Ions Atoms are identified by which particle? PROTONS! Different Isotopes have different? NEUTRONS! So, which particle do you think identifies Ions??? ELECTRONS!

Ions Ions form when an atom gains or loses electrons. Why do they do that? Atoms gain or lose electrons in order to reach a stable configuration. We will talk more about that in a few minutes.

O O O Ions o o o Let’s look at a normal atom of Lithium. Protons? If the atom is neutral, how many electrons? o o o

O O O o o Is the atom still neutral? Can we ever change the number of protons and still have a Lithium Atom? O O O What if the atom lost an electron to become stable. o o Is the atom still neutral? What would be the charge of this atom now?

O O O o o o o Is the atom still neutral? Can we ever change the number of protons and still have a Lithium Atom? O O O What if the atom gained an extra electron to become stable. o o o o Is the atom still neutral? What would be the charge of this atom now?

In review…. If an atom loses electrons, the overall charge of the atom becomes positive (cation). Positive because there will be more protons than electrons. If an atom gains extra electrons, the overall charge of the atom becomes negative (anion). Negative because there will be more electrons than protons.

So what if you see this? An atom of Nitrogen has a -3 charge. What happened? How many electrons does this ion have? An atom of Magnesium has a +2 charge. What happened?

Ion Vocabulary Review An ion is an atom or group of atoms that have a charge. An atom where protons do not equal electrons has a charge. The specific charge that makes it stable is called an oxidation number. A monatomic ion is an atom with a charge. A polyatomic ion is a group of atoms with a charge. A cation is a positive ion. An anion is a negative ion.

So how do we know when its stable? Electrons have a certain amount of energy to them which describes how far away from the nucleus they tend to be Bohr’s model put these into “shells” or “energy levels”

The electrons on the outermost energy level are called valence electrons. Which energy level this is depends on the atom The group number on the PT tells us the number of valence electrons for those atoms! Groups 13-18, just take off the front “1”, so group 13 has 3 valence electrons, etc.

Octet Rule An atom is stable when it has a full valence energy level, called the octet rule Most atoms want to have 8 valence electrons (hence octet), some exceptions in just a sec They can do this by either gaining more electrons to fill their current valence shell Or they can lose electrons to empty the current shell and make the lower energy level the valence shell.

Atoms don’t care! Atoms don’t care which method they use, but don’t like moving electrons very often, so they always prefer to move fewer electrons. Let’s take a look at Boron… Draw the Bohr diagram for it. Remember, how many electrons can go in the first shell?

Look at Boron in it’s normal state  Not stable! – NO OCTET! How would this atom become stable? Gain 5 or lose 3? And the winner is…..

How many valence electrons? Boron only ended up with 2 valence electrons after becoming an ion. Why is that ok? The first 5 elements actually follow the Duet Rule because they prefer using their first energy level for stability, which is filled with 2 electrons instead of 8.

Find the pattern! Using the PT to find the number of valence electrons in each group, we can also figure out the preferred oxidation number of each group!