Class 11th
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6 months agoContributor-Level 10
3.60. In a multi-electron atom, the electrons present in the inner shells shield the electrons in the valence shell from the attraction of the nucleus. They act as a screen between the nucleus and these electrons. This is known as the shedding effect or the screening effect.
As the screening effect increases, the effective nuclear charge decreases. Consequently, the force of attraction by the nucleus for the valence shell electrons decreases, and hence the ionization enthalpy decreases.
New answer posted
6 months agoContributor-Level 10
3.59. The d-block elements are known as transition elements.
They have electronic configuration= (n – 1) d1-10 ns1-2
Characteristics of d-block elements are:
They show variable oxidation states.
Their compounds are generally paramagnetic.
Most of the transition elements form coloured compounds.
They are all metals with high melting and boiling points.
These elements are used in the formation of alloys.
New answer posted
6 months agoContributor-Level 10
3.58. Elements gallium and germanium were unknown at the time Mendeleev published his Periodic Table. He left the gap under aluminium and a gap under silicon, and called these elements Eka-Aluminium and Eka-Silicon. Mendeleev predicted not only the existence of gallium and germanium but also described some of their general physical properties.
New answer posted
6 months agoContributor-Level 10
3.57. Ionisation enthalpy depends on the following factors:
1. Atomic size: The ionization enthalpy decreases with an increase in atomic size because with the increase in the atomic size, the number of electron shells increases. Therefore, the force that binds the electrons to the nucleus decreases.
2. Nuclear charge: The ionization enthalpy increases with the increase in the magnitude of the nuclear charge. This is because as the magnitude of the positive charge on the nucleus of an atom increases, the attraction with the electrons also increases.
3. Screening or shielding effect: Greater the magnitude of the screening effect less w
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6 months agoContributor-Level 10
3.56. The elements of the s-block and p-block are collectively called as representative or main group elements. These include elements of group I (alkali metals), group 2 (alkaline earth metals).
New answer posted
6 months agoContributor-Level 10
3.55. The energy which is released by an atom in gaining an electron from outside the atom or ion to form a negative ion (or an anion) is called electron gain enthalpy.
The unit of electron gain enthalpy is kJ/ mol. In some cases, like in noble gases, atoms do not have any attraction to gain an electron. In that case, energy must be supplied.
New answer posted
6 months agoContributor-Level 10
3.54. The elements of group 1 (alkali metals), group 2 (alkaline earth metals) and group 13 to 17 constitute the representative elements. They are elements of the s-block and the p-block.
New answer posted
6 months agoContributor-Level 10
(a) Eutrophication: When the growth of algae increases in the surface of water, dissolved oxygen in water is reduced. This phenomenon is known as eutrophication. (Due to this growth of fish gets inhibited). (b) Pneumoconiosis: It is a disease which irritates lungs. It causes scarring or fibrosis of the lung. (c) Photochemical smog: Photochemical smog is formed as a result of photochemical decomposition of nitrogen dioxide and chemical reactions involving hydrocarbons. It takes place during dry warm season in presence of sunlight. It is oxidising in nature. (d) Classical smog: Classical smog is formed due to condensation of SO, vapours on particles of carbon in cold climate. It is generally formed during winter when there is severe cold.It is reducing in nature. |
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6 months agoContributor-Level 10
Toxic substance that is used to kill insects are called insecticides. For example: DDT, BHC.
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