Structure of the atom

• The nucleus is made up of protons (positive charge) and neutrons (no charge).
• Atoms can be represented as spheres with a central nucleus containing protons and neutrons surrounded by orbiting electrons.
• E Goldstein and J J Thomson discoverd proton and electron 


  J J Thomson- electrons are embedded in a positive sphere
• Rutherford's experiment - alpha particles fired at gold foil, some deflected but most passed through, concluded that there was a small dense positively charged centre called the nucleus
• Rutherford alpha scattering experiment: discovery of nucleus
• Rutherford's model: very tiny nucleus, electrons revolve around this nucleus.
• Nelis Bohr's model: electrons are distributed in diff shells with discrete energy around nucleus.
• If atomic shells are complete then the atom will be stable and less reactive
• Atomic number = no of protons (positive charge)
• Mass number = total # of protons + neutrons
• Isotopes have same atomic number but different mass numbers due to differing amounts of neutrons
• Mass number = sum of protons + neutrons
• Isotopes have same atomic number but different mass numbers
• Relative atomic mass is average mass of all naturally occurring isotopes
• Relative atomic mass is average mass of all naturally occurring isotopes of an element
• Ions are atoms that have gained or lost electrons to achieve a full outer shell
• J Chadwick : presence of nucleus
• Mass of electron : 1/2000 times of mass of an hydrogen atom
• Proton+ neutron = 1 unit
• Atomic number (Z) - number of protons in the nucleus
• Nuclear model - Rutherford, Bohr, Chadwick
• Isotope - same number of protons but different numbers of neutrons
• Mass number (A) - total number of protons + neutrons in the nucleus
• K L M N : shells of atom
• Valency is combining capacity of an atom
• Atomic number = no. Of protons
• Mass number = protons+ neutrons
• Electrons are defined by the number of protons they possess