Development of the Periodic Table

Before Mendeleev's table, how were elements arranged in order to classify them?

• In order of atomic mass

• In order of atomic weight

• By physical and chemical properties

• They weren't

What were some problems with the early versions of the periodic table?

• Some elements had not been discovered so the tables were not complete.

• The elements did not follow a regular pattern.

• The weight of some elements had been calculated incorrectly.

• Elements were placed in order of atomic weight, so some ended up in the wrong group.

In the periodic table, the ______ number tells us the number of electron shells in an atom.

How did Mendeleev overcome some of the problems in his version of the periodic table?

• He made up new elements to fill in gaps.

• He left gaps for undiscovered elements.

• He ordered the elements in terms of atomic mass.

• He placed elements in groups according to similar properties.

Placing the elements in order of atomic weight was incorrect because some elements have ________ that have different masses.

In the periodic table, the _____ number tells us the number of electrons in the outer shell of an atom.

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Bromine is in Group 7. How many electrons are in the outer shell of a bromine atom?

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An atom of sodium has 3 electron shells. What does this tell us about the atom?

• It is in Group 3 of the periodic table

• It is in Period 3 of the periodic table

• It has 3 electrons

• Molecules of sodium contain 3 atoms

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Magnesium is in Group 3 and Period 2. What is the electronic structure of magnesium?

• 1.1.1

• 3.2

• 2.8.2

• 2.8.8

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An element is in Group 6 and Period 3. How many electrons does it have in total?

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