Slide 1
Bonding can lower the energy of an arrangement
A chemical bond holds atoms in an arrangement with lower energy than the relevant separated state. Electrons and nuclei determine that balance.
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At large separation, attraction can favour approach. At very short distances, strong repulsions prevent unlimited collapse, giving a characteristic bond length where the balance is favourable.
Slide 2
Covalent bonds share electron density
In a covalent bond, electron density is shared between atoms. This can hold atoms together in a molecule or an extended network.
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Sharing need not be equal. Different attractions for electrons produce polar bonds, and molecular shape determines whether individual bond polarities reinforce or cancel in the whole molecule.
Slide 3
Ionic crystals use attraction between charged neighbours
Ionic bonding involves attraction between positively and negatively charged ions. In a crystal, each ion interacts with several neighbours.
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Table salt is not a collection of isolated sodium–chlorine pairs. Its formula records the ratio of ions in an extended structure, a distinction that matters when explaining melting and dissolving.
Slide 4
Breaking bonds costs energy; forming new interactions can return more
Separating bonded atoms requires energy. A reaction releases energy overall only when forming new interactions returns more than breaking old ones requires.
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Describing a fuel as releasing energy by breaking its bonds alone misses half the balance. Reactions rearrange both reactant and product bonding, and the net change determines whether heat is released.
Slide 5
Real bonds can mix ionic and covalent character
Covalent and ionic are valuable descriptions, but real bonds can have mixed character. Electron distribution is richer than a simple binary label.
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Metallic bonding adds another pattern, with electrons spread across many atoms. These different arrangements help explain why materials vary in conductivity, brittleness and other macroscopic properties.
Sources
- Energy Levels, Electrons, and Covalent Bonding
American Chemical Society
- Energy Levels, Electrons, and Ionic Bonding
American Chemical Society