# The ionization energy of hydrogen is often expressed in units other than kJ/mole. What would it be in joules per atom?

Ionization energy of an atom or molecule is the energy needed for a an electron to be removed from gaseous atoms or ions. It is also called Ionization potential.

A ----> A+ + 1e         IE = ___  kJ/mol

It is often expressed in kilojoules per mole.

To...

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Ionization energy of an atom or molecule is the energy needed for a an electron to be removed from gaseous atoms or ions. It is also called Ionization potential.

A ----> A+ + 1e         IE = ___  kJ/mol

It is often expressed in kilojoules per mole.

To convert the units from kilojoule per mole to joules per atom, we have to employ the Avogadro's number (6.022x10^23 atoms / mole)

Let's take the first ionization energy of sodium for example (496 kJ/mol).

First, we convert kJ to J (1000 J = 1 kJ) and then we convert the moles into atoms.

496 kJ/mol x ( 1000J/ 1kJ) x (1mol/ 6.022x10^23 atoms)

= 8.24x10^-19 joule per atom

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