Valence Electrons, The Octet Rule, & Ions

Remember “Create A Table”? What do the spokes represent on this Germanium atom? Electrons on the outer ring. (Valence Electrons) Was there a pattern with the spokes on the Periodic Table? Oh, yes!!

Valence Electrons An electron in the highest occupied energy level of an atom. Valence electrons are usually the only electrons used in chemical bonds. Here are some examples.

Examples of Valence Electrons

What’s the Pattern? To find the number of valence electrons in an atom of a representative element, simply look at its group number.

Check-In How many valence electrons does H have? 1 valence electron How many valence electrons does Al have? 3 valence electrons How many valence electrons does Cl have? 7 valence electrons How many valence electrons does Se have? 6 valence electrons

Another way to show valence electrons … Instead of drawing the atom, like…. Or writing out the electron configuration, like…. 1s22s22p63s23p5

We can use dots to represent only the valence electrons. This is called Lewis Dot Structures or Electron Dot Structures.

For example… How many valence electrons does H have? 1 electron So, we could draw an Electron Dot Structure for H like…. H

Check-In How many valence electrons does Al have? 3 valence electrons Draw the Lewis Dot Structure for Al. Al How many valence electrons does Cl have? 7 valence electrons Draw the Lewis Dot Structure for Cl Cl

You know there is a pattern!

Check-In Draw an electron dot structure for Ne. Draw an electron dot structure for P.

Check-In What do the dots in an electron dot structure represent? a. all the electrons in an atom. b. valence electrons. c. only inner electrons. d. protons and electrons.

Moving on…. Remember, noble gases, such as neon and argon, are unreactive in chemical reactions. That is, they are stable. Their outer ring is full of electrons. What is that magic number???? 2 for He but 8 for the rest of the noble gases. What does an element do if it isn’t stable?

Elements follow the Octet Rule Atoms search for a full outer ring by gaining or losing electrons so as to acquire the stable electron structure of a noble gas, usually eight valence electrons. (Octa- means 8) Atoms that lose or gain electrons are called Ions.

How do atoms lose electrons? Neutral atom Ion Be Be Beryllium will LOSE two electrons to get a full 1st ring. So, the number of electrons is the same as He, but because there are still 4 protons, this atom is still Be. This is a Beryllium atom. The most stable configuration is to have a full outer ring. So, Beryllium can gain 6 electrons to make 8 electrons on the 2nd ring…OR Beryllium can lose 2 electrons to make 2 electrons on the 1st ring.

Once an atom has lost electrons… What do we call an atom that has lost electrons? A Positive Ion or Cation (pronounced cat-ion). How is it shown that an atom has lost electrons? We use superscripts!!!

Going back to our example…. Be Be Be lost 2 electrons. It is a cation. We show that by writing, Be2+

What the …….?! Losing electrons means a positive ion???? Oh Yes!!! Remember, atoms start out neutral. That means they have the same number of protons (positive particles) and electrons (negative electrons).

Losing electrons How many protons are there? 4 protons so 4 positive particles. Imagine the 2 outer ring electrons going away. How many electrons are there now? 2 electrons so 2 negative particles. Now the total charge of the atom is 2 positives. Thus, Be2+ Ta-da!!

Let’s look at another example How many valence electrons does Na have? 1 valence electron Will Na gain 7 electrons to get a full 3rd ring or lose 1 electron to get a full 2nd ring? Lose 1 electron What kind of ion is left? Positive (cation) How would you write that? Na1+ Sodium (Na) Na

How about another example? How many valence electrons does Al have? 3 valence electron Will Al gain 5 electrons to get a full 3rd ring or lose 3 electron to get a full 2nd ring? Lose 3 electron What kind of ion is left? Positive (cation) How would you write that? Al3+ Aluminum Al

Check-In Draw the Lewis Dot Structure for Mg. Mg How many valence electrons will Mg lose to get full outer ring? 2 electrons Write the symbol and notation showing Mg as an ion. Mg2+

You KNOW there is a pattern… 1+ 2+ 3+ Transition Metals have variable POSTIVE ions.

Look at the previous slide… What kinds of elements form Cations? METALS!!!!

Back to Ions Remember, Ions are atoms that lose or gain electrons. Positive ions, or cations, lose electrons. What about atoms that gain electrons?

How do atoms gain electrons? This is a Fluorine atom. The most stable configuration is to have a full outer ring. So, Fluorine can gain 1 electron to make 8 electrons on the 2nd ring…OR Fluorine can lose 7 electrons to make 2 electrons on the 1st ring. Fluorine will GAIN 1 electron to get a full 2nd ring. So, the number of electrons is the same as Ne, but because there are still 9 protons, this atom is still F.

Once an atom has gained electrons What do we call an atom that has lost electrons? A Negative Ion or Anion (pronounced an-ion).

Gaining electrons Fluorine How many protons are there? 9 protons so 9 positive particles. Imagine the 1 electron joining the 7 outer ring electrons. How many electrons are there now? 10 electrons so 10 negative particles. Now the total charge of the atom is 1 negative. Thus, F1- Ta-da!! Fluorine

Let’s look at another example How many valence electrons does O have? 6 valence electrons Will O gain 2 electrons to get a full 2nd ring or lose 6 electrons to get a 1st full ring? Gain 2 electron What kind of ion is left? Negative (anion) How would you write that? O2- Oxygen (O) O

One more example Phosphorus (P) How many valence electrons does P have? 5 valence electrons Will P gain 3 electron to get a full 3rd ring or lose 5 electrons to get a 2nd full ring? Gain 3 electrons What kind of ion is left? Negative (anion) How would you write that? P3-

Check-In Draw the Lewis Dot Structure for Se. Se How many valence electrons will Se gain to get full outer ring? 6 electrons Write the symbol and notation showing Se as an ion. Se2-

Let’s finish out the Pattern 1+ 4+ OR 4- 2+ 3+ 3- 2- 1- Transition Metals have variable POSTIVE ions.

Look at the previous slide… What kind of elements form Anions? NONMETALS!!!!

Practice 1. Write the name and symbol of the ion formed when a. a sulfur atom gains two electrons. b. an aluminum atom loses three electrons. 2. How many electrons are lost or gained in forming each ion? a. Ba2+ b. As3- c. Cu2+