Atoms have the same number of protons as they do electrons. Over the next few years, Rutherford showed that the nucleus of a hydrogen atom is composed of a single positively charged particle, the proton, and that the nuclei of other atoms also contain protons. Following the Planck relation, this energy corresponds to a specific frequency of light, and therefore a specific wavelength is missing from the spectrum.Įmission spectra occur when electrons drop to a lower energy level and emit photons, again this light has an energy determined by the Planck relation, and so the photons always have a specific wavelength.ĭepiction showing the different ways that electrons can move within a hydrogen atom, each possibility produces a different spectral line. 10.2 Spectral linesĪbsorption spectra occur when atoms absorb photons, and their electrons gain enough energy to move into an orbit further from the nucleus. Instead, they seem to disappear from one shell and instantly appear in another. It also explains the nature of the photoelectric effect, spectral lines, and the periodic nature of the elements.īohr showed that electrons do not move gradually from one shell to the next. This can result in atomic emission, fluorescence, and charge-exchange. Energy is taken and given in the form of photons, and so it is quantised, which means that only certain energies are allowed. It takes energy for an electron to move outwards, and it releases energy when it moves inwards. No matter how little energy electrons have, they cannot move closer to the nucleus than the lowest possible shell, and so negatively charged electrons are not pulled into the positively charged nucleus. It takes less energy for an electron to remain in the closest shell to the nucleus, and more energy to remain further away. These are known as shells.Įach shell has an ‘ n’ value, where shell n=1 is the closest shell to the nucleus of the atom, n=2 is the second-closest, and so on.Įach shell is associated with a quantised energy and can only contain a finite number of electrons. It also explained, among other things, fluorescence, the photoelectric effect, spectral lines, and the periodic nature of the elements.īohr showed that electrons can only be found in specific places, and suggested that electrons orbit the nucleus of atoms in circles, with quantised orbital angular momentums (discussed in Chapter 15), at quantised orbital distances. Bohr’s theory of the atom solved the problems with Ernest Rutherford’s atomic theory. Niels Bohr developed his theory of the atom in 1913, two years after the first Solvay Conference on Physics. Reflection, Refraction, and DiffractionĢ0.

Nuclear model of the atom