The Particulate Nature of Matter
1. Kinetic Particle Theory
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๐น Description of States:
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๐น Solids:
๐น Particles are closely packed in a fixed lattice, vibrating in place; strong intermolecular forces; definite shape and volume.
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๐น Liquids:
๐น Particles are close but mobile, sliding past each other; weaker forces than solids; definite volume, no fixed shape.
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๐น Gases:
๐น Particles are far apart, moving rapidly and randomly; very weak forces; no fixed shape or volume.
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๐น Solids:
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๐น Interconversion:
- ๐น Melting: Solid โ Liquid
- ๐น Boiling/Evaporation: Liquid โ Gas
- ๐น Freezing: Liquid โ Solid
- ๐น Condensation: Gas โ Liquid
- ๐น Sublimation: Solid โ Gas (e.g., dry ice)
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๐น Evidence for Particle Movement:
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๐น Diffusion:
๐น Random movement of particles from high to low concentration.
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๐น In Liquids:
๐น Potassium permanganate (KMnOโ) spreads slowly in water.
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๐น In Gases:
๐น Bromine gas spreads in a sealed container.
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๐น Diffusion:
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๐น Everyday Effects:
- ๐น Spread of perfume or cooking aromas through air.
- ๐น Mixing of gases, e.g., car exhaust dispersing in atmosphere.
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๐น Effect on Diffusion:
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๐น Molecular Mass:
๐น Lighter particles diffuse faster (Grahamโs Law: rate โ 1/โmolar mass). Example: NHโ (17 g/mol) diffuses faster than HCl (36.5 g/mol).
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๐น Temperature:
๐น Higher temperature increases particle kinetic energy, speeding up diffusion.
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๐น Molecular Mass:
2. Atomic Structure
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๐น Relative Charges and Masses:
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๐น Proton:
๐น Charge +1, mass 1 u
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๐น Neutron:
๐น Charge 0, mass 1 u
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๐น Electron:
๐น Charge -1, mass ~1/1836 u (negligible)
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๐น Proton:
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๐น Structure of Atom:
๐น Nucleus (protons + neutrons) at center with most mass; electrons orbit in shells around nucleus.
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๐น Proton and Nucleon Numbers:
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๐น Proton Number (Z):
๐น Number of protons; defines the element.
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๐น Nucleon Number (A):
๐น Sum of protons and neutrons.
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๐น Example:
๐น Carbon-12: ยนยฒโC (6 protons, 6 neutrons)
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๐น Proton Number (Z):
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๐น Nuclide Notation:
๐น Written as แดฌ๐ฉX , where A = nucleon number, Z = proton number, X = element symbol.
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๐น Isotopes:
๐น Atoms with same proton number but different neutron numbers. Example: ยนยฒโC and ยนโดโC.
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๐น Deduction of Numbers:
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๐น Neutral Atoms:
๐น Protons = Electrons = Z; Neutrons = A - Z. Example: ยนโถโO โ 8 protons, 8 electrons, 8 neutrons.
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๐น Ions:
๐น Electron count adjusted by charge. Example: Oยฒโป from ยนโถโO โ 8 protons, 10 electrons, 8 neutrons.
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๐น Neutral Atoms:
- โ ๏ธ Particles in solids do not move; actually, they vibrate in fixed positions.
- โ ๏ธ Diffusion rates are the same for all substances; lighter molecules and higher temperatures increase rates.
- โ ๏ธ Proton number is the same as nucleon number; proton number defines element, nucleon number includes neutrons.
- โ ๏ธ Isotopes have different chemical properties; they differ mainly in physical properties like mass.
- ๐ Describe particle arrangement and movement in solids, liquids, and gases, including state changes.
- ๐ Explain diffusion experiments and relate to molecular mass and temperature.
- ๐ Practice calculating proton, neutron, and electron numbers using nuclide notation.
- ๐ Memorize charges and masses of subatomic particles.
- ๐ Distinguish isotopes by neutron count, not chemical behavior.