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 Molecules A metal cation and nonmetal anion are joined together by an ionic bond called SALT A 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 Liquids or gases at room temperature Lower Melting Points than Ionic Compounds (which means that they are weaker than ionic)

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 Example H2O 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? H2 CO CO2 NH3 C2H6O

Practice: True or False All molecular compounds are composed of atoms of two of more elements. All compounds are molecules. Molecular compounds are composed of two or more nonmetals. Atoms in molecular compounds exchange electrons. 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

http://www.diffen.com/difference/Covalent_Bonds_vs_Ionic_Bonds

Check in Make a Venn Diagram from ionic vs covalent bonds

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-)

Electron Dot Structure

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

Check in What was the difference between the pictures Make a guess and tell your neighbor

Practice Lewis Dot Structures Chemical Formula # of Valence Electrons Single Line Bond Structure # of Remaining Electrons Lewis Dot Structure Octet Check All Atoms=8 Hydrogen=2 F2 H2O NH3 CH4

Double Covalent Bonds Sometimes atoms attain noble gas configuration by sharing 2 or 3 pairs of electrons A Double Covalent Bond is a bond that involves 2 shared pairs of electrons (4 e-)

Triple Covalent Bond A Triple Covalent Bond is a bond that involves 3 shared pairs of electrons (6 e-)

Covalent Bonds

Practice Lewis Dot Structure Chemical Formula # of Valence Electrons Single Line Bond Structure # of Remaining Electrons Lewis Dot Structure Octet Check All Atoms=8 Hydrogen=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 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 A Molecular Orbitals is an orbital that applies to the entire molecule, instead of just one atom

Molecular Orbitals Just as atomic orbitals belong to a particular atom, a molecular orbital belongs to molecules as a whole Each 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

S orbitals overlapping P orbitals overlapping end-to-end 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

P orbitals overlapping side-by-side Pi Bond () Pi bonding electrons are likely to be found in a sausage-shape above and below the axis Pi bonds are weaker than sigma bonds because they overlap less P orbitals overlapping side-by-side

Valence Shell Electron Pair Repulsion 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

A Few VSEPR Shapes

Nine possible molecular shapes

Practice drawing

VSEPR Theory Unshared pairs of electrons are very important in predicting the shapes of molecules 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 Use the steric number to predict the molecular geometry VSEPR can only be used with the central atom

Methane (CH4) – tetrahedral Ammonia (NH3) – pyramidal 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 Orbital hybridization provides information about both molecular bonding and molecular shape In hybridization, several atomic orbitals mix to form hybrid orbitals

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

http://www.grandinetti.org/orbital-hybridization

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 Your Turn To Practice What type of bond is HCl? (H = 2.1, Cl = 3.1) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond. 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)

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 charges A dipole is represented by a dipole arrow pointing towards the more negative end

Practice Drawing Dipoles P- Br P = 2.1 Br = 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 Besides ionic, metallic, and covalent bonds, there are also attractions between molecules Intermolecular attractions are weaker than ionic, covalent, and metallic bonds 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 few solids that consist of molecules do not melt until the temperature reaches 1000ºC or higher called network solids (Example: diamond, silicon carbide) A Network Solid contains atoms that are all covalently bonded to each other Melting a network solid would require breaking bonds throughout the solid (which is difficult to do)

Chapter 8 Assessment Page 247 Homework Chapter 8 Assessment Page 247 #’s 39-41, 43-46, 51, 53, 54, 57-59, 61, 65, 68, 83, 85, 86, 89, 96, 99, 100