The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. ~William Lawrence Bragg

Periodic Table Simulator

Introduction Dmitri Ivanovich Mendeleev organized the known elements, and predicted some unknown elements, by grouping according to similar properties. We’ll simulate the methods Mendeleev used to make

the modern periodic table. First, we’ll organize

playing cards by suit order (hearts, spades, diamonds)

and numerical value (aces low to kings high). Separate

card group #1 from your stack of playing cards. The

big green number 1 on the back indicates the card

belongs to group #1. Group cards in a rectangular

pattern by suit and numerical value. Compare your

results to your neighbor’s. Make a

table in your lab journal to

summarize your results.

Fall 2009 How Mendeleev Did It.

More inside!

In the first part of the activity, you will group playing cards by their “properties,” that is by suit and rank. In the second part of

the activity, you will group elements by chemical properties

and atomic weight. Finally, you will graph selected periodic

trends.

Summary

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Find group #2 and arrange the cards in the same

manner. Do you notice a gap? Predict the value and

suit of the missing card. Once you make your

prediction, remove the missing card from the envelope

marked “Undiscovered Elements.” Did your

prediction match the unknown card? Make a table in

your lab journal to summarize your results.

On to card group #3! Repeat the ordering sequence

you used for groups #1 and #2. Again, look for

patterns and gaps. Identify where in your table a

missing element should appear. Predict its properties

(suit and value). Record your predictions and find the

missing card in the Undiscovered Elements envelope.

Make a table in your lab journal to summarize your

results.

Based on what you know about Mendeleev’s work,

what are the connections between what you did with

the playing cards and what Mendeleev did when

making his periodic table? Discuss with you lab

partners and write a brief statement comparing the card

activity with Mendeleev’s work.

Graphing Periodic Trends

Use internet resources to find the atomic radius, electronegativity and first ionization energy for elements 1-56. Create a spreadsheet with atomic number, element name, element symbol and the properties listed above. Use your spreadsheet to create three graphs showing the relationship between: Atomic radius and atomic number First ionization energy and atomic number Electronegativity and atomic number. Look for patterns. How can you use the periodic table to predict properties?

The Tellurium Dilemma When Mendeleev arranged the elements in order of increasing atomic weight, he found that tellurium and iodine ended up in the wrong groups. Iodine (atomic weight = 126.9 AMU) would be placed before tellurium (atomic weight = 127.6 AMU). However, the chemical and physical properties of iodine matched the properties of fluorine, chlorine and bromine. So Mendeleev decided to place iodine with the other halogens, rather than with the oxygen group. It turned out to be the correct grouping, because Moseley re-ordered the periodic table by atomic number several years later.

3

Create your own periodic table!

Get the element cards. They’re the smaller cards with

the names and symbols of the elements on them.

Find the oxygen combination ratio on one of the

cards. You should see something like 2:3 or 1:2.

Group the cards by oxygen combination ratio—that

is, get all the 2:3 elements in the same pile, all the 2:7

elements in the same pile, and so on. Once you have

the cards grouped by oxygen combination ratio,

arrange each element in the group in order of

increasing atomic weight, lightest on top and heaviest

on bottom. Repeat for each oxygen combination

group.

With each group in a stack (lightest element on top),

arrange the stacks in order of increasing atomic

weight, lightest on the left to heaviest on the right.

Expand the ranked groups into a rectangular table.

Leave spaces in the table as needed to maintain the

sequence of increasing atomic weight.

What do the gaps represent? Make predictions about

the properties of the missing elements. Write your

predictions in your lab journal, and “discover” the

missing elements. How close were your predictions?

Julius Lothar Meyer

Mendeleev published his periodic table of all known

elements in 1870. Working completely

independently, a few months later, Meyer published

a revised and expanded version of his 1864 table,

virtually identical to that published by Mendeleev,

and a paper showing graphically the periodicity of

the elements as a function of atomic weight.

Meyer’s and Mendeleev’s work , and the following

supporting evidence from other researchers led to

the development of modern periodic law.

Mendeleev predicted the existence

of several undiscovered elements.

“Eka-silicon” was discovered in

1886 by Winkler. The properties

predicted by Mendeleev match the

actual properties closely.

1.

2.

3.

When arranged by atomic number,

the tellurium-iodine problem was

resolved.

The periodic table was developed by

grouping elements by physical

properties. It also shows grouping

by valence electron configuration.

Henry Moseley’s Contributions Henry Moseley (1887-1915): A British chemist, Henry Moseley studied under Rutherford and brilliantly developed

the application of X-ray spectra to study atomic structure; Moseley's discoveries resulted in a more accurate

positioning of elements in the Periodic Table. In 1913, almost fifty years after Mendeleev, Henry Moseley published

the results of his measurements of the wavelengths of the X-ray spectral lines of a

number of elements which showed that the

ordering of the wavelengths of the X-ray

emissions of the elements coincided with the

ordering of the elements by atomic number.

With the discovery of isotopes of the elements, it

became apparent that atomic weight was not the

significant player in the periodic law, but rather,

the properties of the elements varied periodically

with atomic number.

Accounting for Transition Elements

Tragically for the development of science, Moseley was

killed in action at Gallipoli in 1915.

Look at your table. Without referring to a periodic table, what differences do you notice? Look at one column. Find the “transition property” for the elements in the column. Remove the three elements (two from the fluorine group) that don’t match the others. NOTE: You cannot remove the first card from a column.

Order the removed elements so each group of three is arranged by increasing atomic weight (lightest on top, heaviest on bottom). Arrange each group of three (or two) left to right in order of increasing atomic weight. You should now have two “tables.”

Look at the original elements. Ideally, they will still be arranged by increasing atomic weight from left to right and top to bottom. Find where you can insert the “transition” part of the table into the original table while maintaining the order of increasing atomic weight.

Your table should now look familiar. Compare your table to the modern periodic table. Discuss with your partners—see if you can find similarities and differences. Make a table in your lab journal to summarize your results.

Problems? Talk it out with your lab partners. Remember—understanding is more important than answering! Remember you can visit the tutor room or contact me through e-mail.