Sec 1 Science — Summary Notes

Derived units: area m², volume m³, density kg m⁻³, speed m s⁻¹, force N (= kg m s⁻²), pressure Pa, work J, power W.  |  1 L = 1000 mL = 1000 cm³

• Standard form: a × 10ⁿ where 1 ≤ a < 10. E.g. 45 000 = 4.5 × 10⁴.
• Prefixes: kilo (k) = 10³, milli (m) = 10⁻³, micro (μ) = 10⁻⁶, nano (n) = 10⁻⁹. E.g. 1 km = 10³ m; 1 mm = 10⁻³ m.
• s.f. rules: all non-zero digits count; zeros between non-zero digits count; leading zeros do NOT count (0.045 g → 2 s.f.); in standard form, count the digits in a (4.03 × 10⁴ → 3 s.f.).

Volume of a regular solid: V = length × width × height (e.g. cuboid).  |  Volume of an irregular solid: displacement method — V = final level − initial level in a measuring cylinder (read the bottom of the meniscus at eye level).

Density ρ = mass ÷ volume  |  An object floats if its density is less than the fluid's, and sinks if greater.

• Hardness: Mohs scale (1 = talc, softest → 10 = diamond, hardest); a harder material scratches a softer one.
• Melting point & boiling point: pure substances melt and boil at fixed temperatures; mixtures over a range.
• Conductivity: metals conduct heat and electricity well; non-metals (glass, plastics, ceramics) do not.

• Metals: good conductors of heat and electricity, high melting/boiling points (copper, silver, magnesium).
• Non-metals: poor conductors, low melting/boiling points (neon, oxygen, chlorine).
• Diatomic elements exist as molecules of two atoms: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂ — mnemonic "Have No Fear Of Ice Cold Beer". Noble gases (He, Ne, Ar) are single atoms.

Solubility: increases with temperature for most solid solutes (exceptions: CaSO₄, Ca(OH)₂). Rate of dissolving increases with higher temperature, smaller particle size (more surface area), and faster stirring.

• Evaporation to dryness: solubility does NOT change much with temperature → heat until no liquid remains (salt from seawater).
• Crystallisation: solubility changes greatly with temperature, or solid decomposes on heating → heat to near saturation, cool slowly (copper(II) sulfate crystals).
• Simple distillation: recover the pure solvent — liquid boils off, condenses and is collected separately.

• Luminous objects produce their own light (Sun, bulbs, fires). Non-luminous objects are seen because they reflect light from a source into our eyes (Moon, books).
• Rectilinear propagation: light travels in straight lines — the basis of the ray model.

• Shadow size: the closer an object is to the light source (and further from the screen), the larger its shadow.
• Solar eclipse: Moon between Sun and Earth → Moon's shadow falls on Earth.  |  Lunar eclipse: Earth between Sun and Moon → Earth's shadow falls on the Moon.

Laws of reflection:

1. The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
2. The angle of incidence (i) is equal to the angle of reflection (r), both measured from the normal.

Laws of refraction:

1. The incident ray, the normal at the point of incidence and the refracted ray all lie in the same plane.
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (n = sin i / sin r).

Apparent depth < real depth — a pool looks shallower than it is because light bends away from the normal leaving water. A ray travelling along the normal is not bent. Dispersion: white light splits into its component colours (VIBGYOR) through a prism.

• All living organisms are made of cells — the basic structural and functional unit of life. Unicellular (one cell: amoeba, bacteria) vs multicellular (many cells: plants, animals).

• Magnification = eyepiece × objective (e.g. 10× × 40× = 400×). Coarse knob for initial focus, fine knob to sharpen.
• Division of labour: specialised cells are adapted for specific functions — e.g. red blood cell (biconcave, no nucleus → carries more oxygen), root hair cell (long projection → large surface area for water absorption), sperm cell (flagellum + mitochondria → motility).

Cell → Tissue → Organ → Organ system → Organism.

• Tissue = group of similar cells (muscular tissue); organ = different tissues working together (heart); organ system = organs carrying out related functions (digestive system).
• Animal systems: digestive, skeletal, respiratory, excretory, nervous, circulatory, reproductive. Plant systems: root and shoot.

• Rising sections: temperature increases — particles gain kinetic energy and move faster.
• Flat (constant-temperature) sections: melting/boiling/condensation/freezing occurs — absorbed/released thermal energy is used to overcome or strengthen forces of attraction, so average kinetic energy does NOT change.

Diffusion: net movement of particles from higher to lower concentration. Faster at higher temperature (particles move faster) and in gases (more space, weaker forces).

Atomic no. = no. of protons = no. of electrons (in a neutral atom); mass no. = protons + neutrons; no. of neutrons = mass no. − atomic no.

• Group (vertical column): elements in the same group have the same number of valence electrons → similar chemical properties. Group 18 = noble gases (full outer shell, unreactive).
• Period (horizontal row): equals the number of electron shells.
• 2.8.n rule: first shell holds max 2 electrons, second and third hold max 8. E.g. Nitrogen (7) → 2.5; Magnesium (12) → 2.8.2; Potassium (19) → 2.8.8.1.

• Isotopes: atoms of the same element with different numbers of neutrons (same protons). E.g. carbon-12, carbon-13 and carbon-14 all have 6 protons but 6, 7 and 8 neutrons respectively.
• Particles in elements: single atoms (noble gases: He, Ne) or molecules of identical atoms — the diatomic elements H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂ ("Have No Fear Of Ice Cold Beer").
• Molecules in compounds: two or more different types of atom chemically combined — e.g. water H₂O (2 hydrogen + 1 oxygen), carbon dioxide CO₂.