Ionic Radius Trends, Basic Introduction, Periodic Table, Sizes of Isoelectric Ions, Chemistry

Summary

This 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

00:00

📏 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.

05:02

🔬 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.

10:03

⚖️ 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.

Keywords

💡Ionic Radii

Ionic radii refer to the size of an ion, which can vary depending on the ion's charge and position in the periodic table. In the video, it is explained that ionic radii increase as you go down a group and decrease as you move across a period from left to right. For example, the lithium ion is smaller than the sodium ion, and sodium is smaller than potassium.

💡Cations

Cations are positively charged ions formed when an atom loses electrons. The video explains that cations are generally smaller than their parent atoms due to the loss of an outer electron shell. For instance, the sodium cation is much smaller than a neutral sodium atom because it loses its valence electron and, as a result, shrinks in size.

💡Anions

Anions are negatively charged ions that form when an atom gains electrons. The video illustrates that anions tend to be larger than their neutral atoms because the addition of electrons increases electron-electron repulsion, expanding the electron cloud. For example, the chloride anion is larger than the neutral chlorine atom due to the gain of one extra electron.

💡Effective Nuclear Charge

Effective nuclear charge refers to the net positive charge experienced by an electron in an atom, taking into account both the total positive charge of the nucleus and the shielding effects of other electrons. The video mentions that as you move across a period to the right, the effective nuclear charge increases, which pulls the electrons closer and decreases the ionic radii, as in the case of gallium being smaller than calcium.

💡Isoelectronic Ions

Isoelectronic ions are ions that have the same number of electrons but different nuclear charges. In the video, isoelectronic ions like oxide (O²⁻), fluoride (F⁻), sodium (Na⁺), and magnesium (Mg²⁺) are compared in terms of size, with negatively charged ions being larger than their positively charged counterparts due to electron-electron repulsion.

💡Energy Levels

Energy levels, or electron shells, represent the regions around an atom's nucleus where electrons are likely to be found. In the video, energy levels are crucial for understanding ionic sizes, as ions with more filled energy levels (such as bromide with four shells) are larger than those with fewer energy levels (such as potassium with three shells).

💡Electron-Electron Repulsion

Electron-electron repulsion occurs when electrons in the same atom repel each other due to their like charges. The video explains that this repulsion is greater in anions because of the additional electrons, causing the electron cloud to expand and the ion to increase in size, as seen with the chloride ion being larger than chlorine.

💡Periodic Trend

Periodic trends are the recurring patterns in properties of elements as you move across the periodic table. The video discusses how ionic radii follow a periodic trend: they increase as you move down a group and decrease as you move from left to right across a period. This is exemplified by comparing the sizes of lithium, sodium, and potassium ions.

💡Magnesium Ion

The magnesium ion (Mg²⁺) is a cation that has lost two electrons, resulting in a smaller size compared to neutral magnesium. In the video, the magnesium ion's radius is given as 65 picometers, and it is compared to beryllium, showing that magnesium is larger due to its position below beryllium in the periodic table.

💡Bromide Ion

The bromide ion (Br⁻) is an anion formed when a bromine atom gains an electron. The video illustrates that bromide is significantly larger than the potassium cation due to the extra electron that increases the electron cloud size. The bromide ion's ionic radius is given as 195 picometers, making it much larger than potassium’s 133 picometers.

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