Mass Number, Atomic Structure, and Isotopes

This page provides a comprehensive overview of key concepts in atomic structure and isotopes. It covers the definitions and relationships between atomic number, mass number, and relative atomic mass, as well as explaining the nature of isotopes.

Definition: Mass number (A) is the total number of protons and neutrons in an atom.

Definition: Atomic number (Z) is the number of protons in an atom.

The document explains that the number of neutrons in an atom can be calculated by subtracting the atomic number from the mass number.

Vocabulary: Relative atomic mass is defined as the average mass of an atom relative to 1/12 of the mass of a carbon-12 atom.

The text emphasizes that relative atomic mass takes into account the relative abundances of different isotopes of an element.

Definition: Isotopes are atoms of the same element with the same atomic number but different mass numbers.

The document highlights that isotopes have the same chemical properties due to having the same number of electrons in their outer shell. However, they may have small differences in their physical properties, such as mass and density.

Highlight: The chemical properties of an atom are determined by its electrons, which participate in chemical reactions.

The text explains that the electrostatic attraction between the positively charged nucleus and the negatively charged orbiting electrons holds the atom together.

Example: Lithium (Li) is used as an example to illustrate the concepts of atomic number and mass number.

This comprehensive overview provides a solid foundation for understanding atomic structure, mass number, and isotopes in chemistry, which is essential for students studying chemistry at various levels, including GCSE and class 11.