basicchemistry - In this section: Living organisms and...

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In this section: Living organisms and chemistry | Atoms | Elements | Compounds | Mixtures | Chemical bonds | Molecules | Test your knowledge Some basic chemistry Living organisms and chemistry Biology is about living things - organisms. All living organisms are made of chemicals. To understand biological substances and the changes that take place in living organisms you need a good knowledge of the underlying chemistry. We will build up a picture of the chemicals that make up living organisms by starting small and getting bigger. The starting point is atoms - the building blocks of all matter. We will then look at how these come together to make elements and compounds. Atoms Atoms are the building blocks of all matter. They consist of three sub-atomic particles: protons , neutrons and electrons . Protons and neutrons are found in the nucleus of an atom. Electrons are found in energy levels around the nucleus as shown in the diagram representing a carbon atom with 6 protons, 6 neutrons and 6 electrons. Sub-atomic particles Particle Whereabouts in atom Relative mass Charge Proton Nucleus 1 +1 Neutron Nucleus 1 0 Electron Outside the nucleus 1 / 1840 -1
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Diagram of carbon atom - nucleus with electrons orbitin g In chemistry we are particularly interested in electrons. As you will see later, this is because chemical reactions involve the rearrangement of electrons. Nuclei of atoms (protons and neutrons) usually remain unchanged (except in radioactive decay). Electrons are arranged in atoms according to their energies. This is called the electronic structure or electronic configuration of the atom. A crude but still useful model says the electrons can be in different energy levels. Electrons in a particular energy level all have the same energy as one another. The lowest energy level can accommodate up to 2 electrons. The second level can accommodate up to 8 electrons. The third level can accommodate up to 18 electrons. The diagram shows the situation for a sulfur atom. Importantly it's only electrons in the outermost energy level of an atom that are involved in chemical bonding. Elements An element is a substance made up of atoms with the same number of protons. Elements are the simplest substances known. They can be metals (e.g. iron, copper, sodium magnesium) or non-metals (e.g. carbon, hydrogen, oxygen, nitrogen). There are just over 100 of them. Each element has its own: name and chemical symbol characteristic physical properties, e.g. density, electrical conductivity, melting point and boiling point characteristic chemical properties, e.g. reactions with water, oxygen, acids and other
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chemicals These physical and chemical properties do not change. They can be used to identify an element. Elements are listed in the Periodic table . Many elements have different
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This note was uploaded on 12/14/2009 for the course BIO1A 0012349 taught by Professor Durkka during the Spring '09 term at École Normale Supérieure.

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basicchemistry - In this section: Living organisms and...

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