Everything around us is comprised of a complex mixture of chemical compounds.
And all of these compounds are bonded together with different kinds of atoms.
The manner in which atoms bind together has a profound effect on chemical and physical properties.
Types of Chemical Bonds
Broadly speaking, there are two types of chemical bonds in Chemistry.
1. Ionic Bonds
2. Covalent Bonds
We'll talk a TON about covalent bonds in later posts, but for now let's focus on #1 - Ionic Bonds...
Ionic Bonds = Ionic bonds are stronger than covalent bonds and have a high bond energy.
Bond energy = the energy (J) required to break a bond.
In other words, the stronger the bond, the more (bond) energy that's required to break it.
Ionic compounds form when an atom that loses electrons easily (cation - usually a metal) reacts with an atom that gains electrons easily (anion - usually a nonmetal).
Bond energy is often referred to as the "energy of interaction" between cations and anions.
Here's a bond energy example, which uses Coulomb's Law...
Coulomb's Law Example
ex: Find the energy of interaction ("the bond energy") between a pair of Na+ and Cl- ions, when the distance between them is 2.76Å (0.276nm).
➞ to do this, we must use Coulomb's Law:
Coulomb's Law Formula
E = (2.31 x 10-19 J.nm)(Q1Q2 / r)
➞ here's what I mean, visually:
With Coulomb's Law, we can use the +1 charge on Na+, the -1 charge on Cl-, and the distance between the ion centers (0.276 nm), and plug them in to get:
As stated in the image above, the negative sign means we have an attractive force between Na+ and Cl-.
This attractive force is the bond energy of NaCl.
Bond Length and Bond Energy
Bond Length = the distance between two atoms (or ions) where the energy is minimal.
See the plot that follows below.
Bond Length vs. Bond Energy?
How are these two ideas related?
➞ the shorter the bond length, the stronger the bond,
➞ and therefore the harder it is to break the bond (higher bond energy).
ex: Consider the Potential Energy Diagram of H2 (H—H is a covalent bond).
3 KEY POINTS:
1. In the upper left, the 2 H's are too close together.
The one nucleus ⟷ nucleus repulsion is severe.
It outweighs the two nucleus ⟷ electron attractions.
2. In the upper right, the 2 H's are so far apart that they can't "see" each other.
No interation. (0 kJ/mol).
3. At the bottom of the plot, the H—H bond is the optimum length to achieve lower overall energy of a system.
The two nucleus ⟷ electron attractive interactions outweigh the nucleus ⟷ nucleus repulsion.
What Determines if a Bond is Ionic or Covalent?
To answer this, you must consider the two atoms' or ions' differences in electronegativity.
Electronegativity = the ability of an atom to attract electrons to itself.
We'll talk all about electronegativity in my next video blog post...
In my 2nd post in this series, SECTION 8 - Chemical Bonding, we'll discuss the video notes for
Electronegativity Trends, Bond Polarity, and Dipole Moments :-)