Chapter 8 “Covalent Bonding” Ball-and-stick model

Section 8.1 Molecular Compounds OBJECTIVES: Distinguish between the melting points and boiling points of molecular compounds and ionic compounds.

Section 8.1 Molecular Compounds OBJECTIVES: Describe the information provided by a molecular formula.

Bonds are… Forces that hold groups of atoms together and make them function as a unit. Two types: Ionic bonds – transfer of electrons (gained or lost; makes formula unit) Covalent bonds – sharing of electrons. The resulting particle is called a “molecule”

Covalent Bonds The word covalent is a combination of the prefix co- (from Latin com, meaning “with” or “together”), and the verb valere, meaning “to be strong”. Two electrons shared together have the strength to hold two atoms together in a bond.

Molecules Many elements found in nature are in the form of molecules: a neutral group of atoms joined together by covalent bonds. For example, air contains oxygen molecules, consisting of two oxygen atoms joined covalently Called a “diatomic molecule” (O2)

(diatomic hydrogen molecule) The nuclei repel each other, since they both have a positive charge (like charges repel). How does H2 form? (diatomic hydrogen molecule) + + + +

How does H2 form? But, the nuclei are attracted to the electrons They share the electrons, and this is called a “covalent bond”, and involves only NONMETALS! + +

Covalent bonds Nonmetals hold on to their valence electrons. They can’t give away electrons to bond. But still want noble gas configuration. Get it by sharing valence electrons with each other = covalent bonding By sharing, both atoms get to count the electrons toward a noble gas configuration.

Covalent bonding Fluorine has seven valence electrons (but would like to have 8) F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven F F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… F F

F F Covalent bonding …both end with full orbitals Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals F F

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals F F 8 Valence electrons

F F Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals F F 8 Valence electrons

Molecular Compounds Compounds that are bonded covalently (like in water, or carbon dioxide) are called molecular compounds Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds – this is not as strong a bond as ionic

Molecular Compounds Thus, molecular compounds tend to be gases or liquids at room temperature Ionic compounds were solids A molecular compound has a molecular formula: Shows how many atoms of each element a molecule contains

Molecular Compounds The formula for water is written as H2O The subscript “2” behind hydrogen means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omitted Molecular formulas do not tell any information about the structure (the arrangement of the various atoms).

- Page 215 These are some of the different ways to represent ammonia: 3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement. 1. The molecular formula shows how many atoms of each element are present 2. The structural formula ALSO shows the arrangement of these atoms!