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About 99% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Only about 0.85% is composed of another five elements: potassium, sulfur, sodium, chlorine, and magnesium. All 11 are necessary for life.
A large fraction of the chemical elements that occur naturally on the Earth's surface are essential to the structure and metabolism of living things. Four of these elements (hydrogen, carbon, nitrogen, and oxygen) are essential to every living thing and collectively make up 99% of the mass of protoplasm. [1]
Democritus wrote that atoms and void are the only things that exist and that all other things are merely said to exist by social convention. [10] The objects humans see in everyday life are composed of many atoms united by random collisions and their forms and materials are determined by what kinds of atom make them up. [10]
Because atoms and molecules are said to be matter, it is natural to phrase the definition as: "ordinary matter is anything that is made of the same things that atoms and molecules are made of". (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and ...
In a biochemistry that used sulfuric acid as a solvent, the alkene group (C=C), with two carbon atoms joined by a double bond, could function analogously to the carbonyl group (C=O) in water-based biochemistry. [43] A proposal has been made that life on Mars may exist and be using a mixture of water and hydrogen peroxide as its solvent. [79]
Carbon atoms bond readily to other carbon atoms; this allows the building of arbitrarily long macromolecules and polymers in a process known as catenation. [ 20 ] [ 21 ] [ 22 ] "What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorus", per Stephen Hawking in a 2008 lecture ...
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In terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen (H) atoms to one oxygen (O) atom (H 2 O). [33] Because the O–H bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge. [33]