a) Why do we classify elements?
b) What were the two criteria used by Mendeleev in his periodic table?
c) Why did Mendeleev leave some gaps in his Periodic table?
d) In Mendeleev's Periodic Table, why was there no mention of Nobel gases like Helium, Neon and Argon?
e) Would you place the 2 isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
Answers
a) It is important to classify elements according to their properties. It is also necessary to understand how they form the compounds. Grouping ofelements into different classes is called periodic classification ofelements. It helps us understand how differentelements form different compounds.
b) • He arrange the elements in an increasing order of their atomic masses.
• He put the elements have similar properties in a group.
c) Mendeleev kept some vacant places in the periodic table for the element discovered in future. He also predicted the properties of elements before yet to be discovered. When the element discovered letter Mendeleev was correct.
Forr example :- three of this unknown elements name Eka Boron, Eka aluminium,Eka Silicon, later on these elements were discovered and name that scandium, gallium and Germanium respectively.
d) In Mendeleev periodic table there was no noble gas because they were not known at that time. There was no reserved place for noble gases in Mendeleev original periodic table however when noble gases discovered at the end of 19th century. Mendeleev created the zero group without disturbing the original periodic table and noble gases were fitted.
e) Yes, we would place both in same slot because properties of elements is depend on the atomic number and both the isotopes have the same atomic number and their chemical properties are almost same.
Hope it helps..!
Pls Mark it as a Brainlist..!
(a) Due to discovery of different elements, it was difficult to organize the information and properties of the elements, so there was a strong need to find some pattern in the properties of different elements so that they can be grouped together. That's why we classify elements.
(b) Mendeleev used atomic mass and similarities in chemical properties to classify the elements.
(c) Mendeleev predicted existence of some elements in the periodic table which were not discovered at that time, so he left place for those elements in the periodic table.
(d) Nobel gases are inert and are present in extremely low concentration in the atmosphere. That's why Mendeleev didn't placed Nobel gases in the periodic table. When they were discovered, they were placed in a different group so that they don't create any difference in the periodic table. (d) Since Mendeleev used atomic mass and similar properties as a criteria to classify elements but CI-35 and Cl-37 have different atomic masses, so they should be placed at different places but the two isotopes have similar chemical properties, so they should be placed in same slot. This was a contradiction and therefore, the position of the isotopes of an element was not clear in the Mendeleev's periodic table