// CHEMISTRY L4 — NUCLEAR CHEMISTRY
The energy hiding in the nucleus.
Ordinary chemistry rearranges electrons; nuclear chemistry rearranges the nucleus itself — releasing a million times more energy. Watch a sample decay on its clock, then meet fission and fusion. (Scottish Higher-specific; A-level meets this later as nuclear physics.)
// FIG. 01 — HALF-LIFE DECAY CHAMBER
Half-life is the time for half the radioactive nuclei to decay — from carbon-14's 5,730 years (used to date fossils) to isotopes gone in microseconds.
// NUCLEAR EQUATIONS — BALANCE THE NUMBERS
In a nuclear equation the mass numbers (top) must balance and the atomic numbers (bottom) must balance on each side. That's how we work out what a decaying nucleus turns into:
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// FISSION vs FUSION
FISSION — splitting apart
n + U-235 → Ba + Kr + 3n + energy
A neutron splits a big unstable nucleus (uranium, plutonium) into two smaller ones, firing out more neutrons that split more nuclei — a chain reaction. Controlled, it powers nuclear reactors; uncontrolled, it's an atomic bomb.
FUSION — joining together
H-2 + H-3 → He-4 + n + energy
Two tiny nuclei (isotopes of hydrogen) are forced together into a bigger one, releasing even more energy than fission. It powers the Sun and stars — but needs millions of degrees, so building a fusion reactor on Earth is one of science's great challenges.
// E = mc² — WHERE THE ENERGY COMES FROM
In both fission and fusion, the products weigh very slightly less than the starting nuclei. That missing mass hasn't vanished — Einstein's E = mc² says it has become energy, and because c² (the speed of light squared) is enormous, a speck of mass yields a staggering amount of energy. That's why nuclear reactions release millions of times more energy per atom than chemical reactions like burning fuel.
// REFERENCES & FURTHER READING
Cross-check against your own exam board's specification (AQA, Edexcel, OCR, SQA).