Why is there a difference in atomic and ionic radii for Ca and Zn?

In summary, the difference between the atomic radii of Ca and Zn is greater than the difference between the ionic radii of Ca 2+ and Zn 2+. This is due to the larger nuclear charge of Zn, which pulls the electrons in its shells stronger inward. The electron configuration of Ca and Zn also play a role in the size difference.
  • #1
siriuswishbear
hey guys!
I was just wondering if anyone could help me out a bit on this.
I have the following radii (in angstroms...not that it really matters)
Ca: 1.74 Ca 2+: .99
Zn: 1.31 Zn 2+: .74
Does anyone have any idea why the difference between the atomic radii of the two elements is greater than the ionic radii of the two ions? (atomic difference is .43 and the ionic diff is .25)
I've asked a bunch of people (friends in my class, parents, parents of friends etc.) and no one has any ideas
Can you help?
thanks!
lar
 
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  • #2
That is not so difficult, since both ions have a positive charge of 2, they lost two electrons and thus are smaller.

I'd have to know the electron configuration to comment why the loss of two electrons for one results in a different size difference than the other.
 
  • #3
Ca= 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
Ca 2+= 1s^2 2s^2 2p^6 3s^2 3p^6 (aka [Ar])
Zn= 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10
Zn 2+= 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8
Does that help?
 
  • #4
20Ca: [Ar] 4s2
30Zn: [Ar] 4s24d10

I guess the best explanation in the [tex]\inline\Delta[/tex] radius would be that Zn has a larger nuclear charge than Ca, it thus pulls the electrons in its shells stronger inward.
 
  • #5
Thanks Monique! I've been trying to find the answer for a couple of days, you're the first person that's come up w/ a logical reason (i got a lot of "just cuz..." and "i have no idea, go ask ___"
Thanks!
 
  • #6
Originally posted by siriuswishbear
Ca= 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
Ca 2+= 1s^2 2s^2 2p^6 3s^2 3p^6 (aka [Ar])
Zn= 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10
Zn 2+= 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8
Does that help?
Thanks sirius :) I was thinking that the answer would lie in the suborbitals, since they have a different shape and all, but it also depends on the number of protons that pull the electrons towards the nucleus.
 

Atomic Radii vs. Ionic Radii

Atomic radii and ionic radii are important concepts in chemistry that describe the size of atoms and ions. Let's address some common questions about these two types of radii:

Q1: What Is Atomic Radii?

Atomic radii refer to the size of an atom, specifically the distance from the nucleus to the outermost electron orbit or shell. Atomic radii are typically measured in picometers (pm) or angstroms (Å) and are used to describe the size of individual atoms in a neutral state.

Q2: What Is Ionic Radii?

Ionic radii, on the other hand, describe the size of ions, which are atoms that have gained or lost electrons to become positively or negatively charged. Ionic radii are the distances from the nucleus to the outermost electron shell of ions. They are also measured in picometers (pm) or angstroms (Å) and are used to describe the size of ions in various chemical compounds.

Q3: How Do Atomic Radii Compare to Ionic Radii?

Atomic radii are generally smaller than ionic radii for the same element. This is because when an atom loses electrons to become a positively charged ion (cation), it loses electron shells, making it smaller. Conversely, when an atom gains electrons to become a negatively charged ion (anion), it gains electron shells, making it larger.

Q4: What Are Some Factors that Affect Atomic and Ionic Radii?

Several factors can influence atomic and ionic radii, including:

  • Effective nuclear charge: The attractive force between the nucleus and electrons affects the size of the electron cloud.
  • Number of electron shells: The more electron shells an atom or ion has, the larger its radii.
  • Electron-electron repulsion: Electrons in the same shell repel each other, which can lead to changes in radii.
  • Chemical bonding: The type of chemical bond (covalent or ionic) can affect the size of ions.
These factors collectively determine the size of atoms and ions in a chemical system.

Q5: Why Are Atomic and Ionic Radii Important in Chemistry?

Atomic and ionic radii are essential in understanding chemical bonding, reactions, and the properties of chemical compounds. They play a significant role in predicting the behavior of elements and compounds, including their crystal structures, solubilities, and reactivity.

Q6: Can Atomic and Ionic Radii Change in Chemical Reactions?

Yes, atomic and ionic radii can change during chemical reactions. When atoms form chemical bonds, their radii may decrease or increase depending on the type of bond formed. For example, in ionic bonding, atoms can become ions with significantly different radii than their neutral counterparts.

Q7: Are There Reference Tables for Atomic and Ionic Radii?

Yes, there are reference tables and databases that provide atomic and ionic radii values for various elements and ions. These tables are valuable resources for chemists and researchers to determine the sizes of atoms and ions in different chemical contexts.

In summary, atomic radii describe the size of neutral atoms, while ionic radii describe the size of ions. Atomic radii are generally smaller than ionic radii for the same element, and various factors influence their sizes. Understanding these radii is crucial for comprehending chemical behavior and properties.

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