Name ______Pd ____Date ______

Smells Unit I Test Review

Purpose: To draw Lewis Dot and Structural Formulas for molecules.

Information:

The electrons in involved in bonding are called valence electrons, they are the outermost electrons in an atom, those in the last shell.

Bohr Models:

Lewis Dot Structures:

  1. Draw the Bohr structure for Neon (above).
  1. What relationship exists between an atom’s valence electrons and the number of dots in the Lewis structure of the atom?
  1. What is the relationship between group number and number of valence electrons?
  1. Why does nitrogen’s Lewis Structure has five dots around it while nitrogen’s Bohr diagram contains 7 dots around it?
  1. Recall that oxygen, sulfur and selenium all have the same number of valence electrons (6). They also are in the same column of the periodic table. Predict how many valence electrons tellurium (Te) will have. ______
  1. Draw the Lewis structure for the following elements.

Phosphorus / Bromine / Xenon / Potassium / Arsenic

Which of the elements are nonmetals ______

Information: Chemical Bonding

To understand why atoms bond together, we need to understand what “motivates” an atom. (Of course, atoms don’t actually have thoughts and feelings, but it is helpful to imagine that they do.) The dream of every atom is to feel complete, and atoms accomplish this by having eight electrons in the valence shell. This “full octet” is very stable, and atoms undergo chemical reactions to obtain it. Noble gases already have a full octet, and therefore rarely react with other atoms.

Ionic Bonding (last chapter):

Nonmetals:One way an atom can obtain a full octet is by becoming an ion—by gaining or losing electrons. Atoms in group 17 have 7 valence electrons, so they form a full octet by gaining one more (they become ions with a charge of -1). Atoms in group 16 start with 6 and want two more (they form ions with a charge of -2). Group 15 elements start with 5, and want to gain three (they form -3 ions).

Metals:On the other side of the periodic table, elements behave differently. Group 1 atoms only have one valence electron, and the easiest way for them to get a full valence shell is to lose that electron. Generally speaking, metals lose electrons to become stable and nonmetals gain electrons to become stable. Thus, when metals encounter nonmetals, the metal will transfer its unwanted electrons to the nonmetals, which eagerly snap them up:

Once the two ions are formed, they stick together because ______charges attract: this is called an ______bond.

Ex: NaCl

Magnesium has ______unwanted electrons so it would have to bond with _____ chlorine ions.

Covalent Bonding (this chapter):

When two nonmetals encounter each other they can bond without forming ions. Instead of transferring electrons from one atom to another, they share valence electrons. When two chlorine atoms come in contact, they share a pair of electrons like this:

Because only one pair of electrons is shared, this is called a single bond.

  1. Below draw the electron dot structures for the atoms that make up a water molecule. In this case, represent the Hydrogen valence electrons with an ‘x’ so you can tell them apart from the Oxygen where you should draw them with dots.

Hydrogen / Oxygen / Hydrogen
H / O / H
  1. In order to have an electron configuration like a noble gas, each hydrogen needs access to how many more valence electrons? ______
  2. In order to have an electron configuration like a noble gas, oxygen needs access to how many more valence electrons? ______

  1. Each atom attempts to obtain a Noble Gas Electron Configuration. In a molecule of water, the oxygen atom and the hydrogen atoms share electrons to complete their “Octets.” Fill in the valence electrons on the symbols shown here.
/ H O
H
  1. The compound NH3is made up of one atom of nitrogen and three atoms of hydrogen. Draw the Lewis Dot structures for these four atoms.

Nitrogen / Hydrogen / Hydrogen / Hydrogen
  1. To complete their octets these four atoms share valence electrons. Draw this structure in the space provided. (Hint: the single atom is usually at the center of the molecule.)

  1. Draw the electron dot structures for the following particles.

Nitrogen / Chlorine / Chlorine / Chlorine
NCl3
  1. Draw the electron dot structures for the following particles.

Sulfur / Fluorine / Fluorine
SF2
  1. Draw the electron dot structures for each of the following molecules on the left, then on the right draw the structural formula. (Hint: draw each atom first.

CBr4

SbF3

Extras – Special Occations!!!

Sometimes atoms will have to share more than 1 pair of electrons to achieve an octet between them.

  1. What is the molecular formula for this molecule?

Step 1: Arrange the atoms

Step 2: Show the valence electrons for each atom

Step 3: Connect all elements with a single bond

Step 4: When you run out of bonds to connect and if every element doesn’t have 8

Step 5: Start over with 1 double bond between 2 elements

Step 6: If needed, try two double bonds then

Step 7: If you still can’t give all atoms an octet, try a triple bond

Draw Lewis structures for the following:

SiS2 P2 SO2 SCl2