A period in the periodic table is a horizontal row of elements that share the same number of electron shells. In total, there are seven periods in the periodic table, each containing a different number of elements. The number of elements in a period corresponds to the number of electrons that can occupy the electron shells of atoms in that period.
The first period of the periodic table contains only two elements, hydrogen and helium. These two elements have only one electron shell and are therefore classified as belonging to the first period. The second period contains eight elements, from lithium to neon, which have two electron shells. Each subsequent period contains one additional electron shell, with the seventh period containing the elements with the largest electron shells known to date.
Elements within a period exhibit periodic trends in their properties, including decreasing atomic radius and increasing ionization energy and electronegativity from left to right. The elements within a period also exhibit similar chemical properties due to the number of valence electrons in their outermost electron shell.
The concept of periods in the periodic table was first proposed by Russian chemist Dmitri Mendeleev in the late 1800s. By arranging the elements in order of increasing atomic number and placing elements with similar properties in the same column, Mendeleev created a comprehensive system that allowed for the prediction of undiscovered elements and their properties. The periodic table has since become one of the most fundamental and useful tools in chemistry, providing insight into the behavior and properties of the elements.
On periodic table
|1||– period 1 element||5||– period 5 element|
|2||– period 2 element||6||– period 6 element|
|3||– period 3 element||7||– period 7 element|
|4||– period 4 element|
From top to bottom, the periodic table consists of 7 periods, with each period containing a different number of elements: period 1 has 2 elements, period 2 and period 3 have 8 elements each, period 4 and period 5 have 18 elements each, and period 6 and period 7 have 32 elements each, which makes a total of 118 known elements.
Hydrogen is the lightest and most abundant element in the universe, and also the most abundant element in the Earth’s crust. It is highly reactive and can form covalent, ionic, or metallic bonds with other elements. Hydrogen gas is used in various industrial processes, such as in the production of ammonia and methanol. It is also used as a fuel for rockets and in fuel cells for generating electricity.
Helium is an inert gas and is the second lightest element after hydrogen. It is the most stable of all the noble gases, and is the second most abundant element in the universe. Helium gas is used in various applications, such as in cooling systems for MRI machines and nuclear reactors, in airships and balloons, and as a shielding gas in welding processes.
Period 2 of the periodic table contains eight elements, namely lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon.
Lithium (Li) is a soft, silvery-white metal that belongs to the alkali metal group. It is highly reactive and has the lowest density of all metals. Lithium is commonly used in batteries, ceramics, and as a mood stabilizer in psychiatric medicine.
Carbon (C) is a nonmetallic element that is essential for life. It exists in several allotropes, including graphite and diamond. Carbon is used in a wide range of applications, such as in the production of steel and as a fuel source.
Nitrogen (N) is a colorless, odorless gas that makes up about 78% of Earth’s atmosphere. It is an essential element for life and is used in the production of ammonia, which is used in fertilizers.
Oxygen (O) is a colorless, odorless gas that makes up about 21% of Earth’s atmosphere. It is essential for respiration and is used in a variety of applications, such as in steel production and medical oxygen tanks.
Sodium (Na) is a soft, silvery-white, highly reactive metal. It is an essential element for animal life and is used in various applications, including the production of soap and as a coolant in nuclear reactors.
Magnesium (Mg) is a shiny gray metal that is widely used in alloys, medicine, and pyrotechnics. It is also an essential element for plants and animals, and is found in many foods such as nuts, seeds, and green leafy vegetables.
Aluminum (Al) is a lightweight, silvery-white metal that is widely used in various applications, including packaging, transportation, construction, and electrical systems. It is the most abundant metal in the Earth’s crust and is highly resistant to corrosion.
Silicon (Si) is a metalloid that is widely used in the production of semiconductors, solar cells, and computer chips. It is the second most abundant element in the Earth’s crust and is also found in various minerals and rocks.
Sulfur (S) is a non-metallic element that is found in various forms in the Earth’s crust. It is used in various applications, including the production of fertilizers, chemicals, and pharmaceuticals.
Chlorine (Cl) is a highly reactive, greenish-yellow gas that is used in various applications, including the production of bleach and disinfectants. It is also an essential element for life and is found in various compounds such as salt.
Argon (Ar) is an inert, colorless, odorless gas that is the third most abundant gas in the Earth’s atmosphere. It is used in various applications, including welding, lighting, and as a protective gas in various industrial processes.
The first half of the period consists of elements that have a filling 3d subshell, such as scandium (Sc), titanium (Ti), and iron (Fe). These elements are known for their transition metal properties, such as high melting and boiling points, malleability, and good electrical conductivity. They are also commonly used in various industries, such as construction, aerospace, and electronics.
The second half of the period consists of elements that have a filling 4p subshell, such as germanium (Ge), selenium (Se), and bromine (Br). These elements exhibit more non-metallic properties, such as lower melting and boiling points, and increased electronegativity. They are commonly used in semiconductors, solar cells, and pharmaceuticals. The noble gas, krypton (Kr) is the last element in period 4 and is known for its inertness and use in lighting.
Period 5 of the periodic table contains 18 elements, beginning with the alkali metal rubidium (Rb) and ending with the noble gas xenon (Xe). Elements in period 5 generally have larger atomic radii and lower ionization energies compared to the elements in period 4, although their electron affinities are generally lower due to the trend of decreasing electron affinity down a group. This is due to the fact that the valence electrons in period 5 are in higher energy levels, farther away from the nucleus, and thus experience less attraction from the positively charged nucleus.
One notable characteristic of period 5 elements is their diverse range of chemical properties. For example, the transition metals in period 5, such as molybdenum (Mo) and technetium (Tc), have high melting and boiling points, and are often used as catalysts. On the other hand, iodine (I) is a highly reactive nonmetal belonging to the halogen group, while xenon (Xe) is an inert noble gas with very low reactivity.
Period 6 of the periodic table contains 32 elements, starting with cesium (Cs) and ending with radon (Rn). This period includes some important elements such as barium (Ba), hafnium (Hf), tungsten (W), platinum (Pt), and gold (Au). These elements have important uses in industry, such as hafnium in nuclear reactors and tungsten in the manufacturing of high-temperature alloys. Others, such as gold and platinum, are highly valued for their beauty and rarity.
Period 7 of the periodic table contains 32 elements, starting with francium (Fr) and ending with oganesson (Og). The elements in this period have progressively increasing atomic numbers and are known for their unique chemical properties. Many of the elements in period 7 are synthetic and highly unstable, with short half-lives, making their study challenging. Elements such as uranium (U) and plutonium (Pu) are important in nuclear energy and have been the subject of extensive research. On the other hand, elements like francium (Fr) and oganesson (Og) are highly reactive and have limited practical applications.
Period 8 elements are yet to be discovered, and therefore, their properties and characteristics are still unknown. The theoretical predictions suggest that the eighth period would consist of 18 elements, and their electronic configurations would be similar to the seventh period elements, with 5g orbitals filling up. Theoretical calculations also suggest that the elements of the eighth period would be extremely unstable and radioactive, and their lifetimes would be incredibly short.
The search for the elements of the eighth period is still ongoing, and scientists are actively working to synthesize these elements in laboratories using advanced technologies. However, due to the expected instability of these elements, it remains to be seen whether the predicted elements of the eighth period are physically possible. Until then, the properties and characteristics of the eighth period elements remain a mystery, and the possibility of the ninth period is still uncertain.
- Block (periodic table)
- Group (periodic table)
- Period (periodic table)
- Alkali metal
- Alkaline earth metal
- Transition metal
- Post-transition metal
- Reactive nonmetal
- Noble gas
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