covalent bonding & polarity chapter 6.2. chemical bonding ionic bond – force that holds...
TRANSCRIPT
Covalent Bonding & PolarityChapter 6.2
Chemical Bonding Ionic Bond – Force that holds cations
and anions together and which involves the transfer of electrons. Occurs between a metal and a nonmetal.
Ionic Bonding Elements achieve stable electron configurations
by transferring or sharing electrons between atoms
Transferring Electrons - Those with <4 valence electrons “LEND” them
(Metals)These elements “lose” valence electronsOR
Those with >4 valence electrons “BORROW” them (Nonmetals)These elements “gain” electrons
Chemical Bonding
What do you think will happen when 2 nonmetals bond? Will there be a transfer of electrons?
Why?
FF
Covalent Bonding When two nonmetals meet - one atom is
NOT strong enough to take electrons from the other! So they must share them Covalent
Bond!
Covalent bond - is a chemical bond in which two atoms share one or more pairs of valence electrons.
Covalent Bonding
Electrons want to be in pairs – 4 pairs of 2 to fulfill the octet rule.Paired electrons are ‘happy’!Unpaired electrons are ‘sad’
Paired or Unpaired
Paired ElectronUnpaired Electron
How it Works
+
How it works!
Sharing Creates a Bond
F F
Outer Level Still only hold 8!!!!
Electron Configuration & Lewis Dot Structures
All 3 figures represent the same thing!BAR = Bond of shared electrons
F F
F F F F
This illustration shows four ways to represent a covalent bond between two hydrogen atoms.
As a space shuttle lifts off, it leaves a water vapor trail. A reaction of hydrogen and oxygen produces the water.
Diatomic means “two atoms”.
Many nonmetal elements are often found as diatomic molecules.
Atoms of same element share bonding electrons equally.
Balanced
Covalent Bonds
Single Bond
FFF F OR
Each atom now “Feels Like” it has 8 valence electrons!
Single Bond =
• One Pair of e- Shared Between Two Atoms.
• Each atom gives one e- to the shared pair
How Will These Two Bond?
Oxygen and Oxygen
O O
Double Bond
OR
•Two Pairs of Electrons are Being Shared•Each atom gives one e- to each shared pair
O O
O O
Another example!Sharing Creates a Bond
CO2
Since each are sharing two pairs Double Bond!
CO O
How Will These Two Bond?Nitrogen and Nitrogen
N NN
Triple Bond
OR
• Three Pairs of Electrons Being Shared
N N
N N
Covalent Bonding Problems:
Make a molecule out of Oxygen and two
Fluorine
Covalent Bonding Problems:
FOF
Formula: OF2
OF F
Covalent Bonding Problems:
Try Carbon and two Oxygen
Covalent Bonding Problems
OCO
CO OFormula: CO2
Unequal Sharing of Electrons
Diatomic compounds share electrons equally. Equal forces pulling on the shared
electrons
What happens when atoms do NOT share electrons equally? Unequal forces pulling on the shared
electrons
Polar Covalent Bond:Electrons not transferred from one atom to another, but…
Atom with greater attraction for electrons has a partial negative chargeOther atom has a partial positive charge.
Types of atoms determine whether a molecule is polar or non-polar.
Unequal Sharing of Electrons
Unequal Sharing of Electrons
Electronegativity = Atom’s attraction for electrons Bigger value stronger attraction
Electronegativity trends (attraction for electrons): Right side of periodic table: high
Exception for noble gases (Group #8A) - none Left side of periodic table: low Top of a group: higher Bottom of a group: lower
Prof Mokeur’s Periodic Table
Shared electrons in a hydrogen chloride molecule spend less time near the hydrogen atom than near the chlorine atom.
Unequal Sharing of Electrons
How to predict what type of bond will form between two
atoms:Non-polar covalent
Electronegativity difference is <0.5Polar covalent
Electronegativity difference is >0.5 and <2.0
Ionic bondElectronegativity difference is >2.0
Examples
Boron and HydrogenElectronegativities: B = 2.0 H = 2.1Difference: 0.1 non-polar covalent
Potassium and Iodine: Electronegativities: K = 0.8 I = 2.7Difference: 1.9 polar covalent
Sodium and ChlorineElectronegativities: Na = 0.9 Cl = 3.0Difference: 2.1 ionic