Tag: science & technology

The cerebrum is the largest part of the human brain, making up about 85% of its weight. It handles higher functions like thinking, learning, memory, and voluntary movement. The cerebellum coordinates movement, and medulla controls vital functions.

Calcium phosphate (hydroxyapatite) is the primary mineral component of bones and teeth, making up about 65-70% of bone weight. It provides hardness and strength. Calcium carbonate, sulfate, and nitrate are not the main structural components.

Hemoglobin contains iron in its heme groups, which enables it to bind and transport oxygen throughout the body. Each hemoglobin molecule can carry four oxygen molecules. The iron gives blood its red color.

Jöns Jakob Berzelius, the Swedish chemist, coined the term 'halogen' from Greek words meaning 'salt producer'. He recognized that these elements (fluorine, chlorine, bromine, iodine) form salts when they react with metals. Dalton is known for atomic theory, Curie for radioactivity research, and Heisenberg for quantum mechanics.

Halogens (Group 17 elements: F, Cl, Br, I, At, Ts) are the most reactive nonmetals because they have seven valence electrons and need only one more to achieve a stable octet configuration. This strong tendency to gain an electron makes them powerful oxidizing agents.

Halogens are nonmetals, not metallic. They exhibit nonmetallic properties: poor conductors of heat and electricity, brittle solids (except liquid bromine and gaseous fluorine/chlorine), and high electronegativities. Metallic character decreases across a period and increases down a group - halogens are just before the noble gases.

Astatine is the most unstable halogen. All its isotopes are radioactive with very short half-lives - the most stable, astatine-210, has a half-life of only 8.1 hours. This extreme rarity and radioactivity makes it impractical for most chemical applications. Fluorine, chlorine, and iodine are stable enough to be found in nature or used commercially.

At room temperature (25°C): Fluorine and Chlorine are gases, Bromine is a liquid (the only liquid nonmetal at STP), and Iodine is a solid that sublimes (goes directly from solid to gas). Iodine's higher atomic mass and stronger van der Waals forces between its diatomic molecules (I2) allow it to exist as solid crystals.

Bromine is the only nonmetallic element that is liquid at standard temperature and pressure. Its physical state results from intermediate molecular weight and intermolecular forces - heavy enough to be liquid but not so heavy that it's solid like iodine. Fluorine and chlorine are gases at room temperature.

Halogens belong to Group 17 of the periodic table. They have a valence shell configuration of ns^2 np^5, totaling 7 electrons in their outermost shell, making them highly reactive as they seek one more electron to complete an octet.