Hydrogen lithium sodium potassium rubidium caesium francium
2 nd group
Alkaline earth metals
Beryllium magnesium calcium strontium barium radium
3 to 12 group
Transition element
13 group
Boron family
Boron
Aluminium gallium Indiumthallium neum
14 group
6 Carbon family
Carbon
silicon
germanium
tin
LEAD
Flerovium
15 group
6 Nitrogen family
Nitrogen
phosphorus
arsenic
antimony
bismuth
Moscovium
16 group
6 Oxygen family or chalcogen family
Oxygen
Sulphur
selenium
tellurium
polonium
Livermorium
17 group
6 Halogen family
Fluorine
Chlorine
Bromine
Iodine
Astatine
Tennessine
18 group
7 Noble gases are
Helium
Neon
Argon
Krypton
Xenon
Radon
Oganesson
Each shell consists of one or more subshells in which the electrons are distributed in certain manner.the subshell are
S,p,d,f
______ includes group 1 (alkali metals) and group 2 (alkaline earth metals) elements. They are also called as representative elements.
S block elements
In S block elements The elements of group 1 (except _____) are metals
hydrogen
Group 1 elements react with water to form solutions that change the colour of a vegetable dye from red to blue.
These solutions are said to be highly alkaline or basic. Hence they are called alkali metals.
The elements of group 2 are also metals. They combine with oxygen to form oxides, formerly called ‘earths’, and these oxides produce alkaline solutions when they are dissolved in water.
Hence, these elements are called alkaline earth metals.
The _____ is home to the biggest variety of elements and is the only block that contains all three types of elements: metals, nonmetals, and metalloids.
p-block
d-Block Elements are called
transition elements.
F-Block Elements are called
Inner transition elements.
______ behaves like alkali metals as well as halogens in its properties
Hydrogen
Why
Hydrogen can lose its only electron to form a hydrogen ion (H+) like alkali metals.
(ii) It can also gain one electron to form the hydride ion (H) like halogens.
(iii) Alkali metals are solids while hydrogen is a gas.
The elements Helium, Neon, Argon, Krypton, Xenon and Radon of group 18 in the periodic table are called as
Noble gases or Rare gases.
They (Helium, Neon, Argon, Krypton, Xenon and Radon) are monoatomic gases and do not react with other substances easily, due to completely filled subshells. Hence they are called as
inert gases
They(Helium, Neon, Argon, Krypton, Xenon and Radon) are found in very small quantities and hence they are called as
rare gases
P-Block non metals
: C, N O, P, S, Se, Halogen (F, Cl, Br and I) and inert gases (Heyo Rn).
Elements which have the properties of both metals and non-metals are called as . (.
metalloids
eg) Boron, Arsenic germanium silicon antimony tellurium polonium
During 3500 BC(BCE), people used an alloy named ‘
bronze (copper &tin)
____ are mixtures of two or more metals and are formed by mixing molten metals thoroughly.
Alloys
Rarely nonmetals are also mixed with metals to produce alloys.
the alloy brass is made from
copper and zinc.
When metal is alloyed with mercury, it is called
amalgam
If Dobereiner is related with law of triads, then Newlands is related with
a) Modern periodic law
b) Hund’s rule
C) law of octaves
d) Pauli’s Exclusion principle
law of octaves
Elements in the modern periodic table are arranged in _____groups and ____periods.
a) 7, 18
b) 18,7
c) 17, 8
18 &7
The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was
Atomic mass
Example for liquid metal is
Mercury
Metals can gain electrons
Flase
Metals tend to lose electrons and are electropositive in nature whereas non-metals tend to gain electrons and are electronegative
Alloys bear the characteristics of both metals and nonmetals.
Flase
An alloy is a mixture of metals or a mixture of a metal and another element.
Lanthanides and actinides are kept at the bottom of the periodic table
because they resemble each other but they do not resemble with any other group elements.
Statement: Elements in a group generally possess similar properties but elements along a period have different properties
Reason: The difference in electronic configuration makes the element differ in their chemical properties along a period.
a) Statement is true and reason explains the statement.
