Video Transcript
The energy needed to ionize a
valence electron from an atom of zinc is 1.50 times 10 to the negative 18th
joules. What is this value in electron
volts, eV? Give your answer to two decimal
places.
In this question, we have been
given the amount of energy required to ionize a valence electron from an atom of
zinc. This amount of energy is the
ionization energy, most likely the first ionization energy, which is the amount of
energy required to remove the most loosely bound electron completely from an
isolated gaseous atom.
We’ve been given the ionization
energy measured in the unit joules. The joule is the SI unit for
energy. One joule is the quantity of energy
needed to raise the temperature of one gram of water by one divided by 4.184 degrees
Celsius. A joule is a rather small amount of
energy. For example, the energy contained
in a single slice of bread is approximately 250000 joules. But we can see from the question
that the amount of energy needed to ionize a valence electron from an atom of zinc
is many times smaller than a single joule. So the unit joule is not always the
most practical when working with energy on an atomic scale.
When working with energy on an
atomic scale, scientists often use the unit electron volts. One electron volt is the energy
gained by an electron when it is accelerated through a potential difference of one
volt. One electron volt is equal to 1.602
times 10 to the negative 19th joules. We can use this relationship to
convert the energy in joules into electron volts.
To do this, we need to multiply
1.50 times 10 to the negative 18th joules by the conversion factor written as a
fraction. We’ll need to write the conversion
factor with one electron volt in the numerator and 1.602 times 10 to the negative
19th joules in the denominator. This will cancel out the joule
units, leaving us with electron volts. Performing the calculation gives us
an answer of 9.363 electron volts.
But the question asks us to give
our final answer to two decimal places. Rounding to two decimal places, we
have determined that 1.50 times 10 to the negative 18th joules is equivalent to 9.36
electron volts.
