CHEMICAL BONDING Chapter 3

BASIC IDEA - all elements want to be like the noble gases and have their outermost shell filled with electrons. To achieve this goal atoms will (1) share electrons (covalent bonding),

(2) give away electrons (ionic bonding), or (3) take electrons (ionic bonding).

Atoms share electrons

H · + · H ------> H · · H or H--H or H₂ hydrogen gas

By sharing their electrons, the hydrogen atoms have the s shell filled. They 'feel' like the noble gas, helium.

A single bond means 2 electrons are shared

H -- H

A double bond means 4 electrons are shared

H                             H

            C = C                      ethene

H                           H

A triple bond means 6 electrons are shared.

H-C º C-H

Valence electrons - electrons available for bonding

+1 Column I of chart has 1 electron
+2 Column II of chart has 2 electrons
+3 Column III of chart has 3 electrons
4 Column IV of chart has 4 electrons
-3 Column V of chart has 5 electrons
-2 Column VI of chart has 6 electrons
-1 Column VII of chart has 7 electrons

H Br
H has one electron on outermost level or shell. Br has 7 electrons on outermost level or shell.

Atoms either gives away or takes electrons - no sharing.

NaCl Na Cl Na⁺¹ Cl^-1

Na⁺ Cl^- Na is short one negative charge. Cl got it.

Positive ions are called cations.
Negative ions are called anions.
Most ionic compounds are solids.
Metals lose electrons.

CaCl₂         Ca⁺²         Cl^-1
                            Ca gives away 2 electrons.

Calcium chloride Each chlorine atom takes 1.

Metals - The ion has a smaller diameter than the atom of a given metal.

Sodium atom             Sodium ion

Nonmetals - The ion has a larger diameter than the atom of a given nonmetal.

Chloride atom           Chloride ion

1. A metal and a non metal
2. Metal loses electrons
3. Nonmetal gains the electrons
4. The number of electrons given up by the metal must equal the number of electrons picked up by the nonmetal so the compound has no net charge.

Nomenclature

The metal is written first. NaCl
Say the metal Sodium
Add the suffix 'ide' to the non metal Sodium chloride

hydride, carbide, fluoride, iodide, nitride, oxide, phosphide sulfide.

COVALENT BONDING

If an atom can't give away its electron easily and another atom can't accept it, the two atoms will share their electrons.

Elements or compounds would like to have 8 electrons. The electrons involved in bonding are called valence electrons. The periodic chart gives us an idea of how the elements will react with each other.

We have been working with oxidation numbers. Oxidation number or oxidation state is used to tell us the positive or negative character of an atom. When electrons are removed or shifted away during a reaction, the atom is assigned a positive oxidation number.

This also works for the ionic compounds

Al₂O₃ Means we have 2 aluminum atoms and 3 oxygen atoms

Al is +3 on chart                 (+3) (2) = +6
O is -2 on chart                  (-2) (3) =  -6
                                                         net 0

When electrons are lost, the element is given a positive oxidation number like Na⁺¹ or Mg⁺²

When electrons are gained, the element is given a negative oxidation number, like Cl^-1 or O^-2

The algebraic sum of the positive oxidation number and the negative oxidation number of the atoms and ions present in a compound must always be zero.

MgO CaBr₂

Some atoms will have a greater strength for pulling electrons to itself than other atoms. Sometimes in sharing (covalent) electrons one of the atoms has a greater pull on the electrons. Electrons have a negative charge. So the atoms that can pull the electrons strongly have a greater electronegativity value.

If the difference between two electronegativity values is

1.7 or greater we get ionic compounds

If the difference is zero we have non polar covalent

If the difference is greater than zero and less than
          1.7 we get polar covalent bonds.

Look at the chart for most of the numbers.
Most commonly used elements:

Radicals - Ions pgs 73

( ) Everything inside the brackets stays together and acts as an "element" - ion.

Do the element on the left first Mg(SO₄)

Magnesium sulfate

Sometimes you can have two elements come together in more than one ratio.

NO                             N₂O                         N₂O₃

nitrogen monoxide      dinitrogen monoxide         dinitrogen trioxide

1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa-

7 hepta- 8 octa- 9 ennea- 10 deca-

We will work primarily with just one or two values. For example oxygen will be -2 carbon +4 or -4 hydrogen +1 or -1

nitrogen +5 or -3

Let's see what the formulas of the following would be.

What would the formula be for sodium carbonate?

(NH₄)(OH)     Is it balanced:

Multiple Valences for Metals p 73

Write the formulas using the appropriate subscripts:

Stannic chloride
Mercurous oxide
Cupric oxide
Barium chloride
Potassium chloride
Ferrous sulfate
Aluminun hydroxide

Problems at end of Chapter 3 ---- 3.24; 3.25; 3.43

BALANCING EQUATIONS pgs 87 - 90

No quick, easy way. Requirements: pencil + eraser + patience

The number of atoms on the left side of the equation has to equal the number of atoms on the right side of the equation.

When balancing equations LEAVE THE SUBSCRIPTS ALONE, work with the coefficients.

1. In Al₂(SO₄)₃

a) the number of atoms of Al is _____.

b) the number of atoms of S in the formula is _____.

c) the number of atoms of oxygen in the formula is ______.

2. Balance the following equations: [*H₂O can also be written as H(OH)]

(a) ____H₂ + ____ N₂ -------> ____NH₃

(b) ____C₃H₆ + ___O₂ --------> ____ CO₂ + ____ H₂O

(c) ____ Na + ____ HCl ------> ____ Na Cl + ____ H₂

(d) ____ Na + ____ H₂O -------> ____ NaOH + ____ H₂

(e) ____HCl + ____ NaOH -------> ____NaCl + ____ H₂O*

(f) ____ HCl + ____Ca(OH)₂ -------> ____CaCl₂ + ____H₂O*

(g) ____H₂(SO₄) + ____Na(OH) ------> _____Na₂(SO₄) + ____H₂O*

(h) ____H₂(SO₄) + ___ Ca(OH)₂ -------> ____ Ca(SO₄) + ___H₂O*

(i) ____Al + ___H(NO₃) -------> ____ Al(NO₃)₃ + ____ H₂

(j) ____ Fe + ____ H₂(SO₄) -------> ____ Fe(SO₄) + ____ H₂

Problems at end of Chapter 4 -- 4.28: 4.29

Wednesday, March 21, 2007 01:28:01 PM