Habitable Chemistry

How to Remember the Diatomic Molecules

Diatomic molecules are molecules made of only two atoms. To be specific, we will be looking at homonuclear diatomic molecules, which is a molecule made of two identical atoms.

There are 7 naturally occurring homonuclear diatomic molecules:

• Nitrogren gas (N2)

• Oxygen gas (O2)

• Fluorine gas (F2)

• Chlorine gas (Cl2)

• Bromine gas (Br2)

• Iodine gas (I2)

• Hydrogen gas (H2)

It is helpful to remember these 7 diatomic molecules. Luckily, since this is chemistry, there is an easy trick:

If you look at where these diatomics are placed in the periodic table, you'll see that six of them form the number "7", and the only diatomic left to remember is hydrogen. You can also see that this "7" shape starts with Nitrogen, which happens to have the atomic number 7. How convenient!

Remember: 7 Diatomics, starting with element 7 to make a 7, plus hydrogen.

What are Ions?

Let's see how much you know about ions!

Don't worry if you missed any of the questions! Let's take a look at ions.

But before we do that, let's look at how electrons and protons determine the charge of an atom. We know that atoms are made of electrons, protons and neutrons. Electrons and protons have the same, but opposite charge. An electron has a -1 charge, and a proton has a +1 charge.

So what happens when an atom has the same number of electrons as protons?

The charges cancel out - the atom has no charge!

Let's look at a problem: How many electrons does a neutral nitrogen atom have?

Since we know the atom is neutral and has no charge, that means it has the same amount of electrons as protons.

If we know how many protons a nitrogen atom has, we can figure out how many electrons it has!

By looking at the periodic table, we know that nitrogen has 7 protons. We know that this atom needs to be neutral, meaning it needs to same amount of protons as electrons.

Therefore, a neutral nitrogen atom has 7 electrons.

PTable.com is a decent online periodic table to use.

So what are ions?

An ion is an atom or molecule that has gained or lost electrons.

If you recall from earlier, we learned that the number of electrons in a neutral atom is the same as the number of protons in that atom. The neutral atom has a charge of 0 because:

(Net charge of protons) + (Net charge of electrons) = Net charge of atom

Let's use this on a neutral nitrogen atom, which has 7 protons and 7 electrons:

(7) + (-7) = 0

Notice that the net charge of electrons is a negative value. This is because electrons are negatively charged!

So what happens when an atom gains or loses an electron? Let's look at a fluorine atom that has gained an electron:

A fluorine atom has 9 protons. The number of protons will never change. But we are told that it now has 1 more electron - that is, 1 more electron than a neutral fluorine atom.

How many electrons does a neutral fluorine atom have? That's right, 9! But now that it's gained an extra electron it has 10 electrons total.

Using this equation:

(Net charge of protons) + (Net charge of electrons) = Net charge of atom

(9) + (-10) = -1

Therefore, a fluorine atom that has gained an extra ion has a charge of -1.

Let's take a look at another problem: What happens when a sodium atom loses an electron?

Using the periodic table, we know that sodium has 11 protons, so a neutral sodium atom has 11 electrons as well. But now we're told that this sodium atom has lost an electron - it has one less electron that a neutral sodium atom!

(Net charge of protons) + (Net charge of electrons) = Net charge of atom

(11) + (-10) = +1

Therefore, a sodium atom that has lost an electron has a charge of +1.

Now that you understand the concept, let's look at a shortcut: If an atom gains 2 electrons, what is its charge?

All we have to look at are the keywords: gained and 2 electrons

The value of the charge will always be the number of electrons gained or lost. In this cause, the value of the charge is 2.

Now we have to decide if the charge is negative. If the atom gains an electron, the charge will be negative. If the atom loses an electron, the charge will be positive. In this case, the atom has gained electrons, so the charge is negative.

So the charge of this atom is -2.

When talking about ionic charges, be sure to include the positive (+) or negative (-) sign.

Let's learn two more things before we go:

A cation is a positively charged ion.

An anion is a negatively charged ion.

How do we remember this? Chemistry always has tricks.

A CATion is PAWsitive

Get it? Because a CATion has paws so it's PAWSitive. That's funny, right? Ha... Ha...

An anion is A Negative ion, because the A and N in front of ANion stand for A Negative ion.

Mnemonics for Remembering the Diatomic Molecules

"Have no fear of ice cold beer."

(Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, and Bromine)

(I personally like this one the most.)

"I Bring Clay For Our New House"

(Same logic as #1)

Remember the number 7.

(See more explanation of this number here)

Feel free to add more mnemonics here!