Catalyst 1. Draw the Lewis Structure for BCl3. 2. Draw the Lewis Structure for HCN. 3. Draw the Lewis Structure for PCl5

Formal Charges Many compounds have more than 1 possible Lewis structure. Formal charges tells us the “right” Lewis structure. Formal Charge – The charge an element would have if all electrons were shared equally. The “best” structure has: 1. Atoms that have formal charges closest to 0 2. Highest negative charge on the most electronegative atom

Calculating Formal Charges To calculate formal charge:

Class Example Draw NCS–, calculate its formal charge and pick the “best” Lewis structure.

Table Talk Draw the Lewis structure for PF3 and label the formal charge of all atoms

Meet the Bicarbonate Ion…

HCO3 – + H+  H2CO3  CO2 + H2O

Justify – TPS Which structure of bicarbonate drawn on the board is “right” according to our rules of formal charges?

Lecture 2.2 – Resonance Structures and Polar Covalent Compounds

Today’s Learning Target LT 2.4 – I can discuss the reason for the formation of resonance Lewis Structures and I can draw resonance structures for a variety of covalent compounds.

Resonance Structures Oftentimes, there is more than one “correct” way to draw a Lewis structure. This occurs because there are multiple drawings with the same formal charges.

Class Example Draw all the allowed structures for O3

Resonance Structures For O3, both structures are equally valid Resonance Structures – Molecules that require multiple Lewis Structures to describe the distribution of electrons. Both structures are present in equal amounts

Resonance Structure for Ozone Double bared arrow indicates that we can have either structure. The density of electrons can actually be thought of as residing somewhere in the middle of the two structures.

Table Talk Draw all the correct structures for SO3-

Table Talk Draw all correct resonance structures for HCO2-

Coach and Correct

Question 1 Draw all resonance structures for the nitrate ion

Question 2 Draw all resonance structures for the phosphate ion

Question 3 Draw all resonance structures for S2CO-2

Question 4 Draw all resonance structures for SCN -

Question 5 Draw all resonance structures for CHO2-

Amazing Bending Water!

Justify – TPS What caused the water to bend?

Today’s Learning Targets LT 2.5 – I can characterize ionic and covalent compounds utilizing the idea of electronegativity. Furthermore, I can discuss how electronegativity differences lead to the formation of polar covalent bonds

Electronegativity Electronegativity – The ability of an atom in a molecule to attraction electrons to itself. Increases as you move across a period Adding more protons, but not adding more energy levels Decreases as you go down a group Adding more energy levels makes it harder for the nucleus to attract new electrons

Covalent Bond Polarity Oftentimes, when atoms are in a covalent bond, electrons are not shared equally. Nonpolar Covalent Bond – Electrons shared equally between the atoms Polar Covalent Bond – Electrons shared unequally due to difference in electronegativity Electrons in a covalent bond reside closest to the atom that is most electronegative

H F Because fluorine is drastically more electronegative, it holds electrons closer to itself when in a covalent bond with hydrogen.

H F Hydrogen is given a partial positive charge and fluorine is given a partial negative charge

Table Talk Label the location of the partial positive and partial negative charges in water.

Dipole Moments The creation of a polar compound leads to the concentration of charge at the poles of the element. Indicate dipole moment with an arrow that starts at positive and goes to the negative end H F H F

Bonding is a Spectrum The difference in electronegativity tells us the type of bond that a compound has. Don’t worry about exact values, you can do this qualitatively Electronegativity difference of 0 = non-polar covalent Electronegativity difference of 0.1 to 2 = polar covalent Electronegativity difference of 2 and greater = ionic bond

Around the World Determine if the compounds around the room are ionic, polar covalent, or non-polar covalent

Exit Ticket 1. Draw all the resonance structures for NO3–. Label the formal charges on all atoms. 2. Draw the Lewis structure for HCl. Draw the dipole moment on the compound

Rate Yourself Based on the exit ticket and your current level of understanding, rate yourself 1 – 4 on LT 2.1, 2.2, 2.3, 2.4, and 2.5

Closing Time You should read section 8.1 – 8.7 for Thursday/Friday Answer questions 8.1, 8.4, 8.22, 8.24, 8.39, 8.41, 8.47, 8.48, 8.52, 8.63, and 8.64 for Thursday/Friday