![]() ![]() That’s because they are the most easily disrupted, or the most available for reactions. In a chemical reaction, it is the electrons in the outermost shell that react, that is to say, get transferred from one atom to another. Chemical reactions are fundamentally electron transfers between atoms. In the case of the electrons in the atom, those at lower levels of potential energy (lower shells, or lower n) are more stable and less easily disrupted than those at higher levels of potential energy. Another way of saying the same thing is to say that systems tend towards states of higher stability. Systems do not naturally tend towards states of higher potential energy. Conversely, an object placed in a hole on the ground does not have a tendency to “climb out” because its potential energy is even lower than the object placed at ground level. Systems tend towards lower levels of potential energy, thus the tendency of the plane or the rock to fall. The object that’s placed at high altitude, be it a plane or a rock at the top of a mountain, has a higher “potential” to fall (lower stability) than the object that’s placed at ground level. Objects that are positioned at ground level have lower potential energy than objects placed at high altitudes. As an example consider the objects on the earth. THE RELATIONSHIP BETWEEN POTENTIAL ENERGY AND STABILITY IS INVERSEĪs the potential energy of a system increases, the system’s stability is more easily disrupted. The main energy levels, also called shells, are given by the main quantum number n. ![]() The now outdated solar system model of the atom allows us to visualize the meaning of the potential energy levels. The probability distributions are given by the secondary quantum number l and by the magnetic quantum number m l. The potential energy levels are described by the main quantum number n and by the secondary quantum number l. This arrangement is not given in terms of exact positions, like the photograph of a street, but rather in terms of probability distributions and potential energy levels, much like the mosquito swarm. The quantum numbers provide us with a picture of the electronic arrangement in the atom relative to the nucleus. An alternative picture of the swarm can be obtained by describing the area where the mosquitoes tend to be concentrated and the factors that determine their preference for certain locations, and that’s the best we can do. The uncertainty about their position persists even in the photograph. Electrons are more like fast-moving mosquitoes in a swarm that cannot be photographed without appearing blurred. Therefore, it is impossible to obtain a photographic picture of the atom like we could of a busy street. The exact position of the electron at any given time cannot be known. The allowed values for the spin quantum number m s are +1/2 and -1/2.Īccording to Heisenberg’s uncertainty principle, it is impossible to know the electron’s velocity and its position simultaneously. When this happens, the electrons are said to be paired. Only two electrons can occupy the same orbital, and they must have opposite spins. SPIN QUANTUM NUMBER ( m S) - Represents the two possible orientations that an electron can have in the presence of a magnetic field, or in relation to another electron occupying the same orbital. Since the type of orbital is determined by l, the value of m l ranges between -l and +l such that m l= -l. MAGNETIC QUANTUM NUMBER ( m l) - Represents the number of possible orientations in 3-D space for each type of orbital. This number is sometimes also called azimuthal, or subsidiary.ģ. The value of l depends on the value of n such that l = 0, 1. SECONDARY QUANTUM NUMBER ( l ) - Represents the energy sublevel, or type of orbital, occupied by the electron. It is always a positive integer, that is n = 1, 2, 3. PRINCIPAL QUANTUM NUMBER ( n) - Represents the main energy level, or shell, occupied by an electron. The quantum numbers are parameters that describe the distribution of electrons in the atom, and therefore its fundamental nature. ![]()
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