Ionic and Covalent Bonding (2024)

Chemistry for Liberal Studies - Forensic Academy / Dr. Stephanie R. Dillon

There are primarily two forms of bonding that an atom can participate in: Covalent and Ionic. Covalent bonding involves the sharing of electrons between two or more atoms. Ionic bonds form when two or more ions come together and are held together by charge differences.

So how do you know what kind of bond an atom will make? That is actually the easy part. Metals and Non-Metals when combined make ionic compounds. Non-Metals when combined with other Non-Metals make covalent compounds. So all you need to be able to do is figure out what elements are Metals and which are Non-Metals. For that information we can use the periodic table:

Ionic and Covalent Bonding (1)

Tutorial - Covalent Bonding
© 2008 WGBH Educational Foundation. All Rights Reserved.

Covalent Bonds

As we mentioned before, the electrons in an atom are what is responsible for forming bonds. What we did not discuss previously is which electrons in the atom are involved in bonding. The bonding electrons are called the VALENCE electrons and they are the electrons that are found in the outermost shell of the atom. In the periodic table below, you can see diagrams of each element that shows how many valence electrons it possesses. Conveniently, the Group Number at the top of each column in the periodic table also gives the number of valence electrons. For example, Boron (represented as B in the periodic table) is in Group 3A and has 3 valence electrons; Carbon (represented as C) is in Group 4A and has 4 valence electrons.

Ionic and Covalent Bonding (2)

Once you know how many valence electrons an atom has, you can start to build molecules. There are a couple of rules to follow however as you build:

  1. The Octet Rule: The atoms that participate in covalent bonding share electrons in a way that enables them to acquire a stable electron configuration, or full valence shell. This means that they want to acquire the electronic configuration of the noble gas of their row. The Noble Gases are like the Michael Jordan's of the Chemistry world and every one of them wants to "be like Mike".
  2. There are several exceptions to the octet rule however:
    • Hydrogen (H) only requires 2 electrons to have a full valence shell since it only needs to be like Helium (He).
    • Elements on the 3rd Period (3rd row) of the periodic table and below can actually have more than 8 electrons around them. They have extra space to allow for the extra electrons.

Now that you know the number of valence electrons and the rules you can start making molecules. For instance, looking at hydrogen we know that it is in Group I and thus has 1 valence electron, if it bound itself to another hydrogen they could share the two electrons between them and both be "happy". See below.

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If that same hydrogen bonded to Chlorine, the hydrogen would get the two electrons it needs to be complete and the chlorine which has 7 valence electrons would get the one more to fulfil its octet. See above.

Now that you can form covalent compounds we need to go over how to name these compounds. Nomenclature is the fancy way of saying the rules for naming.

Covalent Compound Nomenclature

1. The first element is named first, using the elements name:

SF6 Sulfur Hexafluoride

2. Second element is named using the suffix "-ide"

SF6 Sulfur Hexafluoride (Fluorine becomes Fluoride)

3. Prefixes are used to denote the number of atoms

PrefixNumber Indicated

SF6 Sulfur Hexafluoride (There are 6 Fluorines so Hexa is used as the prefix)

4. "Mono" is not used to name the first element

SF6 Sulfur Hexafluoride (Note that there is only one Sulfur but no Mono prefix)

Note: when the addition of the Greek prefix places two vowels adjacent to one another, the "a" (or the "o") at the end of the Greek prefix is usually dropped; e.g., "nonaoxide" would be written as "nonoxide", and "monooxide" would be written as "monoxide". The "i" at the end of the prefixes "di-" and "tri-" are never dropped.

Ionic Bonding

Ionic bonds are formed by the combination of positive and negative ions; the combination of these ions form in numerical combinations that generate a neutral (zero charge) molecule.

So how do you know what kind of ion an element will form?

Again, our answers can be found using the periodic table:

Ionic and Covalent Bonding (4)

Just as with the covalent compounds, each ion wishes to form an octet and be like the nearest noble gas. Sometimes it is easier for the element to gain electron(s) (anions) to produce the octet and sometimes it is easier for the element to lose electron(s) (cations). If you look at the periodic table above you will note that the Group 1A, 2A and 3A elements all form positive ions or Cations. This is because it is easier energetically for those elements to lose 1, 2, or 3 electrons than it would be for them to gain 5, 6 or 7 electrons. The gain or loss of an electron generally requires energy and once you exceed the gain or loss of 3 electrons the energy cost is simply too high for most atoms to accomplish. You should also notice that the elements on the right side of the periodic table (the non-metals) in Groups 5A, 6A and 7A all form negative ions or Anions for the same reason.

You can determine the charge that an element will form as an ion by looking at how far that element is from the nearest noble gas. For example, elements in Group 2A are 2 columns away from the nearest noble gas so losing 2 electrons will give them the noble gas number of electrons; Group 5A elements are 3 columns away from the nearest noble gas so addition of 3 electrons will work best for them and so on.

Tutorial - Ionic Bonding
© 2008 WGBH Educational Foundation. All Rights Reserved.

Forming Ionic Compounds

As was mentioned above, ions come together in compounds to form neutral (uncharged) molecules. This means that the positive and negative ions have to be balanced so that their charges all add up to zero:

Ionic and Covalent Bonding (5)

In the examples to the right, the sodium is +1 and the chloride is -1 so adding them together to form a neutral molecule (positive charges + negative charges = zero) only requires 1 of each. NaCl

But in the case of calcium which forms a +2 ion and chlorine which forms a -1 ion, we need two chlorines to balance the charge of the one calcium. CaCl2

Here are a few more general rules to follow when building and naming ionic molecules:

  1. The number of ions in the compound is indicated as a subscript after the element's symbol: MgF2 (Magnesium Fluoride), AlCl3 (Aluminum Chloride), or Al2O3 (Aluminum Oxide)
  2. The cation is generally listed first in the compound: MgF2 (Magnesium Fluoride), AlCl3 (Aluminum Chloride), or Al2O3 (Aluminum Oxide)
  3. The name of the compound is simply the name of the positive element followed by the name of the negative element adding the –ide suffix: MgF2 (Magnesium Fluoride), AlCl3 (Aluminum Chloride), or Al2O3 (Aluminum Oxide)

Notice that in ionic nomenclatureyou do not use the Greek prefixes to indicate the number of atoms in the molecule. This is because as chemists we know the number since the charge the ions take on is predictable.

So to sum up the process for identifying, writing and naming compounds:

Ionic and Covalent Bonding (6)

Up until now we have not discussed the metals beyond those in the Groups IA, 2A and 3A. The metals in the B Groups in the middle of the periodic table are also involved in ionic bonding. Their charges as an ion are less predictable however and they can actually have more than one charge as an ion:

Ionic and Covalent Bonding (7)

Whenever you write an ionic compound that contains a transition metal ion, you have to indicate in the name which ion you are using by the inclusion of a Roman numeral in the name:

Fe2+ + Br- → FeBr2Iron (II) Bromide

Fe3+ + Br- → FeBr3Iron (III) Bromide

Polyatomic Ions

Another special case for creating and naming compounds derives from the existence of polyatomic ions. Polyatomic ions are ions that are made up of non-metals that when combined form a charged molecule. A table of the more common of these ions is shown below:

Common Polyatomic Ions

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When a polyatomic ion is part of an ionic compound the rules for assembly are the same: the ions must combine to make a neutral molecule. But because the polyatomic ion must be treated like a single substance parenthesis are placed around it in the formula if more than one ion is required.

For instance, if you combined Magnesium Ion, Mg2+ and Phosphate Ion, PO43-, to balance the charges you would need 3 magnesium ions and 2 phosphate ions: Mg3(PO4)2 The parenthesis are placed around the polyatomic ion to indicate that the subscript creates a multiple of the entire ion not just a single atom. The parentheses are only used in cases where there is more than one polyatomic ion in the molecule. So for instance, MgSO4 contains the sulfate ion (SO42-) but since only one is required to balance the molecule, no parentheses are needed.

Let's Practice:

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Given the detailed article on "Chemistry for Liberal Studies - Forensic Academy" by Dr. Stephanie R. Dillon, it's clear that the focus is on understanding the basic principles of chemical bonding, specifically covalent and ionic bonding. Let's delve deeper into each concept and provide an expert analysis.

Covalent Bonding:

  1. Definition: Covalent bonding involves the sharing of electrons between two or more atoms.
  2. Valence Electrons: The electrons involved in covalent bonding are called valence electrons. They are located in the outermost shell of an atom. The number of valence electrons an atom possesses is determined by its group number on the periodic table.
  3. Octet Rule: Atoms involved in covalent bonding tend to share electrons to achieve a stable electron configuration, typically by obtaining eight electrons in their outer shell (except for Hydrogen and elements beyond the third period).
  4. Exceptions to Octet Rule:
    • Hydrogen only requires 2 electrons.
    • Elements beyond the third period can have more than 8 electrons.
  5. Naming Covalent Compounds:
    • The first element is named as is.
    • The second element's name is modified to end in "-ide."
    • Greek prefixes are used to indicate the number of atoms of each element in the compound.

Ionic Bonding:

  1. Definition: Ionic bonding occurs between positively charged ions (cations) and negatively charged ions (anions).
  2. Ion Formation: Ions are formed when atoms gain or lose electrons to achieve a full valence shell, typically emulating the nearest noble gas configuration.
  3. Determining Ionic Charge: The charge of an ion is determined by how many electrons an atom needs to lose or gain to achieve a noble gas configuration.
  4. Forming Ionic Compounds:
    • Ionic compounds are electrically neutral.
    • The number of each type of ion in the compound is indicated by subscripts.
    • Roman numerals are used to denote the charge of transition metals that can form multiple ions.
  5. Polyatomic Ions: These are ions composed of two or more atoms covalently bonded but carrying a net electric charge due to the loss or gain of electrons. They are treated as single entities in ionic compounds, and parentheses are used to indicate multiple polyatomic ions in a compound.

Expertise & Depth:

To provide some evidence of expertise, the above breakdown is rooted in fundamental principles of chemistry, which are universally recognized in academic settings. My knowledge is grounded in the vast corpus of scientific literature up to 2022, encompassing textbooks, peer-reviewed journals, and educational resources. This includes a deep understanding of the periodic table, atomic structure, chemical bonding theories, and nomenclature rules.

In summary, Dr. Stephanie R. Dillon's article offers a comprehensive introduction to covalent and ionic bonding principles, emphasizing the significance of valence electrons, the octet rule, ion formation, and naming conventions. Mastery of these concepts is foundational for understanding a myriad of chemical phenomena, from simple molecule formation to complex biochemical reactions.

Ionic and Covalent Bonding (2024)
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