Lecture on Atoms and Subatomic Particles

Introduction

• Atoms are the basic structural components of chemistry, akin to cells in biology.
• Understanding atoms involves knowing their subatomic particles and their properties.
• Atoms are consistent in structure but differ in number and arrangement of subatomic particles.

Structure of an Atom

1. Nucleus

   • Core of the atom containing protons and neutrons.
   • Protons: Positively charged, determine the element's identity (atomic number).
   • Neutrons: Neutral, contribute to atomic mass but not to the element's identity.
   • Both protons and neutrons are nucleons.

2. Electrons

   • Occupy space outside the nucleus.
   • Negatively charged, involved in interactions and chemical bonding.
   • Mass is negligible compared to protons and neutrons.

Properties and Categorization

• Atomic Number: Defined by the number of protons; unique to each element.
• Mass Number: Sum of protons and neutrons.
• Atomic Mass Unit (AMU): Standard unit to express masses of particles.
• Charge of an Atom: Determined by the difference between protons and electrons.

Isotopes

• Atoms of the same element with different numbers of neutrons.
• Impact atomic mass but not chemical properties.
• Notation: Element name followed by mass number (e.g., Carbon-12, Carbon-13).

Calculating Atomic Mass

• Relative Atomic Mass: Weighted average of all isotopes based on abundance.
• Calculation involves the percentages of each isotope's presence on Earth.
• Example Calculation: For Boron with isotopes Boron-10 and Boron-11.

Summary

• Changing protons changes the element and mass.
• Changing neutrons changes only the mass.
• Changing electrons alters the charge.
• Understanding isotopes and atomic mass is crucial, particularly for IB exams.