MCDB 1150 Lecture Notes - Lecture 2: Chemical Polarity, Electron Shell, Covalent Bond
12 Nov 2016
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Chapter 2: water and carbon-the chemical basis of life. An element is a substance that cannot be broken down to other substances by chemical reactions. About 25 of the 92 elements are essential for life. The four main elements are carbon, nitrogen, oxygen and hydrogen that make up 96% of the living matter. Most of the re(cid:373)ai(cid:374)i(cid:374)g 4% of a(cid:374) orga(cid:374)is(cid:373)"s (cid:449)eight consists of phosphorus, sulphur, calcium and potassium. An atom is the smallest unit of matter which still retains the properties of an element. It contains a nucleus which contains protons [+] and neutrons. Electrons are present in clouds are around the nucleus and they can move very fast. It is sum of masses of all components. *the number of protons in an element does not vary-if the ato(cid:373) (cid:373)ass (cid:272)ha(cid:374)ges the(cid:374) it"s a differe(cid:374)t ele(cid:373)e(cid:374)t. Are compounds that have different mass number but the same atomic number and same structure.
