Lewis Structures Practice Exercises Answers PDF

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Lewis Structures Practice Exercises Answers...

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LEWIS STRUCTURES CLIFF NOTES

Name:________________

The goal of the Lewis structure is to have all atoms get an octet after the structure is complete! (H only wants 2 e- and B wants 6) 1. Write the chemical formula, and count the total # of valence electrons. This is the amount of electrons allowed in the Lewis Structure These electrons can be placed anywhere in the structure and don’t belong to any specific atom 2. Arrange the atoms around each other. Hints: a) The least electronegative atom typically goes in the center - usually C b) Hydrogen is terminal (at the end b/c it only can form 1 bond) 3. Put in electrons (dots) around the atoms to satisfy the octet of all the atoms -

-

4. Check to see that you have the same # e s as in step 1, if not, rearrange the # e s and/or atoms.

5. CONNECT THE DOTS between atoms. 2 e- = a bond, denoted by a line ( : = -) Guided practice problems: carbon monoxide

CH2O

Lewis Structures Practice Worksheet 1 Draw the Lewis structures for the following: a)

Nitrogen trifluoride

b)

Methane

c)

Fluorine

d)

oxygen

e)

Water

f)

Sulfur dichloride

g) Phosphorus pentachloride

h) Methyl Alcohol (CH 3 OH)

More detailed information DRAWING LEWIS STRUCTURES Start by learning this basic step-by-step procedure for drawing Lewis structures. 1. Draw a skeleton structure. A skeleton structure is a rough map showing the arrangement of atoms within the molecule. In general, you need to determine the skeleton experimentally, but here are a few guidelines for predicting skeleton structures from molecular formulas. o

Central atoms are usually 

the largest atoms, or



the least electronegative atom.

o

H and the halogens are usually outside atoms.

o

Don't put more than four atoms around a central atom unless the central atom is third period or lower.

2. Count total valence electrons. o

Add the number of electrons in the valence shells of all atoms in the molecule.

o

If the molecule is charged, add an electron for each negative charge and subtract an electron for each positive charge.

o

Noble gas compounds are very uncommon (except on general chemistry tests!) Should you encounter one, each noble gas atom has 8 valence electrons.

3. Connect the structure. o

Draw a bond between the central atom and each outside atom.

o

Each bond uses 2 valence electrons.

4. Place electrons on outside atoms. o

Use remaining electrons to satisfy the octets for each of the outside atoms.

o

If you run out of electrons at this point, the skeleton structure was wrong. Go back to step I.

5. Place all remaining electrons on the central atom. o

If there are more than 8 electrons on the central atom, and the central atom is not third period or lower, you counted the number of valence electrons incorrectly. Go back to step II.

o

If the octet on the central atom is not complete, try sharing lone pairs of outside atoms to form double or triple bonds. Write one multiply bound structure for each outside atom with a lone pair to share; these are resonance structures.

o

If you can't get an octet on the central atom, at this point, check to see whether the total number of valence electrons for this molecule is odd. It's impossible to give octets to all atoms in an odd electron molecules. Get as close to an octet as possible by forming multiple bonds.

Author: Fred Senese [email protected]

Lewis Structures Practice Worksheet 2 Draw the best Lewis structures for the following molecules or ions: a) Phosphorus tribromide

f) oxygen

b) (Diazine) Dinitrogen dihydride

g) nitrogen

c) Methanol CH3 OH

h) formaldehyde CH 2O

d) Nitrite ion

i) nitrite ion (draw differently than letter d)

e) Ethene C 2H4

j) Acetylene C2 H2

Lewis Structures Practice Worksheet 3 Draw the best Lewis structures for the following molecules or ions: k) SBF (keep boron central)

p) bromine

l) HBr

q) iodine

m) C 2H 5OH (ethanol)

r) fluorine

n) dinitrogen tetrafluoride

s) What do you notice about the formulas of the elements of hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine?

All are diatomic molecules with a covalent bond between the two atoms. In oxygen, the covalent bond is a double bond. In nitrogen, it's a triple bond. The bonds in the remaining molecules are single bonds. o) sulfur hexafluoride

t) carbon dioxide...