Question

"Atomic no of an element is considered bro be a more appropriate parameter than its atomic mass for a chemist" . Take the exampleb of an element X (atomic no. 13) to justify this statement.

Answer 1

We know, atomic number gives us the number of protons whereas atomic mass gives us the sum of number of neutrons and number of protons in the nucleus of an atom.

therefore, when atomic number increases by one in going from one element to the next but atomic mass doesn't vary regularly from element to element.

atomic number of element is fixed. but atomic mass doesn't. for example, atomic number of carbon atom is 6 but it has atomic mass of carbon may have 12, or 14(it is known as isotopic nature of elements)

That is why atomic number of an element is considered to be a more appropriate parameter than its atomic mass.

atomic no : 13 , Aluminium. it is metallic in nature.

it's electronic configuration is 1s², 2s²,, 3s², 3p¹

here last electron enters in p- orbital . so, aluminium belongs to p- block.

group of aluminium = 10 + valance electron

= 10 + 3 = 13 [ valance electron of Al = 3 ]

principal quantum number is 3 so, aluminium is 3rd period element.

here, you can see how easily we locate Aluminium in periodic table and by to find electronic configuration using atomic number, how we understand its characters.

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