How are electrons placed in the atom?
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The document explains how electrons are arranged in atoms according to the aufbau principle, Pauli exclusion principle, and Hund's rule, which apply to the ground state of atoms. It also highlights anomalies in electron configurations for elements like chromium and copper, which do not follow typical orbital-filling rules. An analogy is provided comparing these principles to seating preferences on a bus.
![Anomalous Electron Configurations Certain atoms do not follow the orbital-filling rules: Chromium's electron configuration is [Ar]3 d 5 4 s 1 instead of the expected [Ar]3 d 4 4 s 2 if we are to follow the normal rules Copper's electron configuration is [Ar]3 d 10 4 s 1 instead the expected [Ar]3 d 9 4 s 2 There are others in the heavier d -block metals and the f -block metals. Molybdenum and Rhodium are some examples. This occurs when there are enough electrons to produce a half-filled set of degenerate orbitals (as in the case of chromium) or to completely fill a d or f subshell (like copper).](https://image.slidesharecdn.com/howareelectronsplacedintheatomold-110407082214-phpapp02/85/How-are-electrons-placed-in-the-atom-7-320.jpg)
How are electrons placed in the atom?
- 1. How are electrons placed in the atom?
- 2. Introduction Everybody knows that there are electrons orbiting atoms, but how are they arranged in the atom? There are actually a set of rules which govern the placement of electrons. The rules are called AUFBAU Principle, Pauli Exclusion Principle and Hund's Rule. However, these rules only apply to the ground state of an atom or ion .
- 3. AUFBAU Principle The lowest energy levels are always filled first Conversely, electrons are lost from the highest energy levels first The diagram shows the order in which we should fill up the subshells. http://www.100ciaquimica.net/images/temas/tema3/ima/aufbau3g.gif
- 4. Diagram showing different energy levels of various atoms Scale/Quantum Number Arrangement of electrons Orbital Elements http://www.welsch.com/gallery/vektor/Energieniveauschema_634.jpg Subshell
- 5. Pauli Exclusion Principle If there are 2 electrons occupying the same orbital, the 2 electrons must be of opposite spins so as to stay at ground state http://santasusana.org/pakelly/G%20Chemistry/Pauli.gif
- 6. Hund's Rule If multiple orbitals of the same energy are available, Hund's rule states that unoccupied orbitals will be filled before occupied orbitals are filled up by electrons having different spins. http://img.sparknotes.com/figures/5/5578bdf1aec90e46e14325a580fdbf6a/fig1_4.gif Element: Carbon
- 7. Anomalous Electron Configurations Certain atoms do not follow the orbital-filling rules: Chromium's electron configuration is [Ar]3 d 5 4 s 1 instead of the expected [Ar]3 d 4 4 s 2 if we are to follow the normal rules Copper's electron configuration is [Ar]3 d 10 4 s 1 instead the expected [Ar]3 d 9 4 s 2 There are others in the heavier d -block metals and the f -block metals. Molybdenum and Rhodium are some examples. This occurs when there are enough electrons to produce a half-filled set of degenerate orbitals (as in the case of chromium) or to completely fill a d or f subshell (like copper).
- 8. ANALOGY The seat a Singaporean would take in a bus. Orbital: A set of two seats beside one another. AUFBAU principle: One would try to be as near the front as possible since it requires lesser energy. Pauli exclusion principle: No 2 people are exactly the same. Hund's Rule: People would rather not to sit next to each other. Subshell: A set of orbitals beyond which the force of attraction towards the front is lower than the force of repulsion from other people, when it is not completely full.