Topics Covered: Definition of an atom, atomic structure, subatomic particles, mass number, atomic mass, example element, exam-style questions, summary.
What is an Atom?
Fundamental piece of matter; smallest particle of a chemical element.
Everything is made of atoms except for energy.
Models of the Atom:
Thompson's Plum Pudding Model: Central positive sphere with negative electrons.
Rutherford's Model: Central nucleus.
Bohr's Model: Focus on a model similar to Bohr’s.
Atomic Structure
Nucleus: Center of the atom, tiny and dense, contains most of the mass.
Composed of protons and neutrons (nucleons).
Electrons: Orbit the nucleus in shells, tiny, contribute little to the mass.
Subatomic Particles
Protons:
Positive charge (+), relative mass = 1.0.
Neutrons:
Neutral charge, relative mass = 1.0.
Electrons:
Negative charge (-), relative mass = 1/2000.
Neutral Atoms
In neutral atoms, the number of protons = number of electrons, thus no overall charge.
Periodic Table Representation
Element Representation:
Mass number (A): Total protons + neutrons.
Atomic number (Z): Number of protons.
Example: Aluminium
Aluminium
Mass number: 27
Atomic number: 13
Calculation:
Protons = 13
Electrons = 13 (neutral atom)
Neutrons = 27 - 13 = 14
Exam-Style Questions
Sodium Example:
Mass number: 23, Atomic number: 11.
Protons = Electrons = 11.
Answer: 11 electrons.
Chromium vs Vanadium:
Order depends on atomic number.
Vanadium (atomic number 23) before Chromium (atomic number 24).
Subatomic Particles in Calcium and Platinum:
Calcium:
Mass number: 40, Atomic number: 20.
Protons = Electrons = 20, Neutrons = 20.
Platinum:
Mass number: 195, Atomic number: 78.
Protons = Electrons = 78, Neutrons = 117.
Marks awarded for correct calculation of protons, neutrons, electrons.