Dear Students,
General Science is an equally important section containing weightage of 25 questions in Railway Group-D Exam 2018 and has an even more abundant importance in some other exams conducted by SSC. Most of the questions were asked from Periodic Table so here we are with notes on particular this topic. So you should know important facts related to Periodic table so that you can score well in General Science section.
In 1864, Newlands made an attempt to classify elements.
There are seven musical notes in music. Every eighth note is similar to the first one and it is the first note of the nest scale.
Similarly Newland stated that eighth element starting from a given one is a kind of repetition of the first like the eighth notes of an octave of music. So he called this relationship as the Law of octaves.
In Newland's table of elements lithium, sodium and potassium occupied places near each other.
Fluorine and chlorine or oxygen and sulphur were placed near each other.
Note: This classification worked well with the elements with small atomic weights but failed in the case of elements with large atomic weights.
Mendeleev published in 1869, using atomic weight to organize the elements, information determinable to fair precision in his time. Atomic weight worked well enough to allow Mendeleev to accurately predict the properties of missing elements.
The atomic number is the absolute definition of an element, and gives a factual basis for the ordering of the periodic table.
Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
Modern day periodic tables are expanded beyond Mendeleev's initial 63 elements.
☞VALENCY
☞ELECTRONEGATIVITY
The relative tendency of an atom to attract the shared pair of electrons towards itself is called electronegativity.
Newlands' law of octaves
Law of octaves, in chemistry, the generalization made by the English chemist J.A.R. Newlands in 1865 that, if the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements.In 1864, Newlands made an attempt to classify elements.
There are seven musical notes in music. Every eighth note is similar to the first one and it is the first note of the nest scale.
Similarly Newland stated that eighth element starting from a given one is a kind of repetition of the first like the eighth notes of an octave of music. So he called this relationship as the Law of octaves.
In Newland's table of elements lithium, sodium and potassium occupied places near each other.
Fluorine and chlorine or oxygen and sulphur were placed near each other.
Note: This classification worked well with the elements with small atomic weights but failed in the case of elements with large atomic weights.
Mendeleev's table:
Mendeleev published in 1869, using atomic weight to organize the elements, information determinable to fair precision in his time. Atomic weight worked well enough to allow Mendeleev to accurately predict the properties of missing elements.
The atomic number is the absolute definition of an element, and gives a factual basis for the ordering of the periodic table.
Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
Modern day periodic tables are expanded beyond Mendeleev's initial 63 elements.
Modern Periodic Table
☞VALENCY
Valency may be defined as “the combining capacity of the atom of an element with atoms of other elements in order to acquire the stable configuration (i.e. 8 electron in valence shell. In some special cases it is 2 electrons).”
☞ATOMIC SIZE
It refers to the distance between the centre of nucleus of an isolated atom to its outermost shell containing electrons.
The atomic radius decreases on moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.
In a group atomic size increases from top to bottom due to increase in number of shells.
METALLIC AND NON-METALLIC PROPERTIES
- In a period from left to right metallic nature decreases while non-metallic character increases.
- In a group metallic character increases from top to bottom while non-metallic character decrease.
☞ELECTRONEGATIVITY
The relative tendency of an atom to attract the shared pair of electrons towards itself is called electronegativity.
In a period from left to right, the value of electronegativity increases while in a group from top to bottom the value of electronegativity decreases.
☞IONIZATION ENERGY
The ionization energy (IE) is the amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated gaseous atom to form a cation.
In a period from left to right, the value of ionization energy increases while in a group from top to bottom the value of ionization energy decreases.
☞ELECTRON AFFINITY
The electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.
In a period from left to right, the value of electron affinity increases while in a group from top to bottom the value of electron affinity decreases.
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