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: Left-hand side of table Left-hand side of table Most elements are metals Most elements are metals Tend to Tend to

Metals, Nonmetals and Metalloids Nonmetals: Nonmetals: Right side of table Right side of table (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 Usually electrons are transferred

Atomic Radius Increases Increases Each step down = Each step down = More energy levels = More energy levels = Decreases from Decreases from Electrons added to the same energy level Electrons added to the same energy level Increase in positive charge = Increase in positive charge =

Atomic Radius

Ionization Energy The energy required to The energy required to More energy required to remove 2 nd, 3 rd, 4 th, 5 th, etc. electron More energy required to remove 2 nd, 3 rd, 4 th, 5 th, etc. electron Noble gas structure is stable so takes Noble gas structure is stable so takes

Ionization Energy Ionization energy in Group A elements Ionization energy in Group A elements Ionization energy Ionization energy Metals – Metals – Nonmetals – Nonmetals –

Ionization Energy

Lewis Structures Diagram that shows Diagram that shows American chemist Gilbert N. Lewis American chemist Gilbert N. Lewis Dots = Dots = Paired dots = Paired dots = Simple way of showing electrons Simple way of showing electrons Most reactions involve only outermost electrons Most reactions involve only outermost electrons

Lewis Structures When drawing: When drawing: Use Use Move in clockwise direction… Move in clockwise direction… … … Examples: draw Lewis Structures of B, N, F, Ne Examples: draw Lewis Structures of B, N, F, Ne

The Ionic Bond Ionic bond: Ionic bond: Transfer of electrons Transfer of electrons Attraction between electrostatic charges is a strong force which holds atomstogether Attraction between electrostatic charges is a strong force which holds atomstogether

The Ionic Bond NOT A MOLECULE NOT A MOLECULE Bond not just between (for example) one sodium and one chloride Bond not just between (for example) one sodium and one chloride

The Ionic Bond Typically Typically Metals usually Metals usually Nonmetals usually Nonmetals usually

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? Ba must Ba must Forms the ion Forms the ion S must S must Forms the ion Forms the ion So… So…

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 Because they have the same number of valence electrons Because they have the same number of valence electrons Must gain or lose the same number of electrons Must gain or lose the same number of electrons See table 11.4 pg 233 See table 11.4 pg 233

Predicting Formulas of Ionic Compounds The formula for sodium oxide is The formula for sodium oxide is Predict the formula for Predict the formula for Sodium sulfide Sodium sulfide

Predicting Formulas of Ionic Compounds Rubidium Oxide Rubidium Oxide

The Covalent Bond A pair of electrons A pair of electrons Most common type of bond Most common type of bond Stronger Stronger Electron orbital expands to include both nuclei Electron orbital expands to include both nuclei most often found between two nuclei most often found between two nuclei Negative charges allow positive nuclei to be drawn close to each other Negative charges allow positive nuclei to be drawn close to each other

The Covalent Bond Atoms may share more than one pair of electrons Atoms may share more than one pair of electrons Covalent bonding between identical atoms means Covalent bonding between identical atoms means 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

Electronegativity Electronegativity trends and periodic table Electronegativity trends and periodic table See table 11.5 page 237 See table 11.5 page 237

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 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 1.6 = ionic bond Above 1.6 = ionic bond Below 0.3 = nonpolar covalent Below 0.3 = nonpolar covalent 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

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) 1) 2) 2) 3) 3) 4) 4)

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 If multiple structures are possible the molecule shows

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 Behaves as a Sodium carbonate (Na 2 CO 3 ) Sodium carbonate (Na 2 CO 3 )

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 Helpful to know how to predict the geometric shape of molecules… Helpful to know how to predict the geometric shape of molecules…

The VSEPR Model Valence Shell Electron Pair Repulsion Model Valence Shell Electron Pair Repulsion Model Make predictions about shape from Lewis structures Make predictions about shape from Lewis structures

The VSEPR Model Linear Structure Linear Structure

The VSEPR Model Trigonal Planar Trigonal Planar

The VSEPR Model Tetrahedral structure Tetrahedral structure When drawing: When drawing:

The VSEPR Model Pyramidal shape Pyramidal shape

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 But, moledule is “bent” But, moledule is “bent”

The VSEPR Model Predict the shape for CF 4, NF 3, and BeI 2. Predict the shape for CF 4, NF 3, and BeI 2. 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

The VSEPR Model CF 4 CF 4 NF 3 NF 3

The VSEPR Model BeI 2 BeI 2