MATRICULATION CHEMISTRY SK015: 3.2 PERIODICITY (ATOMIC RADII, IONIC RADII & ISOELECTRONIC SPECIES)

Summary

This 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

00:00

🔬 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.

05:02

🌐 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.

10:03

📉 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.

Keywords

💡Periodicity

Periodicity refers to the regular pattern of properties of the elements in the periodic table as their atomic numbers increase. In the context of the video, periodicity is the overarching theme, focusing on how the size of atoms and ions changes predictably across periods and down groups in the periodic table. The video script discusses the periodic trends in atomic radius, which is a fundamental aspect of understanding the chemical behavior of elements.

💡Atomic Radius

The atomic radius is the distance from the nucleus to the outermost shell of an atom. It is a key concept in the video, as it explains how the atomic radius decreases across a period due to increasing nuclear charge and effective nuclear charge, and increases down a group due to the addition of electron shells. The script provides examples of how the atomic radius changes for elements in the first row of transition metals and across periods.

💡Ionic Radius

Ionic radius pertains to the size of an ion, which can be larger or smaller than the parent atom depending on whether electrons are gained or lost. The video script explains that anions, like the chloride ion, tend to have a larger radius due to electron addition and increased electron-electron repulsion, while cations, like the sodium ion, have a smaller radius due to electron loss and stronger nuclear attraction.

💡Isoelectronic Species

Isoelectronic species are atoms or ions that have the same number of electrons, and therefore the same electronic configuration. The video script discusses how isoelectronic species with the same electronic configuration can be compared across periods, and how their ionic radii decrease with increasing atomic number due to stronger nuclear charge.

💡Effective Nuclear Charge

Effective nuclear charge is the net positive charge experienced by the valence electrons in an atom, which increases across a period due to the addition of protons in the nucleus. The video script emphasizes the role of effective nuclear charge in the decrease of atomic radius across a period, as it leads to stronger electromagnetic attraction between the nucleus and valence electrons.

💡Shielding Effect

The shielding effect is the phenomenon where inner electrons shield the outer electrons from the full attractive force of the nucleus. The video script explains that as you go down a group, the increased number of electron shells leads to a greater shielding effect, which weakens the attraction between the nucleus and valence electrons, resulting in an increase in atomic radius.

💡Transition Elements

Transition elements, found in the d-block of the periodic table, are characterized by changes in atomic size that are somewhat different from main group elements. The video script notes that the atomic radius of the first row of transition elements in period 4 decreases across the first five elements but then remains fairly constant for the rest of the period, due to the influence of 3d orbitals on the 4s orbital.

💡Noble Gas Configuration

A noble gas configuration refers to the electron configuration of noble gases, which are particularly stable due to being filled or half-filled. The video script mentions that elements in groups 15 to 17 tend to gain electrons to achieve this stable configuration, which affects the size of the resulting anions.

💡Electronegativity

Although not explicitly defined in the script, electronegativity is implied as a future topic to be discussed in the series. It is a measure of the tendency of an atom to attract a bonding pair of electrons and is related to the periodic trends observed in the periodic table.

💡Ionization Energy

Like electronegativity, ionization energy is mentioned as a future topic. It is the energy required to remove an electron from an atom or ion. The video script suggests that understanding atomic and ionic radii is foundational to understanding ionization energy trends in the periodic table.

💡Electromagnetic Attraction

Electromagnetic attraction is the force that holds electrons in an atom or ion to the nucleus. The video script explains that stronger electromagnetic attraction, resulting from an increase in nuclear charge or a decrease in shielding effect, leads to a smaller atomic or ionic radius.

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