Atomic Radius

[Norah Gidanian 3D]

Can someone explain why the atomic radius decreases as you move across a period? If there are more electrons shouldnt electron-electron repulsion push them farther away, making the radius larger?

[Alexandra Ahlschlager 1L]

The atomic radius decreases as you go across a period because more protons are being added to the nucleus as you go across. With every proton added, the attraction between the electrons and protons grows, bringing the electrons closer and closer to the nucleus. Therefore, the atomic radius gets smaller. Hope this helps!

[Charlotte Adams 1A]

As you move towards the right of the periodic table the atomic number increases which gives the amount of protons in the nucleus, and a more positive nucleus has a greater pull on the electrons, thus decreasing the atomic radius.

[SLai_1I]

As you move across a period, more protons are being added to the nucleus, increasing the atomic number. This makes the nucleus more positive, giving it a stronger pull on the valence electrons, decreasing the atomic radius.

[Emma Strassner 1J]

The radius decreases across the period because the effective nuclear charge increases as you go across. This causes greater attraction to electrons that pulls them in closer to the nucleus, resulting in a smaller radius.

[Yu Jin Kwon 3L]

Everyone above explained why the atomic radius decreases as you go right on the PT. To explain when electron-electron repulsion will occur and how that can impact the radius: when you go down the periodic table, you add more shells, meaning you have much more electrons to shield the positive charge of the nucleus. Firstly, the sheer amount of electrons you now have (as you go down the PT) means that there are more negative charges repelling away from each other, causing the radius to increase. Secondly, the electrons closer to the nucleus (as I mentioned before) shield the pull of the nucleus, meaning more electrons will stray further away from the nucleus, causing a larger radius as well.

I hope this helps in giving a different view of when electron-electron repulsion makes the radius larger :D

[Maya Johnson 2a]

When you move across the periodic table, the atomic radius gets smaller because with more protons, there is a greater pull on the electrons. Ultimately, this results in a smaller atomic radius.

[Joseph_Armani_3K]

As we go across a period, the number of protons increase one by one, which would result in a progressively higher electrostatic attraction

[Katie Nye 2F]

As you go across a period, there are more protons in the nucleus. Because of this, the attraction to the electrons is stronger so they are pulled in tighter, making the atom smaller. My high school teacher always described it as "Coulombic attraction" and it increases as protons are added to the nucleus.

[kateraelDis1L]

As nuclear charge increases there is greater attraction. Keep it simple ;)

[Colin Squire 3B]

There are more protons in each element as we move to the right in the periodic table. This means that the pull they have on the electrons are stronger, which then the radii are going to get increasingly smaller.

[Sofia Lombardo 2C]

Atomic radius decreases as you go across a period because the protons increase and shielding remains constant. Even though you are adding electrons, since the shielding remains constant, the effective nuclear charge is able to have a stronger pull on the electrons, thus making the atom smaller.

[Navdha Sharma 3J]

All the elements in a period have the same number of shells(just the number of valence electrons vary). But, the number of protons across a period increases, and so the effective nuclear charge increases which causes the size to decrease across a period.

[Morgan Gee 3B]

While electrons increase and the repulsion causes the radius to increase slightly, protons are also increasing. The positivity of the protons cause the electron cloud to shrink, resulting in a decrease in atomic radius as you move across a period.

[Binyu You]

The atomic radius decreases when going across the period because there are more protons when moving to the right in the periodic table. As proton is added, the attraction grow, which makes the electrons tightly packed, thus making atomic radius smaller.

[Renny_kim_2G]

The more pairs of electrons and protons you have, the more attraction there is. Therefore, as you move right, these pairs increase and the radius gets smaller.

[Nhu Pham-Dis3G]

It is because across a period, effective nuclear charge increases as electron shielding is maintained. Higher effective nuclear charge = greater attractions to the electrons = electron cloud pulled closer to nucleus = smaller atomic radius.

[Brandon Le 3C]

As you move across a period from left to right, the protons of the atom increases. Because of this, the attraction between the electrons and the nucleus becomes stronger, therefore making the atomic radius smaller as the attraction squeezes it together.

[Leyla Anwar 3B]

Does the atomic radius being smallest at the top right have anything to do with the more complete octet those elements have? Because as you move down the radius increases but it has extra valence electrons that need to be balanced. I guess I'm just wondering if the octet has anything to do with it.

[Jeremy Wei 2C]

Hi, the atomic radius in the top right is related to the complete octet of the elements because as the octet starts to fill up, there are more valence electrons for the protons in the nucleus to interact with, the attraction being stronger.

[Jonathan Banh 1G]

Atomic radius decreases as you go across a period (left to right) because of how electron shielding remains constant while effective nuclear charge increases with the addition of protons. As a result, this increase in protons causes the attraction between the nucleus and electron cloud to increase, meaning the electron cloud will be pulled inwards, making it tighter and smaller. Thus, this explains how atomic radius shrinks in size.

[Mackenzie Stockton 2H]

As you move right across a period, the number of protons increases (positive charge). This positive charge "pulls in" the negative electrons, so the electrons are closer to the nucleus (where the protons are). Because the electrons are more pulled closer to the nucleus as the number of protons increases, atomic radius decreases across a period.

[Danielle DIS2L]

The atomic radius decreases across the periodic table because there are more protons being added to the nucleus where there would be less electron electron attraction thus making the nucleus of an atom smaller.

[Chris_Butler_1A]

I apologize if this has already been asked but because neutrons have a neutral charge, and thus they do not "pull-in" the electrons in the orbitals, can we say that they don't affect the atomic radius? For example, Carbon-12 and Carbon-13 would have the same atomic radius?

[Tobie Jessup 2E]

As your move across the periodic table, more protons are added to the nucleus and therefore there is a stronger positive charge that pulls the electrons closer to the nucleus.

[Andy Hernandez]

As we go across a period, the number of protons increase one by one, it results in a progressively higher electrostatic attraction

[AlbertGu_2C]

More protons equals more positive charge to attract electrons

[Sarah Huang 3A]

Can someone explain why the atomic radius decreases as you move across a period? If there are more electrons shouldnt electron-electron repulsion push them farther away, making the radius larger?

Hi Norah! I originally had the same misconception as well! However, the reason why atomic radius decreases as you move across a period is because as you go along, the elements have a higher nuclear charge. For example, from carbon to nitrogen to oxygen, the amount of protons goes from 6 to 7 to 8. With an increase in protons, there is an increase in nuclear charge, and since there is usually one electron per proton, that is why we see a neutral charge, but even though there is an equal ratio of protons to electrons, protons carry a greater charge, so they create a stronger pull. The stronger pull results in the electrons becoming more tightly held together, closer to the nucleus, thus decreasing the atomic radius.

The electron-electron repulsion applies more when you add electrons to the same element. For example, if you have N and N-, the extra electron in N- generates greater electron-electron repulsion, thus increasing the atomic radius. The nuclear charge stays the same since the amount of protein has not changed. So, if you were to order N, N-, and N+ from largest to smallest atomic radius, what would you get?

If you got N-, N, N+, you are absolutely correct! You should already understand why N- is greater than N, but N+ is the smallest because it lost an electron, so there is a decrease in electron-electron repulsion amongst the remaining electrons and the nuclear charge pulls them even closer, thus decreasing the size of N+'s atomic radius in comparison to N.

I hope that helps!

[Jaden Kwon 3C]

Going across a period nuclear charge increases due to the addition of more protons while electron shielding remains constant which causes a causes electrons to be pulled closer to the nucleus making the atomic radius smaller.

[Brian Nguyen 2I]

It decreases as you move across a period because the atomic number increases. When the atomic number increases, the amount of protons increase. There is more of a positive charge present, increasing the attraction between the electrons and protons, thus decreasing the space between the electrons and protons. This decreases atomic radius.

[Nick Saeedi 1I]

The number of protons increases as you move across a period so there is a stronger pull on the electrons making the atomic radius smaller.

[LovepreetSran_3H]

As you move across the period, the atomic number increases, thus more protons are present. This increases attraction causing the atomic radius to decrease.

[rhettfarmer-3H]

Atomic radius decreases as we move to the right of the periodic table because more electrons we have a closer outer shell because of the attraction of the inner nuclear charge is increasing at the same right while the shielding of electrons is remaining the same so there is a short radius by a stronger force pulling them in despite more electrons.

[Ke Huang 2G]

As you move to the right of the periodic table, the radius decreases because electrons are attracted to the nucleus as the nucleus has more positive charges.

[Chris_Butler_1A]

I apologize if this has already been asked but I had a little confusion in regards to how Atomic Radius is calculated in ionic bonding. From what I understand, the Atomic Radius is half the distance from the center of a neighboring atom. How does this affect our ability to measure the radii of say NaCl where Cl- has a higher electronegativity than Na+?

[Alex Benson]

Hi! The atomic radius decreases as you go down a period because the nucleus increases in size. Although there is more electron-electron repulsion I believe that this force is overpowered by the strength of the nucleus.

[Gustavo_Chavez_1K]

Yeah so although there are more electrons we must keep in mind that this means that there are also more protons. So, the more protons there are in the nucleus then the more the nucleus pulls on the electrons. This ultimately decreases the radius of the atom.

[Brandon McClelland3L]

As you move across a period there are more protons, increasing the effective nuclear charge. However, the reasoning you stated is why ions of the same molecule have different atomic radii.

[Geethika Janga 1L]

As you move across the period, although the total number of electrons increase, they are being added to the same shell. Along with the number of electrons, the number of protons increases too the effective nuclear charge will be greater moving across the period. The electrons will experience a greater attraction to the nucleus and as a result, the atomic radius decreases.