Fundamentals of Chemistry

The substance of the universe—from a grain of sand to a star—is called matter. Scientists define matter as anything that occupies space and …

Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all of these are …

The Greek philosopher Democritus proposed that everything on Earth is made up of tiny particles called atomos, Greek for "indivisible," from which …

A chemical symbol is an abbreviation that is used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. We use the …

The number of protons in the nucleus of an atom is its atomic number (Z). This is the defining trait of an element. Its value determines the identity of …

In the early 1900s, English chemist Frederick Soddy realized that an element could have atoms with different masses that were chemically …

Electrons are negatively charged subatomic particles attracted to and orbit around the positively-charged nucleus of an atom. They reside in spaces …

Chemical Bonds The electrons of the outermost energy level determine the energetic stability of the atom and its tendency to form chemical bonds with …

A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) …

Ions – When an atom participates in a chemical reaction that results in the donation or acceptance of one or more electrons, the atom becomes positively …

Solids, liquids, and gases are the three states of matter commonly found on Earth. A solid is rigid and possesses a definite shape. A liquid flows and …

All chemical reactions begin with a reactant, the general term for one or more substances entering the reaction. Sodium and chloride ions, for example, …

The first law of thermodynamics holds that energy can neither be created nor destroyed—it can only change form. An organism's essential function …

An exchange reaction is a chemical reaction in which both synthesis and decomposition occur, chemical bonds are both formed and broken, and chemical …

Chemical reactions require sufficient energy to cause the matter to collide with enough precision and force that old chemical bonds can be broken and new …

A variety of factors influence the rate of chemical reactions. For a chemical reaction to happen, atoms must collide with enough energy to overcome the …

Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera …

Acids and bases play several important roles in biology. The pH of a biological system can significantly impact the function of biological molecules, …

Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams. Scientists arbitrarily define this amount of mass as one atomic mass …

Overview When atoms gain or lose electrons to achieve a more stable electron configuration they form ions. Ionic bonds are electrostatic attractions …

Overview When two atoms share electrons to complete their valence shells, they create a covalent bond. An atom's electronegativity—the force …