Dimitri Ivanovitch Mendeleev was born on 8th february 1834 as the 17th child in the family of the head master of a local high school in Tobolaok. He could not succeed in the entrance examination to Moscow university.
Mendeleev started working on periodic law in late 1860’s. He was exhorted that he could not survive for more than six months as he had a defect in the lung at his 21st year.
Mendeleev passed away just five days before his 73rd birthday on 2nd february 1907. The 101st element was named ‘Mendeelevium’ in 1955 after 50 years of his death.
Key Words in the Lesson:
Triad: In a group of three elements the atomic weight of the middle element is the average of the atomic weights of the first and third elements.
Octave: When elements are arranged in the ascending order of their atomic weights they fall into a pattern in which their properties repeat at regular intervals. Every eighth element starting from a given element resembles in its properties to that of the starting element.
Periodic law: The periodic law states that the physical and chemical properties of elements are a periodic function of their atomic weights.
Periodic table: The charts of elements arranged in a systematic order of increasing atomic weight or atomic number is called periodic table.
Period: The horizontal rows in Mendeleev’s periodic table are called periods.
Group: The vertical columns in Mendeleev’s periodic table are called groups.
Lanthanides: ‘4f’ elements are called Lanthanides or Lanthanoids. Elements from 58Ce to 71Lu possess almost the same properties as 57La . So the name Lanthanoids is most appropriate one for these elements.
Actinides: The 5f elements are called Actinoids or as Actinides. They are from 90Th to 103Lr.
Element family: Group of elements is also called element family or chemical family. For example group 1 (I A) has from Li to Fr with outershell electronic configuration ns1 and is called alkali metal family.
Metalloids: Metalloids or semi-metals are elements which have properties that are intermediate between the properties of metals and non-metals. They are generally semi conductors. e.g.: B, Si, Ge.
Periodicity: In the periodic table, the properties of elements change gradually with a change in their electronic configurations. This trend repeats itself at regular intervals. This repetition of characters is called ‘periodicity’.
Atomic radius: Atomic radius of elements may be defined as the distance from the centre of the nucleus of the atom to its outermost shell.
Ionization energy: The energy required to remove an electron from the outermost orbit or shell of a neutral gaseous atom is called ionization energy.
Electron affinity: The electron affinity of an element is defined as the energy liberated when an electron is added to its neutral gaseous atom.
Electronegativity: The electronegativity of an element is defined as the relative tendency of its atom to attract electrons towards itself when it is bonded to the atom of another element.
Electropositivity: Metals generally show less electronegative character. In compounds they generally show a tendency to remain as a positive ion. This property is often termed as electropositive character. Metals are electropositive elements.
The Government of Andhra Pradesh will conduct the SSC / 10th Class examinations in the old pattern for the academic year 2014-15. Here we are giving details of Physical Sciences question paper, a part of General Science question paper in 10th Class.