Overview
Chemicals form the basic building blocks of matter in living things as well as nonliving things. Molecules are formed by chemical bonds that join elements and make substances. Chemical reactions are the basis of transformations of molecules into entirely different substances, the release of energy, and the processes of life.
Ionic Chemical Bonds
Ionic bonds are formed by electronic attraction. The simplest and most common example is the attraction between sodium (chemical name Na), and chlorine (Cl), to form NaCl, sodium chloride, common table salt. The outermost level of a sodium atom only has one electron, and can easily give it up in a chemical reaction. The outermost level of a chlorine atom, by contrast, has 7 electrons, and can easily take an electron from another atom. When the sodium atom gives up its electron, it is slightly positively charged, and when the chlorine atom gains an electron, it is slightly negatively charged. The positively charged sodium atom and the negatively charged chlorine atom are held together in a compound be an ionic bond.
Covalent Chemical Bonds
Covalent chemical bonds are stronger than ionic bonds, because more than one element shares electrons. The water molecule, or H2O, is one of the most common examples. The hydrogen atoms share electrons with the oxygen atoms, and the oxygen atoms also share electrons with the hydrogen atoms, so the bond works both ways. Methane is another common compound. Carbon (C) shares electrons with 4 hydrogen atoms (H4), and the hydrogen atoms share electrons with the carbon atoms in covalent bonds.
Common Elements for Life
Elements such as hydrogen (H), carbon (C), nitrogen (N), and oxygen (O),are the most common elements found in life, making up over 99 % of living things. Sodium (S), magnesium (Mg), potassium (K), calcium (Ca), phosphorus (P), sulfur (S), and chlorine (Cl) make up less than 0.7%, although they are crucial to certain chemical reactions. Other trace elements include vanadium (V), chromium (Cr), manganese (Mn), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), silicon (Si), tin (Sn), selenium (Se), and iodine (I).
Chemical Reactions
Chemical reactions occur when the bonds between atoms in a compound are broken down, so that new bonds between atoms may be formed. The most common way is through heat energy. For example, if sugar is heated past a certain point it will turn black, forming carbon, and release water vapor and carbon dioxide. Because most chemical reactions in living organisms use up more energy than they create, living organisms need food for most processes.
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