Introduction
Matter, Elements, and the Periodic Table form the structural foundation of Chemistry — this chapter
covers states of matter, basic atomic structure, and how the Periodic Table organises all known elements.
States of Matter
| State | Shape | Volume | Particle Arrangement |
|---|
| Solid | Fixed | Fixed | Tightly packed, strong forces |
| Liquid | Takes shape of container | Fixed | Close but able to move past each other |
| Gas | Takes shape of container | Not fixed | Widely spaced, weak forces, free movement |
| Plasma | Not fixed | Not fixed | Ionised gas — the fourth state of matter (e.g., inside the Sun) |
Changes of State
| Change | Process |
|---|
| Solid → Liquid | Melting |
| Liquid → Solid | Freezing |
| Liquid → Gas | Vaporisation (Evaporation/Boiling) |
| Gas → Liquid | Condensation |
| Solid → Gas (directly) | Sublimation |
📌 Sublimation Examples: Camphor, naphthalene balls, and solid CO₂ (dry ice) all sublime directly from solid to gas without passing through the liquid state.
Atomic Structure — Basic Particles
| Particle | Charge | Location | Relative Mass |
|---|
| Proton | Positive (+) | Nucleus | 1 |
| Neutron | Neutral (0) | Nucleus | 1 |
| Electron | Negative (−) | Orbits around nucleus | ~1/1836 (negligible) |
| Term | Definition |
|---|
| Atomic Number (Z) | Number of protons in an atom (defines the element) |
| Mass Number (A) | Number of protons + neutrons |
| Isotopes | Atoms of the same element with the same atomic number but different mass numbers (different neutron count) |
Elements, Compounds, and Mixtures
| Term | Definition | Example |
|---|
| Element | Pure substance made of only one type of atom | Oxygen, Iron, Gold |
| Compound | Two or more elements chemically combined in a fixed ratio | Water (H₂O), Salt (NaCl) |
| Mixture | Two or more substances physically combined, no fixed ratio, can be separated | Air, salt water |
The Periodic Table — Organisation
📌 Modern Periodic Law: Elements are arranged in order of increasing atomic number. Elements in the same column (group) share similar chemical properties.
| Term | Description |
|---|
| Groups | Vertical columns (18 total) — elements share similar valence electron configuration |
| Periods | Horizontal rows (7 total) — elements have the same number of electron shells |
| Metals | Majority of elements; good conductors, malleable, ductile, lustrous (left/centre of table) |
| Non-Metals | Poor conductors, brittle if solid (right side of table) |
| Metalloids | Properties intermediate between metals and non-metals (e.g., Silicon, Boron) |
Important Element Groups
| Group | Name | Property |
|---|
| Group 1 | Alkali Metals | Highly reactive metals (Li, Na, K) |
| Group 17 | Halogens | Highly reactive non-metals (F, Cl, Br, I) |
| Group 18 | Noble Gases | Chemically inert/unreactive (He, Ne, Ar) |
Q. An atom has 11 protons and 12 neutrons. Find its atomic number and mass number.
Atomic Number = number of protons = 11 (this is Sodium)
Mass Number = protons + neutrons = 11+12 = 23
✅ Exam Focus: Four states of matter and their particle arrangement · Changes of state (including sublimation examples) · Proton/neutron/electron properties · Atomic number vs mass number · Groups vs periods in the Periodic Table · Metal/non-metal/metalloid classification.