Warm-Up. Write down the equation for Coulomb s Law AND write a sentence that describes how it connects to ionic bonding.

Transcription

1 Warm-Up Write down the equation for Coulomb s Law AND write a sentence that describes how it connects to ionic bonding.

2 Chemical Bonding

3 Ionic Bonding Which spheres below are K + cations and which are Cl - anions? How do you know?

4 Ionic Bond Formation Formation of Cation: o K (g) K + (g) + e - (Ionization Energy) Formation of Anion: o Cl (g) + e - Cl - (g) (Electron Affinity) Electrostatic Attraction: o K + (g) + Cl - (g) KCl (s) (Lattice Formation)

5 Lattice Energy Energy needed to overcome ALL of the electrostatic attractions in one mole of an ionic compound o This is what you need to add to melt an ionic solid! Proportional to Coulomb s Law: o Q 1 and Q 2 are the ionic charges o d is the distance between the nuclei KCl (s) K + (g) + Cl - (g) ΔH = 701 kj/mol

6 Practice! Rank the following ionic compounds in order of INCREASING lattice energy: o Al 2 S 3 o LiF o SrSe o CuCl 2 o NaBr o CaO o FeN

7 Potassium ion: Ion Formation Chloride ion: Iron ions: Silver ion:

8 Ionic Properties High melting points because of strong lattice energies Brittle because of repulsive interactions between like-charged ions

9 Metallic Bonding Unit Cells: You do NOT need to know these, but it is good to have a general idea of metallic structures. If all are of the same metal, which is the most dense?

10 Electron-Sea Model Valence electrons move freely throughout all of the metal cations! Good conductors because of movement of charged particles What else allows the movement of charged particles, and is therefore a good conductor? Malleable and ductile

11 Metallic Properties Transition metals have very high melting points because bonding gets stronger as the number of valence electrons that can be accommodated increases.

12 Warm-Up Draw the Lewis Structures of the following covalent molecules: o Carbon Dioxide o Water o Ammonia

13 Molecular Covalent Bonding Electrons are shared between two nuclei Electron clouds overlap slightly Bond length determined by repulsive forces between valence electron orbitals

14 Lewis Structures Governed by the Octet Rule (for now ) Each atom wants to gain 8 valence electrons by sharing theirs with other atoms Steps for drawing: (this will ALWAYS work) 1) Count the total number of valence electrons you have 2) Place your atoms with the atom that wants to share the most electrons in the middle 3) Connect the atoms with single bonds 4) Draw lone pairs on all of the outside atoms. 5) Draw lone pairs on the central atom until you run out of electrons. 6) If there are not enough electrons to give the central atom an octet, revise your structure by adding double or triple bonds.

15 Practice Use this method to re-draw the Lewis Structures from your Warm-Up. Did you get the same ones? Which bonds that you drew are polar?

16 Bond Polarity Match each structure with its bond type: ionic, nonpolar covalent, polar covalent.

17 Electron Density Models Match each electron density model with the molecule it represents: HF, HBr, HI, HCl

18 Formal Charges If there is more than one Lewis Structure that follows all the rules, assign formal charges to determine which is the best! Formal Charge = ve in bonded atom ve in neutral atom o Lone pairs contribute 2 electrons to their atom o Bonding pairs contribute 1 electron to each of their atoms

19 Practice Draw the 2 possible Lewis structures for CH 2 N 2. Use formal charges to determine which is correct.

20 Warm-Up Draw the Lewis Structures for the following molecules: o Nitrate ion o Ozone (O 3 )

21 Resonance Some molecules have multiple Lewis Structures that are completely equivalent. We call these resonance structures. We can combine all of the resonance structures into one hybrid structure.

22 Practice Draw hybrid structures for the two Lewis Structures from your Warm-Up.

23 Octet Exceptions Three main exceptions: 1) Molecules with an odd number of electrons Ex: nitrogen monoxide 2) Molecules where the central atom has fewer than 8 electrons Often with Boron 3) Molecules where the central atom has more than 8 electrons Often with Group central atoms Central atom MUST be in Period 3 or higher

24 Practice Draw the Lewis Structures that are exceptions to the Octet Rule for the following molecules. Use formal charges to defend the structure that you draw. 1) Phosphate ion 2) Boron trifluoride 3) Superoxide ion (O 2- )