When the Nucleus Itself Changes
- Chemistry
- Ages 14–18 · Grades 9–12
- Hands-on experiment
What you’ll find out
- Unstable nuclei decay by alpha, beta or gamma emission, and may become a different element.
- A half-life is the time for half the nuclei in a sample to decay, and nothing chemical can change it.
- Fission and fusion release far more energy than chemical reactions, because a little mass becomes energy.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Unstable nuclei and half-life
Chemical reactions only move electrons around. The nucleus in the middle of each atom is never changed. Nuclear changes are different. They change the nucleus itself, and they can turn one element into another. Some nuclei are unstable. Sooner or later they break down, or decay, and give out radiation. Alpha radiation is a small clump of two protons and two neutrons. Beta radiation is a fast electron, made when a neutron turns into a proton. Gamma rays are a very strong kind of light. Nobody can say when one nucleus will decay. But in a big sample, half of the nuclei decay in a fixed time, called the half-life. Carbon-14 has a half-life of about 5,730 years. Heat and chemicals cannot change it. Scientists use this to date old bones and wood.
Fission, fusion and E = mc²
Nuclear reactions give out millions of times more energy than chemical ones. When a neutron hits a uranium-235 nucleus, the nucleus can split in two. This is called fission. It gives out energy and two or three more neutrons, which can split more nuclei in a chain reaction. Power stations use control rods to soak up spare neutrons and keep the chain steady. Fusion is the opposite. In the Sun, hydrogen nuclei are squeezed together to make helium, and this gives us sunlight. In both cases, a tiny bit of mass disappears and becomes energy. Einstein described this with E = mc². The speed of light, c, is huge, so a little mass makes a lot of energy. Nuclear power makes no carbon dioxide, but its waste stays dangerous for thousands of years, and accidents like Chernobyl in 1986 have been very serious.
Curriculum links: NGSS HS-PS1-8