Period (periodic table)

Simple Periodic Table Chart-blocks

Madelung rule

Coloured-transition-metal-solutions

Period (periodic table)

A period in the context of the periodic table refers to one of the horizontal rows in the table. All elements that are in the same period have the same number of atomic orbitals. For example, every element in the first period has one orbital for its electrons. Moving across a period, each element has one more proton and is less metallic than the element before it. The periodic table currently has seven periods, including the incomplete seventh period.

Overview

The concept of periods in the periodic table is crucial for understanding the chemical properties and physical properties of the elements. As one moves from left to right across a period, the elements transition from metals, to metalloids, and finally to nonmetals. This change is due to the increase in protons in the nucleus of the atoms, which affects the chemical behavior of the elements.

Periods

The periodic table is divided into seven periods:

• The first period contains only two elements, hydrogen and helium. It is unique because it is the only period that does not have any p-block or d-block elements.
• The second and third periods have eight elements each, filling the s-block and p-block orbitals. These periods include elements from lithium to neon, and sodium to argon, respectively.
• The fourth and fifth periods have eighteen elements each. They start filling the d-block of the periodic table, including elements from potassium to krypton and rubidium to xenon, respectively.
• The sixth period is the first period to include f-block elements, extending from cesium to radon, and includes a total of 32 elements.
• The seventh period is incomplete and extends from francium onwards. It also includes the f-block elements, known as the actinides.

Electron Configuration

The electron configuration of an atom increases across a period. This increase in electrons and protons affects the atomic radius, ionization energy, and electronegativity of the elements. At the start of a period, the atomic radius decreases as the electrons are added to the same orbital. The ionization energy increases because the electrons are closer to the nucleus and more strongly attracted to it. Electronegativity also increases across a period, as the atoms more readily attract electrons to fill their valence shell.

Significance

Understanding periods in the periodic table helps in predicting the chemical behavior of elements. Elements in the same period have similar sizes and electron configurations, which influences their reactivity and the types of bonds they form. This knowledge is fundamental in the fields of chemistry, physics, and materials science.

See Also

• Group (periodic table)
• Block (periodic table)
• Periodic trends
• Electron configuration