What Are Horizontal Rows On The Periodic Table Called

The periodic table, a cornerstone of chemistry, organizes elements based on their atomic structure and properties, revealing fascinating patterns that help us understand the building blocks of our universe. Horizontal rows on the periodic table are called periods. These periods are arranged in order of increasing atomic number, and elements within the same period share the same number of electron shells. This article delves into the concept of periods, their significance, and the properties of the elements they contain.

Understanding the Periodic Table

The periodic table is more than just a chart of elements; it’s a tool that provides a wealth of information about each element, including its atomic number, electron configuration, and chemical properties. The table is arranged in rows (periods) and columns (groups), with elements in the same group exhibiting similar chemical behaviors.

Periods: Horizontal rows that indicate the number of electron shells an atom of the element possesses.
Groups: Vertical columns that indicate the number of valence electrons, which largely determines an element's chemical properties.

What Are Horizontal Rows on the Periodic Table Called?

Horizontal rows on the periodic table are called periods. There are seven periods in the periodic table, numbered 1 through 7, starting from the top. Each period corresponds to the filling of electron shells around the nucleus of the atom.

Significance of Periods

The arrangement of elements in periods is not arbitrary; it reflects the periodic recurrence of chemical properties. As you move from left to right across a period, elements exhibit a gradual change in properties, from metallic to non-metallic. This is due to the increasing number of protons in the nucleus and the corresponding increase in the number of electrons in the outermost shell.

Detailed Look at Each Period

Each period in the periodic table has unique characteristics and elements. Let’s explore them in detail:

Period 1

Period 1 consists of only two elements: hydrogen (H) and helium (He).

Hydrogen (H): The most abundant element in the universe, hydrogen has one proton and one electron. It is unique in its properties and does not neatly fit into any particular group. It can both lose an electron like alkali metals or gain an electron like halogens.
Helium (He): A noble gas with two protons and two electrons, helium is extremely stable and unreactive. Its electron shell is complete with two electrons, making it exceptionally inert.

Period 2

Period 2 contains eight elements, from lithium (Li) to neon (Ne).

Lithium (Li): An alkali metal that is soft, silvery-white, and highly reactive. It readily loses one electron to form a positive ion.
Beryllium (Be): An alkaline earth metal that is harder than lithium and less reactive. It has two valence electrons.
Boron (B): A metalloid that exhibits properties of both metals and nonmetals. It is essential for plant growth and is used in various industrial applications.
Carbon (C): A nonmetal that is the backbone of organic chemistry. Carbon atoms can form long chains and complex structures, making it essential for life.
Nitrogen (N): A nonmetal that exists as a diatomic gas (N₂) under normal conditions. It is a crucial component of the atmosphere and is used in fertilizers and explosives.
Oxygen (O): A nonmetal that is essential for respiration and combustion. It exists as a diatomic gas (O₂) and also forms ozone (O₃).
Fluorine (F): A halogen that is the most electronegative element. It is highly reactive and is used in toothpaste to prevent tooth decay.
Neon (Ne): A noble gas that is inert and used in lighting applications. It emits a distinctive reddish-orange light when electricity is passed through it.

Period 3

Period 3 also contains eight elements, from sodium (Na) to argon (Ar).

Sodium (Na): An alkali metal that is soft, silvery-white, and highly reactive. It reacts violently with water and is essential for nerve function in animals.
Magnesium (Mg): An alkaline earth metal that is lightweight and strong. It is used in alloys and is essential for plant and animal life.
Aluminum (Al): A metal that is lightweight, strong, and corrosion-resistant. It is widely used in construction, transportation, and packaging.
Silicon (Si): A metalloid that is a semiconductor. It is used in electronics and is the second most abundant element in the Earth's crust.
Phosphorus (P): A nonmetal that is essential for DNA, RNA, and energy transfer in cells. It exists in several allotropic forms, including white phosphorus and red phosphorus.
Sulfur (S): A nonmetal that is used in the production of sulfuric acid, fertilizers, and rubber. It has a distinctive yellow color.
Chlorine (Cl): A halogen that is a greenish-yellow gas. It is used as a disinfectant and in the production of plastics and other chemicals.
Argon (Ar): A noble gas that is inert and used in welding and lighting applications. It is the third most abundant gas in the Earth's atmosphere.

Period 4

Period 4 contains 18 elements, from potassium (K) to krypton (Kr), including the first row of transition metals.

Potassium (K): An alkali metal that is soft, silvery-white, and highly reactive. It is essential for nerve function and muscle contraction.
Calcium (Ca): An alkaline earth metal that is essential for bones and teeth. It is also involved in muscle function and blood clotting.
Scandium (Sc): A transition metal that is lightweight and strong. It is used in alloys and high-intensity lighting.
Titanium (Ti): A transition metal that is strong, lightweight, and corrosion-resistant. It is used in aerospace, medical implants, and sporting goods.
Vanadium (V): A transition metal that is used in alloys to increase strength and hardness. It is also used as a catalyst.
Chromium (Cr): A transition metal that is hard, brittle, and corrosion-resistant. It is used in stainless steel and chrome plating.
Manganese (Mn): A transition metal that is essential for plant growth and is used in steel production.
Iron (Fe): A transition metal that is the main component of steel. It is essential for oxygen transport in blood.
Cobalt (Co): A transition metal that is used in alloys, magnets, and catalysts. It is also a component of vitamin B12.
Nickel (Ni): A transition metal that is corrosion-resistant and used in alloys, batteries, and electroplating.
Copper (Cu): A transition metal that is an excellent conductor of electricity and heat. It is used in wiring, plumbing, and coins.
Zinc (Zn): A transition metal that is used in galvanizing steel to prevent corrosion. It is also essential for immune function and wound healing.
Gallium (Ga): A metal that has a low melting point and is used in semiconductors and LEDs.
Germanium (Ge): A metalloid that is a semiconductor. It is used in transistors and other electronic devices.
Arsenic (As): A metalloid that is toxic and used in pesticides and semiconductors.
Selenium (Se): A nonmetal that is essential for thyroid function and is used in photocopiers and solar cells.
Bromine (Br): A halogen that is a reddish-brown liquid at room temperature. It is used in flame retardants and disinfectants.
Krypton (Kr): A noble gas that is inert and used in lighting applications.

Period 5

Period 5 contains 18 elements, from rubidium (Rb) to xenon (Xe), including the second row of transition metals.

Rubidium (Rb): An alkali metal that is soft, silvery-white, and highly reactive. It is used in atomic clocks.
Strontium (Sr): An alkaline earth metal that is used in fireworks and in the production of glass and ceramics.
Yttrium (Y): A transition metal that is used in alloys and in the production of phosphors.
Zirconium (Zr): A transition metal that is corrosion-resistant and used in nuclear reactors and surgical implants.
Niobium (Nb): A transition metal that is used in alloys and in the production of superconductors.
Molybdenum (Mo): A transition metal that is used in steel alloys to increase strength and hardness.
Technetium (Tc): A transition metal that is radioactive and used in medical imaging.
Ruthenium (Ru): A transition metal that is used in electrical contacts and as a catalyst.
Rhodium (Rh): A transition metal that is used in catalytic converters and jewelry.
Palladium (Pd): A transition metal that is used in catalytic converters and in the production of jewelry.
Silver (Ag): A transition metal that is an excellent conductor of electricity and heat. It is used in jewelry, coins, and photography.
Cadmium (Cd): A transition metal that is toxic and used in batteries and pigments.
Indium (In): A metal that is used in semiconductors, LCD screens, and solar cells.
Tin (Sn): A metal that is used in solder, tin cans, and alloys.
Antimony (Sb): A metalloid that is used in flame retardants, alloys, and semiconductors.
Tellurium (Te): A metalloid that is used in solar cells and alloys.
Iodine (I): A halogen that is essential for thyroid function and is used as a disinfectant.
Xenon (Xe): A noble gas that is inert and used in lighting applications and anesthesia.

Period 6

Period 6 contains 32 elements, from cesium (Cs) to radon (Rn), including the third row of transition metals, lanthanides, and hafnium to mercury.

Cesium (Cs): An alkali metal that is soft, silvery-gold, and highly reactive. It is used in atomic clocks and photoelectric cells.
Barium (Ba): An alkaline earth metal that is used in X-ray imaging and in the production of glass and ceramics.
Lanthanum (La): A lanthanide that is used in alloys, lighting, and high-refractive-index glass.
Cerium (Ce): A lanthanide that is used in catalytic converters, lighter flints, and polishing compounds.
Praseodymium (Pr): A lanthanide that is used in magnets, lasers, and colored glass.
Neodymium (Nd): A lanthanide that is used in magnets, lasers, and colored glass.
Promethium (Pm): A lanthanide that is radioactive and used in pacemakers and luminous paints.
Samarium (Sm): A lanthanide that is used in magnets, nuclear reactors, and cancer treatment.
Europium (Eu): A lanthanide that is used in lasers, fluorescent lamps, and control rods in nuclear reactors.
Gadolinium (Gd): A lanthanide that is used in MRI contrast agents, neutron capture therapy, and magneto-optical disks.
Terbium (Tb): A lanthanide that is used in lasers, fluorescent lamps, and magneto-optical disks.
Dysprosium (Dy): A lanthanide that is used in magnets, data storage, and lighting.
Holmium (Ho): A lanthanide that is used in lasers, nuclear control rods, and colored glass.
Erbium (Er): A lanthanide that is used in lasers, optical amplifiers, and colored glass.
Thulium (Tm): A lanthanide that is used in portable X-ray machines and neutron sources.
Ytterbium (Yb): A lanthanide that is used in infrared lasers, stress gauges, and chemical reduction.
Lutetium (Lu): A lanthanide that is used in catalysts, scintillators, and PET scanners.
Hafnium (Hf): A transition metal that is corrosion-resistant and used in nuclear control rods and high-temperature alloys.
Tantalum (Ta): A transition metal that is corrosion-resistant and used in surgical implants and electronic components.
Tungsten (W): A transition metal that has the highest melting point of all elements. It is used in light bulb filaments and high-temperature alloys.
Rhenium (Re): A transition metal that is used in high-temperature alloys and as a catalyst.
Osmium (Os): A transition metal that is the densest naturally occurring element. It is used in electrical contacts and fountain pen tips.
Iridium (Ir): A transition metal that is corrosion-resistant and used in electrical contacts, spark plugs, and crucibles.
Platinum (Pt): A transition metal that is used in catalytic converters, jewelry, and electrical contacts.
Gold (Au): A transition metal that is corrosion-resistant and used in jewelry, coins, and electronics.
Mercury (Hg): A transition metal that is a liquid at room temperature. It is used in thermometers, barometers, and dental amalgams.
Thallium (Tl): A metal that is toxic and used in pesticides and infrared detectors.
Lead (Pb): A metal that is toxic and used in batteries, solder, and radiation shielding.
Bismuth (Bi): A metal that is used in pharmaceuticals, cosmetics, and alloys.
Polonium (Po): A metalloid that is radioactive and used in antistatic brushes and thermoelectric devices.
Astatine (At): A halogen that is radioactive and has no known uses.
Radon (Rn): A noble gas that is radioactive and can accumulate in buildings, posing a health risk.

Period 7

Period 7 contains 32 elements, from francium (Fr) to oganesson (Og), including the fourth row of transition metals and actinides. Many of these elements are synthetic and radioactive.

Francium (Fr): An alkali metal that is radioactive and extremely rare.
Radium (Ra): An alkaline earth metal that is radioactive and was formerly used in cancer treatment.
Actinium (Ac): An actinide that is radioactive and used in neutron sources.
Thorium (Th): An actinide that is radioactive and used in nuclear fuel and gas mantles.
Protactinium (Pa): An actinide that is radioactive and used in scientific research.
Uranium (U): An actinide that is radioactive and used in nuclear fuel and weapons.
Neptunium (Np): An actinide that is radioactive and used in nuclear reactors and research.
Plutonium (Pu): An actinide that is radioactive and used in nuclear weapons and reactors.
Americium (Am): An actinide that is radioactive and used in smoke detectors and neutron sources.
Curium (Cm): An actinide that is radioactive and used in neutron sources and research.
Berkelium (Bk): An actinide that is radioactive and used in scientific research.
Californium (Cf): An actinide that is radioactive and used in neutron sources and cancer treatment.
Einsteinium (Es): An actinide that is radioactive and used in scientific research.
Fermium (Fm): An actinide that is radioactive and used in scientific research.
Mendelevium (Md): An actinide that is radioactive and used in scientific research.
Nobelium (No): An actinide that is radioactive and used in scientific research.
Lawrencium (Lr): An actinide that is radioactive and used in scientific research.
Rutherfordium (Rf): A transactinide element that is synthetic and radioactive.
Dubnium (Db): A transactinide element that is synthetic and radioactive.
Seaborgium (Sg): A transactinide element that is synthetic and radioactive.
Bohrium (Bh): A transactinide element that is synthetic and radioactive.
Hassium (Hs): A transactinide element that is synthetic and radioactive.
Meitnerium (Mt): A transactinide element that is synthetic and radioactive.
Darmstadtium (Ds): A transactinide element that is synthetic and radioactive.
Roentgenium (Rg): A transactinide element that is synthetic and radioactive.
Copernicium (Cn): A transactinide element that is synthetic and radioactive.
Nihonium (Nh): A transactinide element that is synthetic and radioactive.
Flerovium (Fl): A transactinide element that is synthetic and radioactive.
Moscovium (Mc): A transactinide element that is synthetic and radioactive.
Livermorium (Lv): A transactinide element that is synthetic and radioactive.
Tennessine (Ts): A transactinide element that is synthetic and radioactive.
Oganesson (Og): A transactinide element that is synthetic and radioactive.

Trends Across Periods

As you move across a period from left to right, several properties of the elements change in a predictable manner:

Atomic Radius

The atomic radius generally decreases across a period. This is because the number of protons in the nucleus increases, leading to a greater positive charge that pulls the electrons closer to the nucleus.

Ionization Energy

The ionization energy, which is the energy required to remove an electron from an atom, generally increases across a period. This is because the increased nuclear charge makes it more difficult to remove an electron.

Electronegativity

Electronegativity, which is the ability of an atom to attract electrons in a chemical bond, generally increases across a period. This is because the increased nuclear charge makes the atom more attractive to electrons.

Metallic Character

Metallic character decreases across a period. Elements on the left side of the periodic table are metals, while those on the right side are nonmetals.

The Underlying Science

The properties and behaviors of elements in each period are deeply rooted in the principles of quantum mechanics and electron configurations.

Electron Shells

Each period corresponds to the filling of electron shells around the nucleus. The first period corresponds to the filling of the first electron shell (n=1), which can hold up to two electrons. The second period corresponds to the filling of the second electron shell (n=2), which can hold up to eight electrons, and so on.

Quantum Numbers

The arrangement of electrons in atoms is described by a set of four quantum numbers:

Principal Quantum Number (n): Determines the energy level or shell of the electron.
Azimuthal Quantum Number (l): Determines the shape of the electron's orbital.
Magnetic Quantum Number (ml): Determines the orientation of the electron's orbital in space.
Spin Quantum Number (ms): Determines the intrinsic angular momentum of the electron.

Electron Configuration

The electron configuration of an element describes the arrangement of electrons in its atoms. This configuration determines the chemical properties of the element. For example, elements in the same group have similar valence electron configurations, which is why they exhibit similar chemical behaviors.

Why Is This Important?

Understanding the periodic table and the properties of elements in each period is crucial for various fields:

Chemistry: It helps predict chemical reactions and understand the properties of compounds.
Materials Science: It aids in designing new materials with specific properties.
Biology: It is essential for understanding the role of elements in biological systems.
Environmental Science: It helps in studying the behavior of pollutants and the impact of chemicals on the environment.

Conclusion

The horizontal rows on the periodic table, known as periods, are fundamental to understanding the organization and properties of elements. Each period reflects the filling of electron shells around the nucleus, leading to predictable trends in atomic radius, ionization energy, electronegativity, and metallic character. The periodic table is an invaluable tool in chemistry and various other scientific fields, offering a framework for understanding the building blocks of matter and their interactions. By grasping the significance of periods, we gain deeper insights into the nature of elements and their role in the universe.