Atoms & Elements

Atoms & Elements

1. The Nucleus

   • http://www.docbrown.info/page05/page05.htm  Contains more depth & quizzes to test your knowledge
   • The nucleus is found in the middle of an atom and has an overall positive charge

2. Sub-Atomic particles

   • These include protons, neutrons and electrons
     • Protons are positively charged (+1) and have a mass of 1
     • Neutrons have a charge of 0 (neutral) and have a mass of 1
     • Electrons have a charge of -1 and a mass of 1/1800

3. Proton & Mass Number

   • Atomic (Proton) number is the number of protons
     • The number of protons=the number of electrons
   • Mass number is the number of protons and neutrons

4. Symbols

   • Elements can be represented using one or two letter symbols
     • E.g. Carbon=C Symbols save time when writing an equation Remember if it's a two letter symbol, the first letter is capital and the second is lower case e.g. Sodium = Na

5. The Periodic Table

   • http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/ 
   • Vertical columns are called groups and horizontal rows are called periods
     • There are 8 groups and 7 periods
     • All the elements in each group have similar properties e.g the elements in group 0 are all inert

6. Electron Shells

   • Electrons occupy shells called energy levels
     • In the exam, you might be expected to fill in shells. Use the group number to help you fill in the shells e.g Na(Sodium) is in group 1, therefore it has one electron in its outer shell
     • The lowest energy levels are filled first as they're the closest ones to the nucleus
       • http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/periodic_table/electronsrev3.shtml
       • The minimum amount of electrons a shell can hold is 2. The first shell can't hold more than 2 electrons. The second, third, fourth etc can hold a maximum of 8 electrons
         • When outer shells are not full, atoms react to gain an electron or lose an electron depending on the atom it reacts with

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