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Chemistry - Atomic Structure Week 1 Grade 7 Thursday Atomic Structure Atomic number = number of protons Atomic number = number of electrons in a neutral atom (not an ion) Atomic weight - atomic number = number of neutrons Isotopes have different numbers of neutrons, H normally has 0 neutrons Neutrons Protons are all positively charged. If left alone, they would repel each other. Neutrons provide additional mass that is neutral and can keep the nucleus together. Hydrogen doesn’t have one because its one proton can’t repel itself... Valance Valance is the number of electrons an atom will donate or accept during a reaction Usually, it is the lower of: the number of electrons in the outermost shell OR the number of empty spaces in the outermost shell. Valance Anything with a filled outer shell has a valance of zero. Carbon is AMAZING - it has exactly half of its shell filled (4 out of 8) so it is incredibly versatile in what it will accept or donate. No wonder life is based on it! Building Atoms, Element by Element Start with one of the blank atomic diagrams. Add the number of protons, and the number of neutrons. Add the electrons into positions on the shells, innermost shell first. Building Atoms, Element by Element Hydrogen 1 __p __n 0 Helium Carbon 2 __p __n 2 6 __p __n 6