Did you know that some types of chemical bonds behave similarly to the way that children play with toys? In this lesson, you will learn about two types of bonds called polar and nonpolar covalent bonds.
Nonpolar Covalent Bonds
Have you ever watched toddlers playing together with a toy? Sometimes they equally share toys, and other times, one child takes the other child’s toy away. Some types of chemical bonding are very similar to the way that children play with toys.
Nonpolar covalent bonds are a type of bond that occurs when two atoms share a pair of electrons with each other. These shared electrons glue two or more atoms together to form a molecule. Like children who share toys, atoms involved in a nonpolar covalent bond equally share electrons. An example of a nonpolar covalent bond is the bond between two hydrogen atoms because they equally share the electrons. Another example of a nonpolar covalent bond is the bond between two chlorine atoms because they also equally share the electrons. Nonpolar covalent bonds are very strong bonds requiring a large amount of energy to break the bond.
Nonpolar covalent bonds are extremely important in biology. They form the oxygen we breathe and help make up our living cells. One kind of nonpolar covalent bond that is very important in biology is called a peptide bond. A peptide bond joins together chains of amino acids, which are involved in the construction of our DNA. Amino acids are comprised of several atoms like carbon, oxygen, nitrogen and hydrogen.
Polar Covalent Bonds
Have you ever seen two children play and one child acts like a bully toward the other child? The bully child seems to spend more time playing with the toy than the other child. They are not equally sharing the toys.This unequal sharing also happens with a type of bond called polar covalent bonding. Polar covalent bonding is a type of chemical bond where a pair of electrons is unequally shared between two atoms. In a polar covalent bond, the electrons are not equally shared because one atom spends more time with the electrons than the other atom. In polar covalent bonds, one atom has a stronger pull than the other atom and attracts electrons. Remember how electrons carry a negative charge? Well, when electrons spend more time with one atom, it causes that atom to carry a partial negative charge.
The atom that does not spend as much time with the electrons carries a partial positive charge. To remember a polar covalent bond, instead say ‘puller covalent,’ and remember one atom has more ‘pull’ on electrons than the other atom.
Your life actually depends on polar covalent bonding. You drink water, right? A water molecule, abbreviated as H2O, is an example of a polar covalent bond. The electrons are unequally shared, with the oxygen atom spending more time with electrons than the hydrogen atoms.
Since electrons spend more time with the oxygen atom, it carries a partial negative charge.Another example of a polar covalent bond is between a hydrogen and a chlorine atom. In this bond, the chlorine atom spends more time with the electrons than the hydrogen atom. Because of this unequal sharing of electrons, the chlorine atom carries a partial negative charge, and the hydrogen atom carries a partial positive charge.
How to Predict Bonding Type Using Electronegativity
You may be wondering: How do you know what type of bond will occur between atoms? You can predict which type of bond will form by looking at the electronegativity of each atom involved in the bond. Electronegativity is how strongly an atom will attract electrons from another atom in a chemical bond. Some atoms have a higher electronegativity, while others have a lower electronegativity.
Electronegativity is like a tug of war game between two atoms. If you have one person on the side of the rope that is stronger than the other person, then that stronger person will tug harder, pulling the other person in their direction. On the other hand, if you had two people of equal strength, then the rope would not shift in any one direction and would stay in the same place.
Like tug of war, if you have a stronger atom with a higher electronegativity, then it will be able to tug electrons in its direction. Since the atoms have a different electronegativity, the electrons are unequally shared. On the other hand, if you have two atoms with the same strength, or the same electronegativity, then the electrons will not be tugged in any one direction and will stay in the middle of the two atoms. Since there is no tugging, electrons are equally shared between the two atoms.Remember how the periodic table is a like a roadmap that can tell you the properties of each element? An additional trend the periodic table can tell you is the electronegativity of an element.
Before I describe the trend, first remember that hydrogen is considered a nonmetal and is moved to the far right with the other non-metals. The electronegativity trend I am about to describe excludes the noble gases and most transition metals. Remember, noble gases are located in the last column of the periodic table, and the transition metals are located in groups 3 through 12 on the periodic table. Now that you know the exclusions, the main trend is as you move from left to right, the electronegativity increases, and as you move from bottom to top, the electronegativity increases.Using this trend, you can see the most electronegative elements are found on the top right, such as oxygen, chlorine and fluorine.
And, the least electronegative elements are found on the bottom left, such as francium, cesium, barium and radium.Now that you know the trends of electronegativity of the periodic table, you can determine the type of bond that will form within a molecule. If the electronegativity between two atoms is basically the same, a nonpolar covalent bond will form. For example, two atoms of fluorine each have the same electronegativity. Since there is no difference between electronegativity between the two atoms, they will equally share electrons forming a nonpolar covalent bond.If atoms are located close together on periodic table, they will have a slightly different electronegativity. If the difference of electronegativity between two atoms is slight, then a polar covalent bond will form.
This slight difference of electronegativity causes one atom to have a stronger pull on electrons than the other atom. This stronger pull causes electrons to be unequally shared and spend more time near the atom with the higher electronegativity. For example, looking at the atoms involved in a water molecule, you can see the hydrogen and the oxygen atoms are located fairly closely on the periodic table. Since they are located pretty near each other, there will be only a slight difference of electronegativity. The oxygen atom has a higher electronegativity than the hydrogen atoms, so the electrons spend more time around oxygen.
In this lesson, you learned about two types of bonds: nonpolar covalent and polar covalent. Nonpolar covalent bonds are a type of chemical bond where two atoms share a pair of electrons with each other. Polar covalent bonding is a type of chemical bond where a pair of electrons is unequally shared between two atoms. You also learned how you can look at the electronegativity trends of the periodic table to predict the type of bond that will form. Electronegativity is how strongly an atom will attract electrons from another atom in a chemical bond.Looking at the periodic table, as you move from left to right, the electronegativity increases, and as you move from bottom to top, the electronegativity increases. Using this trend, you can see the most electronegative elements are found on the top right, such as oxygen, chlorine and fluorine.
And, the least electronegative elements are found on the bottom left, such as francium, cesium, barium and radium. If the electronegativity of two atoms is basically the same, a nonpolar covalent bond will form, and if the electronegativity is slightly different, a polar covalent bond will form.
After this lesson, you’ll be able to:
- Differentiate between nonpolar and polar covalent bonds
- Provide examples of each type of bond
- Explain what a peptide bond is
- Define electronegativity
- Explain how to predict whether a nonpolar covalent bond or a polar covalent bond will form using electronegativity trends of the periodic table