The periodic classification of the elements is an arrangement of the elements in order of their…
A. atomic weights
B. isotopic weights
C. molecular weights
D. atomic numbers
Elements in the periodic table are arranged from left to right and from top to bottom according to their atomic numbers and not according to their atomic masses.
Now, atomic number is the number of positively charged protons present in the nucleus of an atom.
Now for the right answer to the above question:
- Option A is incorrect. atomic weight is the sum of protons and neutrons of an atom, the existence of isotopy has made it very difficult to accurately arrange elements using atomic weights or mass.
- Option B is incorrect. isotopic weights too are quite inconsistent, and the isotopic weight of different elements overlap with one another, this makes proper arrangement difficult.
- C is incorrect. molecules are made up of two or more atoms, this is quite far from a factor to be considered when arranging elements in the periodic table.
- D is the correct answer. Atomic number is a more straight-forward and clean parameter used to better arrange elements in the periodic table.
You may please note these/this:
- If atomic mass is used to arrange elements in the periodic table instead of atomic number, there will certainly be irregularities as the mass number of different atoms and their isotopes will always be found to be inconsistent with one another.
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/ culled from 2018 JAMB-UTME Chemistry question 1 /