January 10, 2018 SQRS: The equation below represents a chemical reaction that releases energy. 2Na + 2H20 2NaOH + H2 + energy Which part of the equation is a reactant? A. 2NaOH B. H2 C. 2H20 D. energy Answer is C: The reactants are on the left side of the equation and the products are on the right side.

I can draw an element’s Lewis Dot Structure. So yesterday we learned how to draw the electron configuration for the 1st 20 elements. Which element is represented by this diagram? Sulfur

We also know that the outer shell electrons are important in determining the chemical properties of an element. Therefore, it can be helpful to have a model that shows only the outer shell electrons to show what happens to these electrons during reactions.

Drawing only the outer shell electrons is easier than drawing ALL the electrons in an element. It’s the outer shell electrons that primarily determine how an element reacts with another element. So it makes sense to have an easier to way to model ONLY the outer shell electrons.

It was first used by Gilbert Lewis in 1916. Electron dot diagrams are also called Lewis Dot Structures. It was first used by Gilbert Lewis in 1916. It’s an easy way to represent the valence electrons of an atom. Bohr Diagram for all the electrons in the element Te. Lewis Dot Structure showing ONLY the valence electrons

Electron Dot Diagram An electron dot diagram is the symbol for the element surrounded by as many dots as there are electrons in its outer energy level. Only the outer energy level electrons are shown because these are what determines how an element can react.

How do you know how many outer shell electrons (valence electrons) an element has? The Group that the element is located in tells you the # of valence electrons. Group 1 have 1 valence electrons, Group 2 has 2, Group 13 (3A) has 3 and so on… Remember, the one exception to this rule is He which is in Group 18 (8a) but it ONLY has 2 valence electrons!

X Cl So how do we draw Lewis Dot Structures… 1. Write the element’s symbol. X Cl 2. Split the atom into 4 sides by drawing an “X”. 3. Find the # of valence electrons. Cl has 7. 4. Draw one dot (electron) for each valence electron. Electrons want to be alone before they are paired up. So only 1 electron goes on each side before having any sides with 2 electrons.

X Let’s Practice. Mg 1. Write the element’s symbol. 2. Split the atom into 4 sides by drawing an “X”. 3. Find the # of valence electrons. Mg has 2. 4. Draw one dot (electron) for each valence electron. Electrons want to be alone before they are paired up. So only 1 electron goes on each side before having any sides with 2 electrons. Once you’re comfortable writing these, you no longer have to include the X.

Your Turn… Complete the following Lewis Dot Structures and turn in before you leave!