1. Characteristics and organization
The Periodic Table
Characteristics and organization

2. Analogy
Orderly classification allows you to enter a grocery store and quickly find the item you need in the dairy section.
The periodic table gives chemists the same advantage when they are looking for elements with particular properties

3. Synonyms for Columns and Rows
The periodic table is arranged in columns, which are called groups or families
Elements in each group share similar properties for a very important reason that we will discuss later.
The table is also arranged in rows called periods – remember periodicity means having a predictable repeating interval!
Each period on the table reflects an added energy level.

4. Periods Each period begins a new energy level
Elements on the first row have one energy level occupied by electrons in the ground state
Elements on the second row have two energy levels occupied by electrons, and so on.
Each period has the same number of elements as the number of electrons that its designated energy level can hold.

5. Periods Continued
Notice that colors in the middle groups don’t line up with the outside groups.
This misalignment will be covered more in your chemistry class
For now, just know that energy levels fill in the same order as the atomic numbers on the periodic table.
Even though Period 3 has 18 green boxes (electrons), after the first eight electrons show up, the next two land in Period 4 and then Period 3 continues to get the next 10 electrons.

6. Groups
Groups are divided into two main categories: Group A and Group B
We will focus most of our attention on the Group A elements for this course
The Group A elements are shown here in color. The groups are numbered 1A through 8A from left to right across the table.
Elements in the same group demonstrate similar properties to each other – let’s look at why that happens.

7. Valence Electrons
The electrons in the outermost energy level of an atom are called valence electrons.
Valence electrons are the only electrons involved in chemical reactions.
For example, when paper burns, the valence electrons in the atoms of the paper are reacting with the valence electrons with atoms of oxygen in the air.
The inner electrons are not involved in the reaction

8. Valence Electrons Continued
Another cool feature of the periodic table is that all elements in the same A Group have the same number of valence electrons.
And, the number of valence electrons for each element matches the group number
Group 1A elements have one valence electron
Group 2A elements have two valence electrons
Etc.

9. Valence Electrons Continued
Since all elements in the same group have the same number of valence electrons,
And since only the valence electrons are involved in chemical reactions,
It makes sense that elements in the same group will exhibit similar chemical properties to each other.
Keep in mind that the valence electrons are in higher energy levels as you move down through a group.

10. Valence Electrons Continued
We never have more than 8 valence electrons
This can be explained by looking at Period 3
The first 8 electrons in the third energy level take us to the end of the row
Then the next two start a new energy level, so we are back to one and two valence electrons
Then next ten go into the 3rd level so they are not in the highest
Then the next 6 electrons go in the 4th level, and we hit the end of the row and start over again.

11. Electron Dot Diagrams
Electron dot diagrams (also called Lewis dot structures) are a convenient way to show the valence electrons of an atom.
We simply write the element symbol and add one dot per side for each valence electron.
If there are more than four valence electrons, we keep going by adding a second dot to each side until we have drawn all valence electrons.

12. Regions There are three major areas on the periodic table
Most of the known elements are metals and occur on the left side of the table
Nonmetals are found mostly on the right side of the table
And, metalloids are found between the metals and nonmetals and share characteristics of both groups