Chemical Bonding 1

Video http://ed.ted.com/lessons/how-atoms-bond-george-zaidan-and-charles-morton

Chemical Bonding Atoms lose, gain, or share electrons to have an octet (8e-) in its outer energy level.

Types of Bonding Ionic Covalent Metallic

Ionic Bonding Transfer of electrons Metal (loses e-) forms a + ion nonmetal (gains e-) forms a negative ion Ex: NaCl, KBr, KNO3

Ionic Bonding Example: Na and Cl In ionic bonding one atom has a stronger attraction for electrons than the other, and “steals” an electron from a second atom e– 1) 2) Na Cl 3) Cl– Na+

Properties of Ionic Compounds Crystalline solids High melting point Brittle Conducts electricity in molten form and when dissolved in water Forms a crystal lattice Held together by electrostatic attraction (opposite charges)

Crystal Lattice

Sodium and Chlorine NaCl

Calcium and Chlorine CaCl2

Potassium and Sulfur K2S

Covalent (Molecular) Bonding Share e- Nonmetals only Ex: H2O, CCl4

Electronegativity Measure of the attraction for a shared electron. Which family would have the highest electronegativity? Which element would have the highest electronegativity?

Electronegativity increases decreases Don’t include the noble gases

Electronegativities and Bond Type The type of bond or degree of polarity can be calculated by finding the difference in electronegativity of the two atoms that form the bond.

Two types of covalent bonds Nonpolar bond- share e- equally Ex: Cl2, O2 Polar bond- unequal sharing of e-, 2 different nonmetals Ex: C-O, N-H

Electronegativity Difference Used to determine if a bond is ionic or covalent Atoms that have electronegativity differences greater than 1.7 form ionic bonds. Ex: Na-Cl If the difference is 0 to 0.4 the bond is nonpolar covalent. Ex: Cl2. Atoms that have electronegativity differences less than 1.7 and greater than 0.4 form polar covalent bonds. Ex: H-O The greater the electronegativity difference the more polar the bond will be. 19

Electronegativity Difference 0------------0.4-------------1.7------------ nonpolar polar ionic

Examples Classify as polar, nonpolar, or ionic. P-Cl polar 2. Cl-Cl 3. Ca-F ionic

Polar Bonds Partial positive charge Partial negative charge F has a higher electronegativity than H. H and F are sharing the electrons, but F has a greater pull on the shared electrons. F wins the “tug of war” and pulls the electrons closer giving F a partial negative charge. The electrons are pulled away from the H atom. This gives H a partial positive charge. These are NOT complete charges like in an ionic bond.

Polar, Nonpolar and Ionic Bonds

Video https://www.youtube.com/watch?v=_M9khs87xQ8

PROPERTIES OF COVALENT COMPOUNDS Solids, liquids and gases Lower melting points than ionic compounds Nonconductors (nonelectrolytes) All nonmetals Ex: C12H22O11 (solid) H2O (liquid) CO2 (gas)

Octet Rule Octet rule- atoms form bonds to have 8 valence electrons Exception: H (2 e- ) B (6 e-)

Lewis Dot Structures F2

MATH METHOD Count the total # of e- needed to satisfy the octet rule. (NEED) Count the total # of valence e-. (HAVE) Subtract #2 from #1 and divide by 2. This equals the # of bonds. Make sure every atom obeys the octet rule.

Bond Energy BOND ENERGY – energy required to break a bond. Triple bond has the _____________ bond energy and a single bond has the ____________ bond energy. Triple bond has the _____________ bond length and a single bond has the ____________ bond length.

Resonance Resonance Structures- occur when more than 1 Lewis structure can be drawn for a molecule. Ex: CO3-2 SO2

Exceptions Exceptions to the octet rule: H ______ B_______ Be __________ Expanded Octet: _______than 8 e- on the central atom (Honors)

Examples (Honors) Ex: PCl5 SF6

Video http://ed.ted.com/lessons/what-is-the-shape-of-a-molecule-george-zaidan-and-charles-morton

MOLECULAR SHAPES VSEPR MODEL Bonds are made up of e- Bonds repel each other Bonds will spread out around the central atom to be as far apart as possible Lone pairs of electrons repel more than bonds repel each other Count the number of bonded atoms and the number of lone pairs on the CENTRAL atom to determine the shape.  

Molecular Shapes Two atoms bonded to central atom. Can be single, double, or triple bonds. Ex: BeH2 Shape: linear Bond angle: 180°

Linear

Linear

Molecular Shapes 2. Three atoms bonded to central atom. Ex: BH3 Shape: trigonal planar Bond angle : 120°

Trigonal Planar

Trigonal Planar Ex: CH2O

Molecular Shapes 3. Two atoms and one or two lone pairs on the central atom. Ex. H2O Shape: bent Bond angle: 104.5°

Bent

Bent Ex: SO2

Molecular Shapes 4. Three atoms and one lone pair on the central atom. Ex: NH3 Shape: Trigonal Pyramid Bond angle: 107°

Trigonal Pyramid

Molecular Shapes 5. Four atoms around the central atom. Ex: CH4 Shape: Tetrahedral Bond angle: 109.5°

Tetrahedral

(Honors) Additional Shapes 6. Five atoms around the central atom. Ex: PCl5 Shape: Trigonal Bipyramidal Bond angle: 90° and 120°

Trigonal Bipyramidal

One Last Shape 7. Six atoms around the central atom. Ex: SF6 Shape: Octahedral Bond angle: 90°

Octahedral

Polarity of Molecules Nonpolar Molecule- equal distribution of electrons. Symmetrical around the central atom. Must be the same atom around the central atom.

Nonpolar Molecule with Polar Bonds

Polar Molecule – unequal electron distribution Polar Molecule – unequal electron distribution. Not symmetrical around the central atom.

Polar Molecule

Polar Molecule

Hybridization (Honors) Examples: Be in BeCl2 B in BCl3 C in CH4 P in PCl5 S in SF6

How to Determine Hybridization COUNT THE ELECTRON GROUPS AROUND AN ATOM DOMAINS- # OF ATOMS BONDED TO A CENTRAL ATOM + # UNSHARED PAIRS OF ELECTRONS

# OF DOMAINS HYBRIDIZATION 2 sp 3 sp2 4 sp3 5 sp3d 6 sp3d2

Molecular Shape # Domains Hybridization Examples Linear 2 sp CO2 Trigonal planar 3 sp2 BCl3 Bent 3 (2 bonds + 1 unshared pair) SO2 Tetrahedral 4 sp3 CH4 4 (2 bonds + 2 unshared pairs) H2O Trigonal pyramid 4 (3 bonds + 1 unshared pair) NH3 Trigonal bipyramidal 5 sp3d PCl5 Octahedral 6 sp3d2 SF6

Metallic Bonding 61

Metallic Bonding Metallic Bonds are a special type of bonding that occurs only in metals Characteristics of a Metallic Bond. A metallic bond occurs in metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons. Good conductors of heat and electricity Great strength Malleable and Ductile Luster This diagram shows how metallic bonds might appear 62