An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is made up of neutral or ionized atoms.
one of the four substances (earth, water, air, or fire) considered as a person's or animal's natural environment.
A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge.
A chemical compound is an entity consisting of two or more different atoms which associate via chemical bonds.
the atomic number of a chemical element (also known as its proton number) is the number of protons found in the nucleus of an atom of that element, and therefore identical to the charge number of the nucleus.
The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.
Isotopes are variants of a particular chemical element which differ in neutron number, although all isotopes of a given element have the same number of protons in each atom.
The spontaneous transformation of an unstable atomic nucleus into a lighter one, in which radiation is released in the form of alpha particles, beta particles, gamma rays, and other particles
the time taken for the radioactivity of a specified isotope to fall to half its original value.
is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs and the stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding.
the electrostatic force of attraction between two oppositely charged ions. The positive ion is called cation, and the negative ion is the anion. It is like the north and south poles of a magnet.
an asymmetric molecule with non-uniform positive and negative charges; also called dipole. A polar molecule has a partial positive charge in one part of the molecule and complementary negative charge in another part.
chemical substance that neutralizes alkalis, dissolves some metals, and turns litmus red; typically, a corrosive or sour-tasting liquid of this kind.
a substance capable of reacting with an acid to form a salt and water, or (more broadly) of accepting or neutralizing hydrogen ions.
Law of Conservation of matter
states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed.
compound that is considered not "organic". Inorganic compounds are traditionally viewed as being synthesized by the agency of geological systems. In contrast, organic compounds are found in biological systems.
member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon.[this is an extracted definition from wiki encyclopedia organic compound
is the radiant energy released by certain electromagnetic processes. Visible light is one type of electromagnetic radiation, other familiar forms are invisible electromagnetic radiations such as radio waves, infrared light and X rays.
is the energy that an object has due to its position in a force field or that a system has due to the configuration of its parts.
the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes.
A unit of energy in the SI system. One joule is 1 kg. m2/s2 which is also 0.2390 calorie.
energy that is produced by mechanical, electrical, or other means and used to operate a device
first law of thermodynamics
is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed.
second law of thermodynamics
In any cyclic process the entropy will either increase or remain the same. Entropy: a state variable whose change is defined for a reversible process at T where Q is the heat absorbed. Entropy: a measure of the amount of energy which is unavailable to do work.
is the goal to reduce the amount of energy required to provide products and services.
refers to differences in the ability of a unit of energy to produce goods and services for people. The usefulness of an energy system is determined by a complex combination of physical, technical, economic, and social attributes.
negative feedback loop
occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances.
positive feedback loop
enhance or amplify changes; this tends to move a system away from its equilibrium state and make it more unstable. Negative feedbacks tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable.