Video Transcript
Atoms change from the ground state
to the excited state when they gain energy. Which of the following figures
shows an excited-state atom?
This question is asking us to
determine what the diagram of an excited-state atom will look like. When an atom is in an excited
state, it does not have all electrons in the lowest possible energy state. For an atom to become excited, it
starts from its ground state, which means it does have its electrons in their lowest
possible energy states.
All of the figures in the answer
choices are diagrams of atoms like this one. The amount of energy of the levels
shown, K, L, M, N, is related to its distance from the nucleus. For example, level N is the
farthest from the nucleus and thus has the highest amount of energy of the four
levels. Each level can hold a maximum
amount of electrons, with level K holding up to two, level L holding up to eight,
and level M holding up to 18.
The energy levels are filled with
electrons by filling lower energy levels first. Let’s look at an example of a
diagram of an atom with three total electrons. The energy levels will be filled
from lower energy to higher energy. And the first electron is in energy
level K. Energy level K can hold up to two
electrons. So the next electron will also be
in the K energy level. With two electrons, energy level K
is filled. And so the third electron must be
in the next energy level. The third electron will be found in
the energy level L. This diagram represents the ground
state of an atom with three electrons, where all the electrons are in the lowest
possible energy states as expected.
The diagram of an excited-state
atom would not be filled as expected. One of the electrons might absorb
enough energy to move into a higher energy level. Because this electron is not in its
lowest possible energy state, this diagram now represents an excited-state atom.
Answer choices (B), (D), and (E)
have level K filled and the first two electrons are in their lowest possible energy
state. The rest of the electrons of (D)
and (E) are also filled in order, and none are occupying a higher energy level than
expected. These three figures show atoms in
their ground state, and so we can eliminate them.
Answer choice (A) does not have its
level K filled. However, this atom contains only
one electron. Because its single electron is in
its lowest possible energy state, we can eliminate it.
Finally let’s look at answer choice
(C). This atom also contains only one
electron and seems to have gained energy. It is not in the lowest possible
energy state. Thus, the atom represented in the
figure of answer choice (C) is in an excited state.
So the figure that shows an excited
state atom is answer choice (C).
