Unit 3: Bonding and Nomenclature
Content Outline: Chemical Bonds (3.1)
I. Chemical Bonds
A. These are mutual attractions between atom’s valence shell electrons to create new molecules.
B. Bonds can affect the electrical charge of an atom or molecule.
C. Bonding of atoms promotes atomic or molecular stability in nature. (It mimics the stability of Noble gas elements.)
1. Potential Energy (PE) per atom decreases in a bond. More stable atoms mean less Potential Energy per molecule.
2. Molecules release energy when a bond is created; and to break apart molecules require energy input.
D. There exists three types of chemical bonds:
1. Covalent Bonds
a. The atoms valence shells “share” electrons to make each atom more stable. Each behaves like a Noble gas. (“Co” means together; “valent” means “of the valence”.)
b. Two types of molecules can result from this type of bonding:
i. Non-polar molecule
α. In this type of molecule, there is an equal distribution of electrons.
b. These molecules typically have electronegativity (desire for electrons) differences
ranging from 0 (no desire) to 0.3 (minimal desire).
ii. Polar molecules
α. These molecules have unequal distribution of electrons within the molecule.
* This makes one end (pole) positive (less electron presence).
* This makes one end (pole) negative (more electron presence).
b. These molecules typically have electronegativity differences ranging from
0.3 –1.7.
c. The negative end is represent by (δ-); the positive end is (δ+).
d. Water is the most important polar molecule on the planet. This polar quality helps
support life in all organisms.
c. Covalent bonds tend to be stronger than other bonds, but not always.
2. Ionic Bonds
a. This bond forms from the electrical charge attraction (positive to a negative) between oppositely charged atoms.
i. The charge on the atom is the result of an “electron swap” between the two atoms.
a. This swap allows both atoms to behave “like” a Noble gas.
b. The atom that lost an electron (called oxidation), is now positively charged and
called a cation. (Think “Cats have a positive happy effect on people.”)
· It is called oxidation because an atom usually loses the electron to an
Oxygen atom, just like at the end of the Electron Transport Chain in Cellular Respiration.
c. The atom that gained an electron (called reduction), is now negatively charged
and is called an anion. (Think “Angry people are negative.”)
· Remember the Law of Conservation of Matter? Matter is neither
created, nor destroyed; just transferred or transformed. Well the electrons have been transferred from one atom to another atom and thereby transformed the atoms charge and properties.
b. These molecules typically have electronegativity differences greater than 1.7.
c. These bonds are usually stronger than covalent bonds, but can be weaker sometimes.
3. Metallic Bonds
a. These are bonds involving very dense, electrically charged metal atoms.
b. Metals tend to have very few valence shell electrons. (Look at the Periodic Table to see.)
c. These electrons tend to be highly mobile and therefore can travel from one atom to another adjacent atom. This moving field of electrons is often referred to as “a sea of electrons” and is the reason why metals are great for generating electricity.
i. The electrons are said to be delocalized. (They can roam from atom to atom).
d. Metals tend to have luster (Shine).
i. Remember, the Photoelectric effect and electrons coming off the surface and emitting light (energy loss).
e. Metals are also malleable. (Think mallet [hammer].)
i. This means they can be hammered into thin sheets. (Such as aluminum foil.)
f. Metals are also ductile.
i. This means they can be “pulled” into long thin wires.
g. The strength of metallic bonds varies with nuclear charge and the number of valence electrons present in the atoms of those metals.
h. Enthalpy (The total amount of energy in a system.) of Vaporization is used to calculate the relative strength.
i. This is the total amount of energy require to turn a liquid metal into a gas (vapor) at
a constant pressure.
ii. More valence electrons in the “sea” the higher the amount of energy.