So, let's look at an example of equilibrium in the cookie market and see what happens when things change. Let's say the equilibrium price for a chocolate chip cookie is $3. Here's an example of the supply and demand curves, with an equilibrium price of $3, which is at the intersection of the supply and demand curves.
A sigma bond is the end-to-end overlap of the bonding orbitals, usually hybrid orbitals. The sigma bond is a single bond. A pi bond is the side-to-side overlap of unhybridized p-orbitals. A pi bond, along with a sigma bond form a double bond. A triple bond is two pi bonds and a sigma bond. Take a look at this diagram showing a sigma bond and a pi bond, forming a single bond and a double bond. http://metafysica.nl/ethylene01.jpg.
A single bond is usually a sigma bond. Pi bonds are weaker and are due to lateral overlap between p (or d) orbitals. A double bond between two given atoms consists of one sigma and one pi bond, and a triple bond is one sigma and two pi bonds. Covalent bonds are also affected by the electronegativity of the connected atoms which determines the chemical polarity of the bond. Two atoms with equal electronegativity will make nonpolar covalent bonds such as HâH.