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

Periods Each row is called a “period” The elements in each period have the same number of shells 1st Period = 1 Shell(2 Electrons) 2nd Period = 2 Shells(8 Electrons) 3rd Period = 3 Shells(18 Electrons) 4th Period = 4 Shells(32 Electrons) 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. You wrote them on your P.T., as cations and anions. 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

Drawing Bohr Models Draw the nucleus. Write the number of neutrons and the number of protons in the nucleus. Draw the first energy level. Draw the electrons in the energy levels according to the rules below. Make sure you draw the electrons in pairs. Keep track of how many electrons are put in each level and the number of electrons left to use.

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 table Ne Name the element. Number of shells ? Valence electrons ?

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

H Name the element. Number of shells ? Valence electrons ?

H Name the element. Number of shells ? Valence electrons ? Hydrogen 1st Period = 1 shell 1st Group = 1 valence electron

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

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

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

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

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

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

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

Write your answers on your paper. 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.

Warm Up For the following elements list: Name of the element #of shells Total # of electrons #of valence electrons Mg N Ar B Na H

Mg For the following elements list: Name of the element-Magnesium #of shells-3 Total # of electrons-12 #of valence electrons-2

N For the following elements list: Name of the element-Nitrogen #of shells-2 Total # of electrons-7 #of valence electrons-5

Ar For the following elements list: Name of the element-Argon #of shells-3 Total # of electrons-18 #of valence electrons-8

B For the following elements list: Name of the element-Boron #of shells-2 Total # of electrons-5 #of valence electrons-3

Na For the following elements list: Name of the element-Sodium #of shells-3 Total # of electrons-11 #of valence electrons-1

H For the following elements list: Name of the element-Hydrogen #of shells-1 Total # of electrons-1 #of valence electrons-1

www.middleschoolscience.com 2008 How to Draw Lewis Structures Also referred to electron dot configurations www.middleschoolscience.com 2008

Lewis Structures Find your element on the periodic table. Determine the number of valence electrons. This is how many electrons you will draw.

Lewis Structures Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons. www.chem4kids.com

Groups - Review 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

C Lewis Structures Write the element symbol. Carbon is in the 4th group, so it has 4 valence electrons. Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol. C

C Lewis Structures Check your work. Using your periodic table, check that Carbon is in the 4th group. You should have 4 total electrons, or dots, drawn in for Carbon. C

C Lewis Structures On your paper, try these elements on your own: H P Ca Ar Cl Al C

H Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al H

P Lewis Structures On your worksheet, try these elements on your own: Ca Ar Cl Al P

Ca Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Ca

Ar Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Ar

Cl Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Cl

Al Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Al

Atoms Ions and isotopes

When atoms lose or gain an electron, the atom turns into an ion. When an atom gains or lose a neutron, it is called an isotope. When either of these two things happen, then we no longer use the term element to describe the atoms. Remember, it is the number of protons that determines what type of atom it is.

Recreate and complete the chart below Atom Atomic Symbol Atomic Number #of Protons Atomic Mass Rounded # of Neutrons #of Electrons Lithium Lithium Ion (Loses an electron) Beryllium Isotope

Recreate and complete the chart below Atom Atomic Symbol Atomic Number #of Protons Atomic Mass Rounded # of Neutrons #of Electrons Lithium Lithium Ion (Loses an electron) Beryllium Isotope Li 3 3 7 4 3 Li+ 3 3 2 7 4 Be 4 4 9 5 4 Be-8 4 4 8 4 4

Write a definition for ion Write a definition for isoptope

When atoms come together, they form molecules and compounds. What is the difference between a compound and a molecule? A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. *All compounds are molecules but not all molecules are compounds.

Molecular hydrogen (H2), molecular oxygen (O2) and molecular nitrogen (N2) are not compounds because each is composed of a single element. Water (H2O), carbon dioxide (CO2) and methane (CH4) are compounds because each is made from more than one element. The smallest bit of each of these substances would be referred to as a molecule. For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen while a single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

How do molecules form? Two ways (Well, actually three, but we are only going to look at two.)   As it turns out, atoms bond together for a very simple reason: Atoms like to have full valence shells!

1st way- Covalent Bond: This is when two atoms SHARE an electron. 2 hydrogen atoms equally share electrons to form a covalent bond. Each covalent bond is represented by a line in the Lewis dot structure, so the molecule shown above would be represented as  H-H and the chemical formula would be H2 (the subscript indicates the number of atoms of a single type in a compound). 

Atoms can form multiple covalent bonds if they need more than one electron to complete their valence shells.  Oxygen, for example, bonds with itself to form 2 bonds between the atoms (since each atom needs to share 2 electrons).  The Lewis dot structure would be showing that each oxygen atom has 4 shared electrons (2 per bond) and 4 unshared electrons, giving each a total of 8 and filling the valence shells. If two atoms have equal electron affinities they form covalent bonds.

2nd way- Ionic Bonding So, if one atom has a much greater affinity for electrons than another, the two may form an ionic bond.  For sodium to have a full valence shell it can do one of 2 things: pick up 7 new electrons (which is a very difficult thing to do) or give up one.  If sodium gave up the 1 electron in its 3rd shell, this shell would now be empty and the 2nd shell (which is filled with 8 electrons) would become its valence shell.  Thus chlorine and sodium are a perfect match for each other. 

When the chlorine atom gets close enough to the sodium atom, it strips away the sodium's electron and the two ions formed attract each other because of their opposite charges.  Using the Lewis dot structure to represent the reaction we would write:

Covalent share with Non-Metals The compounds which form Covalent Bonds are those that result from a sharing of electrons between Non-Metal Elements (Groups IIIA through VIA of the Periodic Table and Hydrogen (Group IA). Ionic bonds share with metals The compounds which form Ionic Bonds are those that result from an exchange of electrons between Metals (Groups IA, IIA and IB through VIIIB of the Periodic Table) and the Halogens (Group VIIA).

H2 H H H

NaCl Na Cl Na1+ Cl1-

H20 O H O H H

Na 2O O Na Na Na 21+ O 2-

CaCl2 Cl Cl Ca Ca2+ Cl21-

C H4 C H H H H C H

CO2 O C O=C=O

CHCl3 C H Cl H H H H H