Unit 6: Chemical Bonding Refer to Ch. 8 & 9 for supplemental reading.

1. Chemical Bond: an attractive force that holds 2 atoms together 3 types: ionic, covalent, metallic

Valence Electrons The electrons in the outer energy level of an atom. They are like the front lines of an army. They are the electrons involved in bonding.

Review How do you find valence electrons? How do you find valence electrons? Hint there are two ways! Hint there are two ways! Examples: Look at the group # for the representative elements. Examples: Look at the group # for the representative elements. Mg ___ Mg ___ O ___ O ___ Ar ___ Ar ___ Si ___ Si ___ Examples: Write the electron configuration. Examples: Write the electron configuration. Mg Mg O s 2 2s 2 2p 6 3s 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2p 1s 2 2s 2 2p 4

Electron Dot Structures Depicts element symbol w/ valence e - shown as dots. Depicts element symbol w/ valence e - shown as dots. Na MgAl ClAr Si ON

Ionic Bonds Occurs when ions of opposite charge (+,-) attract each other. Occurs when ions of opposite charge (+,-) attract each other. Metal ion – Nonmetal ion Metal ion – Nonmetal ion Simplest attraction Simplest attraction NaCl MgF 2 NaCl MgF 2 Polyatomic ions: Molecules that are charged. Polyatomic ions: Molecules that are charged. Al(PO 4 (NH 4 ) 2 (SO 4 ) Al(PO 4 ) (NH 4 ) 2 (SO 4 ) PO 4 is phosphate with a -3 charge PO 4 is phosphate with a -3 charge SO 4 is sulfate with a -2 charge SO 4 is sulfate with a -2 charge

Formation of Ionic Bond Cation- positive ion (+) (Cats have paws) Cation- positive ion (+) (Cats have paws) Forms when a metal atom loses e - to become stable. Forms when a metal atom loses e - to become stable. Anion- negative ion (-) (A Negative Ion) Anion- negative ion (-) (A Negative Ion) Forms when a nonmetal atom gains e - to become stable Forms when a nonmetal atom gains e - to become stable An ionic bond is formed when e - are transferred between atoms and the resulting ions stick together. An ionic bond is formed when e - are transferred between atoms and the resulting ions stick together.

Examples Formation of NaCl Formation of NaCl Na Cl → [Na] + [ Cl ] - = NaCl Na Cl → [Na] + [ Cl ] - = NaCl Formation of MgF 2 Formation of MgF 2 Mg F F  [Mg] 2+ [ F ] - [ F ] - = MgF 2 Mg F F  [Mg] 2+ [ F ] - [ F ] - = MgF 2 How would a compound form between two aluminum and three oxygen? How would a compound form between two aluminum and three oxygen?

Electron Configuration of Ions Cation example: (metal) Cation example: (metal) Ca atom:1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Ca atom:1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Ca 2+ ion:1s 2 2s 2 2p 6 3s 2 3p 6 Lost 2 electrons to obtain noble gas configuration (octet) Ca 2+ ion:1s 2 2s 2 2p 6 3s 2 3p 6 Lost 2 electrons to obtain noble gas configuration (octet)

Electron Configuration of Ions Anion example: (nonmetal) Anion example: (nonmetal) N atom:1s 2 2s 2 2p 3 N atom:1s 2 2s 2 2p 3 N 3- ion:1s 2 2s 2 2p 6 N 3- ion:1s 2 2s 2 2p 6 Gained 3 electrons to obtain noble gas configuration (octet)

Properties of Ionic Compounds IONIC Bond Formation Type of Structure Boiling Point Electrical Conductivity Other Properties high yes * (solution or liquid) high Melting Point Crystal lattice Physical State Solid (hard and rigid) Hard, rigid and brittle e - transferred from metal to nonmetal The force that holds ionic compounds is really strong. So you see all of these characteristics.

Electrolyte A substance that conducts electricity A substance that conducts electricity Because of ionic bonds ionic (charged) nature, ionic compounds conduct electricity in the molten or aqueous (dissolved in water) forms. Because of ionic bonds ionic (charged) nature, ionic compounds conduct electricity in the molten or aqueous (dissolved in water) forms.

Covalent Bonds Occurs when 2 nonmetals share pairs of electrons to become stable. These are called molecular compounds. Occurs when 2 nonmetals share pairs of electrons to become stable. These are called molecular compounds. Examples: Examples: H 2 OCO 2 C 6 H 12 O 6 PCl 5 H 2 OCO 2 C 6 H 12 O 6 PCl 5 Notice all of these elements in the molecule are nonmetals! Notice all of these elements in the molecule are nonmetals!

Covalent Bonds Covalent bonds can be Covalent bonds can be single (1 shared pair) single (1 shared pair) double (2 shared pairs) double (2 shared pairs) or triple (3 shared pairs) or triple (3 shared pairs) Bond strength: triple > double > single Bond strength: triple > double > single Bond length: single > double > triple Bond length: single > double > triple

Creating Lewis Structures Follow this system: Follow this system: Example: H 2 O Example: H 2 O 1) Draw a “skeleton” of the molecule. It generally works to place the “different” atom in the center. 1) Draw a “skeleton” of the molecule. It generally works to place the “different” atom in the center. H O H

Creating Lewis Structures Find the needed electrons (N) for each atom and add them up. N will be 8 for most elements, with these exceptions: Find the needed electrons (N) for each atom and add them up. N will be 8 for most elements, with these exceptions: H gets 2 valence e - H gets 2 valence e - Be gets 4 valence e - Be gets 4 valence e - B gets 6 valence e - B gets 6 valence e - N = 12 H = 2 O = 8 H = 2

NEED

3) Find the available (valence) electrons (A) for each atom and then add them up*. 3) Find the available (valence) electrons (A) for each atom and then add them up*. A = A = *special note: when completing a Lewis structure for a polyatomic ion, you will need to correct A by adding the absolute value of the charge if negative, and subtracting the charge if positive. For example, for the ion PO 4 3-, you would add 3 to A. For the ion NH 4+, you would subtract 1 from A. (You do the opposite of the charge.) *special note: when completing a Lewis structure for a polyatomic ion, you will need to correct A by adding the absolute value of the charge if negative, and subtracting the charge if positive. For example, for the ion PO 4 3-, you would add 3 to A. For the ion NH 4+, you would subtract 1 from A. (You do the opposite of the charge.) H = 1 O = 6 H = 1 Total A = 8 N = 12 A = 8

Figure out through e config Available

4) Find the shared (S) electrons for the entire molecule by this formula: S = N – A 4) Find the shared (S) electrons for the entire molecule by this formula: S = N – A S = S = S= 12 – 8 = 4 N = 12 A = 8 S = 4

5) The shared electrons are the bonding electrons. Place all of the shared electrons between the atoms. 5) The shared electrons are the bonding electrons. Place all of the shared electrons between the atoms. H O H 6) You must place all of the available (A) electrons in the picture. The shared electrons are part of the available. See how many of the available electrons still need to be placed, and put them in the picture as lone pairs (unshared pairs) so that every atom gets an octet (remember H only needs 2). 6) You must place all of the available (A) electrons in the picture. The shared electrons are part of the available. See how many of the available electrons still need to be placed, and put them in the picture as lone pairs (unshared pairs) so that every atom gets an octet (remember H only needs 2). H O H N = 12 A = 8 S = 4 N = 12 A = 8 S = 4 4

H O H

F B F F

F S F F

CF 4 CF 4 N=A=S= F F C F F 8+(4x8) = 40 4+(4x7) =

BeCl 2 BeCl 2 N=A=S= 4+(2x8) = 20 2+(2x7) = Cl Be Cl

CO 2 CO 2 N=A=S= 8+(2x8) = 24 4+(2x6) = O C O

Polyatomic Ions To find total # of valence e - (A): To find total # of valence e - (A): Add 1e - for each negative charge. Add 1e - for each negative charge. Subtract 1e - for each positive charge. Subtract 1e - for each positive charge. Place brackets around the ion and label the charge. Place brackets around the ion and label the charge.

Polyatomic Ions ClO 4 - ClO 4 - O O Cl O O N=A=S= 8+(4x8) = 40 7+(4x6) = =32 8

Nonpolar Nonpolar Polar Polar Ionic Ionic View Bonding Atomic Bonding : Chemistry ZoneAnimations.Atomic Bonding : Chemistry Zone Bond Polarity

Most bonds are a blend of ionic and covalent characteristics. Most bonds are a blend of ionic and covalent characteristics. Difference in electronegativity determines bond type. (subtract) Difference in electronegativity determines bond type. (subtract) If  EN is: Bond type is: < 0.4Nonpolar covalent  EN < 1.7 Polar covalent > 1.7Ionic

Nonpolar Covalent Bond Nonpolar Covalent Bond e - are shared equally between the atoms e - are shared equally between the atoms symmetrical e - density symmetrical e - density usually occurs between identical atoms usually occurs between identical atoms Bond Polarity

Polar Covalent Bond Polar Covalent Bond e - are shared unequally e - are shared unequally One atom “hogs” the electrons One atom “hogs” the electrons asymmetrical e - density asymmetrical e - density results in partial charges (dipole) results in partial charges (dipole) O is more electronegative than H and pulls the electrons closer to itself.

Electronegativity Chart If ΔEN is:Bond type is: < 0.4Nonpolar covalent 0.4 < Δ EN < 1.7Polar covalent > 1.7Ionic Use the Electronegativity Chart to determine if the bond between atoms is nonpolar covalent, polar covalent, or ionic. Larger EN minus the smaller EN

If ΔEN is:Bond type is: < 0.4Nonpolar covalent 0.4 < Δ EN < 1.7Polar covalent > 1.7Ionic Examples: Cl 2 Cl 2 HCl HCl NaCl NaCl =0.0Nonpolar =0.96Polar =2.23Ionic

Metallic Bond Bond between metal and metal. Bond between metal and metal. An “electron sea” is created where electrons overlap into neighboring atoms. An “electron sea” is created where electrons overlap into neighboring atoms. The electrons move around. The electrons move around.

Metallic Bond Because the electrons are free to move around from atom to atom, we see the properties that we know of metals. Because the electrons are free to move around from atom to atom, we see the properties that we know of metals. Click on this for a cool interactive on metal properties.

Metal Properties Malleable and ductile: the electrons can move past each other so the shape can change. Malleable and ductile: the electrons can move past each other so the shape can change. Free flowing electrons can conduct heat and electricity quickly to other atoms. Free flowing electrons can conduct heat and electricity quickly to other atoms.

VSEPR Theory Valence Shell Electron Pair Repulsion Theory Valence Shell Electron Pair Repulsion Theory Electron pairs place themselves so that they are as far apart from each other as possible. Electron pairs place themselves so that they are as far apart from each other as possible.

A. VSEPR Theory Types of e - Pairs Types of e - Pairs Bonding pairs - form bonds between the atoms Bonding pairs - form bonds between the atoms Lone pairs - nonbonding e - (electrons that are not between atoms) Lone pairs - nonbonding e - (electrons that are not between atoms) Lone pairs repel more strongly than bonding pairs!!!

A. VSEPR Theory Lone pairs reduce the bond angle between atoms. Lone pairs reduce the bond angle between atoms. VS

Draw the Lewis Diagram. Draw the Lewis Diagram. Tally up e - pairs on central atom. Tally up e - pairs on central atom. double/triple bonds = ONE pair double/triple bonds = ONE pair Shape is determined by the # of bonding pairs and lone pairs. Shape is determined by the # of bonding pairs and lone pairs. B. Determining Molecular Shape

Common Molecular Shapes 2 bonding pairs 0 lone pairs LINEAR BeH 2

Common Molecular Shapes 2 bonding pairs 1 lone pair BENT120° SO 2

2 bonding pairs 2 lone pairs BENT109.5° H2OH2OH2OH2O Common Molecular Shapes

3 bonding pairs 0 lone pairs TRIGONAL PLANAR TRIGONAL PLANAR Common Molecular Shapes

3 bonding pairs 1 lone pair PYRAMIDAL NH 3 Common Molecular Shapes

4 bonding pairs 0 lone pairs TETRAHEDRAL CH 4 Common Molecular Shapes

PF 3 PF 3 3 bond 1 lone PYRAMIDAL F P F F Examples Examples

CO 2 CO 2 O C O 2 total 2 bond 0 lone LINEAR180°Examples

Examples H 2 SCCl 4 BF 3 SiO 2