Chemical Bonding revised

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Electron Exchange and Ionic Bond Formation

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Metallic Bonding

Metals can form bonds with other metals, but it is neither covalent or ionic

Metals cannot share electrons to form an octet of electrons around each atom

Imagine 8 sodium atoms all trying to share the same 8 electrons

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Although metal atoms do not form covalent or ionic bonds with each other, there must be relatively strong attractive forces holding the atoms together or else the metals would be in a gaseous state

In metallic bonding, the valence electrons are delocalized, which means they are free to move from one atom to the next

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Because the electrons are free to move, all of the atoms share all of the valence electrons

It is the electrostatic force between the positively charged metal ions and the negative electrons that make the metallic bond

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Ionic Crystals

Rather than one metal bonding to one non-metal, ionic substances have their ions packed together in a crystal lattice

The crystals can also be represented in a ball and stick model

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The sticks represent the attractive forces between the ions

Since all the attractions are equal, there are no pairs of ions to be identified as molecules

Therefore the formula only represents the ratio of the ions in the crystal

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The smallest ratio of ions in the crystal is called a formula unit, not a molecule

Shape of the macroscopic crystals is determined by the way their ions pack together

The smallest set of ions in a crystal needed to make the pattern is called a unit cell

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Table Salt Sucrose Uncut Diamond

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The size of each ion influences the pattern of ions

Another influence is the relative charge of the ions, and therefore the ratio of ions in the crystal

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Crystal formation

Many beautiful crystal formations can be found in nature as well as in the laboratory

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