Ionic Radius Trends, Basic Introduction, Periodic Table, Sizes of Isoelectric Ions, Chemistry
Summary
TLDRThis video explains the concept of ionic radii and how ion sizes change across the periodic table. It highlights trends such as ions getting larger as you move down a group and smaller as you move right across a period. The video also explores differences between cations (positively charged ions) and anions (negatively charged ions), noting that anions are generally larger due to additional electrons. Multiple examples, including magnesium, beryllium, calcium, and bromide ions, are used to illustrate these trends and how nuclear charge and energy levels influence ionic size.
Takeaways
- 🔍 Ionic radii follow the same trend as atomic radii, increasing as you go down a group in the periodic table.
- 🔬 Positively charged ions (cations) decrease in size from left to right across a period.
- ⚖️ Cations with higher positive charges are smaller than those with lower charges (e.g., Al3+ is smaller than Mg2+).
- 🔄 Negatively charged ions (anions) are generally larger than positively charged ions.
- ⬆️ Anions increase in size as the negative charge increases (e.g., O2- is larger than F-).
- 📉 Ionic radii decrease as effective nuclear charge increases, making cations smaller.
- 📏 Beryllium (Be2+) is smaller than magnesium (Mg2+) because it is higher in the periodic table.
- 🧲 Bromide (Br-) is larger than potassium (K+), because anions are larger due to electron gain and increased electron repulsion.
- ⚛️ The sodium atom (Na) is larger than the sodium ion (Na+) because the loss of an electron reduces the number of electron shells.
- 🔋 Isoelectronic ions have the same electron configuration but vary in size based on their charges, with the most negatively charged being the largest (e.g., O2- > F- > Na+ > Mg2+).
Q & A
What trend does ionic radii follow in the periodic table?
-Ionic radii increase as you move down a group and decrease as you move across a period from left to right.
Why is the potassium ion (K⁺) larger than the lithium ion (Li⁺)?
-The potassium ion is larger than the lithium ion because it is lower in the periodic table. As you move down a group, the number of energy levels increases, resulting in a larger ion.
How do the sizes of cations compare to anions of the same element?
-Cations (positively charged ions) are smaller than anions (negatively charged ions) of the same element. This is due to the loss of electrons in cations, which reduces electron-electron repulsion and energy levels, while anions gain electrons, increasing the electron cloud.
Why is the magnesium ion (Mg²⁺) smaller than the sodium ion (Na⁺) despite being in the same period?
-Magnesium ion is smaller than the sodium ion because it has a higher positive charge (+2 vs +1), which increases the effective nuclear charge, pulling the electrons closer and reducing the ionic radius.
How does the charge of an ion affect its size?
-The more positive the charge on an ion, the smaller the ion. The more negative the charge, the larger the ion. Positive charges reduce electron-electron repulsion, shrinking the ion, while negative charges increase repulsion, expanding the ion.
What is the size of the bromide ion (Br⁻) compared to the potassium ion (K⁺), and why?
-The bromide ion is larger than the potassium ion. Bromide has 36 electrons, which occupy more energy levels and create more electron-electron repulsion, making it larger than the potassium ion with only 18 electrons.
Why are cations smaller than their parent atoms?
-Cations are smaller than their parent atoms because they lose one or more electrons, resulting in fewer electron shells and reduced electron-electron repulsion, making the ion more compact.
Why are anions larger than their parent atoms?
-Anions are larger than their parent atoms because they gain one or more electrons, increasing electron-electron repulsion and expanding the electron cloud, making the ion larger.
What is the general rule for the size of isoelectronic ions?
-For isoelectronic ions (ions with the same number of electrons), the more positive the charge, the smaller the ion. Conversely, the more negative the charge, the larger the ion.
Why is chloride (Cl⁻) larger than chlorine (Cl) even though both have the same number of energy levels?
-Chloride is larger than chlorine because the extra electron in chloride increases electron-electron repulsion, causing the electron cloud to expand, making the anion significantly larger than the neutral atom.
Outlines
📏 Ionic Radii and Ion Sizes
The ionic radii trend follows the same pattern as atomic radii, where ions increase in size as you move down a group on the periodic table and decrease as you move to the right. For instance, lithium, sodium, and potassium ions grow larger as you go down the group. This trend applies to positively charged ions (cations). Interestingly, negatively charged ions (anions) tend to be larger than cations. For example, the sulfide ion is much bigger than the aluminum ion, and in general, ions with more negative charges are larger, while those with more positive charges are smaller.
🔬 Beryllium vs. Magnesium and Calcium vs. Gallium
Magnesium is significantly larger than beryllium due to its position lower on the periodic table, despite both ions having a +2 charge. Magnesium's larger size is due to having more energy levels (two versus one in beryllium). On the other hand, gallium is smaller than calcium, even though they have different charges (+3 and +2, respectively). This is because gallium has a higher effective nuclear charge and is to the right of calcium on the periodic table, making its ionic radius smaller.
⚖️ Comparing Potassium and Bromide Ions
When comparing cations (positively charged ions) and anions (negatively charged ions), the anion is usually larger. Bromide is much bigger than the potassium ion because it has more electrons and a greater number of filled energy levels. Potassium has three filled shells, while bromide has four. This additional shell causes the bromide ion to be larger. Generally, anions are larger due to having more electrons and energy levels, which expand the electron cloud.
Mindmap
Keywords
💡Ionic Radii
💡Cations
💡Anions
💡Effective Nuclear Charge
💡Isoelectronic Ions
💡Energy Levels
💡Electron-Electron Repulsion
💡Periodic Trend
💡Magnesium Ion
💡Bromide Ion
Highlights
Ionic radii follows the same trend as atomic radii, with ions getting larger as you go down a group in the periodic table.
As you move across a period, ionic radii decrease for cations, while anions tend to be larger due to added electrons.
Lithium, sodium, and potassium ions increase in size going down the group, with radii of 60, 95, and 133 picometers, respectively.
Magnesium and aluminum ions are smaller than sodium, with magnesium at 65 pm and aluminum at 50 pm, showing the trend across periods.
Negative ions (anions) are generally larger than positive ions (cations) due to the addition of electrons expanding the electron cloud.
The more positive the charge on the ion, the smaller it becomes; the more negative the charge, the larger it becomes.
Sulfide (S²⁻) is larger than aluminum (Al³⁺) and chloride (Cl⁻) due to its negative charge, with sulfide at 184 pm and chloride at 181 pm.
Magnesium ion (Mg²⁺) is twice as large as beryllium ion (Be²⁺), with sizes of 65 and 31 pm, respectively, because magnesium has more energy levels.
Gallium (Ga³⁺) is smaller than calcium (Ca²⁺), with ionic sizes of 62 and 99 pm, due to gallium’s higher effective nuclear charge.
When comparing cations and anions, negatively charged ions (anions) like bromide (Br⁻) are generally larger than cations like potassium (K⁺).
Potassium ion (K⁺) has only three filled electron shells, while bromide ion (Br⁻) has four, contributing to bromide's larger size.
A sodium atom is larger than a sodium ion because the ion loses an energy level when it loses an electron, reducing its size.
Chloride (Cl⁻) is significantly larger than its parent chlorine atom due to electron-electron repulsion caused by the added electron.
Cations are always smaller than their parent atoms, while anions are larger due to changes in electron configurations.
Isoelectronic ions (ions with the same number of electrons) can be ranked by size based on their charge, with more negative ions being larger.
Transcripts
in this video we're gonna talk about
ionic radii and the sizes of ions and
ionic radii follows the same trend as
atomic radii that is the ions get bigger
as you go down so for example let's draw
some ions so here we have the lithium
plus ion and then the sodium plus cation
and also the potassium cation now the
lithium ion is about sixty Pico meters
the sodium ion is ninety five and
potassium is 133 so as you can see as
you go down the sizes of the ions
increases so sodium is a bigger ion and
then lithium now as equal to the right
it decreases as well magnesium is a lot
smaller than sodium and aluminum is a
lot smaller than magnesium so this is if
you're looking at positively charged
ions magnesium is 65 Pico meters
aluminum is 50 with a plus three charge
now as you cross over from cations to
anion something interesting happens
sulfide is a lot bigger than the
aluminum cation and so is chloride the
sulfite ion is 184 Pico meters and
chloride is 181 so as you can see the
ions with negative charges are a lot
bigger than the ions with positive
charges in fact the more positive the
charge
the smaller the ion the more negative
the charge that bigger the ion and
that's a general trend so ionic radii
increases as you go down and it
decreases as you go to the right however
as you cross from cation to anion
it's gonna change now let's work on some
problems which ion is larger so Part A
is it the beryllium ion or is it the
magnesium iron now both of these ions
contain a positive 2 charge so which one
is it
now if we place these ions in their
respective positions on the periodic
table you'll see that magnesium is below
beryllium and ionic radii increases as
you go down so therefore magnesium
should be a lot bigger than beryllium
beryllium has a net ionic size of 31
Pico meters and magnesium is 65 so
magnesium is more than twice the size of
beryllium now let's understand why an
atom of beryllium has 4 electrons so the
beryllium ion has only 2 electrons an
atom of magnesium has 12 electrons but
the mg plus 2 ion it loses two so it has
10 electrons if we draw the structure of
beryllium let's say this is the nucleus
it only has one shell which contains two
electrons so that's the beryllium ion
the nucleus has a charge of plus four
because that's the atomic number
and it only has two electrons in its
first shell magnesium has 12 protons so
the nuclear charge is plus 12 and it has
10 electrons 2 in the first shell and
then 8 in the second show so that's why
Venezia is a lot bigger than beryllium
it has two energy levels as opposed to
one
now what about Part B let's compare
calcium with a gilliam now the charges
of these two ions are different in a
last example they were the same whenever
you have two positively charged cations
typically the one that's smaller is
going to be the one of the higher
positive charge so it turns out gallium
is smaller than Kappa calcium the size
of the calcium plus two ion is about 99
Pico meters and gallium is 62 the
gallium plus 3 ion so why is gallium a
lot smaller than calcium for one reason
gallium is to the right of calcium on a
periodic table and as you go towards the
right
the ionic radii decreases gallium has a
higher effective nuclear charge than
calcium and so Gilliam it makes the
higher effective nuclear charge causes
Gilliam to be smaller than calcium so
anytime you increase the effective
nuclear charge the ionic radii decreases
so the sizes of the ions become smaller
now let's move on to Part C so which ion
is larger is it the potassium ion or the
bromide ion when you compare an cations
and anions the one with a negative
charge is usually the bigger ion so
bromide is a lot bigger than the
potassium cation the ionic radii of
these two ions are 133 and 195
as you can see bromide is a lot bigger
than the potassium cation now the
potassium cation only has 18 electrons
it lost one bromine has 35 but he gained
one so the bromide ion has 36 electrons
so the potassium ion is a lot smaller
because it only have 3 shells filled
with electrons
the first show has two the second has
eight and the third one has another
eight so that's a total of 18 now the
bromide ion is gonna be a lot bigger
because instead of having three energy
levels it's gonna have four to fill up
the 36 electrons and so an ion with more
energy levels is going to be a bigger
ion and that's why negatively charged
ions are usually bigger than positively
charged ions because in order to form a
negative charge you have to add an
electron and that causes the electron
cloud to be bigger to expand now let's
move on to Part D let's compare the
sodium atom with the sodium ion so which
one is going to be bigger when you
compare a cation with its parent atom
the cation is always smaller the atom is
going to be bigger and the reason for
that is simple it has to do with the
number of energy levels that sodium has
sodium contains 11 electrons it has a
positive 11 charge at the nucleus the
first shell has 2 the second has 8 and
the third shell contains 1
now the sodium cation it loss and the
valence electron so therefore it only
has ten electrons tuna first show eight
in a second so because it lost an energy
level it's going to be a lot smaller
than the parent atom so cations are
usually smaller than the neutral parent
atom now let's consider the last example
chlorine versus chloride which one's
going to be bigger
while chloride has one more electron and
chlorine chlorine has 17 electrons
chloride has 18 electrons now granted
both particles have three energy levels
however the extra electron causes
electron-electron repulsion which causes
the electron cloud to expand so chloride
is actually a lot bigger than chlorine
in fact the ionic radius of chlorine is
about 99 Pico meters and for the
chloride ion it's a hundred and
eighty-one so the chloride ions a lot
bigger than the chlorine atom that extra
electron added to it makes a huge
difference so negatively charged ions
are a lot bigger than the parent atoms
but positively charged ions are a lot
smaller in the case of sodium the atomic
size for sodium or rather the atomic
radii is 186 and for the sodium ion it's
95 so as you can see the cations are a
lot smaller than their parent neutral
atoms but the anions are a lot bigger so
those are some things that you want to
keep them on number to rank the
following isoelectronic ions in order of
decrease in ionic radii so what does the
word Iced electronic means it means that
these ions have the same
electron configuration and that they
have the same number of electrons there
isoelectronic with neon they all have
ten electrons and so therefore the
electron configuration for each of these
ions is going to be 1s2 2s2 2p6 so how
do we know which ion is going to be
smaller which ones are big so remember
the general rule positively charged ions
are very small
negatively charged ions are big so just
by knowing that you can go ahead and
rank it so we want to rank it in order
of decrease in ionic radii
so we want to start from the big ions
and then go towards the small ions the
biggest ion is going to be oxide because
it has a very high negative charge and
then it's gonna be fluoride which is
bigger than the sodium cation which is
bigger than the magnesium plus two
cation the oxide ion
is a hundred and forty picometers
fluoride is 136 sodium is 95 and
magnesium is 65 so as you can see the
negatively charged ions are
significantly larger than the positively
charged ions
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