Characteristics and organization The Periodic Table Characteristics and organization

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

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.

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.

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.

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.

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

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.

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.

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.

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.

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