Radiation interacting with matter
The The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. of an The smallest part of an element that can exist. is surrounded by Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. These are arranged energy levels at different distances from the nucleus:
- the lowest energy level is closest to the nucleus
- electrons usually occupy the lowest energy levels available to them
The arrangement of electrons differs from element to element, and is responsible for the chemical properties of each element. However, the arrangements may change when Energy travelling as waves in the form of changing electrical and magnetic fields. is absorbed or emitted.
Exciting electrons
An inner electron in a low energy level can rise to a higher energy level. We say that it becomes 鈥榚xcited鈥. An electron can be excited when its absorbs energy from electromagnetic radiation.
Different changes in energy level need different frequencies of electromagnetic radiation. The absorption of radiation can be analysed by an 鈥榓bsorption spectrum鈥. The different black lines show the frequencies absorbed by electrons in atoms.
An excited electron can fall to a lower energy level. When this happens, energy is lost as electromagnetic radiation. Different changes in energy level cause the emission of different frequencies. The emission of radiation can be analysed by an 鈥榚mission spectrum鈥. The different coloured lines show the frequencies emitted by electrons in atoms.
Demonstrating excitation
Changes in atoms and Nuclei is the plural of nucleus. The nucleus is the central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. can produce and absorb radiation over a wide range of frequencies. For example, tonic water (a type of colourless fizzy drink) contains a substance called quinine. This glows when Electromagnetic radiation with a greater frequency than visible light but less than X-rays. Humans cannot see it but it can damage eyes and skin in high doses. from a 鈥榖lack light鈥 or from the Sun shines through it.
When a chemical absorbs ultraviolet light and releases it as visible light. lamps contain mercury Vapour is a cloud of liquid particles. Steam is water vapour.. An electric Moving electric charges, eg electrons moving through a metal wire. excites electrons in mercury atoms. These emit ultraviolet light when the excited electrons return to lower energy levels. A substance coated on the inside of the glass absorbs the ultraviolet light and emits visible light.
Ionisation
Atoms are electrically neutral because:
- Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. have a +1 charge and electrons have a -1 charge
- the number of protons equals the number of electrons
However, an outer electron may absorb enough electromagnetic radiation to leave the atom entirely. When this happens, the atom becomes a positively charged Electrically charged particle, formed when an atom or molecule gains or loses electrons.. The process is called 'ionisation' - the atom has been To ionise is to convert an uncharged atom or molecule into a charged particle by adding or removing electrons..
A collection of two or more atoms held together by chemical bonds. can be ionised if one or more of their atoms become ionised. Radiation that can ionise atoms and molecules is called Radiation that is able to remove electrons from atoms or molecules to produce positively charged particles called ions.. Alpha, beta and gamma radiations are examples of ionising radiation.