Chapter4Lecturepart2

Chapter4Lecturepart2 - Chapter 4 About electron transfers...

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6 Copyright: 2010 Prof. Magde Chapter 4: About electron transfers • The protons on the previous slide were so tiny that they really are wherever we assign them. • Electrons are big and diffuse, roughly the size of the entire atom. The ones closest to the nucleus get sucked in by electrostatic forces and really must be said to be associated with the nucleus they go with; but even they are huge compared to the nucleus itself. • The outer electrons of an atom can move around. They can hop to another atom to make ions, as we have seen. • But even when there are no ions, when the atoms are joined in the same molecule, the electrons are often caught neglecting their own home to some extent and philandering a bit with a neighbor atom. • We want some bookkeeping to account for this.
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6 Copyright: 2010 Prof. Magde Chapter 4: Oxidation Numbers • We assign oxidation numbers to every atom to indicate whether it has exactly and fully its own electrons and no more, or it is cheating a bit and inviting electrons from neighbors to visit. • Like other words in science, there is a history to where the name came from, but it is not helpful to worry about that. Oxidation numbers are what they are. No more, no less. • Redox reactions result in changes in the oxidation numbers of atoms in a molecule as a result of total or partial movements of electrons. • So we need to learn to assign oxidation numbers to every atom in any molecule. • Memorize the rules.
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6 Copyright: 2010 Prof. Magde Chapter 4: Oxidation Numbers 1. The rules are in priority order. Higher rules must be satisfied before lower rules. 2. The sum of the oxidation numbers in any neutral molecule must be 0 and in any ion it must equal the charge of the ion. So for O 2 the sum must be zero, and for SO 4 2 the sum is minus two. 3. If two atoms appear to be identical, they must
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Chapter4Lecturepart2 - Chapter 4 About electron transfers...

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