Chapter 8 – Covalent Bonding Mr. Calmer Lawndale High School.
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Transcript of Chapter 8 – Covalent Bonding Mr. Calmer Lawndale High School.
Review of Chapter 7
In Chapter 7, we learned about electrons being transferred (“given up” or “stolen away”)
This type of “tug of war” between a METAL and NONMETAL is called an IONIC BOND, which results in a SALT being formed
Chapter 8.1 – Molecular Compounds
In this chapter, you will learn about another type of bond in which electrons are shared
Covalent Bonds are atoms held together by SHARING electrons between NONMETALS
Salt versus MoleculesA metal cation and nonmetal anion are joined together by an ionic bond called SALTA group of atoms joined together by a covalent bond is called a MOLECULE
Monatomic vs. Diatomic Molecules
Most molecules can be monatomic or diatomic
Diatomic Molecule is a molecule consisting of two atoms
There are 7 diatomic molecules (SUPER 7) – N2, O2, F2, Cl2, Br2, I2, H2
Properties of Molecular Compounds
Lower Melting Points than Ionic Compounds (which means that they are weaker than ionic)
Liquids or gases at room temperature
Check in
Write a 5 word sentence describing molecules
Make a venn diagram for monoatomic vs diatomic molecules
Molecular Formulas
The Molecular Formula is the formula of a molecular compound
It shows how many atoms of each element a molecule contains
ExampleH2O contains 3 atoms (2 atoms of H, 1 atom of O)
C2H6 contains 8 atoms (2 atoms of C, 6 atoms of H)
Practice
How many atoms total and of each do the following molecular compounds contain?
1. H2
2. CO
3. CO2
4. NH3
5. C2H6O
Practice: True or False
1. All molecular compounds are composed of atoms of two of more elements.
2. All compounds are molecules.
3. Molecular compounds are composed of two or more nonmetals.
4. Atoms in molecular compounds exchange electrons.
5. Molecular compounds have higher melting and boiling points than ionic compounds.
TRUE
FALSE
TRUE
FALSE
FALSE
Ionic versus Covalent
IONIC COVALENT
Bonded Name Salt Molecule
Bonding Type Transfer e- Share e-
Types of Elements Metal & Nonmetal Nonmetals
Physical State Solid Solid, Liquid, or Gas
Melting Point High (above 300ºC) Low (below 300 ºC)
Solubility Dissolves in Water Varies
Conductivity Good Poor
Chapter 8.2 – Covalent Bonding
Remember that ionic compounds transfer electrons in order to attain a noble gas electron configuration
Covalent compounds form by sharing electrons to attain a noble gas electron configuration
Regardless of the type of bond, the Octet Rule still must be obeyed (8 valence electrons)
Single Covalent Bond
A Single Covalent Bond consists of two atoms held together by sharing 1 pair of electrons (2 e-)
Shared versus Unshared Electrons
A Shared Pair is a pair of valence electrons that is shared between atoms
An Unshared Pair is a pair of valence electrons that is not shared between atoms
Practice Lewis Dot Structures
Chemical Formula
# of Valence
Electrons
Single Line Bond
Structure
# of Remaining Electrons
Lewis Dot Structure
Octet Check All Atoms=8Hydrogen=2
F2
H2O
NH3
CH4
Double Covalent Bonds
A Double Covalent Bond is a bond that involves 2 shared pairs of electrons (4 e-)
Sometimes atoms attain noble gas configuration by sharing 2 or 3 pairs of electrons
Triple Covalent Bond
A Triple Covalent Bond is a bond that involves 3 shared pairs of electrons (6 e-)
Practice Lewis Dot Structure
Chemical Formula
# of Valence
Electrons
Single Line Bond
Structure
# of Remaining Electrons
Lewis Dot Structure
Octet Check All Atoms=8Hydrogen=2
O2
CO2
N2
HCN
Bond Dissociation Energy
Bond Dissociation Energy is the energy required to break a bond between two atoms
A large bond dissociation energy corresponds to a strong bond which makes it unreactive
Carbon has strong bonds, which makes carbon compounds stable and unreactive
Chapter 8.3 - Bonding Theories
A Molecular Orbitals is an orbital that applies to the entire molecule, instead of just one atom
So far, the orbitals we have been discussing are atomic orbitals (s, p, d, f) for each atom
When two atoms combine, their atomic orbitals overlap and they make molecular orbitals
Molecular Orbitals
Just as atomic orbitals belong to a particular atom, a molecular orbital belongs to molecules as a wholeEach orbital is filled with 2 electrons
A Bonding Orbital is an orbital that can be occupied by two electrons of a covalent bond (it’s the space in between the two atoms)
There are 2 types of bonding orbitals: sigma and pi
Sigma Bond ()
A Sigma Bond is when 2 atomic orbitals combine to form a molecular orbital that is symmetrical around the axis
S orbitals overlapping P orbitals overlapping end-to-end
Pi Bond ()
Pi bonding electrons are likely to be found in a sausage-shape above and below the axisPi bonds are weaker than sigma bonds
because they overlap less
P orbitals overlapping side-by-side
VSEPR Theory
VSEPR Theory predicts the 3D shape of molecules
According to VSEPR, the repulsion of electrons causes the shape of the molecule to adjust so that the electrons are far apart
Valence Shell Electron Pair Repulsion
VSEPR Theory
Unshared pairs of electrons are very important in predicting the shapes of molecules
Each bond (single, double, or triple) or unshared pair is considered a steric number
VSEPR can only be used with the central atom
Unshared pairs of electrons are very important in predicting the shapes of molecules
Use the steric number to predict the molecular geometry
Practice
Methane (CH4) – tetrahedral
Ammonia (NH3) – pyramidal
Water (H2O) – bent
Carbon Dioxide (CO2) - linear
Hybrid Orbitals
VSEPR is good at describing the molecular shapes, but not the types of bonds formed
In hybridization, several atomic orbitals mix to form hybrid orbitals
Orbital hybridization provides information about both molecular bonding and molecular shape
Bond Hybridization
Hybridization Involving Single Bonds – sp3 orbital Ethane (C2H6)
Hybridization Involving Double Bonds – sp2 orbital Ethene (C2H4)
Hybridization Involving Triple Bonds – sp orbital Ethyne (C2H2)
Try Drawing them
https://www.khanacademy.org/science/organic-chemistry/gen-chem-review/hybridization/v/pi-bonds-and-sp2-hybridized-orbitals
Chapter 8.4 – Polar Bonds and Molecules
There are two types of covalent bonds Nonpolar Covalent Bonds (share equally) Polar Covalent Bonds (share unequally)
Polar Covalent
• A Polar Covalent Bond is unequal sharing of electrons between two atoms (HCl)
• In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge
Nonpolar Covalent Bond
• A Nonpolar Covalent Bond is equal sharing of electrons between two atoms (Cl2, N2, O2)
Classification of Bonds
You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements
Type of Bond Electronegativity Difference
Nonpolar Covalent 0 0.4
Polar Covalent 0.5 1.9
Ionic 2.0 4.0
Practice
What type of bond is HCl? (H = 2.1, Cl = 3.1)
Your Turn To Practice N(3.0) and H(2.1)
H(2.1) and H(2.1)
Ca(1.0) and Cl(3.0)
Al(1.5) and Cl(3.0)
Mg(1.2) and O(3.5)
H(2.1) and F(4.0)
Difference = 3.1 – 2.1 = 1.0Therefore it is polar covalent bond.
Dipole
• No bond is purely ionic or covalent … they have a little bit of both characters
When there is unequal sharing of electrons a dipole exists
Dipole is a molecule that has two poles or regions with opposite chargesA dipole is represented by a dipole arrow pointing towards the more negative end
Practice Drawing Dipoles
P- BrP = 2.1Br = 2.8
P –Br + -
Practice H(2.1) – S(2.5) F(4.0) - C(2.5) C(2.5) - Si(1.8) N(3.0) – O(3.5)
Attractions Between Molecules
Intermolecular attractions are weaker than ionic, covalent, and metallic bonds
Besides ionic, metallic, and covalent bonds, there are also attractions between molecules
There are 2 main types of attractions between molecules: Van der Waals and Hydrogen
Van der Waals Forces
Van der Waals forces consists of the two weak attractions between molecules
1. dipole interactions – polar molecules attracted to one another
2. dispersion forces – caused by the motion of electrons (weakest of all forces)
Hydrogen Bond
Hydrogen Bonds are forces where a hydrogen atom is weakly attracted to an unshared electron pair of another atom
Hydrogen Bond
This other atom may be in the same molecule or in a nearby molecule, but always has to include hydrogen
Hydrogen Bonds have about 5% of the strength of an average covalent bond
Hydrogen Bond is the strongest of all intermolecular forces
Intermolecular Attractions
A Network Solid contains atoms that are all covalently bonded to each other
A few solids that consist of molecules do not melt until the temperature reaches 1000ºC or higher called network solids (Example: diamond, silicon carbide)
• Melting a network solid would require breaking bonds throughout the solid (which is difficult to do)