Academic Chemistry Mrs. Teates Newport High School Chapter 6 – Chemical Bonding Academic Chemistry Mrs. Teates Newport High School

Lesson 1 – Introduction to Chemical Bonding Lesson Essential Questions: Why do atoms form chemical bonds? How is the type of chemical bond determined? Vocabulary: chemical bond, ionic bonding, covalent bonding, nonpolar-covalent bonding, polar, polar-covalent bonding

Vocabulary Chemical Bond attractive force between atoms or ions that binds them together as a unit bonds form in order to… decrease potential energy (PE) increase stability

Na+ NO3- Vocabulary ION 1 atom 2 or more atoms Monatomic Ion Polyatomic Ion Na+ NO3-

Types of Bonds IONIC COVALENT Bond Formation e- are transferred from metal to nonmetal e- are shared between two nonmetals Type of Structure crystal lattice true molecules Physical State solid Solid, liquid, or gas Melting Point high low Solubility in Water yes usually not Electrical Conductivity yes (solution or liquid) no Other Properties odorous

Types of Bonds METALLIC e- are delocalized among metal atoms Bond Formation e- are delocalized among metal atoms Type of Structure “electron sea” Physical State solid Melting Point very high Solubility in Water no yes (any form) Electrical Conductivity Other Properties malleable, ductile, lustrous

Ionic Bonding - Crystal Lattice Types of Bonds Ionic Bonding - Crystal Lattice RETURN

Covalent Bonding - True Molecules Types of Bonds Covalent Bonding - True Molecules Diatomic Molecule RETURN

Metallic Bonding - “Electron Sea” Types of Bonds Metallic Bonding - “Electron Sea” RETURN

Bond Polarity Most bonds are a blend of ionic and covalent characteristics. Difference in electronegativity determines bond type.

Bond Polarity Electronegativity Attraction an atom has for a shared pair of electrons. higher e-neg atom  - lower e-neg atom +

Bond Polarity Electronegativity Trend Increases up and to the right.

Bond Polarity Nonpolar Covalent Bond e- are shared equally symmetrical e- density usually identical atoms

+ - Bond Polarity Polar Covalent Bond e- are shared unequally asymmetrical e- density results in partial charges (dipole) + -

Bond Polarity Nonpolar Polar Ionic View Bonding Animations.

Bond Polarity 3.0-3.0=0.0 Nonpolar 3.0-2.1=0.9 Polar 3.0-0.9=2.1 Ionic Examples: Cl2 HCl NaCl 3.0-3.0=0.0 Nonpolar 3.0-2.1=0.9 Polar 3.0-0.9=2.1 Ionic

More Bond Polarity Practice What type of bonding would be expected between the following atoms? Li and Cl Ca and Ga I and Cl K and Na

Lesson 2 – Covalent Bonding and Molecular Compounds Lesson Essential Questions: How is a molecular compound formed? What are some of the characteristics of a covalent bond? Vocabulary: molecule, chemical formula, molecular formula, bond energy, electron-dot, Lewis structure, structural formula, single bond, multiple bonds, resonance

Vocabulary Covalent bond – bond that is created by the sharing of electrons Molecule – neutral group of atoms held together by covalent bonds Molecular compound – chemical compound made of molecules

NaCl CO2 Vocabulary CHEMICAL FORMULA IONIC COVALENT Formula Unit Molecular Formula NaCl CO2

Energy of Bond Formation Potential Energy based on position of an object low PE = high stability

Energy of Bond Formation Potential Energy Diagram attraction vs. repulsion no interaction increased attraction

Energy of Bond Formation Potential Energy Diagram attraction vs. repulsion increased repulsion balanced attraction & repulsion

Energy of Bond Formation Bond Energy Energy required to break a bond Bond Energy Bond Length

Energy of Bond Formation Bond Energy Short bond = high bond energy

Lewis Structures Electron Dot Diagrams Pick the central atom Count the valence electrons (they are what electron dot diagrams show) Place electrons around the atom

Ne Lewis Structures Octet Rule Most atoms form bonds in order to obtain 8 valence e- Full energy level stability ~ Noble Gases Ne

Lewis Structures - + Nonpolar Covalent - no charges Polar Covalent - partial charges + -

Practice Drawing Lewis Structures On page 186 in your text book do practice problems #1-4 Draw the Lewis structure of ammonia, NH3 Draw the Lewis structure for hydrogen sulfide, H2S Draw the Lewis structure for silane, SiH4 Draw the Lewis structure for phosphorus trifluoride, PF3

Multiple Covalent Bonds Some elements can share more than one electron pair. Double bond (two pairs of electrons are shared) Triple bond (three pairs of electrons are shared)

Practice of Lewis Structures for multiple bonds Draw Lewis structures for each of the following molecules: O2 CO2 N3 N2

Resonance Occurs when more than one valid Lewis structure can be written for a particular molecule (due to position of double bond) These are resonance structures of benzene. The actual structure is an average (or hybrid) of these structures.

Resonance in Ozone Note the different location of the double bond Neither structure is correct, it is actually a hybrid of the two. To show it, draw all varieties possible, and join them with a double-headed arrow.

Polyatomic ions – note the different positions of the double bond. Resonance in a carbonate ion (CO32-): Resonance in an acetate ion (C2H3O21-):

Molecular Nomenclature Prefix System (binary compounds) 1. Less e-neg atom comes first. 2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element. 3. Change the ending of the second element to -ide.

Molecular Nomenclature PREFIX mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca- NUMBER 1 2 3 4 5 6 7 8 9 10

Molecular Nomenclature CCl4 N2O SF6 carbon tetrachloride dinitrogen monoxide sulfur hexafluoride

Molecular Nomenclature arsenic trichloride dinitrogen pentoxide tetraphosphorus decoxide AsCl3 N2O5 P4O10

Lesson 3 – Ionic Bonding and Ionic Compounds Lesson Essential Questions: How is an ionic bond formed? What are some of the characteristics of an ionic bond? Vocabulary: ionic compound, formula unit, lattice energy, polyatomic ion

Vocabulary: Ionic compound – composed of positive and negative ions that are combined so that the charges are equal.

NaCl CO2 Vocabulary CHEMICAL FORMULA IONIC COVALENT Formula Unit Molecular Formula NaCl CO2

Forming Ionic Compounds Electron dot notation is used to note changes. Form to create an atmosphere of stability

Lewis Structures and Ionic Compounds Covalent – show sharing of e- Ionic – show transfer of e-

Characteristics of Ionic Bonding Ions minimize potential energy in crystals by forming a crystal lattice. Distance between all ions represent a balance of attraction between oppositely charged particles and repulsion between like charged particles

Energy of Bond Formation Lattice Energy Energy released when one mole of an ionic crystalline compound is formed from gaseous ions

Ionic vs. Covalent Ionic High melting temperature High boiling point Hard Brittle, because slight shift of crystal can cause it to break Conduct electricity when dissolved in water Covalent Low melting temperature Low boiling point Do not conduct electricity Not as brittle

Ionic Nomenclature Ionic Formulas Write each ion, cation first. Don’t show charges in the final formula. Overall charge must equal zero. If charges cancel, just write symbols. If not, use subscripts to balance charges. Use parentheses to show more than one polyatomic ion. Stock System - Roman numerals indicate the ion’s charge.

Ionic Nomenclature Ionic Names Write the names of both ions, cation first. Change ending of monatomic ions to -ide. Polyatomic ions have special names. Stock System - Use Roman numerals to show the ion’s charge if more than one is possible. Overall charge must equal zero.

Ionic Nomenclature Consider the following: Does it contain a polyatomic ion? -ide, 2 elements  no -ate, -ite, 3+ elements  yes Does it contain a Roman numeral? Check the table for metals not in Groups 1 or 2. No prefixes!

Ionic Nomenclature Common Ion Charges 1+ 2+ 3+ NA 3- 2- 1-

Ionic Nomenclature potassium chloride magnesium nitrate copper(II) chloride K+ Cl-  KCl Mg2+ NO3-  Mg(NO3)2 Cu2+ Cl-  CuCl2

Ionic Nomenclature NaBr Na2CO3 sodium bromide FeCl3 sodium carbonate iron(III) chloride

Lesson 4 – Metallic Bonding Lesson Essential Questions: How is a metallic bond formed? What are some of the characteristics of a metallic bond? Vocabulary: metallic bond, alloy

Characteristics of Metallic Bonds Metal ions held together by attraction to free floating electrons. (Sea of electrons) Good conductors of electricity – Why?

Characteristics of Metallic Bonds Cont. Malleable Ductile Bond strength – related to enthalpy of vaporization The more energy required to vaporize, the stronger the bond. See table on page 196.

Alloys A mixture of two or more substances, one of which must be a metal. Common alloys include steel, 14K gold, 18K gold, cast iron, sterling silver, and bronze. Within different alloys, there can be different types of mixtures – ex. Steel Where do we find alloys?

Compare/Constrast Use the 3 circle Venn diagram to compare and contrast ionic, metallic, and covalent bonding.

Lesson 5 – Molecular Geometry Lesson Essential Questions: How is the VSEPR Theory useful? What are the different forces present in bonding? Vocabulary: VSEPR theory, hybridization, dipole, hydrogen bonding, London dispersion forces

VSEPR Theory Valence Shell Electron Pair Repulsion Theory Electron pairs orient themselves in order to minimize repulsive forces.

Lone pairs repel more strongly than bonding pairs!!! VSEPR Theory Types of e- Pairs Bonding pairs - form bonds Lone pairs - nonbonding e- Lone pairs repel more strongly than bonding pairs!!!

VSEPR Theory Lone pairs reduce the bond angle between atoms.

Determining Molecular Shape Draw the Lewis Diagram. Tally up e- pairs on central atom. double/triple bonds = ONE pair Shape is determined by the # of bonding pairs and lone pairs. Know the 8 common shapes & their bond angles!

VSEPR Table

Common Molecular Shapes 2 total 2 bond 0 lone BeH2 LINEAR 180°

Common Molecular Shapes 3 total 3 bond 0 lone BF3 TRIGONAL PLANAR 120°

Common Molecular Shapes 3 total 2 bond 1 lone SO2 BENT <120°

Common Molecular Shapes 4 total 4 bond 0 lone CH4 TETRAHEDRAL 109.5°

Common Molecular Shapes 4 total 3 bond 1 lone NH3 TRIGONAL PYRAMIDAL 107°

Common Molecular Shapes 4 total 2 bond 2 lone H2O BENT 104.5°

Common Molecular Shapes 5 total 5 bond 0 lone PCl5 TRIGONAL BIPYRAMIDAL120°/90°

Common Molecular Shapes 6 total 6 bond 0 lone SF6 OCTAHEDRAL 90°

Examples PF3 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107°

Examples CO2 2 total 2 bond 0 lone LINEAR 180°

Practice Problems Identify the molecular geometry for the following molecules: HI CBr4 CH2Cl2

Intermolecular Forces Intermolecular forces = forces between molecules. The boiling point of a liquid is a good measure of the intermolecular forces between its molecules: the higher the boiling point, the stronger the forces between the molecules. Types of intermolecular forces Dipole-dipole forces Hydrogen bonding London dispersion forces

Dipole – Dipole Forces Dipole – created by equal but opposite charges that are separated by a short distance. A dipole is represented by an arrow with its head pointing toward the negative pole and a crossed tail at the positive pole. The dipole created by a hydrogen chloride molecule is indicated as follows: Dipole-dipole forces are the forces of attraction between polar molecules.

Dipole-dipole forces cont. The negative region in one polar molecule attracts the positive region in adjacent molecules. So the molecules all attract each other from opposite sides. Dipole-dipole forces act at short range, only between nearby molecules.

Hydrogen Bonding Hydrogen bonding = intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons in a nearby molecule.

London Dispersion Forces London Dispersion Forces = intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles. http://itl.chem.ufl.edu/2045/matter/FG11_005.GIF

Works Cited Modern Chemistry Textbook www.nclark.net http://mrsj.exofire.net/chem/ http://cottonchemistry.bizland.com/chem/chemnotes1.htm http://www.unit5.org/chemistry/