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Science
Exam: Tomorrow 14:00 · 45 minutes

Atoms & Reactions

Signs of a chemical reaction

A chemical reaction makes a new substance. Clues: colour change, temperature change, gas (bubbles/fizzing), or a precipitate (a solid forming in a liquid).

Word equations

Starting substances are the reactants; what you make are the products.

Examplemagnesium + oxygen → magnesium oxide

The Atom

+ + 0 0 nucleus electron
A nucleus of protons & neutrons, with electrons in shells.
ParticleChargeLocation
proton+1nucleus
neutron0nucleus
electron−1shells
Key factsAtomic number = protons · Mass number = protons + neutrons

Energy

Energy stores

thermal (heat) · kinetic (movement) · chemical (food, fuel, batteries) · gravitational (height) · elastic (stretched/squashed).

Transferred by

heating · electricity · forces · radiation (light & sound).

RenewableNon-renewable
solar, wind, hydroelectriccoal, gas, oil (fossil fuels)

Digestion

Digestion breaks food into small, soluble molecules that pass into the blood.

  1. Mouth – teeth chew; saliva starts digestion
  2. Oesophagus – food tube to the stomach
  3. Stomach – acid & enzymes break food down
  4. Small intestine – nutrients absorbed into blood (using villi)
  5. Large intestine – water absorbed
  6. Rectum & anus – waste leaves the body

Key organs

Liver makes bile · gall bladder stores bile · pancreas makes enzymes.

Food Tests

Tests forMethodPositive
Starchiodineblue-black
SugarBenedict's + heatgreen→orange→red
ProteinBiuretpurple
Fatethanol emulsioncloudy white
Memory aidProtein → Biuret turns purple (like a king's robe).

Enzymes

Enzymes are proteins that speed up reactions (biological catalysts). Each has a specific shape, like a key in a lock.

EnzymeBreaks downInto
Amylasestarchsugars
Proteaseproteinamino acids
Lipasefatsfatty acids + glycerol
CarefulIf it gets too hot or the pH is wrong, an enzyme denatures (loses its shape) and stops working.

Waves

Waves transfer energy, not matter.

Transversee.g. light Longitudinal — e.g. sound
RememberLongitudinal waves vibrate along the direction they travel.

Describing a wave

  • Amplitude = height of the wave
  • Wavelength = distance from one wave to the next
  • Frequency = waves per second (hertz, Hz)

Light

Light travels in straight lines and reflects off surfaces. White light contains all the colours.

normal ir
Angles are measured from the normal (dashed line).
Law of reflectionangle of incidence (i) = angle of reflection (r)

Refraction: light bends when it enters a new material because its speed changes.

Working Scientifically

Variables

  • Independent = what you change
  • Dependent = what you measure
  • Control = what you keep the same
Meanmean = total ÷ number of values

Independent variable goes on the x-axis (across); dependent on the y-axis (up).