The Periodic Table

Chapter 5.1

Organizing the Elopements

• When scientists were organizing the elements they had to decide what categories to use and where to place each element.

• An organized table of the elements is one of the most useful tools in chemistry.

• The placement of elements on the table reveals the link between the atomic structure of elements and their protons.

Organizing the Elements

1. In 1789 Antoine Lavoisier grouped the known elements into categories called metals, nonmetals, gases, and earths.A. Scientists used this organizing method for the next 80 years.B. During this time scientists were trying to come up with a new way to organize the elements that provided an organizing principle that worked for all the known elements.

Dmitri Mendeleev

2. Dmitri Mendeleev was a Russian teacher and chemist who would find

a better way to organize the elements. A. His strategy for organizing the elements was modeled after the card

game Solitaire. In Solitaire the cards are arranged by suite and value.

Dmitri Mendeleev

B. Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column.C. Mendeleev’s chart was a periodic table.D. A periodic table is an arrangement of elements in columns, based on a set of properties that repeat from row to row.

Mendeleev’s Table

Mendeleev’s Table1. How is the table organized?

*Elements are arranged in order of increasing mass.

2. What do the empty squares stand for?* They represent undiscovered elements.

3. Why are masses listed with some of the spaces, but not with all of them?

* Mendeleev was able to predict properties for some unknown elements based on the properties of neighboring elements.

Mendeleev’s Prediction

3. Mendeleev’s PredictionA. Mendeleev could not make a complete table because many elements had not yet been discovered.B. To account for these elements he left spaces in his table for them.C. Mendeleev knew where to leave spaces at due to the specific properties of the elements.

Ex. 1) Mendeleev placed bromine in group VII because bromine and chlorine have similar properties. This left four spaces in row four between zinc and bromine. He had only two elements left to fill in those spaces, arsenic and selenium. He placed them where they fit best according to their properties and left gaps in group III and IV.

Mendeleev’s PredictionD. He was not the first to arrange elements

in a periodic table or the first to leave spaces in the table. E. He was able to offer the best explanation for how the properties of an element were related to its location and mass. F. Some scientists didn’t accept his predictions of undiscovered elements and some used the table to help discover new elements.

Evidence4. Evidence Supporting Mendeleev’s Table

A. As time went on scientists began finding new elements and comparing them to the spaces left in Mendeleev’s table. B. Mendeleev had already stated the masses of some of the undiscovered elements.C. The new elements discovered matched the predicted masses.

Evidence• C. The new elements discovered

matched the predicted masses. • D. The close match between

Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.

• E. Scientists now realize they can explain the chemical behavior of different groups of elements without even discovering the elements.

Review5. What is the main idea of

Mendeleev’s proposal?• Mendeleev arranged the elements in

order of increasing mass so that elements with similar properties were in the same column.

Review6. What is the main idea of

Mendeleev’s prediction?• Mendeleev used the properties of

existing elements to predict properties of undiscovered elements.

Review7. What is the evidence supporting

Mendeleev’s table?• The close match between

Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.