1.6 Development of the periodic table

chemistry topic 1

How did Mendeleev arrange the elements in his periodic table?

Elements arranged with increasing atomic masses. Elements with similar properties put into groups (due to periodic trends in chemical properties). Switched the position of some elements. Gaps left for undiscovered elements.

How was Mendeleev able to predict the properties of new elements?

Mendeleev left gaps in his periodic table. He used the properties of elements next to these gaps to predict the properties of undiscovered elements.

Mendeleev’s table lacked some amount of accuracy in the way he’d ordered his elements. Why was this?

Isotopes were poorly understood at the time. Protons and neutrons had not yet been discovered.

How are elements arranged in the modern periodic table?

In order of increasing atomic number.

Fill in the blank: ‘Elements in the same group (column) have similar _’

Chemical properties

Why do elements in the same column have similar chemical properties?

Same number of outer shell electrons. Number of outer shell electrons determines how an atom reacts.

What does the period (row) number tell you about all the elements in that period?

Elements in the same period have the same number of electron shells. e.g. all elements in period 4 have 4 shells of electrons.

What does group (column) number tell you about all the elements in that group?

All elements in the same group have the same number of outer electrons. e.g. all elements in group 2 have 2 electrons in their outer shell