Covalent Bonding Chemistry Lesson #1

Sections 8.1, 8.2, 9.3, and *8.4* Sections 6.1 16.1, 6.5 and *16.3*

Remember… Ionic bonds form between… An ionic bond happens when one atom… and the other atom…

Remember… The definition of ionic bond is… The chemical formula of an ionic compound represents a…

Covalent Bonds The four sentences above represent four of the most essential differences between covalent and ionic compounds. These differences are so important that…

Essay Question! Define ionic bond and covalent bond. Outline and define, in detail, four major differences between ionic compounds and molecular (covalent) compounds.

Molecular Compounds Formed by covalent bonds Ionic compounds are generally crystalline solids at room temperature. Molecular compounds (CO2 and water, for example, have VERY different properties.)

Molecular Compounds Molecular compounds are formed through covalent bonds. Covalent bonds are created when atoms SHARE electrons, instead of gaining and losing them.

Vocabulary Molecule: group of atoms joined by covalent bonds Diatomic molecules: molecules consisting of two atoms Molecular formula: shows how many atoms of each element a molecule contains

Think About It… Chlorine is a diatomic element, meaning that it exists in its atomic state as two bonded atoms. Draw two chlorine atoms. Is the bond between these two atoms ionic or covalent? How do you know?

Properties of Molecular Compounds Covalent bonds usually occur between… Often are gases or liquids at room temperature Images will show atoms “stuck” to one another

Properties of Molecular Compounds In general, melting and boiling points of molecular compounds are lower than ionic compounds

Molecular Formulas Molecular formula of a molecular compound shows how many atoms of each element are in ONE MOLECULE of the compound. (Contrast this with the chemical formula of ionic compounds, which show only the ratio of elements in the compound.)

Molecular Formulas Example: IONIC: Calcium chloride – CaCl2 Means that in the compound there are two chloride ions for every one calcium ion COVALENT: Carbon dioxide – CO2 Means that each carbon dioxide molecule consists of one carbon atom bonded to two oxygen atoms

Molecular Compounds Molecular compounds can be significantly larger than ionic compounds. Benzoic Acid: C7H6O2 2,4-Dichlorophenoxyacetic acid: C8H6Cl2O3

Molecular Compounds Formulas not always in lowest terms Example: Ethane C2H6 Formulas do not give molecule’s structure. (It must be inferred.)

Structural Diagrams Molecular Formula Structural Formula Ball-and-stick model Space Filling Model Perspective drawing

Forming Covalent Bonds Chemistry Lesson #1

Octet Rule In covalent bonds, atoms share electrons so that they fill their valence levels Usually 8 (but only 2 for hydrogen)

Single Covalent Bonds Atoms held together by sharing one pair of electrons are said to form a SINGLE COVALENT BOND Each atom donates one electron to the bond

Single Covalent Bonds Cl Cl Cl Cl

Single Covalent Bonds Cl Cl Cl Cl

Single Covalent Bonds Single Bond Cl Cl Cl Cl Lone Pairs

Covalent Bonds Electrons that do not take part in the bond are called “lone pairs” or “unshared pairs”

Covalent Bonds There are exceptions! Different elements can form different numbers of bonds Group 7A elements need one more electron, and can form one bond Group 6A elements need two more electrons and can form two bonds Group 5A – three bonds Group 4A – four bonds Hydrogen, too!

Working With Covalent Bonds Draw the electron dot structures. Determine arrangement. Replace shared pairs of electrons with a line. (Leave lone pairs.)

Draw Structural Formulas NH3 H2S PBr3

Draw Structural Formulas H2O CH4 OF2

Draw Structural Formulas SCl2 N2H4 CCl4 CHCl3 C2H6 HF Usually, the atom that can form MORE bonds will be in the center of the molecule!

Draw Structural Formulas, Part 2 CHBr3 C2Cl6 HCl OBr2 P2H4 CI4 Usually, the atom that can form MORE bonds will be in the center of the molecule!

Double and Triple Bonds Chemistry Lesson #3

Double Covalent Bonds Atoms attain noble gas configuration by sharing two pairs of electrons (four) Bond length is shorter

O O Double Covalent Bonds Oxygen has 6 valence electrons O (Group 6A) can form two bonds O O

O O Double Covalent Bonds Oxygen has 6 valence electrons O (Group 6A) can form two bonds O O

Double Covalent Bonds OCTET RULE NOT FULFILLED! O O

Double Covalent Bonds OCTET RULE NOT FULFILLED! O O

Double Covalent Bonds OCTET RULE FULFILLED! O O

Other molecules with double covalent bonds are… Ethene, C2H4 Carbonyl, COH2

Double Covalent Bonds When counting number of valence electrons, double bonds count as 4 shared electrons. Hydrogen will not form double covalent bonds… why?

Triple Covalent Bonds Atoms attain noble gas configuration by sharing three pairs of electrons (six) Bond length is even shorter

N N Triple Covalent Bonds Nitrogen has 5 valence electrons N (Group 5A) can form three bonds N N

N N Triple Covalent Bonds Nitrogen has 5 valence electrons N (Group 5A) can form three bonds N N

Triple Covalent Bonds OCTET RULE NOT FULFILLED! N N

Triple Covalent Bonds OCTET RULE NOT FULFILLED! N N

Triple Covalent Bonds OCTET RULE NOT FULFILLED! N N

Triple Covalent Bonds OCTET RULE NOT FULFILLED! N N

Triple Covalent Bonds OCTET RULE FULFILLED! N N

Other molecules with triple covalent bonds are… Acetylene, C2H2 Hydrogen Cyanide, HCN Propyne, C3H4

Triple Covalent Bonds When counting number of valence electrons, triple bonds count as 6 shared electrons.

Diatomic Elements Chemistry Lesson #4

Diatomic Elements Diatomic elements exist in their atomic forms as binary molecular compounds, since covalent bonds form between the atoms i.e. a “molecule” of oxygen gas is O2, not O

Diatomic Elements F2 Cl2 Br2 I2 H2 N2 O2

Exceptions To The Octet Rule Chemistry Lesson #5

Exceptions Compounds cannot satisfy the Octet Rule for all atoms if the total number of valence electrons is odd. NO2 – total number of valence electrons is 17 O N O

More Exceptions… Nonmetals in the third period and beyond can form more than 4 bonds, since they have empty d orbitals where they can “promote” or “store” extra s or p electrons. Ex.: Phosphorus can form 5 bonds.

Naming Binary Molecular Compounds Chemistry Lesson #6

Naming Molecular Compounds CO and CO2 are very different compounds How can we distinguish them in their names?

Naming Molecular Compounds Confirm that the compound is molecular, not ionic. Name the elements in the order listed in the formula. Add prefixes to identify the numbers of each atom in the compound.

Prefixes Used Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10

Naming Molecular Compounds Omit the prefix “mono-” on the first element in the name. Add “-ide” as a suffix at the end of the second element’s name.

Examples N2O Nitrogen oxygen Dinitrogen monoxygen DINITROGEN MONOXIDE

Practice: Write the Molecular Formula Nitrogen trichloride Carbon tetrabromide Diphosphorus trisulfide

Practice: Write the Name Cl2O8 PH3 N2O4 SF6 H2O S2F10 PCl5 N2F6

Polar Bonds and Molecules Chemistry Lesson #7

Electronegativity A measure of how well an atom attracts electrons Measured in “Paulings” In a molecule, some atoms more forcefully attract electrons than others

Electronegativity Decreases from top to bottom Increases from left to right

Polar Bonds Polar bond – covalent bond in which electrons are shared UNEQUALLY Difference in electronegativity values controls whether bond is nonpolar, polar, or ionic

Polar Bonds Differences: 0.0-0.6  nonpolar covalent 1.8+  ionic

Polar Bonds Greek letter Delta (δ) represents the partial charge acquired by atoms in a polar bond H2O HF CO2

Intermolecular Attractions Polar molecules attracted to one another (called dipole interactions) Hydrogen bonds are attractions that occur between hydrogen and unshared electrons on another molecule

Test Review Chemistry

Test Review Covalent bonds – definitions Molecular vs. ionic compounds Writing structural formulas Writing molecular formulas (from name or from structure) Writing compound names Information on Polar Bonds