Chemical bond
A mutual electrical attraction between the nuclei and valence
electrons of different atoms that binds the atoms together.
Why Bond?
• Potential energy is lowered
• More stable
Types of bonds
• Ionic
• Covalent
• metallic
Ionic bonding
• Bonding that results from the electrical attraction between large numbers of cations and anions.
Covalent bonding
• Results from the sharing of electrons pairs between two atoms.
Metallic bonding
• Bonding that results from the attraction between metal atoms and the surrounding “sea of electrons”
– Delocalized electrons – electrons that freely move around; empty orbitals overlap, electrons very mobile making a “sea” of electrons
How can you tell if a bond is ionic or covalent?
• A bond is rarely purely ionic or covalent. Usually falls somewhere between the two extremes.
• Diatomic – covalent
electronegativity• Measure of an atom’s ability to attract
electrons.
• The degree to which bond is ionic or covalent depends on the difference in electronegativities.
How to do
• Look up the electronegativities of the atoms involved on a chart.
• Subtract the two numbers
• Find where they fall on the ionic- covalent scale.
Polar
• Polar – an unequal sharing of electrons that lends a molecule to be partially negative at one end and partially positive at another. Water is an example.
Reading the chart
• Values above 1.7 are ionic, the closer you are to 3.3 the more ionic.
• Values under 1.7 are covalent.– Values under 0.3 are nonpolar -covalent– Values between 1.7 and .3 are polar -covalent
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