Revision Exercise

What are the limitations of Rutherford model of atom?

You have learnt that the value of e/m for electron is $2000$ times that of the proton or ${\mathrm{H}}^{+}$. Calculate the charge to mass ratio for ${\mathrm{He}}^{+}$ and ${\mathrm{He}}^{2+}$ in comparison to e/m of the electron. Mass of helium is four times that of hydrogen. 

Isotopes of an element differ in the number of neutrons.

Element having electronic arrangement 2, 7 is fluorine.

Matter is electrical and negative in nature.

Mass of electron is about nearly $1840$ times that of proton.

Neutrons were discovered by Henry Becquerel.

Neutron is sum of proton and electron, therefore, it is neutral.