Bond Types

Covalent Bonds

Covalent Bonds form when electrons are shared between atoms, happening when the electronegativity difference is less than an ionic bond. This usually happens between 2 nonmetals, something that can be found out by seeing how many electrons they have when trying to bond together (covalently bonded atoms should have an abundance of valence electrons). Covalent molecules and compounds are usually insulating, are dull in coloration, and have low melting points.

To figure out the covalent formulas one method that can be used is:

Figure out the charges of each atom, change one from negative to positive, then balance the charges like it was an ionic compound.
Example:
- Oxygen has a -2 charge and Fluorine has a -1 charge
- Change either one of them into a positive # instead of a negative (O = -2, F = +1)
- Balance the charges to get 0 like they were ionic bonding (-2 +1 +1 = 0 so it's OF2)

Another method that can be used is to draw pictures and connect the bonds to see how many of each atom would be needed, similar to Lewis Structures (we'll see these next week).

Oxygen makes 2 bonds while Fluorine makes 1 bond. Due to this, there needs to be 2 Fluorine atoms to make sure all atoms have a full octet!

Diatomic Molecules are covalent compounds where an element bonds to itself! These 7 elements generally won't be found alone in nature due to their electronegativity and how they bond with themselves. Whenever one of these elements are refereed to it's assumed that the diatomic molecule is what's being talked about (such as oxygen gas being O2 and liquid nitrogen being N2).

Lewis Structures

We also have a quick way to represent covalent molecules on paper known as Lewis Structures - a combination of element symbols, lines, and dots.

Lines are "bonds" - these represent covalent bonds, so they are made of 2 electrons.
Symbols represent the elements.
Dots are electrons and are placed around each symbol in pairs. These are known as lone pairs and only represent the outermost electrons.

Oxygen has 2 bonds needed while Fluorine has 1 bond needed. Due to this we'd need 1 more fluorine to fill every possible bond.

To make a Lewis Structure, follow these steps:

Place the element closest to carbon in the center, surrounded by the other atoms as much as possible.
Add valence electron dots around each element based on how many they start with.
Make bonds that connect the atoms together, using 1 dot from each atom used to make the bond.
Check for the octet rule, adding more bonds to the atoms that need it. To do this, you add additional lines to have more than 1 bond between the same atoms. These are double bonds or triple bonds that are used to fill the octet. An example is shown here:

VSEPR Shapes

VSEPR Stands for Valence Shell Electron Pair Repulsion. It’s basically the different shapes molecules can form based on the bonds it can make and the amount of electrons also taking up space on the molecule. When valence electrons are taking up space or bonds are connecting atoms together they try to separate out as much as possible just like magnets with the same poles would, leading to the following shapes:

Other Types of Molecules and Bonds

Hydrogen is special with its charge since it can either lose all electrons to become stable (with a +1 charge) or gain 1 electron to act like Helium (with a -1 charge). It will not form an octet; it's too small to do so and helium is the closest noble gas to it on the periodic table.

Allotropes are elements that bond with themselves in different ways, allowing them to have more than one type of physical form in a single phase. The form the element takes can be based on many things, such as temperature, pressure, and how quickly the substance is cooled. Allotropes have different properties from one another based on how they are bonded and their overall structure.

Metallic Bonds are a special type of bonding that occurs when a material is primarily made of metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons. The electrons act as glue that hold together the metal. These bonds are what make metals malleable, ductile, lustrous, and able to conduct both heat and electricity. While they still give up their electrons like ionic bonds the electrons are shared by all atoms in a metal and don’t fill octets, instead undergoing a mixing process known as alloying to make metals with unique properties. They usually don’t have a specified formula unless they are purely one element.

The electrons can go anywhere in metallic bonding, making it easy for metals to both conduct electricity and heat.

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