MATRICULATION CHEMISTRY SK015: 3.2 PERIODICITY (ATOMIC RADII, IONIC RADII & ISOELECTRONIC SPECIES)
Summary
TLDRThis educational video delves into the concept of periodicity within the periodic table, focusing on atomic, ionic, and iso-electronic species radii. It explains how atomic radius decreases across a period due to increasing nuclear charge and strengthens electromagnetic attraction. Conversely, it increases down a group due to more electron shells and shielding effects. The video also discusses the trends in the first row of transition elements and the impact of electron configurations on ionic radii, illustrating the differences between cations and anions. Lastly, it touches on isoelectronic species and how their radii are influenced by nuclear charge and electron configurations across periods.
Takeaways
- 🌐 The script discusses the concept of periodicity in the periodic table, focusing on the trends of atomic and ionic radii.
- 🔬 Atomic radius decreases across a period due to increasing proton number and effective nuclear charge, leading to stronger electromagnetic attraction between the nucleus and valence electrons.
- 📉 The smallest atomic radius is found at the far right of a period due to the strongest nuclear-valence electron attraction.
- 📈 Atomic radius increases down a group due to the addition of electron shells and an increase in the shielding effect, which weakens the attraction between the nucleus and valence electrons.
- 🏙️ The largest atomic radius is found at the bottom of a period due to the weakest nuclear-valence electron attraction.
- 🔄 For the first row of transition elements in period 4, atomic radius decreases and then remains fairly constant, influenced by the 3d and 4s orbitals' electron configurations.
- 🔮 Ionic radius is affected by the gain or loss of electrons; anions expand due to electron addition and increased electron-electron repulsion, while cations contract due to electron loss and reduced repulsion.
- 📊 Ionic size decreases across a period for both cations and anions due to increasing nuclear charge and effective nuclear charge.
- 🧬 Isoelectronic species, which have the same electronic configurations, can be compared across periods to understand trends in ionic radii.
- 🔑 The trend in isoelectronic species can be segmented and explained by the number of protons, effective nuclear charge, and the resulting nuclear-electron attractions.
- 🚀 The script also mentions upcoming discussions on other periodic trends such as ionization energy and electronegativity.
Q & A
What is the primary factor affecting atomic radius trends across a period?
-The primary factor affecting atomic radius trends across a period is the increasing proton number in the nucleus, which leads to an increase in effective nuclear charge, resulting in stronger electromagnetic attractions between the nucleus and valence electrons and causing the radius to shrink.
Why does the atomic radius decrease as we move from left to right across a period?
-The atomic radius decreases across a period because the increasing number of protons in the nucleus enhances the effective nuclear charge, leading to stronger attractions between the nucleus and valence electrons, which in turn pulls the electrons closer to the nucleus and reduces the atomic radius.
How does the atomic radius trend when moving down a group in the periodic table?
-When moving down a group, the atomic radius is expected to increase due to the addition of more electron shells. This results in an increased number of electrons and a stronger shielding effect, which weakens the attraction between the nucleus and valence electrons, leading to a larger atomic radius.
What is the shielding effect and how does it influence atomic radius?
-The shielding effect is the phenomenon where inner electrons shield the nucleus from the valence electrons, reducing the effective attraction between them. As a result, the nucleus's attraction towards the valence electrons decreases, leading to an increase in the distance between the nucleus and electrons, and thus a larger atomic radius.
Why does the atomic radius of elements in the first row of transition metals show a noticeable decrease across the first five elements and then remain fairly constant?
-The atomic radius of the first row of transition metals decreases due to the increasing nuclear charge across the period. However, after the first five elements, the presence of 3d inner orbitals filled with electrons shields the 4s orbital more effectively from the nucleus, even as the nuclear charge increases, making the size remain fairly unchanged.
How does the ionic radius differ from the atomic radius and why?
-Ionic radius differs from atomic radius because electrons repel each other. When an atom gains electrons to form an anion, the electron cloud expands, increasing the ionic radius. Conversely, when an atom loses electrons to form a cation, the electron cloud shrinks, decreasing the ionic radius.
What happens to the atomic radius when an atom forms a cation by losing an electron?
-When an atom forms a cation by losing an electron, the electron cloud shrinks due to a decrease in electron-electron repulsions. This results in stronger attractions between the nucleus and the remaining electrons, causing the atomic radius to be smaller than that of the neutral atom.
How does the ionic radius trend when comparing isoelectronic species across a period?
-For isoelectronic species across a period, the ionic radius decreases as the atomic number increases due to the stronger effective nuclear charge. This results in stronger attractions between the nucleus and the electrons, leading to a smaller ionic radius.
What causes the significant jump in ionic radius between cations and anions formed in the same period?
-The significant jump in ionic radius between cations and anions is caused by the difference in the number of electron shells. Cations have fewer shells and thus stronger nucleus-electron attractions, while anions have more shells, leading to increased electron-electron repulsions and a larger ionic radius.
How can the trend of isoelectronic species be segmented and explained?
-The trend of isoelectronic species can be segmented based on the groups of elements with the same electronic configurations. By identifying the species involved and their electronic configurations, one can explain how the trend across a period affects the size of the ions, considering the increasing nuclear charge and the resulting changes in nucleus-electron attractions.
Outlines
🔬 Atomic and Ionic Radius Trends
This paragraph introduces the concept of periodicity within the periodic table, focusing on the atomic radius and its variations. It explains how atomic radius decreases across a period due to increasing proton numbers and effective nuclear charge, leading to stronger electromagnetic attractions and a smaller radius for elements on the right side of the period. Conversely, the atomic radius increases down a group due to additional electron shells and increased shielding effect, which weakens the nucleus-valence electron attraction. The paragraph also discusses the atomic radius trend across the first row of transition elements in period 4 and the concept of iso-electronic species radius, emphasizing the importance of understanding these trends for a comprehensive grasp of periodic properties.
🌐 Understanding Ionic Radius and Isoelectronic Species
The second paragraph delves into the specifics of ionic radius, contrasting it with atomic radius by highlighting the effects of electron addition or removal on size. It illustrates the process of forming ions, such as Cl- from Cl, and explains how the addition of an electron leads to an expansion of the electron cloud and increased electron-electron repulsion, resulting in a larger ionic radius compared to the atomic radius. Conversely, the removal of an electron, as in the case of Na+, results in a smaller ionic radius due to decreased electron-electron repulsion and stronger nucleus-valence electron attraction. The paragraph also explores the trend of isoelectronic species, showing how ionic radii decrease across a period for both cations and anions with the same electronic configurations, influenced by the increasing nuclear charge.
📉 Trends in Ionic Radii Across Periods
The final paragraph continues the discussion on isoelectronic species, emphasizing the trend in ionic radii across period 3. It segments the analysis into three parts, explaining the species involved in each segment and their electronic configurations. The paragraph clarifies how the increase in proton number and effective nuclear charge across a period leads to stronger nucleus-electron attractions and a decrease in ionic size. It also addresses the significant size difference between cations and anions formed within the same period, attributing this to the increased number of electron shells and the resulting higher energy and electron-electron repulsion in anions. The summary concludes with a preview of upcoming topics, such as ionization energy and electronegativity.
Mindmap
Keywords
💡Periodicity
💡Atomic Radius
💡Ionic Radius
💡Isoelectronic Species
💡Effective Nuclear Charge
💡Shielding Effect
💡Transition Elements
💡Noble Gas Configuration
💡Electronegativity
💡Ionization Energy
💡Electromagnetic Attraction
Highlights
Introduction to the sub-topic of periodicity in the periodic table.
Explanation of atomic radius and its three cases: atomic radius, ionic radius, and iso-electronic species radius.
Trend of atomic radius across a period with increasing proton number and effective nuclear charge.
Atomic radius decreases from left to right within a period due to stronger electromagnetic attraction.
Atomic radius increases down a group due to more electron shells and increased shielding effect.
Shielding effect definition and its impact on atomic size.
Trend of atomic radius across the first row of transition elements in period 4.
Atomic size decrease in the first five transition elements, then remains constant due to 3d orbital electron shielding.
Understanding ionic radius and its difference from atomic radius due to electron repulsion.
Process of forming an ion and its impact on size, exemplified by chlorine becoming chlorine minus.
Ionic size decreases when an electron is removed, as seen when sodium becomes sodium ion.
Trend of ionic size across a period and its comparison to atomic size trends.
Introduction to iso-electronic species and their definition.
Trend of iso-electronic species radius across period 3 and its segments.
Explanation of iso-electronic species trend for cations and anions with the same electronic configurations.
Impact of increased number of shells on the size of iso-electronic species.
Upcoming discussion on other periodic trends such as ionization energy and electronegativity.
Transcripts
hello everyone in this video we're going
to learn about a new sub topic in
chapter 3 periodic table called
periodicity
[Music]
the first periodic trend we're going to
look at is radius or the size of the
atom so we could divide this radius
strand into three cases first is atomic
radius
second is ionic radius and the last one
going to be the iso-electronic species
radius
for atomic radius we'll go through the
trend across the period
down a group and across the first row of
transitions elements
first across a period the atomic radius
decreases because we are moving within a
shell
and each element on the right has one
more proton in the nucleus than the one
in the left
so we could say across a period
increasing proton number will also
increase the effective nuclear charge so
this is the most important point for
discussing the trend across a period so
don't forget to include this as part of
your discussions
and then this will result in stronger
electromagnetic attractions between the
nucleus and also the valence electrons
which then will makes the radius shrink
so
the element
in the
far right of the period one will have
the smallest atomic radius
due to the strongest
electromagnetic nucleus valence electron
attraction that results in distance from
the nucleus to be the closest
next is trend when going down a group so
down a group atomic radius of an element
is expected to increase due to
increasing number of shell so in period
one we have one shell period two we have
to shell period three we have richelle
and so forth
so our explanations regarding this trend
we'll start by mentioning by having more
shell obviously the number of electrons
will increase
so by having more electrons means the
shielding effect will also
increase
so what does this shielding effect
really means shelby effect is
an effect caused by the inner electrons
which will shield the nucleus and also
valence electron attractions to be
weakened from time to time
[Music]
since the nucleus attractions towards
balance in electron decreases means the
distance between electrons and nucleus
will also increase
resulting bigger radii
down a group
element that is located at the bottom of
this period one will have the largest
atomic ray dye
due to weakest electromagnetic nucleus
valence electron attractions that
results in existence from the nucleus
the fathers
lastly is the atomic radius across the
first row of transitions element that is
located in period 4 of the periodic
table
so the trend is fairly similar to the
trend across a period which suggests
atomic radius consistently decrease
as for the first row of transitions
element
the atomic size will show a noticeable
decrease across the first five elements
but then starts from here they will
start to remain fairly constant for the
rest of the period
so what what have caused this
so this happens due to massive electrons
occupied by the 3d inner orbitals in
here so we know of all principles
suggests that
4s or metal should comes before 3d
orbital means
the there are already electrons in 3d
orbital so
the 3d inner orbitals
will shield the 4s orbital more
effectively from the nucleus even though
the nuclear charge
increases across the period hence
4 as electrons are not pulled closer
making the size remain
fairly unchanged
apart from knowing atomic radius trend
you also need to know
how to explain the ionic radius so ionic
radius is a little different electrons
repel each other so by adding more
electrons will makes the atom bigger so
to explain the trend you need to compare
the ion to be formed to the apparent
atom
first you need to take out the
electronic configurations for both
parent atom and ion like this so
for example we have these chlorine to
become chlorine minus
then take out the electronic
configurations of 3s2 3p5 to become
3s23p6
then make a storyline of the process
you have to explain
specifically if they already provide you
with the species so we'll start by first
telling the type of ion to be formed and
what should be done so since we could
see
we need another one electrons
to form these octet configurations
means you have to emphasize to form cl
minus
one electron is added from the outer
shell to the 3p orbital in here
once that one electron is added to 3p
orbital so we need to expect the
electron cloud to be expand
and once the electron clock expanded the
repulsions between electrons also
increases
then what happened to the nucleus
valence electron attractions so the
attractions of nucleus towards the
remaining electrons becomes weaker
and lastly will affect the size of
chlorine ion to become bigger than the
cl atom as you can see from these
illustrations
taking one electron out from the parent
atom will makes the ions smaller for
example we have this sodium
to become sodium ion so sodium atom with
configurations of 1s22s22p63s1
in order to achieve stability of octet
configurations we need to remove one
electron from the outer 3s orbital to
form this
sodium ion with configurations of 1s2
2s2 to b6
so by removing electron will results in
the shrink of electron cloud
so we have this one electron to be
removed so the electron clock will
shrink
electron clock string means there will
be decrease in electron electron
repulsions once the electron electron
proportion decrease means the nucleus
valence electron attractions become
stronger
because they are stronger means the size
of sodium ion is smaller than sodium
atom
in short the ionic size decreases across
a period but increases significantly
from cat ion to an ion in here so from
these illustrations we could see
these ion have the same electronic
configurations while these ions have the
same electronic configurations even
though they are located in the same
period but they have different
electronic configurations
so
same electronic configurations will have
their radar decrease as the atomic
number increases across a period by
applying the knowledge of our unit
radius we're going to apply it to
understand the trend of iso-electronic
species
isoelectronic species are groups of
atoms or ions which have the same
electronic configurations as long as
they have the same electronic
configurations whether we mix up the
periods to compare the trend there won't
be any problems
let's see the iso-electronic species
trend across period 3 since we already
looked at the ionic radius of its
element in general before this
neutral atom would give us same
electronic configurations of 1s2 2s2 2p6
therefore we need to first change these
elements sodium magnesium aluminium and
silicon two become ions
so and a m g a l and s i all have
partially filled three s or triple
orbital if we look at the number of
proton given
therefore
they have the tendency to remove
electrons to achieve stable octet
configurations like these
we know the bigger
the nuclear charge
where we could see from the number of
frontend axes
the stronger attractions of nucleus
towards remaining electrons thus the
smaller the species
therefore ionic radii decreases from
sodium ion to magnesium ion to aluminium
ion and to silicon ion
the remaining element
phosphorus sulfur and chlorine located
in group 15 until 17 have the the
tendency to gain electrons to achieve
stable noble gas configurations of 1 s 2
2 s 2 2 p 6 3 s
3 b6
we know when proton number increase
stronger attractions of nucleus and
outermost electron
so we need to expect that chlorine ion
to be formed will have the smallest size
compared to
sulfur ion and also phosphorus ions
therefore ionic radii decreases from
3 3 minus to s to minus 2cl minus
the trend of isoelectronic species could
be explained by segment so from this
example across period 3 there will be 3
segment this is the first segment second
and third
as for the first and third segments you
need to first mention
who are the species involved together
with your electronic configurations so
let's see
we mentioned about this first segment
they are iso electronic so mentioned
about the species and a plus mg2 plus
al3 plus si4 plus they all got 10
electrons with the same electronic
configurations of 1 s2 2s2 to p6 as for
the third segment you can also do the
same
they are isoelectronic from p3 minus to
cl minus all together 18 electrons with
electronic configurations up until 3 b6
next you need to
tell how other species will be affected
by the trend across a period so moving
from sodium ion to silicon ion the
number of protons increased as well as
its effective nuclear charge so the
trend is pretty similar to across a
period for atomic size
and then
what will happen to their nucleus
electron attractions so the nucleus
electron attractions become stronger as
you across this period for both state
for both segments and lastly the trend
in iso electronic species so size of ion
is expected to decrease from na plus to
si4 plus
same goes to p3 minus 2cl minus
we could see there is a great chunk
between cat ion and anion formed in this
period
so this grid jumped is caused by the
increased number of shell
indicates higher energy as we know the
electronic configurations in cation and
n ions here refresh by one shell as i-4
plus got only 10 electrons p3 minus got
18 electrons so when the number of
shells increase the electron electron
repulsion caused by the email orbital
also increase
so that's why the attractions of outer
electrons and the nucleus are shielded
effectively
hence the size increases rapidly
that's all for the first part of 3.2
periodicity discussing about radius or
the size of atom
in the upcoming videos we're going to
discuss about the other periodic trends
such as ionization's energy and
electronegativity
thank you
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