Chapter 6.2 Covalent Bonding and Molecular Compounds Chemical Bonding

POINT > Define molecule and molecular formula POINT > Identify the diatomic molecules POINT > Explain relationships between bond length and bond energy POINT > Describe the octet rule POINT > Use Lewis structures/electron dot notation to represent valence electrons

POINT > Define molecule and molecular formula A molecule is a neutral group of atoms bonded together covalently Molecules are composed of one or more nonmetals Molecules exist as discrete entities

POINT > Define molecule and molecular formula A molecular formula shows the number of each type of atom in a single molecule Ex. H2O, C6H12O6, C8H10N4O2, O2 A molecule with more than one type of atom is a molecular compound

POINT > Identify the diatomic molecules Seven elements exist as diatomic molecules: H2 O2 F2 Br2 I2 N2 Cl2 These are not compounds (only 1 type of atom) You must know them! (maybe “hofbrincl”)

WB CHECK: A molecule is two or more atoms chemically bound together a metal and nonmetal covalently bound two or more metals covalently bound two or more nonmetals covalently bound

WB CHECK: Show the molecular formula for glucose. Which of the following form diatomic molecules? oxygen argon boron iodine hydrogen f) nickel g) all of the above h) a, d, and e i) c, d, and e

WB CHECK: Which of the following is a molecular compound O2 CH4 N H2O e) HF f) all of the above g) b, d, and e h) a, b, d, and e

POINT > Explain relationships between bond length and bond energy When two atoms approach each other, three forces interact: 1. The two electron clouds repel each other 2. The two nuclei repel each other 3. The nucleus of each atom attracts the electron cloud of the other The bond length is the distance between the nuclei where attractive and repulsive forces balance

POINT > Explain relationships between bond length and bond energy The bond length varies for different atoms, but always minimizes the potential energy

POINT > Explain relationships between bond length and bond energy The bond energy is the energy required to break a bond and form two neutral atoms The bond energy is equal to the energy released when a bond forms

POINT > Use Lewis/electron dot notation to represent valence electrons We use electron dot notation to represent the valence electrons in atoms Recall that the number of valence electrons in main group elements (s and p blocks) is equal to the Group number (using the A/B system)

POINT > Use Lewis/electron dot notation to represent valence electrons We use electron dot notation to represent the valence electrons in atoms Recall that the number of valence electrons in main group elements (s and p blocks) is equal to the Group number (using the A/B system)

POINT > Use Lewis/electron dot notation to represent valence electrons We use electron dot notation to represent the valence electrons in atoms Recall that the number of valence electrons in main group elements (s and p blocks) is equal to the Group number (using the A/B system)

POINT > Use Lewis/electron dot notation to represent valence electrons We use electron dot notation to represent the valence electrons in atoms Recall that the number of valence electrons in main group elements (s and p blocks) is equal to the Group number (using the A/B system)

WB CHECK: Show the electron dot notation for Chlorine Magnesium Potassium Nitrogen Sodium

s2p6 POINT > Describe the octet rule When two H atoms form H2, they share two electrons This gives each atom a 1s2 e- config (the same config as He) When atoms form covalent bonds they are most stable when they attain a noble gas e- configuration s2p6 = 8 electrons  the “octet rule”

POINT > Describe the octet rule The octet rule: Compounds tend to form so that each atom ends up with an octet (8) of electrons in its highest energy level

POINT > Use Lewis/electron dot notation to represent valence electrons We use Lewis structures to represent the valence e- in atoms bonded together. Ex. Methane:

POINT > Use Lewis/electron dot notation to represent valence electrons We use Lewis structures to represent the valence e- in atoms bonded together:

POINT > Use Lewis/electron dot notation to represent valence electrons Steps for drawing Lewis structures: Add up all the valence e- in all the atoms in the molecule If 3 or more atoms, identify the central atom. Hints: Always use carbon if it’s there If no carbon, use the least numerous atom Arrange the other atoms symmetrically around the central atom; bond each atom to the central atom

POINT > Use Lewis/electron dot notation to represent valence electrons Satisfy the octet rule for all atoms by arranging remaining electrons into lone pairs and shared pairs Check your work: Count the total # of e- in your structure. Does it agree with your count from Step 1? Do all atoms have 8 valence e-? Boron and (sometimes) sulfur are exceptions

Ex. CF4 one carbon and four fluorines: POINT > Use Lewis/electron dot notation to represent valence electrons Ex. CF4 one carbon and four fluorines: C . F : .. . 4 + (4x7) = 32 e- to write a Lewis structure for CF4 : F .. C 32 e- The octet rule is satisfied for carbon and each fluorine 4

We can represent the two e- in a covalent bond with a line: POINT > Use Lewis/electron dot notation to represent valence electrons We can represent the two e- in a covalent bond with a line: : F .. C Represent .. C F .. : as 4

We can represent the two e- in a covalent bond with a line: POINT > Use Lewis/electron dot notation to represent valence electrons We can represent the two e- in a covalent bond with a line: .. : F .. C C F .. : Lewis structures: F Structural formula: F C F Shows bonds and arrangement, but not unshared pairs F 4

WB CHECK: Draw the Lewis structure for ammonia, NH3 Draw the structural formula for ammonia Write the molecular formula for ammonia

Homework: Read 6.2 pages 168-179 Practice 1-4 page 176 Practice 1-2 page 178 F.A. 1-5 page 179