Moscovium
Moscovium is a synthetic chemical element with the symbol Mc and atomic number 115. It is a superheavy, radioactive element in Group 15 of the periodic table, known from a small number of atoms made in nuclear-fusion experiments.
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Nihonium
Nihonium is a synthetic chemical element with the symbol Nh and atomic number 113. It is a superheavy, radioactive element in Group 13 of the periodic table, known from a very small number of atoms made in accelerator experiments.
Oganesson
Oganesson is a synthetic chemical element with the symbol Og and atomic number 118. It is the heaviest named element on the periodic table, placed in the noble gas group, but only a few short-lived atoms have been made, so its chemistry is mostly predicted rather than directly observed.
Tennessine
Tennessine is a synthetic chemical element with the symbol Ts and atomic number 117. It is a superheavy, radioactive element placed in the halogen group, but only a few atoms have been made, so most of its chemistry is predicted rather than observed directly.
Astatine
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It is the heaviest naturally occurring halogen, exists only in tiny amounts because all its isotopes are radioactive, and is studied mainly for nuclear chemistry and possible targeted alpha therapy with astatine-211.
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. It is a halogen that appears naturally mostly as iodide and iodate compounds, and it is essential for thyroid hormones, nutrition, iodized salt, antiseptics, medical imaging, and some nuclear-safety and environmental monitoring uses.
Bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the only nonmetallic element that is liquid near room temperature, a reactive halogen found mostly as bromide salts in nature, and an important chemical in flame retardants, drilling fluids, photography, pharmaceuticals, and water treatment.
Fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and the most reactive chemical element, appearing in nature mostly as fluoride compounds rather than free fluorine gas. Fluorine chemistry matters in dental health, medicines, polymers, refrigerants, minerals, and nuclear-fuel processing.
Chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. It is a reactive halogen that forms chlorine gas, chloride salts, disinfectants, bleach compounds, and many industrial chemicals, making it important for water treatment, public health, manufacturing, and chemical safety.
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a rare noble gas found in trace amounts in air, used in some high-intensity lamps, ion thrusters, medical imaging, anesthesia research, scientific detectors, and isotope studies.
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a rare noble gas found in trace amounts in air, used in some lighting, lasers, insulated glazing, scientific instruments, and isotope applications.
Argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is the most abundant noble gas in Earth's atmosphere, a colorless and inert gas used in welding, light bulbs, insulated windows, laboratories, semiconductor manufacturing, and argon-argon dating.
Neon
Neon is a chemical element with the symbol Ne and atomic number 10. It is a colorless noble gas in ordinary conditions, best known for the reddish-orange glow it produces in discharge tubes and neon signs, and also used in lasers, indicators, high-voltage devices, and some cryogenic applications.
Helium
Helium is the chemical element with the symbol He and atomic number 2. It is a light, colorless, nonflammable noble gas found in stars, natural gas deposits, balloons, cryogenic systems, MRI magnets, leak detection, welding, and scientific instruments.
Hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. It is the lightest element, the most abundant element in the universe, a major part of water and organic molecules, and a gas that can be produced, stored, burned, or used in fuel cells under carefully managed conditions.
Oxygen
Oxygen is a chemical element with the symbol O and atomic number 8. In Earth's atmosphere it is mostly found as molecular oxygen, O2, a colorless gas essential for aerobic respiration, combustion, many chemical reactions, and the chemistry of water, rocks, living cells, oceans, and the ozone layer.
Nitrous oxide
Nitrous oxide is a colorless gas with the chemical formula N2O. It is used in medicine and industry, produced naturally by microbes in the nitrogen cycle, and emitted by agriculture, fuel combustion, wastewater, and chemical production. It is also a long-lived greenhouse gas and an ozone-depleting substance.
Methane
Methane is a colorless, flammable gas with the chemical formula CH4. It is the simplest alkane, the main component of natural gas, a product of many oxygen-poor biological processes, and a powerful greenhouse gas whose emissions affect near-term climate warming.
Carbon dioxide
Carbon dioxide is a colorless gas made of one carbon atom and two oxygen atoms. It is a normal part of air, respiration, photosynthesis, oceans, volcanoes, combustion, and the carbon cycle, but rising atmospheric carbon dioxide from human activity is also a central driver of modern climate change.
Demand-controlled ventilation
Demand-controlled ventilation adjusts outdoor-air ventilation based on changing need, often using carbon dioxide, occupancy, or air-quality sensors. Instead of ventilating every zone at a fixed maximum rate all day, a DCV system can reduce airflow when spaces are lightly occupied and increase it when people or pollutants rise.
Heat recovery ventilation
Heat recovery ventilation uses a heat exchanger to transfer heat between outgoing stale indoor air and incoming outdoor air. HRV and ERV systems provide controlled fresh air while reducing the heating or cooling energy lost through ventilation, especially in airtight buildings.
Stack effect
Stack effect is air movement caused by density and pressure differences between warmer and cooler air columns. In buildings, it can pull air in through lower leaks and push air out through upper leaks in cold weather, or reverse direction in some cooling conditions, affecting comfort, energy use, moisture, smoke, odors, and ventilation.
Blower door test
A blower door test measures building air leakage by using a calibrated fan, temporary door panel, and pressure gauge to pressurize or depressurize a building. The result helps builders, auditors, and homeowners understand airtightness, find leaks, verify code targets, and plan air-sealing work.
Air barrier
An air barrier is a continuous system of materials, joints, and transitions that limits uncontrolled air leakage through a building envelope. It helps reduce drafts, energy loss, moisture transport, pollutants, and comfort problems, while planned ventilation supplies outdoor air in a controlled way.
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