You've probably learned about the different elements in the periodic table and how many electrons they have up to this point. Now, let's learn about what happens when these neutral elements gain or lose electrons in their valence shell!
So, without further ado, let's dive into the charges of ionic compounds!
- First, we will talk about ionic compounds and ionization energy.
- Next, we'll talk about ionic charge.
- After, we will explore the trends for ionic charge on the periodic table and make a chart showing the most common ions of metals and nonmetals.
- Lastly, we will look at some questions involving ionic charge.
Trends for Ionic Charge and Ionization Energy
To be able to understand what an ionic charge is and its trends, let's review the basics of ions and ionic compounds.
In chemistry, an ionic compound is a compound formed by the reaction between a metal and a nonmetal.
There is an interesting structure to ionic solids: they are made of alternating negative ions and positive ions, held together by an ionic bond. This arrangement is called a lattice structure.
For example, potassium chloride (KCl) is an ionic compound formed from a chemical reaction between potassium (K) and chlorine (Cl). The lattice structure of KCl is composed of a repeating pattern of potassium (K+) and chloride (Cl-) ions.
$$ \text{Balanced Reaction: }\text{2 K + Cl}_{2}\text{ }\longrightarrow \text{ 2 KCl } $$
Figure 1. Lattice structure of KCl - Isadora Santos, Vaia Originals.
There are several characteristics that are associated with ionic compounds and their lattice structure:
- Because it takes a lot of energy to overcome the attraction between the ions, ionic compounds have high melting points.
- Solid ionic compounds are incapable of conducting electricity. Only ionic solids that have been dissolved in water or molten can conduct electricity.
- Ionic solids are crystalline.
Now, remember that, in ionic bonding, the valence electrons in a metal are transferred to the nonmetal. In the case of potassium chloride (KCl), the potassium (K) atoms lose electrons, while chlorine gains electrons.
Now, when this transfer of electrons happen, ions are formed!
- The loss of an electron in a metal atom results in the formation of a positively charged ion, also called a cation.
- When a nonmetal atom gains an electron, it turns into a negatively charged ion, known as an anion.
In ionic bonding, ions are formed when atoms gains or lose electrons.
But why do metal atoms readily lose their valence electrons? This has do to with their ionization energy. Metals have low ionization energies, and therefore, they lose their valence electrons in order to form positive ions with the same electron configuration as its closest noble gas!
The reason elements want to gain or get rid of its valence electrons and be like a noble gas has to do with stability! Nobles gases are very stable because they possess a full outer shell comprising 8 valence electrons, which is the max. number of valence electrons their outer shell can hold.
Helium is the exception, since its outer shell can only hold 2 valence electrons. Therefore species like lithium will lose electrons to have 2 valence electrons
So, elements will want to gain/lose electrons to achieve a full outer shell like that of noble gases, and become more stable!
In chemistry, the ionization energy (IE) is referred to as the amount of energy required to remove one or more electrons from a neutral atom.
For instance, when a sodium atom (Na) loses one valence electron to become a sodium ion (Na+), its electron configuration turns into that of neon (Ne).
On the other hand, nonmetals have high ionization energies, and they gain one or more electrons to achieve a stable electron configuration.
The trend in ionization energy is that ionization energy decreases down a group, and increases from left to right.
Trends for Ionic Charge Meaning
Now that we know what ions are, let's dive into ionic charges and its trends! When an atom turns into a positively or negative ion, it acquires a certain charge known as ionic charge.
Ionic charge is the specific charge an atom acquires after it has lost/gained valence electrons.
For example, when sodium chloride (NaCl) dissolves in water, it separates into sodium ions and chloride ions.
- The sodium ion has a charge of +1, whereas the chloride ion has an ionic charge of -1.
Trends for Ionic Charge: Periodic Table
Now, let's explore the trends for ionic charges in the periodic table. The general ionic charge trend in ionic compounds is as follows:
- Elements in group 1 (Alkali metals) will lose one valence electrons to form ions with a charge of +1
- In group 2 (Alkali earth metals), two valence electrons are lost to form +2 ions.
- Elements in groups 3 to 12 possess varying ionic charges.
- Group 13 elements have ions with a +3 charge because they lose three electrons.
- The nonmetals in group 14 do not typically form ions. However, the metals Sn and Pb tend to lose electrons to form positively charged ions.
- Elements in group 15 will gain three electrons to form ions with a -3 charge.
- Elements in group 16 will gain two electrons to form ions with a -2 charge. For example, oxygen in group 16 will gain two electrons to form an oxygen ion with a -2 charge.
- Elements in group 17 will gain one electron to form ions with an ionic charge of -1.
The periodic table below shows the ionic charges of the different elements in the periodic table.
Did you know that there are many ions that are very important to our bodies? These ions play a vital role in different physiological and metabolic functions. For example, sodium ion (Na+) helps regulate and control body fluids, potassium (K+) ions helps regulate body fluids and cellular functions, Calcium ions (Ca2+) is important in muscle contraction, whereas magnesium ions (Mg2+) is essential for certain enzymes, muscles, and nerve control!
Periodic Trends: Ionic Radius
When a neutral atom gains or loses electrons, its radius changes in size. For example, when Lithium loses an electron to form Li+ ion, its radius changes from 145 pm to 76pm.
In the periodic table, the general trend in ionic radius is as follows: positively charged ions (cations) tend to have a smaller radius compared to their parent atoms, whereas negatively charged ions (anions) tend to be bigger than their parent atoms.
This difference in atomic and ionic size is mainly to the electrons being added or removed to form the ions. When an atom loses electrons to form a cation, its resulting ionic mass is lower. On the other hand, when an atom gains extra electrons to form an anion, its resulting ionic mass is higher.
Trends for Ionic Charge Chart
To display the ions and their charges, let's make a chart showing ionic charges of some common metal and nonmetal ions.
Group Number | Cation | Charge | Group Number | Anion | Charge |
1 (1A) | $$\text{Li}^{+}$$ | +1 | 15 (5A) | $$\text{N}^{3-} $$ | -3 |
| $$\text{Na}^{+}$$ | +1 | | $$\text{P}^{3-} $$ | -3 |
| $$\text{K}^{+}$$ | +1 | 16 (6A) | $$\text{O}^{2-} $$ | -2 |
2 (2A) | $$\text{Mg}^{2+} $$ | +2 | | $$\text{S}^{2-} $$ | -2 |
| $$\text{Ca}^{2+} $$ | +2 | 17 (7A) | $$\text{F}^{-} $$ | -1 |
| $$\text{Ba}^{2+} $$ | +2 | | $$\text{Cl}^{-} $$ | -1 |
3 (3A) | $$\text{Al}^{3+} $$ | +3 | | $$\text{Br}^{-} $$ | -1 |
| | | | $$\text{I}^{-} $$ | -1 |
Let's look at a problem!
State the number of protons and electrons in S2-.
This problem asks us to find out the number of protons and electrons that the sulfur ion S2- has. The first thing we need to do it look at the atomic number of sulfur (S) in the periodic table. According to the periodic table, sulfur has an atomic number of 16, meaning that it has 16 protons, and hence, 16 electrons.
In order to become a sulfur ion with a charge of -2, sulfur needs to gain 2 electrons. Therefore, we can say the the sulfur ion (S2-) contains 16 protons and 18 electrons
Remember: An element's atomic number is its number of protons. Electrons equal proton number in neutral atoms.
Trends for Ionic Charge Questions
To finish off, let's look at some questions involving ionic charge.
Question 1: How many electrons does strontium (Sr) need to gain/lose to form an ion?
The first step is to look at the periodic table to see in which group strontium (Sr) is found. Notice that strontium is a part of group 2.
There are two electrons in the outermost shell of all group 2 elements, and they want to get rid of them in order to achieve a more stable configuration. So, strontium (Sr) will lose these two electrons to form a strontium ion with a +2 charge (Sr2+)!
Question 2: How many electrons does nitrogen (N) need to gain/lose to form an ion?
Nitrogen is a nonmetal found in group 15. It has 7 electrons in total, with 5 of them on the outermost shell. In order to fill its outer shell, nitrogen needs to gain three electrons. By gaining three electrons, nitrogen (N) turns into an ion with an ionic charge of -3 (N3-).
A full outer shell of 8 electrons is the most stable configuration! To learn more about this, check out "The Octet Rule"!
Now, I hope that you feel more confident in your understanding of ionic compounds and the trends in ionic charges!
Trends in Ionic Charge - Key takeaways
- In chemistry, an ionic compound is a compound formed by the reaction between a metal and a nonmetal.
- The structure of ionic compounds consists of alternating negative ions and positive ions held together by an ionic bond. This arrangement is called a lattice structure.
- In ionic bonding, ions are formed when atoms gains or lose electrons.
- Ionic charge is the specific charge an atom acquires after it has lost/gained valence electrons.
- The ionic charge of an element depends on the amount of electrons an element loses or gains to achieve its most stable configuration (full outer shell).
References
- Timberlake, K. C., & Orgill, M. (2019). General, organic, and biological chemistry : structures of life. Pearson.
- Theodore Lawrence Brown, Eugene, H., Bursten, B. E., Murphy, C. J., Woodward, P. M., Stoltzfus, M. W., & Lufaso, M. W. (2018). Chemistry : the central science (14th ed.). Pearson.
- Zumdahl, S. S., Zumdahl, S. A., & Decoste, D. J. (2019). Chemistry. Cengage Learning Asia Pte Ltd.
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