Chapter 9 Covalent Bonding

Section 9.1 Atoms bond together because they want a stable electron arrangement consisting of a full outer energy level. Atoms bond together because they want a stable electron arrangement consisting of a full outer energy level. Two ways that atoms can bond together are ionically & covalently. Two ways that atoms can bond together are ionically & covalently. A covalent bond is a chemical bond that results from the sharing of the valence electrons. Covalent bonds are usually formed between elements close to each other on the periodic table and nonmetallic elements. A covalent bond is a chemical bond that results from the sharing of the valence electrons. Covalent bonds are usually formed between elements close to each other on the periodic table and nonmetallic elements.

Nonmetals bonded with nonmetals

Section 9.1 A molecule is formed when 2 or more atoms bond covalently. A molecule is formed when 2 or more atoms bond covalently. Example Example HI HI F 2 F 2 Practice problems Practice problems 1. HBr2. O 2 3. H 2 O

` Diatomic molecules are molecules of like atoms. Diatomic molecules include hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, & iodine. Diatomic molecules are molecules of like atoms. Diatomic molecules include hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, & iodine. Write the formulas & structures for the diatomic molecules. Write the formulas & structures for the diatomic molecules.

The number of covalent bonds that these groups form are: The number of covalent bonds that these groups form are: Halogens  single covalent bond Halogens  single covalent bond Group 6A  double/two covalent bond Group 6A  double/two covalent bond Group 5A  triple/three covalent bond Group 5A  triple/three covalent bond Group 4A  four covalent bonds Group 4A  four covalent bonds

Practice Practice H F H F O Cl 2 O Cl 2 H 2 S H 2 S N 2 N 2 P H 3 P H 3 Si H 4 Si H 4

Section 9.1 Single covalent bonds are also called sigma bonds, symbolized by the Greek letter  Single covalent bonds are also called sigma bonds, symbolized by the Greek letter  A sigma bond results when orbitals overlap. A sigma bond results when orbitals overlap. s orbitals can overlap s orbitals s orbitals can overlap s orbitals s orbitals can overlap p orbitals s orbitals can overlap p orbitals p orbitals can overlap p orbitals p orbitals can overlap p orbitals

Section 9.1 Multiple covalent bonds occur when more than one pair of electrons are shared. Multiple covalent bonds occur when more than one pair of electrons are shared. A pi bond, , is formed when parallel orbitals overlap to share electrons. A pi bond, , is formed when parallel orbitals overlap to share electrons. A double bond is made of 1 sigma bond & 1 pi bond A double bond is made of 1 sigma bond & 1 pi bond A triple bond is made of 1 sigma bond & 2 pi bonds A triple bond is made of 1 sigma bond & 2 pi bonds

Practice Draw the lewis dot structure for each molecule. 1. PH 3 1. PH 3 2. H 2 S 2. H 2 S 3. HCl 3. HCl 4. CCl 4 4. CCl 4 5. SiH 4 5. SiH 4 6. CO 2 6. CO 2

If H 2 O is water, what is H 2 O 4 ? If H 2 O is water, what is H 2 O 4 ? Drinking, bathing, washing, swimming… Drinking, bathing, washing, swimming…

Section 9.1 The strength of covalent bonds depend on the length of the bond, the distance between the bonded nuclei. The strength of covalent bonds depend on the length of the bond, the distance between the bonded nuclei. Bond length is determined by the size of the atoms & the number of shared electron pairs. Bond length is determined by the size of the atoms & the number of shared electron pairs. As the number of shared pairs increases, the bond length decreases. As the number of shared pairs increases, the bond length decreases.

The shorter the bond, the stronger the bond. The shorter the bond, the stronger the bond. Energy is released when a bond forms & energy is added to break a bond. Energy is released when a bond forms & energy is added to break a bond. Which has a shorter bond? H 2 or S 2 Which has a shorter bond? H 2 or S 2 The amount of energy needed to break a bond is the “ Bond Dissociation Energy ” The amount of energy needed to break a bond is the “ Bond Dissociation Energy ” Among F 2, O 2, & N 2, which would have the greatest bond dissociation energy? Least? Among F 2, O 2, & N 2, which would have the greatest bond dissociation energy? Least?

Section 9.1 Endothermic reactions  occur when a greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the product molecules Endothermic reactions  occur when a greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the product molecules Exothermic reactions  occur when more energy is released forming new bonds than is required to break bonds in the initial reactants Exothermic reactions  occur when more energy is released forming new bonds than is required to break bonds in the initial reactants

Measuring heat Exothermic Rxn Exothermic Rxn Endothermic Rxn

Section 9.2 Naming Binary Molecular Compounds Naming Binary Molecular Compounds 1st element—use entire element name 1st element—use entire element name 2nd element—use root word & “ ide ” 2nd element—use root word & “ ide ” use prefixes to indicate # of atoms for each element use prefixes to indicate # of atoms for each element prefixes prefixes mono—1 mono—1 di—2 di—2 tri—3 tri—3 tetra—4 tetra—4 penta—5 penta—5 hexa—6 hexa—6 hepta—7 hepta—7 octa—8 octa—8 nona—9 nona—9 deca--10 deca--10

Section 9.2 **NEVER USE mono WITH 1ST ELEMENT** **NEVER USE mono WITH 1ST ELEMENT** Example Example N 2 Cl 3 N 2 Cl 3 CO 2 CO 2 Practice Practice 1. P 2 O 5 1. P 2 O 5 2. NO 2 2. NO 2 3. CO 3. CO Common names of some molecular compounds— p. 249 Common names of some molecular compounds— p. 249 ** Worksheet “ Naming molecular compounds ”

What is the name for H 2 O? What is the name for H 2 O? What is the name for CH 2 O? What is the name for CH 2 O? Sea water Sea water

Naming acids Naming acids Binary acids—hydrogen plus one other element Binary acids—hydrogen plus one other element Hydro + root of 2nd element + ic acid Hydro + root of 2nd element + ic acid 1. HCl  hydrochloric acid 2. HBr  hydrobromic acid 3. H 2 S  hydrosulfuric acid 4. Hydroiodic acid 

Oxyacids—contain hydrogen & oxygen and one other element Oxyacids—contain hydrogen & oxygen and one other element Root of other element + ic acid Root of other element + ic acid H 2 CO 3  H 2 CO 3  H 2 SO 4  H 2 SO 4  HC 2 H 3 O 2  HC 2 H 3 O 2  Phosphoric acid  Phosphoric acid  Nitric acid  Nitric acid  ** Worksheet “ Naming acids ” ** Worksheet “ Naming acids ”

Section 9.3 Structural formulas use letter symbols & bonds to show relative positions of atoms. Structural formulas use letter symbols & bonds to show relative positions of atoms. Hydrogen is always a terminal atom because it can bond with only 1 other atom. Hydrogen is always a terminal atom because it can bond with only 1 other atom. Resonance is a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion. Resonance is a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion.

Resonance Example Example HCl HCl SO 2 SO 2 Practice Practice 1. SO 3 1. SO 3 2. O 3 2. O 3

A coordinate covalent bond forms when one atom donates both electrons to be shared. A coordinate covalent bond forms when one atom donates both electrons to be shared.

9.4 Molecular Shapes Molecular shape is determined by the overlap of orbitals that share electrons. Molecular shape is determined by the overlap of orbitals that share electrons. The VSEPR model is used to determine the molecular shape of the molecule. VSEPR stands for The VSEPR model is used to determine the molecular shape of the molecule. VSEPR stands for Valence Valence Shell Shell Electron Electron Pair Pair Repulsion model. Repulsion model.

F 2 has linear shape F 2 has linear shape CO 2 has linear shape CO 2 has linear shape BH 3 has trigonal planar shape BH 3 has trigonal planar shape CF 4 has tetrahedral shape CF 4 has tetrahedral shape NH 3 has pyramidal shape NH 3 has pyramidal shape H 2 O has bent shape H 2 O has bent shape

Hydridization is a process where atomic orbitals are mixed to form new, identical hybrid orbitals. Hydridization is a process where atomic orbitals are mixed to form new, identical hybrid orbitals. Carbon is the most common element that undergoes hybridization. Carbon is the most common element that undergoes hybridization. The hybrid orbital of carbon is called sp 3. The hybrid orbital of carbon is called sp 3. It takes shape to look like a tetrahedral. It takes shape to look like a tetrahedral.

9.5 Electronegativity & Polarity Remember that electronegativity is defined as the tendency of an atom to attract electrons. Remember that electronegativity is defined as the tendency of an atom to attract electrons. Fluorine has the highest EN at 3.98 and Francium has the lowest EN at 0.7. Fluorine has the highest EN at 3.98 and Francium has the lowest EN at 0.7.

Polar/nonpolar Polar covalent bond is when electrons are unequally shared—large difference in EN. Electrons spend more time around the element that is more EN. The more EN element has a partial negative charge. A polar covalent bond is also called a dipole. Polar covalent bond is when electrons are unequally shared—large difference in EN. Electrons spend more time around the element that is more EN. The more EN element has a partial negative charge. A polar covalent bond is also called a dipole. Electronegativity occurs in molecules. Electronegativity occurs in molecules. For example H 2 O & HCl Page 263 Page 263

Polar/nonpolar Nonpolar covalent bond is when electrons are shared equally—have small or no EN differences. Symmetrical molecules with balanced charges are nonpolar. (CCl4) These are pure covalent bonds. Nonpolar covalent bond is when electrons are shared equally—have small or no EN differences. Symmetrical molecules with balanced charges are nonpolar. (CCl4) These are pure covalent bonds. Ionic bonds generally form when EN differences are 1.7 or greater. Ionic bonds generally form when EN differences are 1.7 or greater.

Electronegativity difference Bond Type Nonpolar covalent 0.5 – 1.6 Polar covalent 1.7 – 3.2 ionic

Polar, Nonpolar, or Ionic? Example: Example: HCl HCl Practice: Practice: 1. SCl 2 2. H 2 S 3. CF 4 4. CS 2

Properties of covalent compounds- p “ like dissolves like ” “ like dissolves like ” Many different types of forces between molecules. Many different types of forces between molecules. **Worksheet “ Shape/polarity of molecules ”

Mainly gases (some liquids), melt/vaporize easily, hardness varies. Mainly gases (some liquids), melt/vaporize easily, hardness varies. Oxygen gas, acids, parafinn, graphite, diamonds Oxygen gas, acids, parafinn, graphite, diamonds