C1 - Development of Period Table

What is the periodic table?

A table that arranges elements in order of increasing atomic number and groups elements with similar properties into columns called groups.

Why is it called the "periodic" table?

Because elements with similar properties occur at regular intervals or periods.

What do groups in the periodic table represent?

Columns of elements with the same number of electrons in their outer shell and similar chemical properties.

Give examples of highly reactive metals in group 1.

Lithium, sodium, and potassium.

Give examples of highly reactive nonmetals in group 7.

Fluorine, chlorine, and bromine.

What did Johann Dobereiner notice about elements?

Elements with similar chemical properties often occurred in groups of three called triads.

What is an example of a triad?

Lithium, sodium, and potassium.

What was John Newlands' contribution to the periodic table?

He arranged elements by increasing atomic weight and noticed that every eighth element had similar properties, called the Law of Octaves.

Why was Newlands' Law of Octaves not fully accepted?

Because it grouped some elements with very different properties together.

How did Dmitri Mendeleev improve the periodic table?

By arranging elements in order of increasing atomic weight but switching the order of some elements to fit groups and leaving gaps for undiscovered elements.

Why did Mendeleev leave gaps in his periodic table?

He predicted some elements had not yet been discovered and left spaces for them.

How did Mendeleev predict the properties of undiscovered elements?

By using the properties of elements in the same group.

What discovery confirmed Mendeleev's periodic table?

The discovery of missing elements whose properties matched his predictions.

How is the modern periodic table different from Mendeleev's table?

Elements are arranged by increasing atomic number (number of protons) instead of atomic weight.

Why is ordering by atomic number better than atomic weight?

It places elements in the correct groups and avoids problems caused by isotopes.

Give an example of elements that are incorrectly ordered by atomic weight but correctly ordered by atomic number.

Thorium and iodine.

What new group was added to the modern periodic table that was missing from Mendeleev's?

Group 0, the noble gases.

Why was Group 0 not in Mendeleev's original table?

Because noble gases had not been fully discovered at the time.

What is the main reason elements in the same group have similar chemical properties?

They have the same number of electrons in their outer shell.

What are the transition elements?

The block of elements between groups 2 and 3 in the periodic table with varying properties.