The Periodic Table: Properties of Groups and Periods
- 1:21 Dmitri Mendeleev
- 2:14 Periods
- 3:14 Groups
- 4:33 Metals
- 5:14 Nonmetals
- 5:32 Metalloids
How is the periodic table like the map you used on your last road trip? In this lesson, you will be introduced to the periodic table, the road map of chemists. We will discuss how the elements are organized and how you can use this organization to identify some of their major physical properties.
When you're traveling somewhere new, chances are you're going to use a map. Maps come in all forms - some are colorful with little pictures, some have ways of showing different altitudes, and some have the sole purpose of showing state or national boundaries. Either way, just like the spot on a map can tell you information about that location, the position of an element on the periodic table can help you predict some of the element's properties.
An element is a pure substance made up of only one type of atom. Elements are the building blocks of all matter, just like letters are the building blocks of all words. There are currently 118 known elements represented on the periodic table; some are found in nature and others are created in laboratories. Each little block on the periodic table represents one element. Some examples of elements are gold, oxygen, neon, potassium, and tungsten. Each different element has atoms with a different and unique number of protons. This is called the atomic number.
Because there are so many elements, there needs to be a system of organizing them. This is where a Russian chemist by the name of Dmitri Mendeleev comes in. In the late 1800s, when only 60 or so elements had been discovered, Mendeleev decided to arrange the elements in order of increasing atomic weight. While doing this, he also organized them so elements with similar characteristics were grouped together.
In doing this, it was necessary to leave some blank areas in his organization, which later ended up being spots for elements that hadn't been discovered yet. What this means is that his system of organization worked out so well that he could predict both the weights and the properties of undiscovered elements! We are still using this organization today in the periodic table; however, elements are currently organized in order of increasing atomic number.
Periods and Groups
As Mendeleev was arranging the elements in order of increasing atomic weight, he noticed that patterns repeated periodically. Each time a pattern started over, he started a new row. A period on the periodic table is really just a horizontal row. The current periodic table has seven periods with an island of two periods down below. Why is that little island down there? It's really just because if those two rows were put into the periodic table where they belong, the table would take up so much space and would not easily be able to fit onto a piece of paper!
You know how sometimes Alaska gets put in a different location on a map of the United States? Alaska is not REALLY found below California. It's just there to save space. So when you are using the periodic table, just keep in mind where they should belong. The top row of that island is in the 6th period and the bottom row is in the 7th period. Also, you may find that some periodic tables do show these two rows in their correct location.
The vertical columns on the periodic table are called groups or families. Groups probably come in most handy when predicting the properties of an element. Just like people in a family all may share similar traits, elements in the same group on the periodic table also will have similar properties. The groups are numbered from 1-18 from left to right, and some of the groups have special names. For example, excluding hydrogen, all of the elements in Group 1 on the very left-hand side of the periodic table are called alkali metals. Alkali metals are soft and silvery and react violently with water to form an alkaline (or basic) solution.
Alkaline earth metals are found in Group 2 and are shiny and silvery white in color. Moving all the way over to the right-hand side of the table, in Group 17 you will find the halogens. Halogens are all very reactive and poisonous, which is why you may find these bacteria-killers in bleaches and disinfectants. The elements in the last group on the periodic table, Group 18, are called the noble gases. Noble gases are all colorless, odorless, and extremely un-reactive. Their inability to react easily makes them a prime candidate for gases in light bulbs.
Metals, Nonmetals, and Metalloids
Just like some maps show boundaries between states, some periodic tables have a 'staircase' on the right side. This 'staircase' separates the metals from the nonmetals. Metals are found on the left side of this line and they all have very similar properties: they are shiny, good conductors of both heat and electricity, malleable, and ductile. Malleability and ductility refer to the substance's ability to be deformed without cracking. If your car gets dented, it's because it is malleable. If it were to crack, then it would be brittle. Most of the elements on the periodic table are metals.
Elements to the right of the line are called nonmetals. Nonmetals are brittle in their solid form, dull, poor conductors of heat and electricity, and have much lower melting and boiling points than metals, which is why many of them are gases at room temperature. Some elements have the properties of metals and nonmetals. These elements are called metalloids, and they are found ON the 'staircase' line. Elements that are most commonly referred to as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Silicon is the element that is found in computer chips. If you have ever looked at a computer chip, you may have noticed that it is shiny like a metal. However, if you were to ever hit a computer chip with a hammer, you would find that it's very brittle, a property of nonmetals.
The periodic table is one of the most commonly used tools of the chemist. Knowing how it is organized is an essential part in being able to use it. Elements are listed in order of increasing atomic number and organized into columns called groups or families. Elements in the same group share very similar chemical properties. There are seven rows, or periods, which include the two rows found on the island below the table. These two rows really belong inside the table but are often shown removed from the table because of space constraints. The left side and center of the table is made up of the metals, the top-right corner consists of nonmetals, and elements in between (on that zigzag line) are the metalloids.
Chapters in Chemistry 101: General Chemistry
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