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8.3.1The Periodic Table

The Big Bang Theory — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 21 of 23 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Origin and Expansion

The Big Bang model traces the history of the Universe back to a very hot, dense state.

1
Roughly 14 billion years ago, all the matter and space in the Universe was contained in an extremely hot and dense region.
2
A rapid expansion, called the Big Bang, began, and space itself has been stretching ever since.
3
As the Universe expanded it cooled, which allowed matter to form and galaxies to develop later.
4
Galaxies are still moving apart today, which shows that the Universe is still expanding.
5
Tracing the expansion backwards in time suggests that all the matter once occupied a single point.

Part 2 of 5The Balloon Analogy

A model of an expanding balloon helps to visualise how space expands.

Balloon surface
  • Balloon surface Represents space, which expands between galaxies rather than galaxies moving through space.
Dots
  • Dots Represent galaxies, drawn on the surface of the balloon.
Inflation
  • Inflation As the balloon inflates, every dot moves away from every other dot, and the farther apart two dots are, the faster they separate.
Density
  • Density The density of galaxies falls as the Universe expands, because the same galaxies occupy a larger volume.
Limit of the model
  • Limit of the model The balloon surface is two-dimensional, so the analogy is only a simplified model of the real Universe.

Part 3 of 5Evidence for the Big Bang

Evidence for the Big Bang
Galactic red-shift
  • Galactic red-shift Light from distant galaxies is shifted to longer wavelengths, showing that those galaxies are moving away from us.
Cosmic microwave background
  • Cosmic microwave background Microwave radiation arrives uniformly from all directions at about 2.7 K, a remnant of the hot early Universe.
Why the Big Bang is accepted
  • Why the Big Bang is accepted The Big Bang explains both observations better than the rival Steady State theory, so it is the accepted model.

Part 4 of 5Worked Example

Question

  • Galaxy X and Galaxy Y are both moving away from Earth, and Galaxy X is twice as far from Earth as Galaxy Y.
  • Using the idea of an expanding Universe, state which galaxy is receding faster and explain why.

  1. Step 1: In an expanding Universe, galaxies further from Earth move away faster than nearer galaxies.
  2. Step 2: Galaxy X is twice as far away as Galaxy Y.
  3. Step 3: Galaxy X therefore has the greater recession speed, in the same way that the farther dots on the inflating balloon separate faster.

Answer Galaxy X is receding faster than Galaxy Y, because greater distance means greater recession speed in an expanding Universe.

Part 5 of 5Exam Checklist & Tips

8.3.1 – Key Points for the Exam

  • Big Bang The rapid expansion from a hot, dense state that marks the start of the Universe.
  • Expansion of the Universe The increase in the distances between galaxies as space itself stretches.
  • Galactic red-shift The increase in the observed wavelength of light from galaxies moving away from Earth.
  • Cosmic microwave background Uniform microwave radiation from all directions, left over from the early Universe.
  • Steady State theory A rival model in which the Universe has no beginning and galaxies are continually created.

Common Mistakes

  • Saying the Big Bang was an explosion into space that already existed; space itself expanded.
  • Describing galaxies as moving apart through space; the space between them expands.
  • Claiming that the Big Bang happened at one particular location in the Universe.
  • Thinking the cosmic microwave background is high-energy radiation;
    • it has been redshifted to microwave wavelengths.

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