2.1 Basic Concepts of Matter
Matter is defined as anything that has mass and occupies space. Matter is made up of tiny and discrete particles.
States of Matter and Kinetic Theory of Matter
- Solid: Particles are closely packed in an orderly arrangement. Strong attraction forces. Particles vibrate and rotate about fixed positions. Low kinetic energy. Fixed shape and volume.
- Liquid: Particles are packed closely together but not in an orderly arrangement. Medium attraction forces. Particles move, slide, and collide over each other. Moderate kinetic energy. Fixed volume, takes the shape of the container.
- Gas: Particles are very far apart in random arrangements. Weak attraction forces. Particles move rapidly and randomly in all directions. High kinetic energy. No fixed shape or volume.
Changes in States of Matter
- Melting: Solid to liquid (absorbs heat energy).
- Freezing: Liquid to solid (releases heat energy).
- Boiling/Evaporation: Liquid to gas (absorbs heat energy).
- Condensation: Gas to liquid (releases heat energy).
- Sublimation: Solid directly to gas (absorbs heat energy).
- Deposition: Gas directly to solid (releases heat energy).
Heating and Cooling Curves
- Melting Point: Constant temperature at which a solid turns into a liquid at atmospheric pressure.
- Freezing Point: Constant temperature at which a liquid turns into a solid at atmospheric pressure.
- Flat plateau regions on temperature-time graphs indicate phase changes. Heat absorbed during melting overcomes forces between particles; heat released during freezing is balanced by heat lost to surroundings.
2.2 Atomic Structure
Subatomic Particles
An atom consists of three main subatomic particles: protons, neutrons, and electrons.
- Proton ($p$): Charge +1, Relative mass = 1, Located in nucleus.
- Neutron ($n$): Charge 0 (neutral), Relative mass = 1, Located in nucleus.
- Electron ($e^-$): Charge -1, Relative mass = $\frac{1}{1840}$ (negligible), Moves in electron shells around nucleus.
Proton Number and Nucleon Number
- Proton Number ($Z$): Number of protons in the nucleus of an atom. For a neutral atom, proton number = number of electrons.
- Nucleon Number ($A$): Total number of protons and neutrons in the nucleus of an atom.
- $$\text{Nucleon Number } (A) = \text{Proton Number } (Z) + \text{Number of Neutrons } (n)$$
Standard Atomic Notation
$$\mathbf{^{A}_{Z}X}$$
Where $X$ = element symbol, $A$ = nucleon number, $Z$ = proton number.
2.3 Development of the Atomic Model
- John Dalton: Atom is a solid, indivisible sphere that cannot be created or destroyed.
- J.J. Thomson: Discovered the electron. Proposed "plum pudding" model: positively charged sphere embedded with negatively charged electrons.
- Ernest Rutherford: Discovered the proton and nucleus through the gold foil experiment. Proposed nucleus contains protons at center, electrons orbit outside.
- Niels Bohr: Proposed electrons move in fixed spherical shells around the nucleus.
- James Chadwick: Discovered the neutral neutron in the nucleus, contributing to atomic mass without extra charge.
2.4 Isotopes and Their Uses
Definition of Isotopes
Isotopes are atoms of the same element with the same proton number but different nucleon numbers (or different number of neutrons).
Calculating Relative Atomic Mass ($A_r$) from Isotope Abundance
$$A_r = \frac{\sum (\% \text{ Abundance} \times \text{Isotope Mass})}{\text{Total Abundance (100)}}$$
Applications of Isotopes in Various Fields
- Medicine: Cobalt-60 (cancer radiotherapy), Iodine-131 (treats thyroid disorders), Carbon-14 (medical imaging/metabolism research).
- Agriculture: Phosphorus-32 (studies fertilizer uptake in plants).
- Archaeology: Carbon-14 (carbon dating to determine age of fossils/artifacts).
- Industry: Sodium-24 (detects underground pipe leaks), Americium-241 (smoke detectors).
- Nuclear Energy: Uranium-235 (nuclear power generation and reactor fuel).