Atomic Number, Isotopes, and Isobars: Introduction

Atomic Number and Mass Number

• Atomic number (Z) is the number of protons in the nucleus of an atom, which is equal to the number of electrons in a neutral atom.
• Atomic number is represented by Z and determines the chemical properties of an element.
• Hydrogen has an atomic number of 1, as it has only one proton in its atom.
• Mass number (A) is the total number of protons and neutrons present in the nucleus of an atom.
• Mass number is represented by A and is the sum of protons and neutrons in an atom.

Isotopes

• Isotopes are elements with the same atomic number but a different mass number.
• Isotopes occur due to the presence of a different number of neutrons in elements with the same atomic number.
• Many but not all elements have isotopes.
• Examples of isotopes of hydrogen are protium (1 proton, 0 neutrons), deuterium (1 proton, 1 neutron), and tritium (1 proton, 2 neutrons).
• Chemical properties of isotopes are the same due to the same number of protons and electrons.

Isobars

• Isobars are atoms with the same mass number but a different atomic number.
• Examples of isobars include Argon (atomic number 18, mass number 40), Potassium (atomic number 19, mass number 40), and Calcium (atomic number 20, mass number 40).
• Carbon-14 (mass number 14) is an isobar of Nitrogen (atomic number 7, mass number 14).