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The modern periodic table
CHEMISTRY - Secondary 2
In This part we will study
The modern periodic table consists - as shown on the previous page - of:
• 7 periods (horizontal rows). • 18 groups (vertical columns).
The elements are arranged ascending according to :
• Their atomic numbers (number of protons) :
The atomic number of each element exceeds the element which precedes it in the same period by one.

• The sequence of filling their atomic energy sublevels with electrons according to the Aufbau (Building-up) principle, where each element has one electron more than the element which precedes it.

Each period begins by filling a new principal energy level with one electron, then filling the atomic energy sublevels lying in the same period successively, until we reach the last element in the period which is a noble gas that has completely filled energy levels.

The elements of the same vertical group are:
• Similar in the electronic configuration of the highest (outermost) energy level.
• Different in the principal quantum number (n).

* The modern periodic table consists of 118 elements distributed in seven horizontal periods, as follows:
The elements blocks of the modern periodic table:
• The table is divided into four main blocks, these blocks are :
 s-block.
 p-block.
 d-block.
 f-block.

Best wishes to you
Mr.Ahmed Elbasha

كيمياء الصف الثاني الثانوي لغات - الفصل الدراسي الاول
شرح كيمياء لغات تانية ثانوي - مستر احمد الباشا