Overview
In the earlier discussion of atomic theory as it relates to chemistry, protons and neutrons were described as being within the nuclei of atoms. Electrons were in orbit around the nuclei, and were given up or added in the process of ionization. The orbits of electrons are not in fixed, measureable positions, but can only be approximated.
What Is a Line Spectrum?
Ordinary saltwater burns with a yellow flame because of the sodium in it, while lithium will burn with a red flame, and potassium with a blue flame. When light from an burning element is passed through a prism, the resulting spectrum will show the wavelengths for only that element. For example, the line spectrum from the sun shows mostly hydrogen and helium.
How Does the Spectrum Work?
Scientists thought that each element gave off its characteristic spectrum because the electrons could only occupy certain orbits corresponding to amounts of energy. When the electron moved from a higher energy orbit to a lower energy orbit, it would give off particular quanta of energy. Bohr proposed a model for hydrogen that fit its spectrum, because hydrogen is the simplest element, with only one electron. However, the results were approximate for other atoms with more electrons.
What Is Uncertainty?
At the same time that scientists were developing atomic models, other scientists were proposing that light sometimes gives off packets of energy called photons, but that sometimes light behaved in waves. In addition, with small particles such as electrons, both their position and momentum cannot be measured at the same time. Heisenberg proposed that the act of measuring an electron would actually move it in unpredictable ways. Larger objects are not moved by measurement.
What Are Electron Densities?
Electrons can only exist within energy levels, and they give off energy when they move from a higher energy level to a lower energy level. The amount of energy is fixed, as shown by the characteristic line spectra from different elements. However, the exact position of any given electron cannot be measured, only the probability that they might be within an area, in an atomic orbital.
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