chemistry notes for IGCSE students.

7. Comparison of properties ofconstituents of atom No Properties electron proton neutron 1. Symbol e p n 2. Relative charge -1 +1 0 3 Relative mass 0 1 1 4. Position Outside the nucleus In the nucleus In the nucleus 5. Discovered by J.J Thomson E. Goldstein James Chadwick

10. The shell closest to the nucleus has n=1 . Hence the maximum number of electrons in different shells are as follows; First orbit or K shell =2x1 2 = 2 Second orbit or L shell =2x 2 2 =8 Third orbit or M shell = 2x3 2 =18 and so on.

21. Atomic Number ( z) The number of protons present in the nucleus of an atom of an element is called its atomic number.

36. Relative atomic mass and Relative formula mass (RAM and RFM)