Ionic bonding
Definitions & Key takeaways
Ionic bonds exist between the ions formed from metal and non-metal atoms. In ionic bonding, atoms give up or gain electrons to form ions. Ions are atoms that have either gained or lost one or more electrons, and as a result, have an electrical charge. When two oppositely-charged ions come together, they will form a molecule.
When a metal like sodium reacts with a non metal like chlorine, they form an ionic bond. Sodium has the atomic number 11, meaning that it has 11 protons and 11 electrons.
Due to details of its atomic structure, a sodium atom tends to lose one of its electrons causing it to go down to 10 electrons.
When this happens, the particle will still have 11 protons in its nucleus. So 11 protons minus 10 electrons gives us an overall one plus charge.
We refer to charged particles as ions, a positively charged ion is called ac a ion. And metals tend to lose electrons to form cation ions chlorine.
On the other hand, is a non metal nonmetals tend to gain electrons to form negatively charged ions called anions. A chlorine atom has an atomic number of 17.
So it has 17 protons and 17 electrons. When the neutro chlorine atom gains an electron, it ends up with 18 electrons, but it still has 17 protons in its nucleus.
So that creates an ionic bond compounds that contain ionic bonds are called ionic compounds. Now, in sodium chloride, it extends beyond just two ions.
A chloride ion sits next to a sodium ion which sits next to another chloride ion and another sodium ion and on it goes, and this entire crystal structure is held together by electrostatic attractions.
And these tasty little crystals form what we call table salt. On the periodic table.
Elements like sodium appear in the first column on the far left of the table. These group one a elements tend to lose one electron and form a one plus charged cation.
In contrast elements like chlorine are in group seven A. On the other side of the periodic table, these atoms tend to gain one electron and form a one minus charged anion.
So both group one a elements like sodium and group seven A elements like chlorine try to have the same number of electrons as the closest noble gas on the periodic table.
Sodium loses one electron leaving it with eight electrons in its outer shell. So just like the noble gas neon chlorine gains one electron giving it eight in its outer shell just like the noble gas argon.
The pattern extends to other groups on the periodic table. Magnesium is in two A and so it needs to lose two electrons to have the same number of electrons as the noble gas neon.
So magnesium forms a two plus cation oxygen is in group six A and it needs to gain two electrons to have the same number as the noble gas neon.
So oxygen forms a two minus anion nitrogen is in group five A and it needs to gain three electrons to have the same number as neon.
So, nitrogen forms a three minus anion ionic compounds are electrically neutral with no overall charge. This helps us predict how ionic compounds are likely to form.
For example, potassium is in group one A. So it forms a one plus C A and bromine is in group seven A.
So it forms a one minus anion. So potassium and bromine would come together to form potassium bromide or KBR an ionic compound with an overall charge of zero.
Now let's look at a different example. Lithium is in group one A.
So it forms a one plus cation and oxygen is in group six A. So it forms a two minus anion.
So two lithium cations and one oxygen anion would come together to form lithium oxide or I 20 an ionic compound with an overall charge of zero.
An even quicker way to figure out the chemical formula of the ionic compound formula is called crossing over to do it. We just write the charges out on each ion, then we cross over the numbers dropping the signs along the way to get the subscripts in the chemical formula.
So for lithium oxide, the two minus charge on oxygen gets crossed over to give the lithium subscript a value of two. And the one plus charge of the lithium gets crossed over to give the oxygen subscript a value of one.
But because it's not really necessary, we leave out the one as a subscript on oxygen and just write L2 0. Let's do another example with magnesium, which is in group two A and forms a two plus C A ion and nitrogen, which is in group five A and forms a three minus an ion.
If we use crossing over, we end up with the formula MG three N two. Now, if we use crossing over with magnesium and oxygen, there's a little wrinkle magnesium forms a two plus C A ion and the oxygen forms a two minus anion using the crossing over trick we get MG 2 O2.
But this can actually be simplified to MG O for ionic compounds. We need to have the lowest whole number ratio for the subscripts.
In this case, the lowest whole number ratio for the subscripts is 1 to 1 and not 2 to 2. Now, let's look at ammonium or NH four plus which is a polyatomic ion.
Even though neither hydrogen nor nitrogen are considered metals, the ammonium ion bonds to other ions as if it were a metal ion, we can write the structure and put brackets around it and then put the charge of the ion outside of the brackets because the ammonium ion has a one plus charge.
It can combine easily with something with a one minus charge like the chloride and ion that gives us NH four C which is ammonium chloride.
And this is a very interesting compound. It has covalent bonds between the nitrogen and the hydrogen atoms.
In addition to the ionic bond between the polyatomic ion and chloride. Now, let's take the example of another polyatomic ion.
No three minus is the nitrate ion. And it can combine with a magnesium two plus ion.
The nitrate ion is one minus and the magnesium ion is two plus using crossing over the two from the magnesium applies to all of the atoms within the polyatomic ion, both the nitrogen and the three oxygens.
So we use parentheses around these two atoms and then put the two as a subscript outside the parentheses, giving us magnesium nitrate or M GN 32.
The two applies to everything in the parentheses. So we have one magnesium, two nitrogens and six oxygens in this compound.
Now, it can be difficult to predict the charges of the ions formed by the transition metals. Some of the charges would just need to be looked up.
However, you can remember the charges on the silver and zinc ions by looking at the periodic table. Silver forms a one plus C A ion and zinc forms a two plus C A ion.
Aluminum is in group three A and loses three electrons to form the aluminum three plus C A ion. So a nice and easy way of remembering this is to just go along in a line from silver to zinc to aluminum on the periodic table, which is one plus two plus and three plus.
All right, as a quick recap ionic bonds exist between the ions formed from metal and nonmetal atoms. By looking at where each element lies on the periodic table, we can determine how many electrons it wants to lose or gain in order to have a full valent shell just like the nearest noble gas on the periodic table.
Once we have determined the charges on the ions, we can cross over the charges to determine the chemical formula for the ionic compound.
In some cases, polyatomic ions can jointly act as a single ion in an ionic bond.
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