- History of the periodic table
- predictive abilities of the table
- The “geography” of the table
- the trends of the periodic table
Maybe the greatest graphic organizer of all time…
In 1869, Dmitri Mendeleev created one of the most impressive graphic organizers in the history of science…the Periodic Table of elements. This oddly shaped grouping of rows and columns are filled with letters and numbers that may look confusing at first glance and it unfortunately scares many young scientists off. Let me assure you, it isn’t all that bad. Let’s plan to understand the PERIODIC TABLE! (and no, you won’t need to memorize all the little numbers )
Another HUGE shout out to the BBC production The Mystery of Matter. This documentary chronicles not only the story of Mendeleev but of many other scientists on the quest to determine what matter is made up of. Watch part 2 HERE to learn about Dmitri Mendeleev and then about the Curies and their discovery of radioactivity.
In the late 1800s, it was becoming common knowledge that the known elements displayed some repeating patterns in their physical properties. Chemists found that many elements reacted similarly to each other and they were placed in Families.
Dmitri Mendeleev needed to write a chemistry textbook (since none were to be found in Russian) and wanted a guiding principle to run throughout his volumes. He developed a graphic organizer that put the known elements into rows and columns based on their physical and chemical properties. More specifically, he placed the elements in order of their atomic weights with a few exceptions along the way.
After a bit of reworking, the table was turned horizontal and published in his textbook Principles of Chemistry in 1869.
The table informs known properties and can predict the properties of unknown elements.
The table was an excellent record of the known elements. Nothing like this had been constructed before. Dmitri was so confident in his patterns that he even reserved open spaces for the elements that had not yet been found. Mendeleev knew that there were elements missing by Aluminum and Silicon. He predicted their properties
He did this by looking at the properties of the elements around the spaces that were missing. Finding the trends that occur left to right, and top to bottom, Dmitri was able to predict the properties of Gallium (called eka-aluminum) and Germanium (called eka-silicon) BEFORE they had be isolated by future scientists.
It’s like looking at a painting with a piece missing in the middle. By looking at the colors and brushstrokes used around the space, we can accurately guess the what the entire painting might look like.
In fact, Mendeelev predicted the properties of Gallium BETTER than man that discovered it. The Mystery of Matter documents the story in 1875 of Mendeleev criticizing the French scientist Paul E. Lecoq de Boisbaudran for measuring the density of Gallium inaccurately. Mendeleev felt his table predicted the element’s properties better than the scientist that had the substance in his lab. He was correct.
Learning the “geography” of the Periodic Table
Many people have attempted to organize the elements over the years but the classic Mendeleev design works pretty well. The periodic table can look confusing or even overwhelming but if we take it one section at a time we can make it feel like less of a mystery.
1. What information is found inside each element block?
Element Names and Symbols
The periodic table of elements is made up of 118 individual element blocks. In each block we have identifying information as well as numbers that describe what one atom of the element might look like. Each of the elements was given a name. Some were named after people like Mendeleev, Curie, and Bohr (and many others).
Some were named after places. Gallium is Latin for “France”. Polonium pays respect to Poland. Berkelium is named after The University of California – Berkeley where the element was first synthesized.
Many of the elements are named in the Greek or Latin that highlights some characteristic or property. Lithium comes from the Greek Lithos meaning “stone” referring to the minerals it was found in. Phosphorus comes from the Greek work phosphoros meaning “bringer of light”.
The official SYMBOL for each element is a one or two letter abbreviation for the name and is found prominently in the center of each block. USUALLY, the symbol matches the name fairly well.
Sometimes the symbol refers to a traditional Latin or Greek name for the element. These are not as obvious unless you dig into the etymology of the names. Argentum is Latin for Silver. Mercury, being a liquid metal, is known as “quicksilver” and the Latin for that is Hydrargyrum. Lead in Latin is called Plumbum so Pb makes perfect sense 🙂
If you are curious about the process of naming, here is an article you can read about that. Here’s a excerpt from that article :
Currently, the naming process has become much more standardized, and specific steps must be followed to name a new element. When a lab reports that a new element has been discovered, a team from IUPAC and IUPAP (International Union of Pure and Applied Physics) verifies the discovery. Once the team verifies the event, the discoverer(s) are entitled to propose a name. From there, the proposed name goes through several steps of review and comment before it is approved. If the IUPAC rejects the original name, then it gives the discovering group another opportunity to suggest a different name. Once IUPAC approves the name, it is the official name.
IUPAC’s guidelines for a new name states that it can be based on a:
- Mythological concept or character (including an astronomical object)
- Mineral or similar substance
- Place or geographical region
- Property of the element
- Scientist
Find out about the meanings of the element names and symbols.
If you created an element, what name would you give it? It has to end in “ium” at this point.
Just for funzies, here is a classic clip of all of the (known) elements put to song.
…and of course there’s this one from AsapSCIENCE!
Atomic number
The ATOMIC NUMBER is a whole number that increases by 1 for each element left to right across the Periodic Table. This number describe how many tiny positive particles called PROTONS can be found in the nucleus of one atom of the element.
Hydrogen has an atomic number of “1” and therefore has 1 proton in the nucleus. Helium is has two positive protons and has completely different properties than Hydrogen. One little proton means the difference between an element that will explode compared to a stable gas used in party balloons.
Consider for a moment that Gold, a solid, stable metal with a unique color has 79 protons in the nucleus. If we could reach in and place just one more positive proton there the substance would instantly liquefy, turn to a silver color, and be a hazardous nerve toxin called Mercury! The number of protons determines the properties of the element and they are recorded with the atomic number.
Atomic mass
The atomic mass is typically found in the lower portion of the element box and a describes several things about the atom at one time. First of all, the atomic mass tells us how many grams there are in one “mole” of the atom. This won’t mean anything to us unless we know what a “mole” is.
You probably know what a “pair” or a “dozen” of something would be. These common words describe a certain number of something. A “mole” is just like those words except it is MUCH larger.
When we look up Neon on the Periodic Table the atomic mass read 20.180. This means that 6.02 X1023 atoms of Neon would have a mass of 20.180 grams on the balance.
Properties
Sometimes the physical or chemical properties are found on the table as well. It is common to use a periodic table to see which elements are liquid or gas room temperature, which are magnetic, synthetic, or even radioactive. I’ve painted these on my wall.
No need to memorize these. It’s better to look for the trends. Gases are mostly grouped together. Magnetic elements are mostly grouped together. diatomic elements (those that are found in pairs) are grouped together. Larger atoms are typically the ones that are radioactive. Notice that human-made elements (synthetic) are ALL radioactive.
2. The block is located in one of four major regions on the table.
There are (at minimum) four types of elements on the periodic table. Many advanced tables will break these categories down even further but let’s start simple.
METALS (those elements colored blue on the diagram) typically have a high density, a high tensile strength, a high ductility, and are high on the hardness scale. Metals are typically good conductors of heat and electricity and only metals can be magnetic. They are typically solids at room temperature, silver or gray in color, and can have a high luster.
NONMETALS (colored in green on the diagram) typically have a low density, a low tensile strength, a low ductility, and are low on the hardness scale. Nonmetals are typically poor conductors of heat and electricity and none are can be magnetic. They are found in a variety of colors and some are even colorless.
METALLOIDS (colored in pink on the diagram) are the “Tex-Mex” of the periodic table. These elements are on the stair-step border between metals and nonmetals on the periodic table and have physical properties of both.
NOBLE GASES are a type of nonmetal but they are so special they get their own category. Noble gases are colorless, odorless, tasteless and (obviously) a gas at room temperature. While Neon itself is colorless it glows a bright red when electricity is sent through it. The sign below used to hang in Busch stadium and would “fly” every time the Cardinals hit a home run. Now it’s a billboard off of hwy 40/61 as your leave the ballpark.
3. The block is placed in a specific Group or Family.
The Periodic Table is organized into columns and rows based on the physical and chemical properties of the elements. The columns are put together with elements that have similar reactivity to each other. These are the most reactive metals on the table. Notice that Hydrogen isn’t classified as an “Alkali metal” . Hydrogen is a nonmetal but often reacts like the others in this family.
Alkaline Earth metals are the second group. Elements like Magnesium and Calcium are elements in this group and are essential to our health.
Transition metals don’t always react the same way. Sometimes they interact with other elements like an Alkali metal. Sometimes, they play like an Alkaline Earth metal or an element in groups III or IV. We say they are “transition” because of their ability to change reactivity.
The next four Groups are named after their first element. The Boron, Carbon, Nitrogen, and Oxygen Families have a great deal of variety. Some are metals, some are nonmetals, and still others in these families are called metalloids.
Group VII is called the Halogen family. In the Greek, “Halo” “gen” means salt former so it is no surprise that Fluorine, Chlorine, and Bromine are members of this family. They combine with metals to make some of the most commonly used salts.
The eighth group (VIII) is a special bunch of nonmetals named the Noble gases. These are the “happiest” and most stable of all elements. To personify a bit more, all of the other elements would love to be more like the noble gases for reasons we’ll discuss on the page for atomic structure.
The two rows that seem removed from main portion of the table are identified by the first element in each of the rows. We call them the Lanthanide and Actinide series after Lanthanum and Actinium.
4. The block is placed in a specific row called a period.
The Periodic Table is made up of repeating patterns called “periods”. There are currently SEVEN of them needed to house all of the known natural and synthetic elements. Not all periods have the same number of elements. The structure of the atom and placement of their electrons determines the number of elements each period will contain. You’ll find more information on that over on the atomic structure page.
Notice that the Lanthanide and Actinide series are removed from the main table but they still “belong” in periods 6 and 7. These were removed to maintain the similarities within families while saving some space. Sometimes they are placed within the main table like the one pictured below.
The TRENDS of the Periodic table
As we travel from element to element ACROSS a period or DOWN a family group there are many patterns to take notice of. We will look at atomic size, density, electronegativity and ionization energy.
Paul Hewitt’s textbooks have these wonderful 3D bar graphs to display the data. This one inspired me to make something tangible for our tactile learners.
Electronegativity is the tendency of an atom to pull electrons from other atoms. Notice that the noble gases are almost non-existent in this trend. They have no desire to take any more electrons. They already have a FULL outer energy level. Francium and the other Alkali metals would rather get rid of an electron so their electronegativity is also quite low. Fluorine is in Group VII and has 7 valence electrons. This means it is only one away (8) from have electrons that look and act like a noble gas. Fluorine will easily steal an electron to FILL its outer energy level
Ionization energy is the tendency of an atom to keep the electrons it has. The higher an ionization energy is the greater the amount of energy required to rip away the first electron from the atom. You can see that Helium is quite happy the way that it is. It NEEDS two electrons and HAS those two electrons. It would take a tremendous amount of energy to pull one of those electrons away from a Helium. Conversely, the Alkali metals are quite anxious to get rid of the one outer electron they have. The ionization energy for these is relatively low. An electron from Potassium is really cheap compared to an electron from Helium.
