Thursday 3/28/13 - Ionic Lewis Structure Activity

In this activity we will be modeling what an Ionic Bond is by using cereal to represent the valence electrons.

Please follow the following steps for modeling what occurs in the following ionic

compounds:

1. Draw the element’s symbols in the designated box.

2. Assign the proper number of valance electrons (using Cereal) to each original element

3. Make an ionic bond to create a balanced neutral compound by transferring valence electrons (Cereal). The element with the higher electronegativity will gain the electrons.

4. Draw the correct Lewis Structure in the box provided. (after bonding)

5. Write the formula or name of the compound

Compound / Before Bonding / After Bonding
KBr
Name______
Magnesium chloride
Formula______
CaO
Name______
Sodium Sulfide
Formula______
Mg3N2
Name______

NOTES

Lewis Dot Structures for Ions of Single Atoms

For positive ions, the Lewis dot structures are extremely easy: these ions are formed when a metallic atom LOSES it valence electrons! Therefore, the Lewis dot structure for a positive ion has no dots!

The Lewis dot structure for a positive ion is simply the chemical symbol for the element and the charge on the ion written at the upper right of the symbol:

H+1 Ca+2 Al+3

Lewis dot structures for negative ions require that all of the valence electrons be represented. Brackets are then drawn around the chemical symbol and dots, and the ion charge is written at the upper right OUTSIDE the brackets:

.. ..

[ : F : ]-1 [ : P : ]-3

.. ..

Lewis Dot Structures for Ion Pairs (Ionic Compounds)

Write the chemical formula for the ionic compound. Be sure to include any subscripts after element symbols if they are given. Then write the appropriate Lewis dot structures for the respective ions. If there is more than one of a particular ion in the chemical formula, you must write more than one Lewis dot structure for that ion.

For example, the Lewis dot structure for sodium chloride, NaCl, would be written as ..

Na+1 [: Cl : ]-1

..

The Lewis dot structure for calcium chloride, CaCl2, would be written as

..

Ca+2 [: Cl : ]-1

..

..

[: Cl : ]-1

..

Covalent Lewis Activity

In this activity we will be modeling what a Covalent Bond is using cereal to represent the valence electrons.

Please follow the following steps for modeling what occurs in the following ionic

compounds:

1. Draw the element’s symbols in the designated box.

2. Assign the proper number of valance electrons (cereal) to each original element (before bonding)

3. Make a covalent bond(sharing electrons) to create a balanced neutral compound.

4. Draw the correct Lewis Structure in the box provided (after bonding).

5. Mark with stars the compounds that are diatomic.

Compound / Before Bonding / After Bonding
H2O
Name______
Ammonia
Formula______
F2
Name______
Sulfur dioxide
Formula______
O2
Name______

NOTES

Lewis dot structures (a.k.a. Lewis electron dot formulas) use dots arranged around the chemical symbol for an element to represent the valence electron configuration of the atoms in the element.

For example, a hydrogen atom has one valence electron. The Lewis dot structure for hydrogen would be written as

H ·

A hydrogen molecule is formed when two hydrogen atoms mutually share valence electrons. The Lewis dot structure would be written as

H : H

The pair of dots between the two hydrogen symbols represents the pair of shared electrons.

The electron dot formula is simply a two-dimensional representation of the positions of the valence electrons in an atom, ion, or molecule.

Steps in Writing Lewis Dot Structures

1.  Calculate the total number of valence electrons for the molecule by adding up the number of valence electrons for each atom.

2.  Write the skeleton structure of the molecule or ion, connecting every bonded pair of

atoms by a pair of dots (or a dash).

3.  Distribute electrons to the atoms surrounding the central atom (or atoms) to satisfy

the octet rule (having 8 valence electrons) for these atoms (Remember that hydrogen can

only make one single covalent bond.)

4.  Distribute the remaining electrons as pairs to the central atom (or atoms), after subtracting the number of electrons already distributed from the total of valence electrons calculated in Step 1.

If there are fewer than 8 electrons on the central atom, this suggests a multiple bond

is present (double or triple).

Two electrons fewer than 8 suggests a double bond; four fewer suggests a triple bond or

two double bonds.

To write a multiple bond, move one or two electron pairs (depending on whether the

bond is a double or triple bond) from a surrounding atom to the bond connecting the

atom. Atoms that often form multiple bonds are C, N, O, P, and S.