Ions and the Octet Rule (Simplified): Videos & Practice Problems

Main group elements strive for 8 valence electrons, achieving stability through electron transfer. Metals, like sodium (Na), lose electrons to resemble the nearest noble gas, neon (Ne), while nonmetals, such as chlorine (Cl), gain electrons to mimic argon (Ar). For example, sodium loses one electron to become Na⁺, and chlorine gains one to form Cl^-. This electron transfer results in filled outer shells, enhancing stability and reducing reactivity, aligning with the octet rule.

Ions and the Octet Rule (Simplified) Concept 1

There's a tendency of main group elements to achieve 8 valence electrons or a filled outer shell by undergoing chemical reactions. Main group metals lose electrons to resemble the noble gas that precedes them in the periodic table. For instance, consider sodium, which has an atomic number of 11. The noble gas before it is neon, with an atomic number of 10. Sodium wants to lose one electron to become just like neon. Conversely, nonmetals tend to gain electrons to emulate the noble gases that follow them in the periodic table. For example, chlorine has an atomic number of 17. It would need to gain one more electron to be just like the next noble gas, which is argon. This relationship between nonmetals, metals, and noble gases emerges because they aim to create completely filled energy levels, which leads to greater stability and lower chemical reactivity.

If we analyze the situation with lithium and fluorine, we find that lithium has one valence electron as its outer shell electron, with the electron configuration 2-1, signifying it solely possesses one electron in its second shell. In contrast, fluorine has seven valence electrons 2-7. Lithium, belonging to group 1A, aims to lose one electron to attain a +1 charge. This electron loss results in lithium having a filled outer shell, mirroring the electron configuration of helium. The electron transferred from lithium does not disappear; instead, it is acquired by fluorine. By accepting this electron, fluorine acquires a filled outer shell, the electron configuration becoming similar to neon, resulting in an ion commonly referred to as fluoride. This exchange illustrates the essence of the octet rule where atoms either gain or lose electrons to resemble the electron configuration of the nearest noble gas.

Ions and the Octet Rule (Simplified) Example 1

Here it says, "How many electrons must the sodium atom lose in order to obtain a filled outer shell?" So, look at the periodic table. Sodium has an atomic number of 11, which we're told right here. Remember, metals tend to lose electrons to be like the noble gases that came before them. So, what's the noble gas before sodium? If you look, it would be neon. So, we want to go from 11 electrons to 10 electrons, so sodium would have to lose 1 electron. So here, the answer would have to be option A.

Ions and the Octet Rule (Simplified) Example 2

Alright. So we're going to say here with a metal cation, remember cations are positive ions, we first remove electrons from the highest energy level. So here it says write the electron arrangement for the following ion. We have a calcium ion, Ca²⁺. It has an atomic number of 20. Alright. So the steps that we need to take, we're going to provide the electron arrangement for the neutral form of the element. Calcium in its neutral form has 20 electrons. So remember it would have 2 in the first shell, 8 in the second shell, 8 in the second shell, and 2 in the 4th shell. If you don't remember how to do this, remember to go back to my videos on electron arrangements. Now 2+ would mean what? We've lost 2 electrons. So that leads us to step 2: begin removing electrons from the highest energy level to obtain the desired charge. Recall each electron removed causes the ion charge to increase by plus 1. So we're going to lose 2 electrons. Remember, this is the 1st shell, 2nd shell, 3rd shell, and the 4th shell or 4th energy level. This is the highest energy level. So if we're going to lose 2 electrons, it has to come from there. So here, the calcium ion would have the electron arrangement 2-8-8. This would be the electron arrangement of the calcium ion.

Ions and the Octet Rule (Simplified) Example 3

With a nonmetal anion, add an electron or electrons to the orbitals with available space. Alright. So we're going to write the electron arrangement for the following ion. We're dealing with the nitride ion, that's N_3-. Nitrogen has an atomic number of 7. So let's follow the rules here. Here's step 1. We provide the electron arrangement for the neutral form of the element.

Nitrogen is neutral here. The first shell can hold a maximum of 2 electrons, but we need to get to 7 electrons based on its atomic number. So that would mean the second shell would have to have 5 electrons. This represents the electron arrangement of the neutral nitrogen atom. But what about N_3-? What does a minus 3 mean? Well, here step 2 says you add electrons to the energy level that can accommodate more electrons. Minus 3 here means you've gained 3 electrons, so you have to add 3 electrons.

The first shell can only hold a maximum of 2 electrons. So it's full. It can't accommodate any more. The second shell, though, can hold up to 8 electrons. And guess what? If it can hold up to 8, we can add the 3 additional electrons we gained to that second shell. So the nitride ion would have 2-8 for its electron arrangement.

Determine the electron arrangement for the Cl^– ion.

• A. 2-8-7
• B. 2-8-8
• C. 2-8-6
• D. 2-2-6-2-6
• E. 2-2-6-2-5

Answer: (B)

Determine the electron arrangement for the Al³⁺ ion.

• A. 2-8-3
• B. 2-8-6
• C. 2-8
• D. 2-2-6
• E. 8

Answer: (C)

Here’s what students ask on this topic:

What is the octet rule in chemistry?

The octet rule in chemistry states that atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight valence electrons, similar to the electron configuration of noble gases. This rule is particularly applicable to main group elements. For example, sodium (Na) loses one electron to form Na⁺, achieving the electron configuration of neon (Ne), while chlorine (Cl) gains one electron to form Cl^-, achieving the electron configuration of argon (Ar). This electron transfer results in filled outer shells, enhancing stability and reducing reactivity.

How do metals and nonmetals achieve the octet rule?

Metals and nonmetals achieve the octet rule through electron transfer. Metals, such as sodium (Na), lose electrons to resemble the nearest noble gas. For instance, sodium loses one electron to become Na⁺, mimicking neon (Ne). Nonmetals, like chlorine (Cl), gain electrons to achieve a noble gas configuration. Chlorine gains one electron to form Cl^-, resembling argon (Ar). This process results in filled outer shells, leading to greater stability and lower chemical reactivity.

Why do elements follow the octet rule?

Elements follow the octet rule to achieve greater stability and lower chemical reactivity. By gaining, losing, or sharing electrons to fill their outermost shell with eight electrons, they attain a stable electron configuration similar to that of noble gases. This filled outer shell configuration minimizes the energy of the atom, making it less reactive. For example, sodium (Na) loses one electron to become Na⁺, and chlorine (Cl) gains one electron to become Cl^-, both achieving stable configurations.

What happens when sodium reacts with chlorine in terms of the octet rule?

When sodium (Na) reacts with chlorine (Cl), sodium loses one electron to form Na⁺, and chlorine gains that electron to form Cl^-. This electron transfer allows both elements to achieve a stable electron configuration. Sodium, with an atomic number of 11, loses one electron to resemble neon (Ne), while chlorine, with an atomic number of 17, gains one electron to resemble argon (Ar). This results in both elements having filled outer shells, enhancing their stability and reducing reactivity.

How does the octet rule explain the formation of ions?

The octet rule explains the formation of ions by describing how atoms gain or lose electrons to achieve a stable electron configuration of eight valence electrons. Metals, such as sodium (Na), lose electrons to form positive ions (cations) like Na⁺, while nonmetals, like chlorine (Cl), gain electrons to form negative ions (anions) like Cl^-. This electron transfer results in filled outer shells, similar to noble gases, leading to greater stability and lower reactivity.