Clear, Simple & Exam-Focused
Qualification: Pearson Edexcel
-Sarah Garrouch Girón
, Topic A: Periodicity and Properties of Elements
Atomic Structure
Key Definitions
● Atom = smallest part of an element
● Proton = positively charged particle
● Neutron = no charge
● Electron = negatively charged particle
● Atomic number = number of protons
● Mass number = protons + neutrons
● Isotope = atoms of the same element with different numbers of neutrons
Must-Know Facts
● Electrons are arranged in shells (2,8,8)
● Outer shell electrons determine reactivity
● Atoms are neutral (protons = electrons)
Common Mistakes
● Mixing up atomic number and mass number
● Forgetting electrons equal protons in a neutral atom
Exam Question
Q: Define an isotope (2 marks)
A: -Atoms of the same element
-With different numbers of neutrons
Periodic Table Trends
Key Definitions