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Unformatted text preview: 10 1 Dr Lisa Chemistry Sheet for Microbiologists! (you need all the help you can get!!) Atoms, Elements and Compounds The smallest unit of matter having the characteristics of a specific element is called an _________. All matter (bacteria, paper, plastic, soil, water, humans) is made of ____________. The central nucleus of an atom is made up of neutrally charged sub-atomic particles called ______________ and positively charged particles called ______________. Each one of these subatomic particles has a mass of ______________. The nucleus does not take part in reactions and is stable. Negatively charged subatomic particles called _______________ have virtually no mass & surround the nucleus in set arrangements according to their energy level called ____________. The stability of an atom depends on how many ______________ it has and how they are arranged. Electrons are important because they take part in _____________ reactions. Atoms always start out with a ___________ charge because there are always the same number of ____________ as _____________ before an atom undergoes a reaction. Each atom has its own specific position & symbol in the _____________ table. Elements are listed in order of their _____________________ and are arranged by their chemical properties. Atoms with the same atomic number will always react the same way. The atomic number tells you the number of __________ in an atom and also if the atom is neutral it will tell you the number of ____________ present before any reactions have occurred. Notice that next to each element there is a second, larger number called the ______________________. The atomic mass tells you the number of _____________ and _________________ present in the nucleus. The number and arrangement of electrons determines the __________ of an atom. Electrons are arranged in shells. The shell closest to the nucleus is the 1 st shell (lowest energy electrons) & will hold a maximum of ____ e-. The 2 nd shell will hold up to ______e-. When drawing the structure of an atom, you fill the 1 st shell first & when filled go on to fill the next…… Most biologically important atoms have fewer than three shells. Eg Carbon, atomic no. is 6, atomic mass is 12.011 therefore a neutral atom will have 6 protons, 6 electrons & 6 neutrons. The 1 st shell will have 2 e-, & the 2 nd (outermost) shell will not be full having only 4 e-. The outer most shell in any atom is known as the _____________ shell & determines the stability of any given atom. Atoms with ________ outermost shells are always stable & unreactive while those with ________ outermost shells are unstable. Chemists talk about the __________ rule. Why is neon (Ne 10, 20.179) stable?______________________________________________________ Atoms strive to become ___________ by achieving a full outer most shell. This process is called a ____________________ and may occur by gaining, losing or sharing electrons. The valency of an atom is the number of ______ which an atom needs to gain or lose to become stable. Atoms with 5 or more e- is the number of ______ which an atom needs to gain or lose to become stable....
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- Summer '11