Development of the periodic table

Who made the first theory?

Joham Döbereiner

What was his theory?

That elements with similar chemical properties often occurred in 3s.

Who made the second theory?

John Newlands

What was this theory called?

The law of octaves

What was the law of octaves?

That when arranged in order of increasing atomic weight, every eight element reacts in a similar way

Why was the law of octaves dismissed by other scientists?

The theory didn’t always occur and some elements were grouped together even with totally different properties

Who made the third theory?

Dmitri Mendeleev

What did Dmitri do?

1. Arranged all elements by increasing atomic weight

2. Switched the order of specific elements so they fitted the pattern of other elements in the same group

3. Left spaces in the table where he believed elements were missing and predicted the properties of these elements.

In what ways does our modern periodic table differ from Mendeleev’s?

• Arranged by atomic number instead of atomic weight

• Noble gases are now present