📘 Chapter 4: Structure of the Atom

Subatomic particles

Protons, neutrons, and electrons

Proton

Positively charged particle in nucleus

Electron

Negatively charged particle outside nucleus

Neutron

Neutral particle in nucleus

Thomson's model

Sphere of positive charge with electrons embedded (plum pudding)

Rutherford's model

Nucleus at centre, electrons revolve around it

Gold foil experiment

Used to discover nucleus

Rutherford's conclusions

Atom mostly empty, nucleus is small and dense

Drawback of Rutherford's model

Electrons should spiral into nucleus

Bohr's model

Electrons revolve in fixed energy levels without radiating energy

Energy levels (shells)

K, L, M, N or n = 1, 2, 3, 4,…

Maximum electrons in shell

2n² (n = shell number)

Valence electrons

Electrons in outermost shell

Valency

Combining capacity based on electrons gained/lost/shared

Atomic number

Number of protons

Mass number

Sum of protons and neutrons

Isotopes

Atoms with same atomic number but different mass numbers

Isobars

Atoms with same mass number but different atomic numbers

Electronic configuration

Arrangement of electrons in shells

Stable configuration

Fully filled outermost shell (octet or duet)