When Atoms Meet EO4 Bonding

Bonds Forces that hold groups of atoms together and make them function as a unit. Bonding Forces Electron – electron repulsive forces Nucleus – nucleus repulsive forces Electron – necleus attractive forces

Types of Chemical Bonding 1. Metal with nonmetal: electron transfer and ionic bonding 2. Nonmetal with nonmetal: electron sharing and covalent bonding 3. Metal with metal: electron pooling and metallic bonding

Three models of chemical bonding Ionic Covalent Metallic Electron transfer Electron sharing Electron pooling

Classification of Bonds Classify the following bonds as ionic, polar covalent, or covalent: The bond in CsCl; the bond in H2S; and the NN bond in H2NNH2. Cs – 0.7 Cl – 3.0 3.0 – 0.7 = 2.3 Ionic H – 2.1 S – 2.5 2.5 – 2.1 = 0.4 Polar Covalent N – 3.0 N – 3.0 3.0 – 3.0 = 0 Covalent

Electronegativities (EN) The ability of an atom in a molecule to attract shared electrons to itself Linus Pauling 1901 - 1994

Classification of Bonds Difference in EN Bond Type Covalent  2 Ionic 0 < and <2 Polar Covalent Increasing difference in electronegativity Covalent share e- Polar Covalent partial transfer of e- Ionic transfer e-

Polar Covalent Bond A covalent bond with greater electron density around one of the two atoms H F electron rich region electron poor region e- poor e- rich F H d+ d-

Electron density distributions in H2, F2, and HF.

Key Word to work out Polar covalent bond vs pure covalent/non-polar Dipole moment and symbols Electronegativity (delta Xp)

Practice Complete electronegativity difference worksheet.

Metals and Nonmetals

The Octet Rule Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has eight electrons in its highest occupied energy level. The same number of electrons as in the nearest noble gas The first exception to this is hydrogen, which follows the duet rule. The second exception is helium which does not form bonds because it is already “full” with its two electrons

Ionic Bond - [Ne] 1s22s1 [H] Li+ F Li + F 1s22s22p5 1s2 1s22s22p6 Li+

High melting point: strong Intramolecular bonds Crystal Lattice Structure Electrostatic attraction between ions https://www.youtube.com/watch?v=SsHvj15uv-w

Naming Ionics

Electrostatic (Lattice) Energy Lattice energy (E) is the energy required to completely separate one mole of a solid ionic compound into gaseous ions. Q+ is the charge on the cation E = k Q+Q- r Q- is the charge on the anion r is the distance between the ions cmpd lattice energy MgF2 MgO 2957 3938 Q= +2,-1 Q= +2,-2 Lattice energy (E) increases as Q increases and/or as r decreases. LiF LiCl 1036 853 r F < r Cl

Properties of Ionic Compounds Volatility is very low (tendency to vaporize) Electrical conductive in solution and liquid phase but not solid Solubility is high in polar solvents like water but will not dissolve in non-polar solvents such as hexane Solvation or dissociation discuss. https://www.youtube.com/watch?v=EBfGcTAJF4o

Review Ionic Cation + and Anion – Ions formed by oxidation and reduction to be noble gas Electrostatic attraction Lattice structure High b.p. and m.p. Low Volalitility Soluble in water Molten or dissolved electric conducters

Things to Review How is charge on ion predicted? What are the polyatomic ions (oxyanions)? What holds an ionic compound together? How are ionic compounds named? What is oxidized and reduced? Who gets reduced and who gets oxidized (OIL RIG) Ionic are called formula units and not molecules!!! https://www.youtube.com/watch?v=0cPFx0wFuVs

Lewis Structures Developed the idea in 1902. G. N. Lewis

Valence Electrons The outer shell electrons of an atom Participate in chemical bonding Group # of valence e- e- configuration 1A 1 ns1 2A 2 ns2 3A 3 ns2np1 4A 4 ns2np2 5A 5 ns2np3 6A 6 ns2np4 7A 7 ns2np5 9.1

Lewis Dot Symbols

Lewis Dot Symbols Place one dot per valence electron on each of the four sides of the element symbol. Pair the dots (electrons) until all of the valence electrons are used. Nitrogen, N, is in Group 5A and therefore has 5 valence electrons. N : . . N : : N . : N .

Covalent Bond A chemical bond in which two or more electrons are shared by two atoms. How should two atoms share electrons? 7e- 7e- 8e- 8e- F F + F Lewis structure of F2 Non-polar: Why? lone pairs F single covalent bond single covalent bond F

Distribution of electron density of H2

Lewis structure of water single covalent bonds 2e- 8e- 2e- H + O + H O H or Double bond – two atoms share two pairs of electrons 8e- 8e- 8e- double bonds O C or O C double bonds Triple bond – two atoms share three pairs of electrons triple bond 8e- N 8e- or N triple bond

Single bond < Double bond < Triple bond Covalent Bond Energy The energy required to break a particular bond in one mole of gaseous molecules is the bond energy. Bond Energy H2 (g) H (g) + 436.4 kJ Cl2 (g) Cl (g) + 242.7 kJ HCl (g) H (g) + Cl (g) 431.9 kJ O2 (g) O (g) + 498.7 kJ O N2 (g) N (g) + 941.4 kJ N Bond Energies Single bond < Double bond < Triple bond

Triple bond < Double Bond < Single Bond Covalent Bond Lengths Bond Type Bond Length (pm) C-C 154 CC 133 CC 120 C-N 143 CN 138 CN 116 Bond Lengths Triple bond < Double Bond < Single Bond

Light-Matter Interactions 3 x 1020 3 x 1016 3 x 1012 3 x 108 3 x 104 Frequency in Hz Dissociation Ionization Vibration Rotation

Microwaves p. 102 https://www.youtube.com/watch?v=kp33ZprO0Ck

Review Covalent See page 103 Formed between no-metals Electron pairs are shared. Electrostatic attraction for shared pair Called molecules Lower m.p. and b.p. Can be volatile Typically insoluble in water Do not conduct electricity due to lack of ions

Rules for Writing Lewis Structures Draw skeletal structure of compound showing what atoms are bonded to each other. Put least electronegative element in the center. Count total number of valence e-. Add 1 for each negative charge. Subtract 1 for each positive charge. Use one pair of electrons to form a bond (a single line) between each pair of atoms. Arrange the remaining electrons to satisfy an octet for all atoms (duet for H), starting from outer atoms. If a central atom does not have an octet, move in lone pairs to form double or triple bonds on the central atom as needed.

5 + (3 x 7) = 26 valence electrons Write the Lewis structure of nitrogen trifluoride (NF3). Step 1 – N is less electronegative than F, put N in center Step 2 – Count valence electrons N - 5 (2s22p3) and F - 7 (2s22p5) 5 + (3 x 7) = 26 valence electrons Step 3 – Draw single bonds between N and F atoms. Step 4 – Arrange remaining 20 electrons to complete octets F N

4 + (3 x 6) + 2 = 24 valence electrons Write the Lewis structure of the carbonate ion (CO32-). Step 1 – C is less electronegative than O, put C in center Step 2 – Count valence electrons C - 4 (2s22p2) and O - 6 (2s22p4) -2 charge – 2e- 4 + (3 x 6) + 2 = 24 valence electrons Step 3 – Draw single bonds between C and O atoms Step 4 - Arrange remaining 18 electrons to complete octets Step 5 – The central C has only 6 electrons. Form a double bond. 2- O C

Resonance More than one valid Lewis structures can be written for a particular molecule The actual structure of the carbonate ion is an average of the three resonance structures 2- 2- 2- O C - O C - O C -

Exceptions to the Octet Rule The Incomplete Octet Be – 2e- 2H – 2x1e- 4e- BeH2 H Be B – 3e- 3F – 3x7e- 24e- 3 single bonds (3x2) = 6 9 lone pairs (9x2) = 18 Total = 24 F B BF3

Exceptions to the Octet Rule Odd-Electron Molecules N – 5e- O – 6e- 11e- NO N O The Expanded Octet (central atom with principal quantum number n > 2) S F S – 6e- 6F – 42e- 48e- 6 single bonds (6x2) = 12 18 lone pairs (18x2) = 36 Total = 48 SF6

Lewis Dot Key Terms Bonding pair of Electrons (Shared pair of electrons) vs. Non-bonding electrons (Lone pair of electrons) Cation and anion molecules

Practice Complete Lewis-Dot worksheet

Not the same as molecular geometry! Electron Domain Geometry

Bond Angles in Molecular Geometry LP/LP>LP/BP>BP/BP Why, lone pair occupy more space and create greater repulsion. Think balloon geometry with big and little balloons.

VSEPR THEORY When non-bonded pairs are present it is not possible to know the exact bond angles. These are measured using X-ray crystallography. No two molecules with lone pairs have the exact same geometry. Why: differing electronegativity and multiple bonds

VSEPR Valence Shell Electron Pair Repulsion https://www.youtube.com/watch?v=qvPKWcXdo7Y \ Electron Domain: region where pairs of electrons exist. Electron domain geometry vs. molecular shape geometry.

Practice Page 110-114 Ball and stick model

Practice Continued Add to Lewis Dot the Electron Domain Geometry and Molecular Geometries Use Moleview to create ball and stick models and diagram on Lewis Dot but add lone pairs, also draw 3D diagram. Electron Domain Geometry, Molecular Geometry (VSEPR), Ball and Stick with lone pairs, 3D diagram.

Sart Hybridization