![]() Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone. The body's circulatory system transports the oxygen to the cells, where cellular respiration takes place. In tetrapods breathing brings oxygen into the lungs where gas exchange takes place, carbon dioxide diffuses out of the blood, and oxygen diffuses into the blood. Īll plants, animals, and fungi need oxygen for cellular respiration, which extracts energy by the reaction of oxygen with molecules derived from food and produces carbon dioxide as a waste product. Oxygen makes up almost half of the Earth's crust in the form of oxides. Diatomic oxygen gas currently constitutes 20.95% of the Earth's atmosphere, though this has changed considerably over long periods of time. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula OĢ. Oxygen is Earth's most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is the chemical element with the symbol O and atomic number 8. Diamond and graphite, two forms of carbon and compounds like silicon dioxide and silicon carbide are all covalent networks. A covalent network structure consists of a giant 3-dimensional lattice of covalently bonded atoms.īoron, carbon and silicon are all examples of covalent network elements. Substances that consist of covalent molecules are usually gases or liquids at room temperature because the attractions between molecules are weak and easy to overcome.Ĭovalent substances that are solids with high melting points have much larger molecules. Oxygen molecules have a double bond: two shared pairs of electrons. Examples of these are diatomic oxygen (double bond) or nitrogen (triple bond). More than one bond can be formed between atoms leading to double and triple bonds. The oxygen forms two single covalent bonds with the two hydrogen atoms. Oxygen atoms have six outer electrons so need two more for a full outer shell. The shape formed is called trigonal pyramidal. Nitrogen forms three single covalent bonds to hydrogen atoms. Nitrogen atoms have five outer electrons so needs three more for a full outer shell. A methane molecule has four shared pairs of electrons Ammonia (NH 3 ) The carbon forms four single bonds to the hydrogen atoms, so all the atoms now have a full outer shell of electrons. Methane (CH 4 )Ĭarbon atoms have four outer electrons so need four more for a full outer shell. A shared pair of electrons between two hydrogen atoms The shape of the molecule formed is called linear. Hydrogen (H 2 )īoth hydrogen atoms have only one electron, but by forming a single covalent bond, both can have a full outer shell. If you remember " I Br ing Cl ay F or O ur N ew H ouse” then you will have remembered that the seven diatomic elements are Iodine, Bromine, Chlorine, Fluorine, Oxygen, Nitrogen and Hydrogen.ĭiagrams can be used to show how the outer electrons are shared to form the covalent bonds in a molecule. There are seven diatomic elements that you have to remember and a simple mnemonic to help with this. A molecule is a group of atoms held together by covalent bonds.Ī diatomic molecule is a molecule containing only two atoms. Covalent bondingĪ covalent bond is a shared pair of electrons between atoms of two non-metal elements.Ī covalent bond happens when the positive nuclei from two different atoms are held together by their common attraction for the shared pair of electrons held between them.Ītoms that share pairs of electrons form molecules. There are different types of bonds that hold atoms together. To achieve a stable electron arrangement atoms can lose, gain or share electrons. ![]() When atoms form bonds, they can achieve a stable electron arrangement. Atoms can be held together by chemical bonds.
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