The Atom


The Structure of the Atom

  • protons, neutrons, electrons 
  • most of mass of atom concentrated in nucleu
  • relative mass & charge is used
  • electron: -1, 1/200 mass
  • proton: +1, 1 mass
  • neutron: 0, 1 mass
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Mass Number & Atomic Number

  • mass number: top of element, number of protons & neutrons in nucleus of atom
  • atomic (proton) number: bottom of element, number of protons in nucleus - identifies element 
  • all atoms of same element have same number of protons 
  • sometimes atomic number is left out of nuclear symbol as the symbol tells you its value 
  • for neutral atoms: number of electrons is same as number of protons 
  • number if neutrons is mass number - atomic number 
  • atoms form ions - losing/gaining electrons
  • ions have different numbers of protons & electrons
  • negative ions - more electrons than protons
  • positive ions - fewer electrons than protons 
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  • atoms with same number of protons but different number of neutrons 
  • number & arrangement of electrons decides chemical properties 
  • isotopes have same configuration of electrons - have same chemical properties
  • isotopes do have slightly different physical properties 
  • physical properties depend more on mass of an atom 
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