The number of protons, neutrons and electrons an atom has determines what element it is. Hydrogen, for example, has one proton, no neutrons and one electron; the element sulfur has 16 protons, 16 neutrons and 16 electrons.
The wave-mechanical model of the atom is required to explain the spectra of elements with multi electron atoms.
<u>Explanation:</u>
Wave mechanical theory say that every electron surrounding a nucleus occupies a certain orbit and moves in a certain direction, but the orbit is like a wave of energy or cloud but not a ring. It was proposed in the 1920s, when scientists Erwin Schrodinger and Louis Victor de Broglie concluded that the Bohr’s model is not suitable for electron location determination.
Based on many assumptions, scientists began to guess as accurately as possible about the behaviour of electrons at different energy levels around the nucleus. Because all electrons are negatively charged, they tend to push their elbows when they are too close together, moving away and changing direction. Each plane has one or more orbits that have more than one electrons that move around the nucleus in a specific patterns or shape.
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