Chapter 2 - The Chemical Context of Life

• Ants, like other animals, have structures and systems that protect them against predators. Wood ants live in colonies of hundreds or thousands, and the colony as a whole possesses a very efficient defense mechanism. When attacked from above, the ants spray formic acid volleys into the air from their abdomens, and the acid bombards the prospective predator, such as a hungry bird.

• Formic acid is generated by numerous ant species and derives its name from the Latin word for ant, Formica. For many ant species, the formic acid is presumably used as a disinfectant to protect the ants from microbial parasites rather than being fired out.

• Scientists have long known that chemicals play an important role in insect communication, mating attractiveness, and predator protection.

• The study of ants and other insects exemplifies how important chemistry is in the understanding of life. Nature, unlike academic classes, is not cleanly divided into distinct sciences—biology, chemistry, physics, and so on. Biologists study life, yet organisms and their environs are natural systems to which chemistry and physics ideas apply. Biology is an interdisciplinary field.

• Elements are the building blocks of matter. An element is a material that cannot be broken down chemically into other compounds. Chemists now recognize 92 elements found in nature, including gold, copper, carbon, and oxygen. Each element is represented by a symbol, which is generally the first letter or two of its name.

• Some symbols are derived from Latin or German; for example, sodium is represented by the sign Na, which is derived from the Latin word, atrium.

• A compound is a material made up of two or more distinct components mixed in a certain proportion. Table salt, for example, is sodium chloride (NaCl), a chemical formed in a 1:1 ratio of the elements sodium (Na) and chlorine (Cl).

• Pure sodium is a metal, whereas pure chlorine is a nonmetal.

• About 20–25 percent of the 92 natural elements are needed for an organism to have a healthy existence and reproduce. The basic components are similar throughout creatures, although there is considerable variation—for example, humans require 25 elements, but plants require just 17.

• Only four elements—oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)—comprise around 96 percent of all biological stuff. The remaining 4 percent or so of an organism's bulk is made up of calcium (Ca), phosphorous (P), potassium (K), sulfur (S), and a few other elements.

  • The term Trace elements refer to being required by an organism in only minute quantities. Some trace elements, such as iron (Fe), are needed by all forms of life; others are required only by certain species. For example, invertebrates (animals with backbones), the element iodine (I) is an essential ingredient of a hormone produced by the thyroid gland.

• A daily dose of 0.15 milligram (mg) of iodine is sufficient for normal thyroid function in humans. A lack of iodine in the diet leads the thyroid gland to expand to an unnatural size, a disease known as goiter. Consuming seafood or iodized salt lowers the risk of goiter.

• The table attached below shows the relative quantities of all elements in the human body. Some elements found in nature are harmful to organisms. Arsenic, for example, has been related to a variety of illnesses and is potentially deadly in humans. Arsenic occurs naturally in various parts of the world and can enter groundwater.

• Millions of people have been accidentally exposed to arsenic-laden water as a result of drinking water from dug wells throughout southern Asia.

• Efforts are being made to minimize arsenic levels in their drinking water.

• As the metal sodium interacts with the toxic gas chlorine to produce the edible compound sodium chloride or table salt, the emerging characteristics of the combination can be discovered.

• Each element is made up of a unique sort of atom that is distinct from the atoms of other elements.

• An atom is the lowest unit of a substance that retains elemental characteristics. Atoms are so tiny that it would take almost a million of them to span the period at the conclusion of this sentence.

• We use the same shorthand for atoms as we do for the element composed of those atoms. The letter C, for example, represents both the element carbon and a single carbon atom.

• Although the atom is the smallest unit with elemental characteristics, these tiny pieces of matter are made up of even smaller components known as subatomic particles.

• Physicists have created more than 100 types of particles from the atom via high-energy collisions, but only three types of particles are important here: neutrons, protons, and electrons.

• Electrons and protons are both electrically charged. Each proton carries one unit of positive charge and one unit of negative charge. As the name indicates, a neutron is electrically neutral.

• Protons and neutrons are densely packed together in a compact core, or atomic nucleus, in the heart of an atom; protons provide the nucleus with positivity.

• Because neutrons and protons have masses extremely near to 1 dalton, the mass number is close to, but somewhat different from, the overall mass of an atom, known as its atomic mass. For example, the mass number of sodium (23 11Na) is 23, yet its atomic mass is 22.9898 daltons.