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Chemical Bonding
Factors that influence bond type
• Chemical bonds are formed when two or more
atoms lose, gain or share electrons with one
another
• How elements react to form chemical bonds is
one of the properties of an element
• Electronegativity
Bond Type
Bond Characteristics
• When the electronegativity difference is great,
the electrons are transferred completely,
forming ions
• All bonds have some ionic and some covalent
characteristics
• Classification of bond type depends on which
characteristics are more prevalent
• Generally, if the electronegativity difference
between two elements is less than 1.7, the bond
will have more covalent characteristics than
ionic
– The attraction of the cations of one element to the
anions of another element form an ionic bond
• Wh
When the
th electronegativity
l t
ti it difference
diff
between
b t
two elements is relatively small, the electrons
are not completely transferred
– Elements with high electronegativity tend to form
anions
– Elements with low electronegativity tend to form
cations
– The difference in electronegativity between two
elements determines bonding type
– The greater the difference in electronegativity, the
stronger the bond that holds the elements together
– Sharing of electrons forms a covalent bond
Formation of ionic compounds
Energy in bonding
• There are three steps to forming an ionic compound
• The difference in the energy required to form the
cation and the energy to form the anion is the
energy of formation of the compound
• Endothermic
– Formation of the cation
• Energy is required to remove electron (ionization energy)
– Formation of the anion
• Electrons are attracted to nonmetal, releasing energy
(
(electronegativity)
g
y)
– Electrostatic attraction between ions forms compound
– The energy required is greater than the energy given off
• Overall energy s absorbed
• Exothermic
– The energy given off is greater than the energy required
• All ionic bond formation is exothermic
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Ionic compounds
• Ionic compounds can contain more than two
elements
– This usually is because the compound contains a
polyatomic ion
• Polyatomic ions form when nonmetallic elements are
y bonded together
g
q
with an unequal
number of
covalently
protons and electrons
• Compounds held together by electrostatic
attraction between cations and anions
• Conduct electricity in the molten state
• Form electrolytes in solution
– Compound that dissociates into ions in solution that
will then conduct electric current
• Crystalline
• High melting point
• Easily soluble in water
Molecular compounds
Polarity
•
•
•
•
•
•
• Molecular compounds can have polar covalent
or nonpolar covalent bonds
• The higher the percentage of ionic characteristic
the more polar the bond will be
Compounds held together by covalent bonds
Do not conduct electricity
Do not form electrolytes in solution
Low melting point
Brittle
Generally not soluble in water
– 0.4 or less nonpolar
– >0.4 and < 1.0 polar
– > 1.67 ionic
Molecular characteristics
Metallic bonds
• Molecular shape and size is predicted by three
characteristics
•
•
•
•
– Bond axis
– Bond angle
– Bond length
Form between metallic atoms
Ions do not form
Outer levels of adjacent atoms overlap
Electrons delocalize and move freely within the
crystal
y
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Characteristics of metals
•
•
•
•
Luster
Conductivity
Malleability
Ductility
– The more electrons involved in a metallic bond, the
harder the metal will be
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