Dismiss
(/)
Mendeleev's Periodic Table
Practice Now
All Modalities (http://www.ck12.org/physical-science/Mendeleevs-Periodic-Table-in-PhysicalScience/#all)
Share to Groups
Mendeleev's Periodic Table
Look at the left-hand photo above. What a messy closet! Do you have a messy closet too? If you do, then you know how hard it can be to
find a specific item of clothing. If you don’t have a messy closet, just imagine trying to find a particular shirt or pair of jeans in the closet
above. It could take a long time, and it would probably make you late for school! Now look at the closet on the right. It’s very neat and well
organized. With a closet like this, it would be easy to find whatever item you wanted.
Q: What do these two closets have to do with science?
A: They show why it’s important to keep things organized, including the elements (/physical-science/Elements-in-Physical-Science), which
are the pure substances (/chemistry/Substances) that make up all kinds of matter.
Organizing Elements (/physical-science/Elements-in-Physical-Science)
For many years, scientists looked for a good way to organize the elements. This became increasingly important as more and more
elements were discovered. An ingenious method of organizing elements was developed in 1869 by a Russian scientist named Dmitri
Mendeleev, who is pictured below . Mendeleev’s method of organizing elements was later revised, but it served as a basis for the method
that is still used today. You can learn more about Mendeleev and his work at this URL: http://videos.howstuffworks.com/sciencechannel/27862-100-greatest-discoveries-the-periodic-table-video.htm (http://videos.howstuffworks.com/science-channel/27862-100greatest-discoveries-the-periodic-table-video.htm) .
Mendeleev was a teacher as well as a chemist. He was writing a chemistry textbook and wanted to find a way to organize the 63 known
elements so it would be easier for students to learn about them. He made a set of cards of the elements, similar to a deck of playing cards.
On each card, he wrote the name of a different element, its atomic mass, and other known properties. Mendeleev arranged and
rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by increasing
atomic mass.
Q: What is atomic mass? Why might it be a good basis for organizing elements?
A: Atomic mass is the mass of one atom of an element. It is about equal to the mass of the protons (/physical-science/Protons-in-PhysicalScience) plus the neutrons (/physical-science/Neutrons-in-Physical-Science) in an atom. It is a good basis for organizing elements because
each element has a unique number of protons and atomic mass is an indirect way of organizing elements by number of protons.
Groups and Periods
You can see how Mendeleev organized the elements in the Figure below . From left to right across each row, elements are arranged by
increasing atomic mass. Mendeleev discovered that if he placed eight elements in each row and then continued on to the next row, the
columns of the table would contain elements with similar properties. He called the columns groups . They are sometimes called families,
because elements within a group are similar but not identical to one another, like people in a family.
Mendeleev’s table of the elements is called a periodic table because of its repeating pattern. Anything that keeps repeating is referred to
as periodic. Other examples of things that are periodic include the monthly phases of the moon and the daily cycle of night and day. The
term period refers to the interval between repetitions. For example, the moon’s phases repeat every four weeks. In a periodic table of the
elements, the periods are the rows of the table. In Mendeleev’s table, each period contains eight elements, and then the pattern repeats in
the next row.
Filling in the Blanks
Did you notice the blanks in Mendeleev’s table? They are spaces that Mendeleev left blank for elements that had not yet been discovered
when he created his table. He predicted that these missing elements would eventually be discovered. Based on their position in the table,
he even predicted their properties. For example, he predicted a missing element in row 5 of group III. He also predicted that the missing
element would have an atomic mass of 68 and be a relatively soft metal like other elements in this group. Scientists searched for the
missing element, and they found it just a few years later. They named the new element gallium. Scientists searched for the other missing
elements in Mendeleev’s table and eventually found all of them.
An important measure of a good model is its ability to make accurate predictions. This makes it a useful model. Clearly, Mendeleev’s
periodic table was a useful model. It helped scientists discover new elements and made sense of those that were already known.
Summary
In 1869, Dmitri Mendeleev developed a method for organizing elements based on their atomic mass. His method was later revised,
but it served as a basis for the method used today.
Mendeleev created a periodic table of all the elements that were known at the time. The rows of the table, called periods, each
contained eight elements that increased in atomic mass from left to right. The columns of the table, called groups, contained
elements with similar properties.
Mendeleev’s periodic table was a good model because it could be used to predict unknown elements and their properties. All of
these missing elements were eventually discovered.
Explore More
Do the activity at the URL below to simulate how Mendeleev developed his periodic table. After you organize your element cards, answer
the questions provided. Don’t look at the answers until you are finished.
http://www.education.com/reference/article/mendeleev-periodic-table/?page=2 (http://www.education.com/reference/article/mendeleevperiodic-table/?page=2)
Review
1. How did Mendeleev develop his periodic table of the elements?
2. What are the groups in Mendeleev’s table?
3. Describe the periods in Mendeleev’s table.
4. Why was Mendeleev’s periodic table a good model?
Vocabulary
Language:
English ▼
group
group
Column of the periodic table, which contains elements with similar properties.
period
period
Row of the periodic table that contains elements ranging from metals on the left to metalloids and to nonmetals on the right.
periodic table
ABOUT
periodic table
Our Mission (http://www.ck12.org/about/mission/)
Table of elements arranged by increasing atomic number (modern periodic table) or by increasing atomic mass (Mendeleev’s periodic table).
Meet the Team (http://www.ck12.org/about/team/)
Partners (http://www.ck12.org/about/partners/)
Press
(http://www.ck12.org/about/press/)
Show
Details
Careers (http://www.ck12.org/about/careers/)
Community (http://www.ck12.org/about/ck12-community/)
Success Stories (http://www.ck12.org/about/success-stories/)
Blog (http://www.ck12.org/blog/)
Overview
Back to the top of the page ↑
SUPPORT
Webinars (https://www.youtube.com/playlist?list=PLhWx3LZhlpsfluwEqehCU8_N9iK5uio7P)
Implementation Guide (http://www.ck12.org/about/implementation-guide/)
Pilot Program (http://www.ck12.org/about/pilot-program/)
Help (https://ck12support.zendesk.com/hc/en-us)
Contact Us (http://www.ck12.org/about/contact-us/)
By CK-12
Tools and Apps (http://www.ck12.org/about/tools-and-apps/)
BRAINGENIE™ (http://braingenie.ck12.org/)
FlexMath (http://flexmath.ck12.org/)
Stoodle (http://stoodle.ck12.org/)
▼
Select Language
(https://plus.google.com/+C
(https://www.facebook.c
(https://twitter.com/
(http://www.pin
(https://itunes.apple.com/us/app/ck12/id909343639?ls=1&mt=8)
(https://play.google.com/store/apps/details?
id=org.ck12.app.practice)
Please wait...
Please wait...
Terms of Use (http://www.ck12.org/about/terms-of-use/) | Privacy (http://www.ck12.org/about/technology2/privacy-policy/) | Attribution Guide (http://www.ck12.org/about/attribution-guidelines/) |
(http://creativecommons.org/licenses/by-nc/3.0/)
(javscript:return false;)
v2.4.6.49341 | © CK-12 Foundation 2015
Upload Failed