Chapter 9 Covalent Bonding

Why do Atoms Bond? Ionic Bond Get to a stable electron configuration 8 Valence Electrons Called the “Noble Gas” configuration Ionic Bond One atom takes another atom gives electron(s) so each can be at 8 valence electrons Covalent Bond Atoms share electrons so that they are all at 8 valence electrons

What is a Covalent Bond? Covalent Bond: The chemical bond that results from the sharing of electrons The shared electrons are considered to be part of both energy levels of the elements that are bonded and sharing electrons Occurs when elements are close to each other on the periodic table Majority form between non-metallic elements

Formation of a Covalent Bond Diatomic Molecules Two of the same monatomic molecules sharing single or pairs of electrons to get to the stable noble gas configuration Occur in nature because they are more stable than individual atoms F2 N2 O2 Cl2 Br2 I2

Formation of a Covalent Bond Diatomic Molecules

Single Covalent Bonds A covalent bond in which a single electron is shared Bonding Pair = pair of shared electrons Lewis Dot Structure A line is DRAWN to represent the bonding pair Group 7A = forms 1 covalent bond Group 6A = forms 2 covalent bonds Group 5A = forms 3 covalent bonds Group 4A = forms 4 covalent bonds Hydrogen = Forms 1 covalent bond

Single Covalent Bonds

Single Covalent Bonds Sigma Bond Sigma Bond AKA Single Covalent Bonds Symbolized by the Greek Letter σ Occurs when electron pair is centered between two atoms If the electron orbitals overlap end-to-end Concentrates the electrons in a bonding orbital between two atoms

Multiple Covalent Bonds When atoms share more than 1 electron to attain noble gas configuration

Think-Pair-Share Take 30 seconds to think about which diatomic molecules might form double covalent bonds. Write these on your whiteboard/expo sheet Take 30 seconds to discuss your finding with your partner. Add/subtract and change your molecules, as needed Take 30 seconds and be prepared to share with the class

Multiple Covalent Bonds

Multiple Covalent Bonds Pi Bond A pi-bond is formed when parallel orbitals overlap to share electrons Denoted by П Double Covalent Bond has one sigma and one pi bond Triple covalent bond has one sigma and two pi bonds

Multiple Covalent Bonds Pi Bond

Strength of Covalent Bonds Depends on how much distance separates the bonded nuclei More shared electrons = stronger covalent bonds Bond length decreases Endothermic Reaction = occur when a greater amount of energy is required to break existing bonds in the reactants than released when the new bonds formed Exothermic Reaction = occur when a more energy is released forming new bonds than in released in breaking apart the reactants

Naming Binary Molecular Compounds The first element in the formula is always named first, using the entire element name The second element in the formula is named using the root of the element and adding the suffix “-ide” Prefixes are used to indicate the number of atoms of each type that are present within the compound The first element will never use the word “Mono”

Covalent Bond Prefixes Number of Atoms Prefix 1 Mono- 2 Di- 3 Tri- 4 Tetra- 5 Penta- 6 Hexa- 7 Hepta- 8 Octa- 9 Nona- 10 Deca-

Name the Following Compounds CCl4 As2O3 CO SO2 NF3

Name the Following Compounds CCl4 – Carbon Tetrachloride As2O3 – Diarsenic Trioxide CO – Carbon Monoxide SO2 – Sulfur Dioxide NF3 – Nitrogen Trifluoride

Common Names of Some Molecular Compounds Formula Common Name Common Compound Name H2O Water Dihydrogen monoxide NH3 Ammonia Nitrogen trihydride N2H4 Hydrazine Dinitrogen tetrahydride N2O Nitrous Oxide (Laughing Gas) Dinitrogen monoxide NO Nitric Oxide Nitrogen monoxide

Naming Binary Acids Binary acids contains hydrogen and one other element Use the prefix “hydro-” to name the hydrogen part of the compound The rest of the name is element root + “ic” Place the word acid after the name HBr = hydrobromic acid What do you think HCN would be named?

Naming Oxyacids Acids Oxyacids contains an oxyanion and a hydrogen Determine the oxyanion present If it ends with “ate” replace with “ic” If it ends with “ite” replace with “ous” Acid name = element root + proper ending then acid HClO3 = Chloric Acid HClO2 = Chlorous Acid

Structural Formulas Structural Formula: Letter symbols and bonds to show relative positions of atoms The Lewis Structure can be used to predict many structural formulas

Lewis Structure Rules Predict the location of certain atoms Hydrogen is always the terminal (end) atom Central atom is the atom with the least attraction for shared electrons Often closest to the left on the periodic table 2) Determine the total number of electrons available for bonding (valence electrons in the molecule) Determine number of bonding pairs by dividing the number of electrons available for bonding in two Place one bonding pair between the central atom and each of the terminal atoms Subtract number of pairs used in step 4 from total number of bonding pairs. The remaining electrons pairs include lone pairs and those used in double and triple bonds Convert bonds to double and triple bonds until central atom has an octet.

Resonance Structures Resonance is a condition that occurs when more than one valid Lewis Structure can be written for a molecule or ion

Resonance Structures Examples

Exceptions to the Octet Rule Those elements with odd number of valence electrons cannot form a bonded octet Certain compounds form with fewer than 8 valence electrons present Coordinate covalent bond: When one atom donates a pair of electrons to be shared with an atom or ion that needs two electrons to be stable The central atom has more than 8 valence electrons Will form an expanded octet

Octet Rule Exceptions Examples

Coordinate Covalent Bond Examples

Molecular Shape VESPR Model Bond Angle Valence Shell Electron Pair Repulsion Model Based on the arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom Bond Angle The angle formed by any two terminal atoms and the central atom Those predicted by VESPR model are supported by experimental evidence Lone pairs of electrons will have a slightly larger orbit than the shared electrons

Molecular Shape VESPR Model Bond Angle Valence Shell Electron Pair Repulsion Model Based on the arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom Bond Angle The angle formed by any two terminal atoms and the central atom Those predicted by VESPR model are supported by experimental evidence Lone pairs of electrons will have a slightly larger orbit than the shared electrons

Vertical to Horizontal: 90o Horizontal to Horizontal 109.5o sp3d Total Pairs Shared Pairs Lone Pairs Molecular Shape Name Molecular Shape Bond Angle Hybrid Orbital 2 Linear 180o sp 3 Trigonal Planar 120o sp2 4 Tetrahedral 109.5o sp3 1 Trigonal Pyramid 107.3o Bent 104.5o 5 Trigonal Bipyramidal Vertical to Horizontal: 90o Horizontal to Horizontal 109.5o sp3d 6 Octahedral 90o sp3d2

Hybridization A process in which atomic orbitals are mixed to form new, identical hybrid orbitals Each hybrid orbital contains 1 electron to be shared with another atom Lone pairs can also occupy hybrid orbitals

Electronegativity and Polarity Polar Covalent Bonds Formed when there is a large difference in electronegativity Results in the unequal sharing of electrons When formed, the shared electrons are pulled towards one of the atoms Electrons spend more time around this atom, than the other in the bond Forms a partial negative and partial positive charge Polar bonds are often called dipoles

Molecular Polarity Non-polar = Similar electronegativities and charges are balanced within the VESPR Shape a Polar = Dissimilar electronegativities and charges are not- balanced within the VESPR Shape

Solubility Polar molecules and Ionic Molecules are soluble in polar substances Non-polar substances are only soluble by non-polar substances

Properties of Covalent Compounds Differences in properties is result of the attractive forces Covalent: Force between atoms in molecules is strong, but the attraction between individual molecules is weak (intermolecular forces or Van der Waals Forces) Dispersion Force: The intermolecular force between two non- polar compounds Dipole-Dipole Force: The intermolecular force between two polar compounds Hydrogen Bond: Between a Hydrogen and a Flourine, Oxygen or Nitrogen Atom Weak to Strong

Covalent Properties Consist of uncharged or neutral molecules Usually liquids or gasses If solid, soft and waxy Usually a low melting point (exception giant molecular compounds) Not a conductor in all states (think solids) Solubility in water depends on polarity