Ionic vs Covalent

Ionic vs Covalent, what’s the difference and how do I remember which one is which?

Ionic is a type of chemical bond where atoms are bonded together by the attraction between opposite charges.

Covalent is a type of chemical bond where atoms are bonded together by the sharing of electrons.

One way to help distinguish between the two is to remember that ionic bonding occurs between ions and covalent bonding occurs when atoms have electrons in common (they share).

Of course, there is much more to ionic vs covalent than that so let’s discuss them more in depth.

Ionic vs Covalent Background Information

To better understand ionic vs covalent bonds, we must first understand what these bonds are made up of.

Atoms

So, all physical substances that have mass and take up space are known as matter. Matter is made up of atoms, and atoms are the smallest unit of matter.

Atoms consist of a nucleus, and electrons that are bonded to the nucleus. The nucleus of the atom consists of neutrons and protons.

The electrons (outside the nucleus) have a negative charge, the protons (inside the nucleus) have a positive charge, and the neutrons (inside the nucleus) are neutral since they have no electric charge.

Try to remember it as: protons are positive, electrons are negative, and neutrons are neutral (no charge). The reason this is important is that how atoms react with one another is due to their electric charge.

If an atom has an equal amount of electrons and protons, then it is considered neutral.

If an atom has less protons than it does electrons, then it is considered negative.

If an atom has more protons than it does electrons, then it is considered positive.

All atoms start off as neutral, but they can become negative or positive.

Inside the atom, the neutrons and protons are attracted to each other by a force called the nuclear force, and the protons and electrons are attracted to each other by a force called the electromagnetic force.

There are many types of atoms, and these types are known as elements. An example would be the element (aka atom) hydrogen (denoted by H).

Molecules

A molecule is comprised of groups of atoms that have chemically bonded together. For example, H2 (hydrogen gas) is a molecule that consists of two hydrogen atoms that have chemically bonded together.

There are two main types of molecular bonding: ionic bonds and covalent bonds.

Ionic vs Covalent Bonds

Ionic bonding is a type of chemical bonding that is caused by the attraction between oppositely charged ions.

Ions are atoms (or even molecules) that have an unequal number of electrons and protons.

Remember how we were talking about negative and positive atoms earlier? Well, the charge of an atom is the basis for ionic bonding.

So, remember that when an atom has less protons than electrons, it is negative, and when an atom has more protons than electrons, it is positive.

If the atom (ion) is negatively charged, then it is called an anion, and if it is positively charged, it is called a cation.

Molecules can also be ions, and therefore they can be a cation or an anion as well. The same as with atoms, if a molecule is negatively charged, it is an anion, and if it is positively charged, it is a cation.

During ionic bonding, an atom loses an electron (or even multiple electrons) to another atom, and the atoms are then bonded together by the attraction between their opposing charges.

Molecules that are bonded together by ionic bonding normally have no fixed position (a definitive shape). Also, ionic bonding mainly happens when metallic atoms (elements) bond with nonmetallic atoms.

Covalent bonding is a type of chemical bonding that is due to the sharing of electrons between atoms.

During covalent bonding, the atoms share their electrons and are then bonded together by the sharing of their electrons (not the attraction between their opposing charges).

Molecules bonded together by covalent bonding normally have a fixed position (defined shape). Also, covalent bonding mainly happens when nonmetallic elements bond with each other.

Covalent bonds can be broken down further into two different types: polar vs nonpolar bonds.

Polar bonds are chemical bonds where atoms share electrons unequally.

Nonpolar bonds are chemical bonds where atoms share electrons equally.

Electronegativity

The taking or sharing of electrons (whether equal or unequal) is due to electronegativity which is how strongly or weakly an atom can attract electrons from another atom (the pull an atom has over another atom’s electrons).

Negative atoms (with more electrons than protons) can pull electrons from atoms that are weaker than them (have less electrons than them). In contrast, positive atoms (with more protons than electrons) cannot pull electrons from atoms that are stronger than them (have more electrons than them).

This is due to how electrons are organized in atoms. All electrons are organized into shells (also known as energy levels or orbitals). The outermost shell is known as the valence shell.

Every atom wants to have 8 electrons in its outer shell (valence shell) and will try to bond with other atoms whenever possible to achieve this. This tendency of atoms to prefer having 8 electrons in their valence shell is known as the octet rule.

So, if an atom (element) does not have 8 electrons in its outer shell it has two options: it can try to either gain electrons or try to lose electrons. Of these two, the atom will always choose the option that requires the least amount of energy.

For example, if an atom only has 1 electron it will choose to give it up, but if it has 5 electrons, it will try to gain more electrons.

Therefore, the reason that atoms with more electrons (negative atoms) can pull electrons from atoms with less electrons (positive atoms) is because they want to fill their outer shell (valence shell), and this is the option that requires the least amount of energy for them to do so.

An atom’s electronegativity is ranked on a scale called the Pauling scale.  Where the atom’s electronegativity falls on the scale is how the three bonding types (ionic, polar, and nonpolar) are classified.

The scale measures electronegativity from a range of 0.00-4.00 with 0.00 being the weakest force and 4.00 being the strongest force. For example, a sodium atom (Na) has an electronegativity of 0.93 which is very weak. This means that if another atom has a higher electronegativity than sodium, then it can take (pull) sodium’s electron.

The scale is divided into three sections, and these sections are what determine the bonding type. So, if a molecule has an electronegativity greater than 2.00 it is ionic (uses ionic bonding), if it is less than 0.50 it is nonpolar (uses nonpolar covalent bonding), and if it is between 0.50-2.00 it is polar (uses polar covalent bonding).

Examples of Ionic vs Covalent

It can often be confusing to remember the different terms used to describe atoms (and molecules) since they can be many different things at once so let’s look at some examples to help us better understand ionic vs covalent.

Ionic Example

An example of ionic bonding would be the bond between a sodium atom and a chlorine atom (salt which is written NaCl). The chemical name for salt is sodium chloride.

Sodium chloride ionic bond

The sodium atom is neutral because it has an equal number of protons and electrons (sodium has 11 protons and 11 electrons. The chlorine atom is also neutral with an equal number of protons and electrons (chlorine has 17 protons and 17 electrons).

However, when we look at their outer shells (valence shells), both atoms do not have 8 electrons in their outer shell. Sodium only has 1 electron in its valence shell, and chlorine has 7 electrons in its valence shell.

Following the octet rule, it is easiest for sodium to give up its 1 electron and for chlorine to take 1 electron. This enables both atoms to have 8 electrons in their outer shell.

When this happens, it then makes both atoms ions. Remember that ionic bonding occurs between two ions. Sodium becomes a positive ion (a cation) because it has more protons than electrons (it now has 11 protons and 10 electrons).

Conversely, chlorine becomes a negative ion (an anion) because it has less protons than electrons (it now has 17 protons and 18 electrons). Since chlorine has become an ion, it is now called chloride.

Since, chlorine has taken sodium’s electron the two atoms are now bonded together by the attraction between their opposing charges (sodium being positively charged, and chloride being negatively charged) which is ionic bonding. So, there is no sharing of electrons (the electron was taken and not shared), so they cannot bond covalently.

Also, remember that ionic bonds are normally (but not always) formed between metallic and non-metallic atoms. Sodium is a metallic atom and chlorine is a nonmetallic atom.

We can also use the Pauling scale to classify the salt molecule. The sodium atom has an electronegativity of 0.93, and the chloride atom has an electronegativity of 3.16. The difference between the atoms is 2.23 which is greater than 2.00, so the molecule is an ionic molecule.

Polar Covalent Example

An example of polar covalent bonding would be the bond between an oxygen atom and two hydrogen atoms (water which is written as H20). The chemical name for water is dihydrogen monoxide.

The oxygen atom is neutral because it has 8 electrons and 8 protons. The two hydrogen atoms are also neutral because they have an equal number of protons and electrons (both hydrogen atoms have 1 proton and 1 electron).

Oxygen element

 

 

But when you look at their outer shells (valence shells), the atoms do not have 8 electrons in their outer shell. Oxygen has 6 electrons in its valence shell, and hydrogen has 1 electron in its valence shell.

Oxygen really wants to have 8 electrons, so it uses 1 electron from each hydrogen atom to give itself 8 electrons in its valence shell. This gives oxygen a total of 10 electrons and 8 protons making it an ion. It is negative since it has more electrons. Also, since oxygen is now an ion, it is called oxide.

However, the hydrogens cannot fully give up their 1 electron, so they remain neutral. If they gave up their electrons, then they would have none. They also have no way of having 8 electrons in their valence shell even if they lost they lost their 1 electron, so they must share their electrons. Since they are sharing electrons, they are bonded covalently.

Remember that both atoms would need to be ions to form an ionic bond. In this case, only oxygen is an ion (oxide), while the two hydrogen atoms are neutral. Also, covalent bonds form between two nonmetals and both oxygen and hydrogen are nonmetallic.

All three of the atoms (the oxygen ion and both hydrogens) are polar because they share their electrons unequally. Since the oxide (oxygen ion) has more electrons, it is stronger than both of the hydrogens which have less electrons. This means that the oxygen ion has a stronger pull (or attraction) on the electrons than the hydrogens do.

We can also use the Pauling scale to classify the water molecule. The hydrogen atoms have an electronegativity of 2.20, and the oxygen ion (oxide) has an electronegativity of 3.44. The difference between the atoms is 1.24 which is between 0.50 and 2.00, so the molecule is a polar molecule.

Nonpolar Covalent Example

An example of a nonpolar covalent bond would be the bond between two hydrogen atoms (hydrogen gas which is written as H2). The chemical name for hydrogen gas is dihydrogen.

The hydrogen atoms are both neutral since they have an equal number of protons and electrons (both hydrogen atoms have one proton and one electron).

Hydrogen element

When you look at their outer shells (valence shells) both hydrogen atoms only have 1 electron. Since there is no way for either atom to have 8 electrons in its valence shell, they do not need to take electrons from each other.

The easiest option for both hydrogen atoms is to share their one electron. Since they are sharing their electrons (neither one has lost or gained), they are bonded covalently.

The atoms cannot form an ionic bond because neither atom is an ion (they are both neutral) and they are both nonmetallic atoms. Ionic bonding normally occurs between a metallic and a nonmetallic atom.

Both hydrogen atoms are nonpolar because they share their electrons equally. Since they are both the same type of atom (element), they both have the same number of electrons. Therefore, they cannot pull electrons from one another.

We can also use the Pauling scale to classify the hydrogen gas molecule. The hydrogen atoms have an electronegativity of 2.20. The difference between the atoms is 0.00 which is less than 0.50, so the molecule is a nonpolar molecule.

Ionic vs Covalent Interactions

Ionic and covalent atoms, molecules, and bonds can interact in different ways. There are a lot of factors that can influence them, so let’s look at some of these factors more in-depth.

Polarity

An important characteristic of ionic and covalent bonds is polarity. Polarity is merely the distribution of electric charges within a molecule.

Both ionic and polar covalent bonds have polarity, but nonpolar covalent bonds do not (since they share electrons equally). When the electrons are not equally shared, a separation of electric charge occurs.

These separations of electric charge are called charges. In ionic molecules, the electron (or electrons) are taken so the charges can be either positive charges or negative charges. In polar molecules, the electron (or electrons) are unequally shared so the charges can be either partial positive charges or partial negative charges.

Dipoles

When a molecule has two opposing charges such as positive and negative (or partial positive and partial negative), this results in a dipole. You can measure a molecule’s dipole by its dipole moment which is an equation (µ=qr).

Dipoles (and polarity) are due to an atom’s electronegativity and if the atom is positive or negative. We can see this when we look at our previous ionic example: salt (NaCl). Since sodium is positive (less electrons) and chloride is negative (more electrons) this causes unequal distribution (polarity) in the salt molecule.

The chloride is stronger (it has more electrons), and it also has a higher electronegativity. So, the chloride has a negative charge, and the sodium atom has a positive charge.

Now, let’s look at our previous polar covalent example: water (H20). Since both hydrogen atoms are neutral (equal electrons and protons) and the oxygen ion is negative (more electrons than protons) this also causes unequal distribution (polarity) in the water molecule.

The oxygen ion is stronger (it has more electrons), and also has a higher electronegativity. Therefore, it has a greater pull (or attraction) over the electrons in the hydrogen atoms. So, the oxygen ion ends up having a partial negative charge, and the hydrogen atoms end up having a partial positive charge.

So, in summary, nonpolar covalent bonds have no polarity (they are equal in charge), polar covalent bonds have polarity (a difference in charge where atoms share electrons unequally), and ionic bonds have a lot of polarity or “true polarity” (where the difference in charge is so great than an atom can take electrons from another atom).

Electrostatic Force

While polarity plays an important role in determining how molecules react with other molecules, it is not the only factor to consider.

Ionic bonds (with a lot of polarity) are generally stronger than covalent bonds (with less or no polarity), and they require a lot of energy to break their bonds.

However, not all covalent bonds are the same. Within covalent bonds, there are the two types: polar vs nonpolar. Polar bonds (with polarity) are weaker, and they require less energy to break their bonds, while nonpolar bonds (with no polarity) are stronger, and they require more energy to break their bonds.

This is due to polarity as well as electrostatic force (also called Coulomb’s force) which is attraction or repulsion due to electric charge. Electrostatic force is what holds ions (with opposing charges) together.

Polar covalent bonds also have electrostatic force, but it is weaker than the force between ionic bonds. Remember, that the sharing of electrons is what holds covalent bonds together and not the attraction (or force) between opposing charges.

To maximize their electrostatic force, most ionic compounds form large, lattice-shaped networks which are very strong and stable. So, even though ionic bonds have a lot of polarity (therefore they should be weaker), because they have stronger formations (and they have more electrostatic force) they are typically stronger than covalent bonds.

Dipole Interaction

Dipole interaction also plays an important role in how molecules react with one another. The dipoles (on ionic or polar molecules) can interact with other dipoles (on other ionic or polar molecules).

If the dipoles interacting are both on polar molecules the process is called dipole-dipole interaction. If the dipoles interacting are on a polar molecule and an ionic molecule the process is called ion-dipole interaction. If the dipoles interacting are both on ionic molecules the process is called ion-ion interaction.

This interaction between dipoles is due to the negative (or slightly negative) charge on one molecule being attracted to the positive (or slightly positive) charge on another molecule and vice versa.

Because ions have a stronger electrostatic force ion-ion interaction is the strongest type of dipole interaction.

Don’t let the fact that ion-dipole interaction can occur between polar molecules and ionic molecules confuse you. Remember, that ionic bonding occurs between two ions. However, a polar molecule can have one ion and no other ions though.

So, a polar molecule can bond with an ionic molecule, if part of the polar molecule is an ion. However, only the ion (in the polar molecule) is interacting with the ion (or ions) in the ionic molecule.

Examples of Interactions

So, electrostatic force, polarity, and dipole interactions all play a role in determining how molecules interact with one another. This, in turn, determines many of a molecule’s physical properties such as boiling point, melting point, and solubility.

We can see how these forces come into play regarding physical properties when we look at some of our previous examples.

If we look at our ionic example (salt), we know that molecules that are formed by ionic bonding are stronger (have more electrostatic force) and harder to break (requires more energy to break) than those formed by covalent bonds.

Therefore, typically ionic compounds have a higher boiling point (and a higher melting point) than those formed by covalent bonds. Salt (which is ionic) has a boiling point of 2,675oF and water (which is polar covalent) has a boiling point of 212oF. This is because salt has a higher electrostatic force and a stronger dipole interaction (ion-ion interaction).

We can also see how polarity and dipole interaction affects a molecule’s physical properties even within the same bond category. So, if you look at water vs oil both molecules are bonded covalently, but water is a polar covalent molecule (it has more polarity), and oil is a nonpolar covalent molecule (it has less polarity).

This difference means that water can interact with other water molecules, but it cannot interact with oil molecules. Conversely, oil can interact with other oil molecules, but it cannot interact with water molecules. This is the reason why the two are unable to dissolve in one another because they have opposing polarity.

Also, since water is a polar molecule, this means it also has dipoles (the oxygen ion has a partial negative charge, and the hydrogen atoms have partial positive charges). These dipoles can interact with other dipoles and break apart more easily.

Oil, on the other hand, is a nonpolar covalent molecule, so it does not have dipoles. Therefore, it is harder for oil to break apart. This means that it is easier to dissolve substances in water than it is to dissolve them in oil (because of water’s ability to have dipole interactions).

Final Thoughts on Ionic vs Covalent

Ionic vs covalent can initially be very confusing but try to remember that ionic bonding occurs between ions (atoms or molecules with an unequal number of protons and electrons) and covalent bonding occurs when atoms have electrons in common (they share).

Ionic bonding is when an atom loses or gains an electron (or multiple electrons) to or from another atom, and the atoms are then bonded together by the attraction between their opposing charges. This attraction (force) is called the electrostatic force.

Ionic bonding mainly occurs with nonmetallic and metallic atoms bonding together, and the molecules have no fixed position (defined shape).

Covalent bonding is when atoms share an electron (or multiple electrons) with another atom, and the atoms are then bonded together by the sharing of their electrons. Covalent bonding mainly occurs with nonmetallic atoms, and the molecules do have a fixed position (defined shape).

Covalent bonds can be further broken down into polar vs nonpolar. Polar bonds are when atoms share electrons unequally, and nonpolar bonds are when atoms share electrons equally. Polar bonds do have some electrostatic force, but it is much weaker than ionic bonds.

The key difference between ionic vs covalent is that ionic bonds are bonded by the attraction between opposing charges (they must have an unequal number of electrons and protons making them ions), and covalent bonds are bonded together by the sharing of electrons (either equal or unequal).

You can determine if a bond is ionic, polar covalent, or nonpolar covalent based on an atom’s electronegativity which is how strongly or weakly an atom can attract electrons from other atoms. This electronegativity is rated on a scale called the Pauling scale.

If a molecule has an electronegativity greater than 2.00 it is ionic (uses ionic bonding), if it is less than 0.50 it is nonpolar (uses nonpolar covalent bonding), and if it is between 0.50-2.00 it is polar (uses polar covalent bonding).

Ionic and polar covalent bonds have polarity, and nonpolar bonds do not. This polarity creates dipoles in a molecule that result in positive (or partial positive) charges and negative (or partial negative charges).

These dipoles (on ionic or polar molecules) can interact with other dipoles (on other ionic or polar molecules) with either dipole-dipole interactions, ion-dipole interactions, or ion-ion interactions.

Electrostatic force, polarity, and dipole interactions all play a role in determining many of a molecule’s physical properties such as boiling point, melting point, and solubility.

 

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