Atoms join together to form molecules by sharing electrons and this exchange of electrons can sometimes be the same (or almost the same). Other times, an atom has more electrons on average. When one atom has a disproportionate amount of negative charge (electrons), it means that the other atom will have a positive charge. This results in a polar bond, which means that it has a positive and a negative pole. Polar bonds can be identified by looking at the types of atoms bonded together and the electronegativity of those atoms. The bond can then be classified as polar or nonpolar.
Steps
Method 1 of 4: Look at Bonded Atoms
Step 1. Identify any metal
Metals are normally shiny and malleable. They often have loosely bound electrons. That means they have weaker electronegativity than many nonmetals. This allows metals to "give" some of their electrons to nonmetals, resulting in a dipole.
A dipole occurs when a bond has a positive and negative charge at each end. The presence of a dipole indicates a polar bond
Step 2. Take note of any non-metallic items
Nonmetals are often hard and brittle, and lack luster (shine). They often have a higher electronegativity than metals. This means that they can "take" electrons from the metal atoms to which they are attached. This will create a dipole on the link.
Step 3. Take into account the valence electrons for each atom
The valence electrons of an atom are those that reside in its outer shell. For the most part, atoms follow the octet rule, which means that eight valence electrons will create the most stable configuration. Atoms with nearly eight are likely to "take" other electrons, while atoms with one or two valence electrons are likely to "give up" their outer electrons.
For example, sodium (Na) has one valence electron, and chlorine (Cl) has seven. When they join together, they form the sodium chloride (NaCl) salt because sodium gives up its single valence electron and chlorine accepts it. This is a polar bond
Method 2 of 4: Analyze Electronegativity
Step 1. Represent the electron affinity of each atom
The electron affinity of an atom is the measure of the probability that that atom "takes" electrons from another. Electron affinity grows as you go from left to right, and from top to bottom, on the periodic table. In other words, the small non-metallic atoms tend to have the highest electron affinity.
- Electron affinity is a component of the electronegativity of the atom.
- Some high electron affinity atoms are fluorine, chlorine, oxygen and nitrogen.
- Some low affinity atoms are sodium, calcium, and hydrogen.
Step 2. Take into account the ionization energy of each atom
Ionization energy is the amount of energy required to remove an electron from a particular atom. Ionization energy increases as you go from left to right and from bottom to top on the periodic table. This means that it is in the small non-metallic atoms that it is most difficult to remove the electrons. Large, metallic atoms are the easiest.
Ionization energy is the other component of the electronegativity of the atom
Step 3. Use the trends from the periodic table
Observing the periodic table can tell a lot about how polar a bond will be between two atoms. The atoms in the upper right of the table will tend to ionize and have a negative charge. The atoms on the far left of the table tend to form positive ions. The atoms in the middle of the table form less polar bonds.
Method 3 of 4: Classifying Link Types
Step 1. Take into account all nonpolar covalent bonds
By definition, a nonpolar bond must be covalent. That means electrons are shared evenly from atom to atom. A truly nonpolar bond has a negativity difference of zero between the two atoms.
- For example, hydrogen gas (H2) forms a nonpolar bond between the two hydrogen atoms because they have exactly the same electronegativity.
Step 2. Recognize polar covalent bonds
Polar covalent bonds form when there are two atoms with similar (but not identical) electronegativities. This generally occurs between two non-metals, and you have a weak dipole. These bonds have an electronegativity difference that is greater than zero, but less than two.
For example, a carbon-hydrogen bond is weakly polar, so it is a polar covalent bond
Step 3. Define the ionic bonds
Ionic bonds generally form between metals and non-metals. When each atom ionizes into an anion or cation, there is a strong dipole. Ionic bonds have atoms with an electronegativity difference greater than two.
The bonds that form between calcium and chlorine are ionic
Method 4 of 4: Solve Practice Problems
Step 1. Determine the polarity of the table salt
Table salt contains the chemical formula NaCl, as it is made up of one sodium atom and one chlorine atom. To determine the polarity of table salt, you can find that the electronegativity of sodium is 0.9 and that of chlorine is 3.0. You will find that the difference between the two electronegativities is 2.1, which means that the salt of mesa is held together by an ionic bond (and therefore is polar).
It can also be reasonably assumed that the bond is polar simply by noting where each atom is located on the periodic table
Step 2. Find the difference in electronegativity for carbon and hydrogen
First look at a periodic table that lists electronegativities. You will find that that of hydrogen is 2.1 and that of carbon is 2.5. The difference between the two is 0.4, which means that a carbon-hydrogen bond is (slightly) polar.
Step 3. Give an example of a truly nonpolar bond between two different atoms
To achieve this, you must look at a periodic table that marks electronegativities. Locate two atoms that have identical electronegativities. These two atoms will form a covalent bond.