Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms Objectives: Describe the trends in the periodic table Describe the trends in the periodic table Know how to draw Lewis Structures of atoms Know how to draw Lewis Structures of atoms Understand and predict the formation of ionic bonds Understand and predict the formation of ionic bonds Understand and predict covalent bonds Understand and predict covalent bonds Describe electronegativity Describe electronegativity Know how to draw complex lewis structures of compounds Know how to draw complex lewis structures of compounds Understand the formation of compounds containing polyatomic ions Understand the formation of compounds containing polyatomic ions Describe molecular shape, including the VSEPR model Describe molecular shape, including the VSEPR model

Periodic Trends in Atomic Properties Periodic table designed to show trends Periodic table designed to show trends Use trends to predict properties and reactions between elements Use trends to predict properties and reactions between elements Trends include: Trends include: Metals, nonmetals, metalloids Metals, nonmetals, metalloids Atomic radius Atomic radius Ionization energy Ionization energy Electronegativity Electronegativity

Metals, Nonmetals and Metalloids Metals: Metals: Lustrous, malleable, good conductors of heat and electricity Lustrous, malleable, good conductors of heat and electricity Left-hand side of table Left-hand side of table Most elements are metals Most elements are metals Tend to lose electrons and form positive ions Tend to lose electrons and form positive ions

Metals, Nonmetals and Metalloids Nonmetals: Nonmetals: Nonlustrous, brittle, poor conductors Nonlustrous, brittle, poor conductors (Hydrogen displays nonmetallic properties under normal conditions but is UNIQUE element) (Hydrogen displays nonmetallic properties under normal conditions but is UNIQUE element)

Metals, Nonmetals and Metalloids Metalloids Metalloids Found along border between metals and nonmetals Found along border between metals and nonmetals Metal + Nonmetal Metal + Nonmetal Usually electrons are transferred from metal to nonmetal… Usually electrons are transferred from metal to nonmetal…

Atomic Radius Increases down each group Increases down each group Decreases from left to right across a period Decreases from left to right across a period Increase in positive charge = stronger pull on electrons = gradual decrease in atomic radius Increase in positive charge = stronger pull on electrons = gradual decrease in atomic radius

Atomic Radius

Ionization Energy The energy required to remove an electron from the atom The energy required to remove an electron from the atom

Ionization Energy Ionization energy in Group A elements Ionization energy in Group A elements Ionization energy Ionization energy Nonmetals – tend to gain electrons (rather than give them up) Nonmetals – tend to gain electrons (rather than give them up)

Ionization Energy

Lewis Structures Diagram that shows valence electrons Diagram that shows valence electrons Dots = number of s and p electrons Dots = number of s and p electrons Paired dots = Paired dots = Simple way of showing electrons Simple way of showing electrons

Lewis Structures When drawing: When drawing: “3, 6, 9” = “3, 6, 9” = Just like orbital filling diagram… Just like orbital filling diagram… Examples: draw Lewis Structures of B, N, F, Ne Examples: draw Lewis Structures of B, N, F, Ne

Lewis Structures N B Ne F

The Ionic Bond Ionic bond: Ionic bond: Attraction between electrostatic charges is a Attraction between electrostatic charges is a

The Ionic Bond

NOT A MOLECULE NOT A MOLECULE Bond not just between Bond not just between

The Ionic Bond Typically metal + nonmetal Typically metal + nonmetal

Predicting Formulas of Ionic Compounds In almost all stable chemical compounds of representative elements, each atom attains a noble gas electron configuration. This concept forms the basis for our understanding of chemical bonding. In almost all stable chemical compounds of representative elements, each atom attains a noble gas electron configuration. This concept forms the basis for our understanding of chemical bonding.

Predicting Formulas of Ionic Compounds How many electrons must be gained or lost to achieve noble gas configuration? How many electrons must be gained or lost to achieve noble gas configuration?

Predicting Formulas of Ionic Compounds Elements in a family usually form compounds with the same atomic ratios Elements in a family usually form compounds with the same atomic ratios

Predicting Formulas of Ionic Compounds The formula for sodium oxide is Predict the formula for The formula for sodium oxide is Predict the formula for Sodium sulfide Sodium sulfide Sodium [Ne]3s 1 must Sodium [Ne]3s 1 must Sulfur [Ne]3s 2 3p 4 must Sulfur [Ne]3s 2 3p 4 must So…formula must So…formula must

Predicting Formulas of Ionic Compounds Rubidium Oxide Rubidium Oxide Rubidium [Kr]5s 1 must Rubidium [Kr]5s 1 must Oxygen [He]2s 2 2p 4 Oxygen [He]2s 2 2p 4 So…formula must be So…formula must be This makes sense b/c rubidium is in same family as sodium This makes sense b/c rubidium is in same family as sodium

The Covalent Bond A pair of electrons A pair of electrons Most common type of bond Most common type of bond Electron orbital expands to include both nuclei Electron orbital expands to include both nuclei

The Covalent Bond

Atoms may share more than one pair of electrons Atoms may share more than one pair of electrons Double bond – Double bond – Triple bond – Triple bond – Multiple bonds are Multiple bonds are Covalent bonding between identical atoms means electrons are Covalent bonding between identical atoms means electrons are Covalent bonding between different atoms leads to Covalent bonding between different atoms leads to

Electronegativity The attractive force that an atom of an element has for shared electrons The attractive force that an atom of an element has for shared electrons Atoms have different electronegativities Atoms have different electronegativities Electrons will spend more time near atom with stronger (larger) electronegativity Electrons will spend more time near atom with stronger (larger) electronegativity So…one atom assumes a So…one atom assumes a The other assumes a The other assumes a

Electronegativity Electronegativity trends and periodic table Electronegativity trends and periodic table See table 11.5 page 237 See table 11.5 page 237 Generally increases from left to right Generally increases from left to right Decreases down a group Decreases down a group Highest is fluorine (4.0) Highest is fluorine (4.0) Lowest is francium (0.7) Lowest is francium (0.7)

Electronegativity

Electronegativity Polarity is determined by difference in electronegativity Polarity is determined by difference in electronegativity Nonpolar covalent Nonpolar covalent Polar covalent Polar covalent Ionic compound Ionic compound

Electronegativity

Electronegativity If the electronegativity difference is greater than then the bond will be more ionic than covalent If the electronegativity difference is greater than then the bond will be more ionic than covalent Above 2.0 = Above 2.0 = Below 1.5 = Below 1.5 = See Continuum on page 239 See Continuum on page 239

Electronegativity Polar bonds form between two atoms Polar bonds form between two atoms Molecules can also be polar or nonpolar Molecules can also be polar or nonpolar Dipole Dipole Polar Polar Nonpolar Nonpolar

Lewis Structures of Compounds Convenient way of showing ionic or covalent bonds Convenient way of showing ionic or covalent bonds Usually the single atom in a formula is the central atom Usually the single atom in a formula is the central atom

The Ionic Bond LEWIS STRUCTURES of ionic bonds LEWIS STRUCTURES of ionic bonds

The Covalent Bond LEWIS STRUCTURES of covalent bonds LEWIS STRUCTURES of covalent bonds Use dashes instead of dots… Use dashes instead of dots…

The Covalent Bond

Lewis Structures of Compounds 1) Obtain the total number of valence electrons 1) Add the valance electrons of all atoms 2) Ionic – add one electron for each negative charge and subtract one electron for each positive charge

Lewis Structures of Compounds 2) Write the skeletal arrangement of the atoms and connect with a single covalent bond 3) Subtract two electrons for each single bond 1) This gives you the net number of electrons available for completing the structure

Lewis Structures of Compounds 4) Distribute pairs of electrons around each atom to give each atom a noble gas structure 5) If there are not enough electrons then try to form double and triple bonds

Lewis Structures of Compounds Write the Lewis Structure for methane CH 4 Write the Lewis Structure for methane CH 4 1) Total number of valence electrons is eight 2) Draw skeletal structure 1) Dashes equal two electrons being shared 3) Subtract the eight electrons shown as dashes 4) Check that all atoms have a noble gas structure

Lewis Structures of Compounds Methane, CH 4 Methane, CH 4

Lewis Structures of Compounds Carbon Dioxide, CO 2 Carbon Dioxide, CO 2 Total valence electrons = 16 Total valence electrons = 16 Not Enough! Must try double bonds…

Complex Lewis Structures Some molecules and polyatomic ions have strange behaviors… Some molecules and polyatomic ions have strange behaviors… No single Lewis structure is consistent No single Lewis structure is consistent If multiple structures are possible the molecule shows resonance If multiple structures are possible the molecule shows resonance Resonance structures – show all possibilities Resonance structures – show all possibilities

Complex Lewis Structures Carbonate ion, CO 3 2- Carbonate ion, CO 3 2- Carbon only has 6 electrons – try double bonds – more than one location…..form resonant structures…

Compounds Containing Polyatomic Ions Polyatomic ion: stable group of atoms that has a positive or negative charge Polyatomic ion: stable group of atoms that has a positive or negative charge Behaves as a single unit in many chemical reactions Behaves as a single unit in many chemical reactions Sodium carbonate (Na 2 CO 3 ) Sodium carbonate (Na 2 CO 3 ) Carbonate ion (co 3 ) has covalent bonds Carbonate ion (co 3 ) has covalent bonds Sodium atoms are ionically bonded to carbonate ion Sodium atoms are ionically bonded to carbonate ion

Compounds Containing Polyatomic Ions Easier to dissociate ionic bond than break covalent bond Easier to dissociate ionic bond than break covalent bond More in chapters 6 and 7 More in chapters 6 and 7

Molecular Shape Three-dimensional shape of molecule important Three-dimensional shape of molecule important Explains Explains Helpful to know how to predict the geometric shape of molecules… Helpful to know how to predict the geometric shape of molecules… Linear? Linear? V-shaped? V-shaped? Trigonal planar? Trigonal planar? Tetrahedral? Tetrahedral?

The VSEPR Model Valence Shell Electron Pair Repulsion Model Valence Shell Electron Pair Repulsion Model Make predictions about shape Make predictions about shape Electron pairs will Electron pairs will

The VSEPR Model Linear Structure Linear Structure 180 o apart 180 o apart

The VSEPR Model Trigonal Planar Trigonal Planar 120 o apart 120 o apart

The VSEPR Model Tetrahedral structure Tetrahedral structure apart apart When drawing: When drawing: Wedged line to show atom protruding from page; dashed line to show atom receding from page Wedged line to show atom protruding from page; dashed line to show atom receding from page

The VSEPR Model Pyramidal shape Pyramidal shape Four pairs of electrons on central atom BUT only three shared… Four pairs of electrons on central atom BUT only three shared… Electrons are tetrahedral but actual shape is more of a pyramid Electrons are tetrahedral but actual shape is more of a pyramid

The VSEPR Model Electron pairs determine shape BUT name for shape is determined by position of atoms Electron pairs determine shape BUT name for shape is determined by position of atoms

The VSEPR Model V-shaped or bent V-shaped or bent Four electron pairs but only two shared Four electron pairs but only two shared Electron arrangement is Electron arrangement is But, molecule is But, molecule is Water Water Helps explain some properties Helps explain some properties

The VSEPR Model Predict the shape for. Predict the shape for. Draw the Lewis Structure Draw the Lewis Structure Count the electron pairs and determine the arrangement that will minimize repulsions Count the electron pairs and determine the arrangement that will minimize repulsions Determine the positions of the atoms and name the structure Determine the positions of the atoms and name the structure