electronegativity. what is electronegativity? the ability of an element to attract bonding electrons...
TRANSCRIPT
Electronegativity
What is electronegativity?
• The ability of an element to attract bonding electrons to itself
• What does that mean?
What is electronegativity?
• The ability of an element to attract bonding electrons to itself
• What does that mean?– Where do electrons spend more of their time– Where is a reaction more likely to occur
Remember from Physics!
• Opposite charges attract– Positive goes toward negative– Negative goes toward positive
Electronegativity
• Place the following elements from most electronegative to least (these are the CHONPS elements):– Carbon– Hydrogen– Oxygen– Nitrogen– Phosphorous– Sulfur
Electronegativity
– Carbon (C): 2.5– Hydrogen (H) : 2.1– Oxygen (O): 3.5– Nitrogen (N): 3.0– Phosphorous (P): 2.1– Sulfur (S): 2.5
Electronegativity
– Hydrogen = Phosphorous: 2.1– Carbon=Sulfur: 2.5– Nitrogen: 3.0– Oxygen: 3.5
On Your Own
• Place these from most to least electronegative– Lithium – Sodium– Chlorine– Bromine– Iodine
On Your Own
• Place these from most to least electronegative– Lithium (Li)– Sodium– Chlorine– Bromine– Iodine
On Your Own
• Place these from most to least electronegative– Lithium (Li)– Sodium (Na)– Chlorine– Bromine– Iodine
On Your Own
• Place these from most to least electronegative– Lithium (Li)– Sodium (Na)– Chlorine (Cl)– Bromine– Iodine
On Your Own
• Place these from most to least electronegative– Lithium (Li)– Sodium (Na)– Chlorine (Cl)– Bromine (Br)– Iodine
On Your Own
• Place these from most to least electronegative– Lithium (Li)– Sodium (Na)– Chlorine (Cl)– Bromine (Br)– Iodine (I)
On Your Own Answers
• Place these from most to least electronegative– Chlorine: 3.0– Bromine: 2.8– Iodine: 2.5– Lithium: 1.0– Sodium: 0.9
Why do we Need This?
• To determine Bond type of a molecule (non-polar covalent, polar covalent, or ionic)
• To determine whether a reaction will occur and where on a molecule it will occur.
How do we determine Polarity?
• Basic arithmetic• Examples:• Sodium Chloride
How do we determine Polarity?
• Basic arithmetic• Examples:• Sodium Chloride– Sodium = 0.9
How do we determine Polarity?
• Basic arithmetic• Examples:• Sodium Chloride– Sodium = 0.9– Chloride = 3.0
How do we determine Polarity?
• Basic arithmetic• Examples:• Sodium Chloride– Sodium = 0.9– Chloride = 3.0– Sodium Chloride: 3.0-0.9=2.1
What does this tell me?
• If the number is between 0 and 0.5 the bond is non-polar covalent
• If the number is between 0.5 and 1.8, the bond is polar covalent
• If the number is larger than 1.8, the bond is ionic
Is what is Sodium Chloride?
• Sodium Chloride– Sodium = 0.9– Chloride = 3.0– Sodium Chloride: 3.0-0.9=2.1
• Sodium Chloride is ionic!
Another Example
• MgO
Another Example
• MgO (Magnesium Oxide)• Mg=1.2• O = 3.5• 3.5-1.2=2.3• Therefore, another ionic molecule!
Your Turn!
• Hydrogen gas (H2)• Hydrogen Bromide (HBr)• Formaldehyde (CH2O)
• SnCl4 (Give me the name as well)
• CI4 (Give me the name as well)
Your Turn!
• Hydrogen gas (H2):– 2.1-2.1=0 non-polar covalent
• Hydrogen Bromide (HBr): – 2.8-2.1=0.7 polar covalent
• Formaldehyde (CH2O): – C-H bond: 2.5-2.1= 0.4 non-polar covalent– C-O bond 3.5-2.5= 1.0 polar covalent
• SnCl4 Tin Chloride– 3.0-1.8=1.2 polar covalent
• CBr4 Carbon Tertabromide– 2.8-2.5= 0.3 non-polar covalent
And Now an Exception (Just for Fun)
• Hydrogen Fluoride– Hydrogen = 2.1– Fluoride = 4.0– 4.0-2.1=1.9
And Now an Exception (Just for Fun)
• Hydrogen Fluoride– Hydrogen = 2.1– Fluoride = 4.0– 4.0-2.1=1.9
• So it’s ionic by the calculations
And Now an Exception (Just for Fun)
• Hydrogen Fluoride– Hydrogen = 2.1– Fluoride = 4.0– 4.0-2.1=1.9
• So it’s ionic by the calculations• But it’s covalent by the rules you previously
learned
And Now an Exception (Just for Fun)
• Hydrogen Fluoride– Hydrogen = 2.1– Fluoride = 4.0– 4.0-2.1=1.9
• So it’s ionic by the calculations• But it’s covalent by the rules you previously
learned• Rule #1 of Drug Chemistry: Fluorine is
weird!!!!
Where will electrons Spend more Time?
Carbon?Or
Chlorine?
Where will electrons Spend more Time?
Carbon = 2.5Or
Chlorine = 3.0
Where will electrons Spend more Time?
Carbon = 2.5Or
Chlorine = 3.0Rule: The larger the number, the more
electronegative. The more electronegative, the more time electrons spend around that element
Where will electrons Spend more Time?
Carbon = 2.5Or
Chlorine = 3.0
Therefore, Chlorine!!!!
How do we Show This?
• C Cl• δ + δ-
• Arrow ALWAYS goes from + to -
Another Example
• O - H
Calculations
• Oxygen = 3.5• Hydrogen = 2.1
Calculations
• Oxygen = 3.5• Hydrogen = 2.1
• Therefore, Oxygen is more electronegative
Calculations
• Oxygen = 3.5• Hydrogen = 2.1• 3.5-2.1 = 1.4• Polar covalent
Depiction
O Hδ - δ +
Your Turn
• N-H• C-Br• P-O• C-S
Your Turn
• N-H– 3.0-2.1 = 0.9– Nitrogen
• C-Br– 2.5-2.8 = 0.3– Bromine
• P-O– 2.1-3.5 – Oxygen
• C-S– 2.5-2.5=0– Neither!
Your Turn
• N H• C Br• P O• C S