Periodic Classification of Elements I Flashcards
what is lavioisier periodic table
Lavoisier classified the elements simply in metals and non metals.
Metals are the one which have the tendency of losing the electrons.
Non-metals are the one which have the tendency of gaining the electrons.
Drawbacks
-unsuitable for moreelemtns
-he didnt know whr to place metalloids
what is prout hypotheses
considered all the elements to be made up of hydrogen
Atomic weight of element = n × (Atomic weight of one hydrogen atom)
Atomic weight of H = 1
drawback: did not work for elements whose atomic masses where decimal
give examples of dobereiners triads
Cl35.5
Br-80
I-127
Ca Sr Ba
40 87.6 137
Li Na K
7 23 39
drawback of newland’s law of octaves
-> discovering of inert gases and oncliduig it into periodic table, the alkali metals had to be mvoed
what were the different components of lothar meyer
(i) He plotted a curve between atomic weight
(x-axis) and atomic volume(y-axis) of different elements.
(ii) The following observations can be made from the curve –
(a) Most electropositive elements i.e. alkali metals (Li, Na, K, Rb, Cs ) occupy the peak positions on the curve.(maxima)
(b) Less electropositive i.e. alkaline earth metal (Be, Mg, Ca, Sr, Ba) occupy the descending positions on the curve.(descending slopes)
(c) Metalloids (Si, Ge, As, Sb, Te, Po, At) and transition metals occupy bottom part of the curve.( minima)
(d) Most electronegative i.e. halogens (F, Cl, Br, I) occupy the ascending positions on the curve.(ascending curves)
Note : Elements having similar properties occupy similar positions on the curve.
what are chracaters of mendeleeev periodic table
(a) It was based on atomic weight.
(b) 63 elements were known, noble gases were not discovered.
(c) He was the first scientist to classify the elements in a systematic manner i.e. in horizontal rows and
in vertical columns.
what were the no of colums and no of rows in the mendeleev periodic tabl e
Horizontal rows were called periods/series and there were 7 periods in Mendeleev’s Periodic table.
(e) Vertical columns are called groups and there were 8 groups in Mendeleev’s Periodic table.
(f) Each group upto VII was divided into A & B subgroups.’A’ sub group element were called normal
elements and ‘B’ sub group elements were called transition elements.
(g) The VIII group was consisted of 9 elements in three rows (Transition metal group).
(h) The elements belonging to same group exhibit similar properties.
what were the merits of mendeleev periodic table
(i) it enabled more clearer and systematic study of elements
(ii) it led to the discovery of many new elements. Mendeeleev left many spaces in his periodic.
(iii) It led to the correction of atomic wheights of a no of elements. The weights of Beryllium, Indium, Uranium, Aurum( Gold), Platinum.
Atomci weight = valency x equivalent mass
what new elements were discovered in mendeleev table
(i) Ekaboron- Scandium
(ii) Eka-Aluminium is Gallium
(iii) Eka-Silicon is germanium
(iv) Eka- manganese is techetium
what are demerits of mendeleev perioictbale
(a) Position of hydrogen : Hydrogen resembles both, the alkali metals (IA) and the
halogens (VIIA) in properties so Mendeleev could not decide where to place it.
(b) Position of isotopes : As atomic wt. of isotopes differs, they should have been placed at different
position in Mendeleev’s periodic table. But there were no such places for isotopes in Mendeleev’s
periodic table.
Anomalous pairs of elements : There were some pairs of element which did not follow the
increasing order of atomic weights.
Like elements were placed in different groups :
There were some elements like Platinum (Pt) and Gold (Au) which have similar properties but were
placed in different groups in Mendeleev’s table.
unlike elements placed together
Cu, Ag and Au placed in Ist group along with Na, K etc. while they differ in their properties
(Only similar in having ns1 electronic configuration)
It was not clear that ‘lanthanides and Actinides’ are related with IIIA group or IIIB group.
(g) Cause of periodicity : Why physical and chemical properties repeated in a group.
(f)
ive examples of anomalous pairs
Ar K
39.9 39.1
Co Ni
58.9 58.6
Te I
127.5 127
Thorium Protactinium
232 231
who gave modern periodic table
It was proposed by Moseley.
(ii) Modern periodic table is based on atomic number.
(iii) Moseley did an experiment in which he bombarded high speed electron on different metal surfaces and
obtained X-rays.
He plotted a graph with root of frequency of the x rays on y axis and the atomic numbers of the elemtns on the x-axis and obtained a straight line. Proving that frequency directly prop. to atomic number
√v = a (Z-b)
what are the features of modern periodic law
Modern periodic law : The physical & chemical properties of elements are the periodic function of
their atomic number.
(v) Characteristics of modern periodic table :
(a) 9 vertical columns called groups.
(b)
I to VIII group + 0 group of inert gases.
(c) Inert gases were introduced in periodic table by Ramsay.
(d) 7 horizontal rows called periods.
what is the long form periodic table/ extended periodi table
(It is also called as ‘Bohr, Bury, Rang and Werner Periodic Table)
(i)
(ii)
It is based on the Bohr-Bury electronic configuration concept and atomic number.
This model is proposed by Rang & Werner
(iii) 7 periods and 18 groups
(iv) According to I. U. P. A. C. 18 vertical columns are named as 1st
(vi) Elements belonging to same group have same number of electrons in the outermost shell so their properties
are similar.
what is long form periodic law
the phy and chem prop of elements are periodic functions of electronic configuration
