(a) Where is the nucleus of an atom situated ?
(b) What are orbits or shells of an atom ?
(c)What are isotopes ? How does the existence of isotopes contradict Dalton's atomic theory ?
(a) What are valence electrons? Where are valence electrons situated in an atom ?
(b) What is the number of valence electrons in the atoms of an element having atomic number 13 ? Name the valence shell of this atom.
An atomic nucleus A is composed of 84 protons and 128 neutrons.
The atomic nucleus A emits an alpha particle and is transformed into nucleus B. The atomic nucleus B emits a β - particle and is transformed into a nucleus C. What is the composition of atomic nucleus C?