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Models of the Atom. Remember: models are used to help us to understand what we cannot readily see…they can change as we continue to learn. Bohr Model. Electrons travel in orbits/paths These orbits have fixed energies…we can call them energy levels .
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Models of the Atom Remember: models are used to help us to understand what we cannot readily see…they can change as we continue to learn.
Bohr Model • Electrons travel in orbits/paths • These orbits have fixed energies…we can call them energy levels. • A quantum is the amount of energy to move from one to another energy level. • There are different amounts of energy needed to change to different levels.
Quantum Mechanical Model • Determines how much energy an electron can have and how likely it is to be found in various locations around the nucleus. • The realization is that we can only give a probability of where the electrons are…this probability of location is now called an atomic orbital.
Principle Energy Levels • The first number is the energy level. • The second number is the sub-shell; these are named s, p, d, and f. The number of available sub-shells increases as the energy level increases. For example, the first energy level only an s sub-shell while the second energy level contains an s sub-shell and a p sub-shell.
Electron Capacity in Sub-shells • The number in superscript is the number of electrons in a given sub-shell. Each sub-shell can only hold a particular number of electrons. These electrons are held in pairs. • S: has capacity for 2 electrons • P: has capacity for 6 electrons • D: has capacity for 10 electrons • F: has capacity for 14 electrons
Arranging the Electrons • Aufbau Principle: electrons occupy the lowest energy orbitals first. See fig. 5.7, 133. • Pauli Exclusion Principle: an atomic orbital may describe (locate) either one or two electrons, and they must have opposite spins; denoted with ↑ or ↓. • Hund’s Rule: one electron enters each orbital until all are occupied with one of the same spin direction before the second electron, of opposite spin, enters the first orbital. • There are a few exceptions: pg. 136.
QMM, continuedQuantum Numbers • n = 1, 2, 3, ...., denoting energy; • l = 0, 1, ..., n-1, denoting angular momentum • m = -l, ...., l, denoting orientation (the "magnetic quantum number"), • s = -1/2, 1/2, denoting spin (m s is also used in place of s)
