The horizontal row of the periodic table is referred to as the periods. In a period the atomic number increases with an increase in the electrons and hence the chemical properties changes.
Periods are the seven horizontal rows in the table that have the elements arranged based on the protons in the nucleus. The number of the valence electron in the elements of the period increases.
The number of protons are the determinant of the chemical and the physical properties that differ in the elements in a period. As the number of protons increases the atomic number the property of the element varies.
The increase in the valence electron varies the size when moving left to right across a period. The addition of the electron increases the ionization energy and decreases the atomic radii.
Therefore, across the period the atomic size decreases with an increase in the electron.
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