Electron Configuration Shorthand

Name: Valence Electrons
Uploaded: 2015-05-07T14:37:28+00:00
Duration: 15 min 23 s
Channel: Saylor University
Description: Summary and key takeaways on Valence Electrons: Summary & Key Takeaways, covering Electron Configuration Shorthand Noble‑gas notation condenses electron

Saylor University

May 07, 2015

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15 min video

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2 min read

YouTube video ID: _EQTOrfRS9w

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Noble‑gas notation condenses electron configurations by replacing the inner‑core electrons with the symbol of the preceding noble gas. For example, iron is written as [Ar] 4s² 3d⁶, indicating that the electrons of argon are assumed and only the outer shells are shown. In the d‑block, electrons backfill the previous shell; the fourth period fills the 3d subshell before completing the 4p level. This backfilling occurs because, as atoms enlarge, the energy gap between earlier orbitals widens, allowing lower‑energy placement of electrons in inner shells.

Valence Electrons and Periodic Groups

Valence electrons are those residing in the outermost shell. Elements that share a column in the periodic table possess the same number of valence electrons, which explains many of their chemical similarities. For d‑block elements, the outermost electrons are typically the two s‑orbital electrons of the current period, while transition‑metal d‑electrons belong to a lower shell. Lewis dot symbols depict these outer electrons as dots around the element’s symbol.

The Octet Rule

Atoms strive for a stable configuration of eight electrons in their outermost shell—a principle known as the octet rule. Hydrogen and helium are notable exceptions; they achieve stability with just two electrons occupying their single shell. The preference for eight electrons reflects a fundamental property of nature, likely tied to resonance and electron repulsion. As one speaker put it, “It turns out that all atoms want to have eight electrons in their outermost shell.”

Predicting Reactivity

Reactivity follows directly from the drive to complete an octet. Alkali metals in Group 1 have one valence electron and are highly reactive because they “want” to lose that electron and attain a full outer shell. Halogens in Group 17 possess seven valence electrons and are equally eager to gain one electron to complete their octet. This electron‑donor or electron‑acceptor behavior defines metallic nature: “When people in chemistry talk about metallic nature, they're really talking about how badly something wants to give away electrons.” Electron transfer between an alkali metal and a halogen therefore underlies many common chemical reactions.

Takeaways

Noble‑gas shorthand replaces inner electrons with the preceding noble gas, making configurations like iron’s [Ar] 4s² 3d⁶ concise.
Elements in the same periodic group share the same number of valence electrons, which governs their chemical similarity.
The octet rule states that atoms seek eight outer‑shell electrons for stability, with hydrogen and helium as two‑electron exceptions.
Alkali metals lose one electron to achieve an octet, while halogens gain one, driving their high reactivity.
Metallic nature describes an element’s tendency to donate electrons, a key factor in predicting electron‑transfer reactions.

Frequently Asked Questions

Why do alkali metals readily lose an electron?

Alkali metals have a single valence electron in their outermost s‑orbital, and losing that electron gives them a full octet, which is a highly stable configuration. This strong drive to achieve an octet makes them extremely reactive electron donors.

What makes hydrogen and helium exceptions to the octet rule?

Hydrogen and helium each have only one electron shell, so they reach stability with two electrons rather than eight. Their single‑shell structure means a filled 1s orbital satisfies the energetic requirement for a stable atom.

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Helpful resources related to this video

If you want to practice or explore the concepts discussed in the video, these commonly used tools may help.

Large Laminated Periodic Table Of Elements Recommended

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Chemistry Molecular Model Kit For Students

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General Chemistry Textbook For College Students

Offers comprehensive explanations and practice problems for electron configurations, periodic trends, and chemical reactivity.

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Dry Erase Whiteboard For Chemistry Study

Provides a space to practice writing out complex electron configurations and drawing Lewis dot structures.

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Full Transcript YouTube

so far we've learned a little bit about
determining electron configurations
let's see if we can use that information
to group elements on the periodic table
and then guess as to what they might do
when they react with other elements so
let's just figure out the electron
configurations a couple of elements just
for a little bit of practice so lithium
right there what does it look like
lithium's electron configuration you get
the first shell is 1 S2 2 electrons
there and then you have 2 S1 and
sometimes just to be quick to get the
notation as you can imagine lithium's
electron configuration is the exact same
thing as helium's electron configuration
this is helium's electron configuration
plus the 2s1 so this could have also
been written as do it in light blue
could have written been written as
helium 2 S1 which essentially means that
lithium's electron configuration is
exactly what you would have written for
helium's electron configuration and then
you would have written 2s1 you could do
that a bunch of times let's say if we
wanted to figure out the electron
configuration of
iron instead of going through the whole
thing you know it's 1 S2 and then it's
2s2 and 2 P6 instead of doing that whole
thing you could just say Okay iron has
the same electron configuration so you
could say right iron electronic
configuration is the same thing as
argon is the same thing as argon's
electron configuration so I'll just put
argon in
Brackets and then you get what is this 4
S2 4
S2 and then you have 1 2 3 4
56 six so D6 and we learned that when
you're in the in the D subshell or when
you're in the d block of the periodic
table you are actually adding you're
backfilling the previous shell so where
we in the fourth period in the D Block
we're backfilling the third shell so
three D6 and someone had asked and this
is an interesting question why does it
do that why does it not just Contin why
doesn't it fill the fourth D shell and
the way I think about it and this is all
intuition and and things at the atomic
level really start to become on some
levels not inuitive but the way I think
about it is as the atom grows larger and
larger there are more spaces between the
previous orbitals for example and this
is kind of just a you know this is just
how I visualize it is as if you know my
first shell looks like this let's say
the S looks like this and then if I just
cut it out let's say the P's look like
something like
this let's say the P's look like this
this is maybe in the second
shell the P's look like this and then
the next place that an electron might
want to be might be in the third shell
right so the Third
shell would be like
this and then you fill out the third P
shell and I don't know it's I'm just
this is just an intuition this isn't
exactly what electron look like maybe
the third P shell it looks something
like
that looks something like
that and then looks something like that
and then you're in the fourth shell so
you're doing you know the fourth shell
you might be the S subshell might look
something something like
that and then instead of immediately
starting the next p shell you're in the
d block now so this might be so this is
you know let me just write some labels
so this is this is
4S this is
3s this is 3 p this is 2 p this is
2s 2s in there and then One S is inside
of 2s so you don't have to worry about
that too much but my intuition behind
why the D orbital gets backfilled is
because now as as the atom gets larger
and larger you have these spaces in
between the previous orbitals so now
after
filling after filling the
4S subshell or the 4S
orbital so this is 4S here after filling
this out here we go back and we fill in
the 3D orbitals so we're going back and
we're filling D spaces right
here
so this is a lower energy State than
this it takes more energy to to cram an
electron back into the 3D Shell back
there but then once you do that now
you're ready to then add back you go to
the four P shell which might look
something like which might look
something like this so an electron would
rather go to another shell which is the
fourth shell rather than backfill the
three the 3D Shell sorry the 3D shells
but once it fills out the fourth shell
then it fills in those spaces in in
between and as the electron gets bigger
and bigger there's more and more spaces
in between So eventually when the
electron gets big enough there's going
to be spaces between the D shells and
that's where the F subshells or the the
D orbitals and that's where the F
orbitals will go that's my intuition
behind it's working and obviously when
we're dealing at the atomic scale as as
far as I'm concerned that's the best
that I can do but fair enough that's not
what I wanted to do here but that was a
good question as to you know why do you
go and backfill the third shell when
we're in the fourth period Fair enough
this is an easy way to write um to write
Iron's electron configuration the reason
why I'm doing all of this is to just
figure out how many electrons you have
in the outermost shell in the case of
lithium you have one electron in your
outermost shell right this is your
outermost shell right here you have one
electron and you could have done the
same thing right there in the case of
iron how many electrons in the outermost
shell remember the outermost shell is
the period you're in and this is the
outermost shell so even though these are
higher energy electrons it took more
energy to backfill those into the lower
energy shell it's these that are on the
outside energy shell the fourth shell
that are going to be the ones that are
reacting and how many are there there
are
two and this is an important thing so
there's two here there's two on their
outside shell here and actually there's
going to be two for any of these in pink
right here any of the ones in the D
Block what happens you go you fill
whatever period you're in let's say
you're in period five here right you're
going to have 5 S1 5 S2 and then you're
going to go back and you're going to
fill the 4D shell right but in terms of
how many electrons you have on the
outside shell in this case the fifth
shell you're going to have two electrons
so all of these are going to have two
electrons in their outermost
shell in the case of these the outermost
electrons are going to be
4s2 right cuz then you go back backet
fill the 3D but the outer ones are 4s2
so this one also has two electrons in
its outermost shell how many do the does
this group have and I I've just used a
word that I don't know if I've defined
before but the groups are the columns in
the periodic table and as you can see
they all have kind of patterns to them
that everything in this first group has
one electron in its outermost shell if
you don't believe me look at hydrogen
what's the hydrogen's electron
configuration is 1 S1 it's OU shell is 1
s and has one electron there right and
that's true for all of these all of
these guys have two electrons in their
outermost shell these guys have those
same two electrons we can view it that
way in their outermost shell but then
they go and back fill the D shell but if
in terms of their outermost shell only
two electrons then once you fill the d
block or you go back fill you know in
the case of the fourth period you go and
backfill the the third D suborbital then
you go back to to filling the fourth
shell again now the P block right so
this one's going to have
three
three electrons and its outside orbital
or you could say three veence electrons
this is four 5 6 7 and 8 let me do one
more just in case you don't believe me
what's the electron configuration
for oh I don't know what is SN this is
what Selen
I think I'm not even sure but let's say
SN what's the electron configuration
it's going to have the same electron
configuration as
Crypton yes that element is Krypton
there is such an
element so it'll have the same electron
configuration as Krypton so I could have
figured out krypton's electron
configuration just by going through the
whole periodic table but this is just a
faster way of doing it same thing as
Krypton and then it has 5
S2 5
S2 then it goes back back and back fills
the D Block so then there's 10 there so
4
d10 4
d10 and then it starts filling up the P
Block in the fifth shell again so 5
P2 5 P2 so how many veence electrons
does it have where veence electrons or
electrons in the outermost shell well
what's the outermost shell it's the
fifth shell so it's
these and these These are these
electrons have a higher energy State
than that it would took a little bit
more energy to cram them back into that
previous shell than it took to put these
on the the S orbital but if you talk
about the electrons that will react and
that's why I'm emphasizing these These
are the electrons that are going to
react with other uh other atoms or
sometimes with just kind of the other
electrons even this one has four outside
electrons and you see that right there
four outside electrons and since the
outside electrons are for the most part
the ones that you're going to care about
there's a you you there's a a I guess
you could say a notation where you only
draw the outermost electrons so let's
say for hydrogen you could write it like
this you're only drawing the outermost
veence electrons veence electrons are
just the outermost electrons you could
write it like that you could write it
like that but this says Hey I just have
one outside electron for hydrogen if I
wanted to draw it for iron iron right
here how would I do that I have two
electrons in my outermost shell so iron
I could just do like
this and electrons they tend to be
paired so you you you you know if I have
let's say I wanted to take the example
of if this is SN this is selenium let me
do carbon carbon I have four electrons
in my outermost shell so carbon I could
write like this
carbon I could write like that or if I
didn't want to pair them if I didn't
want to pair them in theory I could
write them like
that as well and now they're ready to
react with other things now what does
this tell me about you know this one has
one electron in its outermost shell this
one these blue these noble gases and
we'll talk a little bit about them in in
a second these have eight electrons in
the outermost shell how does that help
me when I'm actually trying to figure
out how things react well it turns out
that all atoms want to have eight
electrons in their outermost shell and
that number is important eight
they want to have
eight eight electrons in their outermost
shell this is the most stable
configuration for atoms or I guess you
could say to some degree a better energy
State for the atom and why is it the
number eight well that's something to
think about this is just another um this
is another kind of fundamental number
that just pops out of Nature and I've
thought a little bit about it it must be
something about the atoms when you know
on the outermost shell when you have
eight they resonate well with each other
and they they I don't know they and
somehow don't get in the way of each
other or don't want to push away from
each other I don't know the answer to
that and frankly if someone could really
answer the question of
why why8 exactly why8 they you know
maybe that's that they they they they
make a good career for themselves in
physics or chemistry but through
experimentation it has been well
established that atoms want to have
eight electrons in their outermost shell
so the question is if you're dealing
with something like let's say you're
dealing with pottassium
right potassium has one electron in its
outermost shell and then you have stuff
like let's say you have stuff like
chlorine chlorine that has seven
electrons in its outermost shell what do
you think's going to happen if you put
some potassium in in near some chlorine
what's going to happen well what's the
easiest way for the chlorine to get to
to get to the uh to to get eight
electrons well it has seven in its
outermost shell what's the easiest way
well it'll want to gain an electron
really really badly and what's the
easiest way for potassium to have eight
electrons in its outermost shell well if
it lost that one electron then it will
have eight electrons in its outermost
shell right its outermost shell won't be
the fourth shell anymore it'll be the
third shell but it'll have eight
electrons in the third shell its
configuration will then look like argon
if it loses that that one electron so
and so it'll be in a kind of a more
stable state so if you put sodium in the
presence of chlorine what's going to
happen this electron wants to jump off
of sodium real bad so that sodium can
have eight electrons in its outermost
shell or have an electron configuration
like argon and that electron is going to
jump to chlorine and then chlorine will
have eight electrons in its outermost
shell and also have electron
configuration like argon and so as you
can imagine these things this group
right here which are called The Alkali
Metals alkal metals and we'll talk
probably in the next video why they're
called Metals this group here alkal
metals and they tend to exclude hydrogen
and we'll talk about that and these
really want to give away electrons and
because of that they're highly highly
reactive especially if you put them in
the presence of these elements these
yellow elements right here which are
called the halogens these really really
want to take electrons from other things
because they just need one to get to
eight these really want to give away
electrons cuz they just have to give
away one to get to eight and the reason
why hydrogen actually isn't included is
because hydrogen doesn't want to give
away its electron as bad as these guys
hydrogen this eight this rule that your
outermost shell wants to get to eight
that's true for everything except for
hydrogen and helium hydrogen and helium
just because they have one shell they're
happy with just two electrons and so
with hydrogen sure it could Lo it could
lose an electron but could just easily
gain an electron and be happy because
it'll have a full first shell but all of
these other ones these alkal metals they
want to give away electrons really bad
when people in chemistry talk about
metallic nature they're really talking
about how badly something wants to give
wants to give away electrons anyway I'm
all out of time now in the next video
we'll continue discussing the groups and
the periodic tables and any Trends we
can ascertain from them