Chapter 8 Lecture- Basic Bonding

Bellwork Question4-Style #4 1)Write a balanced net ionic equation for the reaction that occurs when sodium metal is added to pure water. a)How could you verify the identity of the gas evolved? b) What would be the pH of the resulting solution? Less than 7, near 7, or greater than 7?

Chemical Bonds ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Bonding always involves valence electrons which can be represented by Lewis dot symbols OCTET RULE- Atoms seek to gain a noble gas configuration, which is usually eight valence electrons. Remember Helium only has 2 valence electrons, so elements closest to He are most stable when they obtain 2 valence e - like H, Li, and Be. Hydrogen is also stable as a H + ion which has no electrons and is simply a proton + . Li 1 valence e - Be 2 valence e - B 3 valence e - C 4 valence e - N 5 valence e - O 6 valence e - F 7 valence e - Ne 8 valence e -

Energetics of Ionic Bonding ,[object Object]

Energetics of Ionic Bonding ,[object Object],[object Object]

Lattice Energy ,[object Object],[object Object],[object Object],E el =  Q 1 Q 2 d

[object Object],Q 1 Q 2 d Like charges produce a positive value equal to the energy of repulsion. Opposite charges produce a negative value equal to the energy of attraction. For an ionic solid this is called LATTICE ENERGY. Coulomb’s Law describes the energy of interactions between charges. Here we apply it to ions. First ion’s charge Second ion’s charge Distance between the two ions depends on ionic size!!! Constant. If I only ask you for RELATIVE energies then it doesn’t matter!

Lattice Energy ,[object Object],[object Object],The higher the charges on the ions the greater the energy holding them together. BIGGEST FACTOR The smaller the distance between the two ions the higher the lattice energy

Arrange the following ionic compounds in order of increasing lattice energy: LiCl, NaCl, MgCl 2 ,[object Object],[object Object],[object Object]

Correct Answer: ,[object Object],[object Object],[object Object],Lattice energy depends on size of the ions and their charges. MgCl 2 has the highest lattice energy because it has a more positive cation. LiCl is higher than NaCl because the interatomic distance between cation and ion is shorter .

When they form ions, transition metals lose valence electrons first and d-electrons second (if at all).

The electron configuration of Fe 3+ is which of the following? ,[object Object],[object Object],[object Object],[object Object]

Correct Answer: ,[object Object],[object Object],[object Object],[object Object]

Covalent Bonding ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object]

Polar Covalent Bonds ,[object Object],[object Object],[object Object]

Electronegativity: ,[object Object],[object Object],[object Object],[object Object]

Polar Covalent Bonds ,[object Object],[object Object],[object Object],[object Object]

Polar Covalent Bonds ,[object Object],EN difference < 0.5 (non-polar covalent) ≥ 2.0 (ionic)

Boron (B) has an electronegativity of 2.0; chlorine (Cl) has an electronegativity of 3.0. Which of the following BEST describes a B  Cl bond? ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],Correct Answer: The difference in electronegativities is 1.0 because Cl = 3.0 and B = 2.0. This is too low to be an ionic bond but too high to be a nonpolar covalent bond.

Based on the electronegativities of the atoms, which of the following bonds would you predict is most polar? ,[object Object],[object Object],[object Object],[object Object],[object Object]

Correct Answer: The difference in electronegativities is greatest between O (3.5) and C (2.5) for a net difference of 1.0. Each of the other combinations yields a smaller value for electronegativity difference. ,[object Object],[object Object],[object Object],[object Object],[object Object]

Nomenclature for ionic & covalent binary compounds ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Section 8.5 - 8.7- Lewis Dot Structures

Lewis Structures ,[object Object]

Writing Lewis Structures ,[object Object],[object Object],[object Object],[object Object],5 + 3(7) = 26

Writing Lewis Structures ,[object Object],Keep track of the electrons: 26  6 = 20

Writing Lewis Structures ,[object Object],Keep track of the electrons: 26  6 = 20  18 = 2

Writing Lewis Structures ,[object Object],Keep track of the electrons: 26  6 = 20  18 = 2  2 = 0

Writing Lewis Structures ,[object Object],[object Object]

Writing Lewis Structures ,[object Object],[object Object],[object Object]

Which of the following BEST describes the formal charges on the atoms in the cyanide ion, CN  ? ,[object Object],[object Object],[object Object],[object Object]

Correct Answer: The formal charges are calculated from the difference between number of valence electrons and number of electrons assigned to each atom in the Lewis structure, thus: C: 4 valence e   5 e  =  1 N: 5 valence e   5 e  = 0 ,[object Object],[object Object],[object Object],[object Object]

Considering formal charge, what is the preferred Lewis structure of NCO - ?

Resonance ,[object Object],- +

Resonance ,[object Object],[object Object],[object Object]

Resonance ,[object Object],[object Object]

How many resonance structures can be drawn for NO 3 - ? ,[object Object],[object Object],[object Object],[object Object],[object Object]

Exceptions to the Octet Rule ,[object Object],[object Object],[object Object],[object Object]

Odd Number of Electrons ,[object Object],[object Object]

Fewer Than Eight Electrons ,[object Object],[object Object],[object Object]

Fewer Than Eight Electrons ,[object Object]

Famous Lewis Acid/Base reaction

More Than Eight Electrons ,[object Object],[object Object],[object Object]

More Than Eight Electrons ,[object Object]

More Than Eight Electrons ,[object Object],[object Object]

The stability of a molecule is related to the strength of the bonds in the molecule.

Covalent Bond Strength ,[object Object],[object Object],[object Object],[object Object],[object Object]

Average Bond Enthalpies ,[object Object],[object Object]

Bond enthalpies can be measured through the “enthalpy of atomization”, which measures the energy required to break a molecule into free gaseous atoms. D(C-H) = 1660kJ divided by 4 because there are 4 C-H bonds in methane.

Breaking bonds = endothermic energy must be provided to break a bond Bond formation = exothermic a stable bond is always lower energy than the non-bonded atoms

Molecules with strong (stable) bonds tend to be less reactive. Naturally abundant compounds are usually very stable with strong bonds. Ex. O=O is 495kJ/mol O-O is 146 kJ/mol O 2 is stable & abundant H 2 O 2 is not

Enthalpies of Reaction ,[object Object],[object Object],[object Object],[object Object]

Enthalpies of Reaction ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],Calculate  H from the following bond enthalpies for the reaction: 2 NCl 3  N 2 + 3 Cl 2 D(N  Cl) = 200, D(N  N) = 941, D(Cl  Cl) = 242 (all kJ/mol).

Correct Answer:  H =  (bond enthalpies of bonds broken)   ( bond enthalpies of bonds formed)  H = 6(200)  [941 + 3(242)]  H = 1200  (1667)  H =  467 ,[object Object],[object Object],[object Object],[object Object]

Bond Enthalpy and Bond Length ,[object Object],[object Object]

The higher the bond order the shorter & stronger the bond Bond order = 1 Longest & weakest Bond order = 2 Med length & strength Bond order = 3 shortest & strongest

Which of the following carbon – carbon atom bonds would be expected to be the shortest? ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],Correct Answer: The bond length decreases as the bond enthalpy increases; in general, as the number of bonds between two atoms increases, the bond grows shorter and stronger.

Which is predicted to have the longest carbon – oxygen bonds: CO, CO 2 , or CO 3 2  ? ,[object Object],[object Object],[object Object]

Correct Answer: In CO, the carbon – oxygen bond is a triple bond, while in CO 2 both carbon – oxygen bonds are double bonds. In CO 3 2  , there are three resonance structures and the average carbon – oxygen bond is 1 1/3. ,[object Object],[object Object],[object Object]

Chapter 8 Lecture- Basic Bonding

Chapter 8 Lecture- Basic Bonding

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Chapter 8 Lecture- Basic Bonding