Define atomic number.

Define quantum numbers.

Define the terms nucleus, nucleons, atomic number, mass number, isotopes, isobars, isotones.

Atom A has a mass number 209 and atomic number 82. Atom B has a mass number 209 and atomic number 83. (i) How many protons atom A has ?

Atom A has a mass number 209 and atomic number 82. Atom B has a mass number 209 and atomic number 83. (ii) How many protons atom B has ?

Atom A has a mass number 209 and atomic number 82. Atom B has a mass number 209 and atomic number 83. (iii) Are atoms A and B isotopes of the same element ?

What is the number of valence electrons in the atoms of an element having atomic number 13 ? Name the valence shell of this atom.