Joshua Siktar's documents science Chemistry chemical Bonding and Structure Lewis structures Octet dominance


In chemistry bonding, there room some patterns that apply to the bulk of chemical compounds. One of these is known as theOctet Rule. This preeminence states that an atom will always attempt to have actually a full set of eight valence electron by bonding with various other atoms either covalently or ionically. The way that the Octet rule works varies because that different types of compounds, for this reason in this write-up we will explore the various possibilities in an organized fashion. Overall, the Octet ascendancy is among the most vital fundamentals of chemistry bonding.

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General Trends

The lot of electrons an element will often tend to gain or lose depends ~ above the number of electrons in the atom's valence shell. One atom will certainly always try to ionize come its steady state with the move of the fewest electrons possible.

Example 1:Afluorine atom can get a complete valence shell by either gaining one much more electron, or by shedding seven electrons. The former requires the move of less electrons, for this reason the fluorine atom will shot to gain one electron first. Therefore, (F^-) ions are much more common than (F^7+) ions.

Example 2: A magnesium atom can gain a complete valence covering bt either shedding two electrons, or by acquiring six. The previous requires the transport of fewer electrons, for this reason (Mg^2+) ion are more common than (Mg^6-) ions.

Example 3:Note that a carbon atom's valence shell has actually (4) electrons. It have the right to either lose four electrons or gain four electrons to obtain a full valence shell. Note that either transition requires the transfer of the same variety of electrons, therefore which ion results depends on the various other chemicals involved. Keep in mind that in one ionic compound consisted of of a metal and also carbon, carbon will type the (-4) carbide ion and form compounds such as magnesium carbide (Mg_2C) and sodium carbide (Na_4C).

Here is a table that the team that a chemistry is in and its most typical transaction of acquiring or shedding electrons to gain a complete valence shell.

Group electron gained/lost


1 lose 1 electron

2 lose 2 electrons

3 shed 3 electrons

4 shed 4 electrons/gain 4 electrons, depends on situation

5 acquire 3 electrons

6 obtain 2 electrons

7 gain 1 electrons

8 this chemicals, known as thenoble gases, already have a complete valence shell and thus have tendency to it is in unreactive (inert).

Binary Ionic Compounds

In one ionic compound, electrons room not shared in between ions. Every valence electron is designated to belong come a specific ion in the bond. In a binary ionic link (one with just two different varieties of ions), each valence electron belonging to one of two people the cation or anion. As soon as either the cation or anion is polyatomic, it becomes an ext complicated. We can say that the electron belongs to one of two people the cation or anion, yet then we need to determine exactly how it is shared between atoms that comprise the polyatomic ion. We will certainly worry about this special instance later, in the last section that the article.

Example 4:Consider sodium Chloride, (NaCl). Salt atoms have one valence electron and also chlorine atoms have seven. If a single electron is moved from the sodium atom come the chlorine atom, climate we gain (Na^+) and also (Cl^-), two ions in steady states. For this reason we only need one of each atom to kind this stable ionic compound, and also both ion now accomplish the Octet Rule.

Example 5:Consider Aluminum Bromide, (AlBr_3). Aluminium is in group III, and also it tends to shed three electrons to form an ion v a full octet (meaning it obeys the Octet Rule). Bromine atoms often tend to acquire just one electron to gain to a full octet, together Bromine is in team VII. A chemistry consisting of an aluminum ion and also a bromide ion in your stable says would it is in (AlBr^2+), but it is no an ionic compound because it has a charge. Therefore, us need more negatively charged bromide ions to obtain an ionic compound. Each such ion has a fee of (-1), so we need two more to gain a neutral compound. Therefore aluminum bromide is (AlBr_3), v each ion being in its secure octet form.

Example 6:Consider Magnesium Nitride, (Mg_3N_2). Magnesium is in group II and also has 2 electrons in that valence shell. Hence it has tendency to shed two electrons. In this case, the next collection of electrons closer to the nucleus is the new valence shell, and also it is full. Nitrogen, top top the other hand, is in group V and has five valence electrons, therefore it demands to acquire three electrons to gain a full valence shell. Hence the many stable state for nitrogen ion is the (N^3-) ion.

Covalently external inspection Compounds

In covalently bonded compounds, electrons space shared between two atoms with the bonds in between them. Every such bond is composed of two electrons, which count in the direction of both atoms' full set of eight valence electrons. For this reason in a compound where two atoms have a solitary bond to every other, if both atoms are stable, then each will have actually six extr valence electrons.

Example 7:Consider (F_2), fluorine's elemental form. Use the Octet dominion to describe why fluorine is a diatomic molecule (exists naturally in groups of two atoms external inspection together).

Solution:Fluorine is in group VII, and a single fluorine atom has actually seven valence electrons. However, by the Octet ascendancy it would like to get one electron to get a full octet the valence electrons. Two fluorine atoms have the right to each "sacrifice" one of their valence electron to kind a solitary bond between the atoms. Currently each fluorine atom has actually six valence electrons to itself. However, the bond consists of two additional valence electrons because that each fluorine atom (as the electrons room shared), for this reason both fluorine atoms now have actually a full octet. Therefore fluorine is more stable together a diatomic molecule.

Below is a Lewis framework for elemental fluorine because that reference. Keep in mind that only valence covering electrons are consisted of in the picture. This is a basic convention for illustration Lewis Structures.


Now, remind that twin bonds and also triple binding exist. These have slightly different advantages compared to single bonds. In particular, they permit even much more electrons to be shared between two atoms. If a twin bond exists in between two atoms, they share 4 valence electrons; if over there is a triple bond, the 2 atoms share six valence electrons. The Octet dominion still applies regardless of which type of covalent link is involved.

Example 8:Consider (O_2), oxygen's element form. Lone oxygen atoms have actually six valence electrons. However, oxygen is even an ext stable in teams of two atoms, due to the fact that each oxygen atom have the right to "sacrifice" two valence electrons, providing a full of four electrons used to link the 2 atoms. Due to the fact that there are four valence electrons to share, this is a double bond. Each oxygen atom has four valence electron to itself and four that are mutual through the dual bond. Hence each oxygen atom now has actually a full octet. Listed below is the Lewis Structure.


Example 9:Consider (N_2), nitrogen's element form. Unequal oxygen, nitrogen atom have 5 valence electrons, for this reason they require three much more to obtain a full octet. This is where a triple shortcut comes right into play. Nitrogen atom share three of your valence electrons, and also in return obtain three more that initially belonged to an additional nitrogen atom. Hence there are two valence electrons the belong solely to one of the nitrogen atoms, and there are 6 that space shared, so each nitrogen atom has eight valence electrons. Listed below is the Lewis Structure.


Ionic Compounds through a Polyatomic Ion

When a molecule has a nonzero charge, it i do not care a polyatomic ion. One or much more atoms in the molecule will have actually violated the Octet Rule, do them stormy unless they space in the existence of a different ion of the contrary charge. Most polyatomic ions space anions. In this case, one or an ext atoms will have actually one of the following: much more lone pairs 보다 they should, or anexpanded octet, a collection of more than eight valence electrons. This section is quite facility and its therapy is often minimal in high college chemistry classes.

Example 10:Consider magnesium sulfate, (MgSO_4). The sulfate ion's structure is displayed below:


Two the the oxygen atoms (the left and also bottom ones) have actually an extra lone pair, yet still have actually a full octet and also no extra valence electrons. These oxygen atoms have actually a negativeformal charge, definition they host some electrons much longer than they would certainly in the perfect stable situation (two lone pairs, two bonding pairs). In lieu the a 2nd bonding pair, this oxygen atoms have actually a third lone pair. This electrons space not common with various other atoms, for this reason they further add to an unfavorable charge roughly the oxygen atom.

When assigning formal charges, we assume the the two atoms in a bond share bonding pair electron equally, so every bonding pair electron basically contributes (frac12) the charge of an electron to each atom connected in the bond. Therefore, as soon as two electrons walk from being mutual to being hosted only by the oxygen atom, your "charge contribution" come the oxygen atom boosts by (frac12) an electron's charge each, raising the charge around the oxygen atom by (-1). Hence the oxygen atom's formal fee is (+1).

Next, note that the top and also right oxygen atoms have two lone pairs and also two bonding pairs (as we debated earlier as typical) and also obey the Octet Rule.

Now, let's talk around the Sulfur atom. It has actually an broadened octet, together it has twelve apparent valence covering electrons (six single bonds' worth; counting the bonds). However, in an increased octet, part electrons native the shell of electrons within the valence shell participate in bonding. That is why it appears sulfur has twelve valence electron in this case, yet this is simply an illusion.

This is a confusing subject and you likely have unanswered questions at this point, however do no worry! the is argued from right here that girlfriend do more reading (either with or another resource) ~ above Octet dominion exceptions and also formal charges. The discussion gets even more technical and also will it is in omitted here.

Now let's talk about where the Octet dominion does apply: the ionic bond. The magnesium atom offered to kind this link still desires a full octet, and as that is in team II, that achieves this most conveniently by losing two valence electrons, providing this magnesium ion a charge of (+2). The amount of the official charges that the atoms of the sulfate ion is (-2), therefore the fee of the ion is (-2) (this will constantly be true because that a polyatomic ion). Therefore the magnesium cation and also sulfate ion complement up in a 1:1 ratio, offering (MgSO_4).

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Thanks to because that the Lewis framework diagram pictures.