chemical bonds notes atoms combine to form compounds by holding pairs of electrons between them....
TRANSCRIPT
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Chemical Bonds Notes• Atoms combine to form compounds by
holding pairs of electrons between them.
• *(Draw the picture below)• The paired electrons are known as a
chemical bond. HH C H H
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Chemical Bond Classification
• Chemical bonds are classified by the way the electrons are held between the atoms that are bonding to each other.
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Chemical Bond Classification
• Electrons can be held in a bond by one of two ways:–Electrons are equally shared by both
atoms. (Covalent)–Electrons are “exchanged” from one
atom to another forming ions. (Ionic)
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Properties of Covalent Bonds
• Covalent bonds occur between two non-metal atoms.
• In covalent bonds electrons are shared by the atoms involved in the bond.
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Examples of Covalent Bonds
• Examples of compounds formed with covalent bonds include:–Hydrogen gas (H2)
–Ammonia (NH3)– Large biological molecules such as
glucose (C6H12O6).
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Properties of Ionic Bonds
• Ionic bonds occur between a metal atom and a non-metal atom.
• In ionic bonds electrons are exchanged or transferred from the metal atom to the non-metal atom.
• After the transfer of electrons, both atoms become oppositely charged, keeping both atoms together (bonded).
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Examples of Ionic Bonds• Examples of compounds formed with
ionic bonds include:– Sodium chloride (NaCl)– Strontium sulfide (SrS)
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Next steps…if you’ve mastered bonding
All elements have a certain ELECTRONEGATIVITYThis describes tendency of an atom to attract electrons towards itself. (aka-it’s hunger for electrons)
High Electronegativity = High attraction/hunger for electrons.
Low Electronegativity = Low attraction/hunger for electrons.
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Electronegativity differences and bonding
• If atom A is very electronegative (electron hungry) and atom B is not, the electrons will move toward atom A and this will result in an IONIC BOND where the electrons are transferred.
• If atom A’s electronegativity is only a little greater than atom B, they will share the electrons unevenly (POLAR COVALENT BOND) (electrons will be closer to atom A and one end of the group is more negative than the other.)
• If atom A and atom B have the same or very similar electronegativities the electrons are evenly shared and it makes a NONPOLAR COVALENT BOND.
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ELECTRONEGATIVITY DIFFERENCES
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Electronegativity Difference
Type of Bond Electrons
0-.5 Non Polar Covalent
Electrons equally shared
Greater than .5- 1.7
Polar Covalent Uneven sharing of electrons
Greater than 1.7 Ionic Electrons are Transferred
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Some periodic tables will also list the electronegativity.
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Ionic Bond or Covalent Bond1. NaCl2. FeCl3
3. SO3
4. H2O
5. MgO
• Ionic• Ionic• Covalent• Covalent• Ionic
How do you know? Look at the atoms and determine whether there are metal atoms present or not. (Metal & Nonmetal=Ionic!)
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Practice!! Get your whiteboards
Ionic Bonding• Potassium and Fluorine• Magnesium and Iodine• Sodium and Oxygen• Sodium and Chlorine• Calcium and Chlorine• Aluminum and Chlorine
Covalent Bonding • Hydrogen and Hydrogen• Hydrogen and Oxygen• Chlorine and Chlorine• Carbon and Hydrogen• Oxygen and Oxygen• Carbon and Oxygen