covalent bonding notes formed only between 2 or more nonmetals
TRANSCRIPT
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Covalent Bonding NotesFORMED ONLY BETWEEN 2 OR MORE NONMETALS
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Electronegativity
Less electronegative goes first followed be the more electronegative.•Electronegativity: atom’s ability to attract electrons in a chemical bond. (higher electronegativity means the atom wants electrons more)Example: HF (Hydrogen Flouride)• H (2.1) and F(4.0)
How do you know which nonmetals to write first?
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Yes, there are 2 kinds of covalent bonds!
• Polar covalent: the electrons are shared, but one atom is pulling on the electrons a lot more. The electrons spend more time around that atom.
• Nonpolar covalent: the electrons are evenly shared between the two atoms. Ex. Cl2, H2
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O(3.5) – O (3.5) = 0Nonpolar covalent bond
O2
• The electronegativity difference is zero.• The electrons are equally shared between two
oxygen atoms forming a nonpolar covalent bond.
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O(3.5) – H (2.1) = 1.4Polar covalent bond
H2O
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Properties of Covalent Compounds
1) Covalent compounds generally have much lower melting and boiling points than ionic compounds. 2) Covalent compounds are soft and squishy (compared to ionic compounds, anyway).
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Properties, Cont’d
• 3) Covalent compounds tend to be more flammable than ionic compounds.
– There are exceptions to this rule!
• 4) Covalent compounds don't conduct electricity in water.
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How to Name Covalent Compounds
• 1. Name the first element (normal name)
• 2. Name the second element (root name + “-ide”)
• 3. Add prefixes to indicate how many atoms of each element are in the molecule
(Subscripts)• Exception: no need to use “mono” for first element.
Example: CO2 = carbon dioxide
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Prefixes
Subscript prefix1 Mono2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octa-9 Nona-10 Deca-
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Diatomics• Diatomic elements are elements that do not
exist singularly in nature because they are highly reactive.
“Which elements are the diatomics?”“HON, it’s the halogens!”
• H2, O2, N2, F2, Cl2, Br2, I2
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Ionic vs Covalent Bonding
• Ionic: electron(s) leave one atom & gained by another atom to satisfy both atoms’ octets, this results in the formation of ions. The resulting opposite charges attract each other.
• Covalent: electrons are shared by two or more atoms to satisfy their octets.
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How can you tell if a bond is IONIC or COVALENT?
• Subtract the two electronegativity values (look at an electronegativity chart p. 263).
>1.7 to 4.0: Ionic >0.4 to 1.7: Polar Covalent 0.0 to 0.4: Non-Polar Covalent
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How can you tell if a bond is IONIC or COVALENT?
• Easy way:
All metals = metallic bondNonmetals and Metals = ionic bondAll nonmetals = covalent bond
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• The closer the elements are on the periodic table, their electronegativities are more similar… more likely to form covalent bonds
• Farther away… greater difference in electronegativity… more likely to form ionic bonds.
• Metal + nonmetal = usually ionic• Nonmetal + nonmetal = usually covalent.
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Bond Dissociation Energy
• Bond dissociation energy = energy required to break a covalent bond.
Highest bond energy Lowest bond energyHardest to break Easiest to break
Triple Double Single Bond Bond BondShortest bond length Longest bond lengthStrongest Weakest
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Memorize these exceptions
Chemical formula name
H2O water
CH4 Methane
NH3 ammonia
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MEMORIZE THESE ACID NAMES
Acid Name
HCl Hydrochloric acid
H2SO4 Sulfuric acid