Determining Shells and Valence Electrons www.middleschoolscience.com 2008 All images are from www.Chem4kids.com

Where are the electrons? As you know, electrons are always moving. They spin very quickly around the nucleus of an atom. As the electrons spin, they can move in any direction, as long as they stay in their shell. Any direction you can imagine - upwards, downwards, or sidewards - electrons can do it. The atomic shell or orbital is the distance from the nucleus that the electron spins. If you are an electron in the first shell you are always closer to the nucleus than the electrons in the second shell.

Orbital Basics Let's cover some basics of atomic orbitals. 1. A shell is sometimes called an orbital or energy level. 2. Shells are areas that surround the center of an atom. 3. The center of the atom is called the nucleus. 4. Electrons live in something called shells. 5. Each of those shells has a name.

There are a couple of ways that atomic orbitals are named There are a couple of ways that atomic orbitals are named. You may have heard of the SPDF system before. Chemists also use letters to name the orbitals around a nucleus. They use the letters "k,l,m,n,o,p, and q". The "k" shell is the one closest to the nucleus and "q" is the farthest away.

Not all shells hold the same number of electrons Not all shells hold the same number of electrons. For the first eighteen elements, there are some easy rules. The k-shell only holds two electrons. The l-shell only holds eight electrons. The m-shell only holds eight electrons (for the first eighteen elements). The m-shell can actually hold up to 18 electrons as you move farther along the periodic table. The maximum number of electrons you will find in any shell is 32.

We've been telling you that electrons reside in specific shells or move in specific directions. We can't really tell you exactly where an electron is at any moment in time. We can only approximate, or guess, where an electron is located. According to something called quantum theory, an electron can be found anywhere around the nucleus. Using advanced math, scientists are able to approximate, or guess, that electrons are in general areas. These general areas are called the shells.

Periods Each row is called a “period” The elements in each period have the same number of shells 1st Period = 1 Shell 2nd Period = 2 Shells 3rd Period = 3 Shells 4th Period = 4 Shells www.chem4kids.com

Groups Group 8 = 8 electrons Group 1 = 1 electron Except for He, it has 2 electrons Group 2 = 2 electrons Each column is called a “group” 3, 4, 5, 6, 7 Each element in a group has the same number of electrons in their outer orbital, also known as “shells”. The electrons in the outer shell are called “valence electrons” www.chem4kids.com

Transition Metals Transition Metals have slightly different rules for shells and valence electrons. This is something you will learn about in High School Chemistry. www.chem4kids.com

Determine the number of shells and the number of valence electrons for: Carbon - C 2nd Period = 2 shells 4th Group = 4 valence electrons www.chem4kids.com

Determine the number of shells and the number of valence electrons for: Sodium - Na 3rd Period = 3 shells 1st Group = 1 valence electron www.chem4kids.com

Write your answers on your handout. Ne Name the element. Number of shells ? Valence electrons ?

Write your answers on your handout. Ne Name the element. Number of shells ? Valence electrons ? Neon 2nd Period = 2 shells 8th Group = 8 valence electrons

Write your answers on your handout. Name the element. Number of shells ? Valence electrons ?

Write your answers on your handout. Name the element. Number of shells ? Valence electrons ? Hydrogen 1st Period = 1 shell 1st Group = 1 valence electron

Write your answers on your handout. Be Name the element. Number of shells ? Valence electrons ?

Write your answers on your handout. Be Name the element. Number of shells ? Valence electrons ? Beryllium 2nd Period = 2 shells 2nd Group = 2 valence electrons

Write your answers on your handout. Name the element. Number of shells ? Valence electrons ?

Write your answers on your handout. Name the element. Number of shells ? Valence electrons ? Sulfur 3rd Period = 3 shells 6th Group = 6 valence electrons

Write your answers on your handout. K Name the element. Number of shells ? Valence electrons ?

Write your answers on your handout. K Name the element. Number of shells ? Valence electrons ? Potassium 4th Period = 4 shells 1st Group = 1 valence electron

Write your answers on your handout. He Name the element. Number of shells ? Valence electrons ?

Write your answers on your handout. He Name the element. Number of shells ? Valence electrons ? Helium 1st Period = 1 shell 8th Group = 2 valence electrons Helium is the exception in Group 8. Since it has just one shell, that shell can only fit 2 electrons instead of 8. It is in this group because all the elements have a full outer shell.

Be sure to have all your answers on the worksheet. End of Study Guide Be sure to have all your answers on the worksheet.