• The National 5 Chemistry Unit 1 Summary Sheet PDF explains the periodic table and how elements are identified.
• Elements are composed of protons, neutrons, and electrons, and their atomic structure is organized by increasing atomic number.
• Electrons are arranged in shells, and valency determines the charge of ions formed by the loss or gain of electrons.
• Isotopes have the same atomic number but different mass numbers, and compounds are formed by chemically bonding elements together.
• The octet rule guides atoms to attain full electron arrangements, and molecules can have various shapes and include diatomic elements.

For more information, students can refer to the National 5 Chemistry Unit 1 Questions and Answers and the National 5 Chemistry Notes for a comprehensive understanding of chemical changes and structure in the context of National 5 Chemistry.