Chemistry notes

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Structure and bonding:

                                                             Valence electrons

• The electrons in the outer shell (largest n) are called valence electrons

• Very important for chemical reactions and holding matter together • If the outer shell is filled, the atom is inert

• If not, there is a tendency for the outer shell to become filled

Electronegative – if it is almost full, the atom has a tendency to gain enough electrons to fill the shell

Electropositive – if it is almost empty, it easily losses the electrons in the outer shell

                                                         Types of atomic bonds

1. Ionic (large interatomic forces, nondirectional, electron transfer, coulombic forces)

When sodium is burned in a chlorine atmosphere, it produces the compound sodium chloride. This has a high melting point (800 ºC) and dissolves in water to to give a conducting solution. Sodium chloride is an ionic compound, and the crystalline solid has the structure shown on the right. Transfer of the lone 3s electron of a sodium atom to the half-filled 3p orbital of a chlorine atom generates a sodium cation (neon valence shell) and a chloride anion (argon valence shell). Electrostatic attraction results in these oppositely charged ions packing together in a lattice. The attractive forces holding the ions in place can be referred to as ionic bonds.

2. Covalent (large interatomic forces, localized (directional), electron sharing)

The other three reactions shown above give products that are very different from sodium chloride. Water is a liquid at room temperature; carbon dioxide and carbon tetrafluoride are gases. None of these compounds is composed

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