Atomic Radii

[Tracy Tran 3L]

Why does atomic radii increase down a group but decrease across a group?

[Chance Lee 1G]

Atomic Radii increases down a group since each level down the periodic table groups is energy level. At higher energy levels, the overall level of electrons is more, which therefore requires a larger size, which therefore proves that atomic radii increase down a group. Atomic radii decrease across a group because as you move over each element, each element has more photons, as shown by the atomic number. This allows us to know that there's an increase in photons as you go across a group, thereby having a higher attraction between the nucleus and electrons overall. The increase in attraction thus leads to smaller atomic radii thanks to the fact that a greater attraction means that the valence electrons are being pulled in closer towards the nucleus.

[Darren Apostol 2L]

When you go down a group, new shells with higher energy levels are added, which means they are farther and farther away from the nucleus hence increasing atomic radii. When you go across a period, the electrons are filling the same shell (e.g. p- and d- orbitals) but the number of protons at the nucleus increase. More protons means more positive charge, which means a stronger attractive force pulling the electrons closer hence decreasing atomic radii.

[Alexander Moroz 1B]

Atomic radii decrease across a group because when you move across a group in the periodic table, the energy level, n, stays constant but the atomic number of elements increases so more protons are added. An increase in protons increases the pull, or nuclear charge, that they have on the electrons orbiting the nucleus so the molecule shrinks closer to the center and has a smaller radius. Radii increase down a group because electrons in higher energy levels are added, so even though there are more protons as you move down a group, the new energy level distance from the nucleus is too far to be pulled in like the inner/closer energy levels. Also, the inner electrons shield the outer electrons from the nuclear charge, so this prevents outer electrons from being pulled closer, and helps the atomic radius increase.

[Elsie_Lin_2K]

Atomic radii increase as you go down a group because there are more shells that are being added which causes the electrons to be pulled further away from the nucleus. The radius also increases down a group because of shielding that causes the electrons from a previous orbital to block the electrons in the further orbital to be attracted to the nucleus. However, the atomic radii decrease from left to right because there are more protons that are being added which causes the electrons to become increasingly drawn to the center of the atom.

[Isabelle Kim 3E]

When we're talking about the atomic radius, this has to do with the size of the atom because of the # of shells. As we go down the columns in the PT, there is an increasing energy level, meaning that the principle quantum # (n) is increasing. More specifically, the increasing n indicates that there are more shells surrounding the nucleus of the atom. Another way to see this increasing atomic radius trend is in a diagonal direction starting from the upper right corner to the bottom left corner. This is due to the same reason as explained.
We also need to understand that the size of atoms connects to the idea of electron shielding. Knowing that there's an attraction between positive and negative charges, the size of atom decreases as we go to lower energy levels. The positively charged protons within the nucleus has a stronger pulling effect on the surrounding negatively charged electrons when the # of shells are reduced. Hence, the decreasing trend of atomic radius is shown.

[Shriya_Amara_1G]

Atomic radii increases down a group since the number of shells increase, and as the n value of the shell increases, the number of electrons increase. As the number of electrons increase, the amount of electron-electron repulsions increase, resulting in the electron being held less tightly to the nucleus, thus farther from the nucleus. It decreases across a group because the number of protons is increasing, so the nucleus is more positively charged, which attracts the electrons more, holding them tighter to the nucleus.

[Niyati 1F]

Atomic radii increase down a group because when additional energy shells are added, the size of the atom increases. Across a period, the atomic radii will decrease because of the effective nuclear charge from the nucleus. The charge increases across a period pulling the electrons closer to the nucleus and therefore decreasing the size of the atom.

[Sean Sanders 1E]

Atomic radii increases down a group because there are more total shells. Atomic radii decreases across a period because of increased nuclear attraction as there are more protons in the nucleus as you go across a period.

[Chris Korban 1D]

Atomic Radii increases down a group due to excess electron shells and this causes electron shielding and less effective nuclear force so the radius increases. It decreases across a period because effective nuclear force increases and electrons collapse down closer to the nucleus

[Simone Byun 1F]

As you go down a group, more shells and subshells are added. These additional shells would be farther away from the nucleus, thus a larger radius. However, as you move across the table, the number of shells is not increasing, but the number of protons. More protons will have a stronger pull on the electron shells than less protons, thus brining the shells in more tightly and leading to a smaller radius.

[Divya Hebbar]

atomic radius increases down a group as n increases because more subshell are added, however across a group the number of subshells stays the same but the number of protons increases. This causes a stronger attraction and pulls the electrons closer to the nucleus making the radius smaller.