REVISION atomic structure and bonding

• where is the first energy level located?


  the ring closest to the nucleus
• where is most of the mass of an atom?

  the nucleus
• what gives us relative atomic mass of an element

  protons + neutrons
• what gives us the atomic number 


  no of protons
• what does chromium do with electron configuration?


  one of the 4s electrons gets transferred to 3d to make the atom more stable.

  So, It is 1s2, 2s2, 2p6, 3s2, 3p6, 4d1 and 3d5
• what does copper do with electron configuration?


  one of the 4s electrons gets transferred to 3d to make atom more stable.

  So, its 1s2, 2s2, 2p6, 3s2, 3p6, 4s1 and 3d10
• what happens to electron configuration when a transition metal loses electrons to form ions?


  the electrons are lost from the 43 sub shell first not 3d.