Which element(s) do they represent and what is the relationship between them?

CBSE Class 9 CBSE Class 9 Science
1
    • Which of the two would be chemically more reactive element ‘A’ with atomic number 18 or element ‘D’ with atomic number 16 and why?
    • Out of the three sub-atomic particles known, which is called universal particle?
  2. A and B are two atoms in which the number of protons and neutrons (in its nuclei) are
Atoms Protons Neutrons
A 6 6
6 6 7
  • Which element(s) do they represent and what is the relationship between them?
  • Will A and B have different valencies?
2
    • Electronic configuration of 18A = 2, 8, 8
      It would be chemically inert due to its complete octet.
      Electronic configuration of 16D = 2, 8, 6
      To complete its octet, it will gain 2 electrons, therefore it will be more reactive.
    • Electron is known as universal particle because it has no known components or sub-structure, while protons and neutrons are made up of varieties of still smaller particles called the ‘quarks’.
    • Mass number of ,4 = 6 + 6 = 12
      Mass number of 6 = 6 +7 = 13
      Since, A and 6 have same atomic number, i.e. 6, but have different mass number, i.e. 12 and 13, so they are atoms of carbon and are isotopes of each other and hence they have same valence electrons and valencies.
    • No, as they are isotopes of each other and hence they have same valence electrons and valencies