Making Sense of the Periodic Table Trends and what they mean adapted from:

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Where does the “period” in periodic come from?

Based on where in the periodic table you are, you will see different common properties

We will learn more about the chemical and physical properties of these groups of elements and the molecules they make later in the unit… for now...back to individual elements.

This is a close up of the first 20 elements Many common substances are made from these 20 elements

To understand how these 20 elements make many different types of substances we must first understand their electrons. Electrons are the key to making compounds through covalent and ionic bonds (more to come)

Electron “shells” Electrons are in regions around the nucleus that are different distances away from the nucleus The electrons surround the nucleus in 3 dimensions bu it is easier to show an energy level model in two dimensions like the model that looks like a target.

For example… Take an Oxygen Atom This energy level model shows two electrons on the first energy level and six electrons on the second energy level Since this atom has a total of eight electrons, it also has eight protons the atom with eight protons in its nucleus (atomic number 8) is oxygen

Here’s how that looks for the first 20 elements

Lewis Dot Structures ●Lewis Dot Structures are like simplified electron energy level model ●The lewis structure contains the element symbol with dots representing electrons ●The only electrons shown are those on the outer energy level, which are known as valence electrons ●The electrons are placed around the element symbol, one at a time, clockwise or counterclockwise, and then grouped in pairs as more electrons are needed

Finding the number of valence electrons going across the periodic table, each group has one more valence electron except helium (which only has 2) The number of valence electrons is incredibly important to bonding