atomic structure for igcse edexcel chemistry (9-1). simple and straight forward definitions, formulas and bullet points. also includes isotopes and relative atomic mass. best for learning for exams, tests and assessments. in accordance to the marking schemes by edexcel. good luck!

1. ATOMIC STRUCTURE
BY HUDA FATIMA

2. ATOMS
• Smallest part of an element.
• Consists of a nucleus, which contains protons, and is surrounded by electrons.
• Since atoms are so small, they can’t be measured in conventional units, such as grams. Therefore they
are measured in a unit called “Relative Atomic Mass”
• Protons have a positive charge, electrons have a negative charge, and neutrons have no charge, so they
are neutral.

3. MOLECULES
• Atoms chemically bond together to make molecules.
•

4. DEFINITIONS AND FORMULAS
• ATOMIC NUMBER: number of protons and electrons in an atom
• MASS NUMBER: sum of the number of neutrons and protons in an atom.
• RELATIVE ATOMIC MASS: the average weight of an atom.
• FORMULA FOR MASS NUMBER = ATOMIC NUMBER + NUMBER OF NEUTRONS
• NUMBER OF NEUTRONS = MASS NUMBER – ATOMIC NUMBER

5. ISOTOPES
• Isotopes are atoms of the same element which have the same number of electrons and protons, but a
different number of neutrons.
• Therefore, the have the same atomic number, but different mass number.

6. CALCULATING RELATIVE ATOMIC MASS OF ISOTOPES
• The relative atomic mass of an element with isotopes can be found through the percentage abundances
and mass number.