# How Do Atom and Ion Sizes Compare in Various Elements?

• spiderflower
In summary, the order of the atoms and ions from largest to smallest is: Br- > Cs > P > N > Mg2+. However, it is important to note that the size of an atom or ion can vary based on its charge and position on the periodic table. Generally, as you move down the periodic table, the size increases, and as you move across a row, the size decreases. Anions are typically larger than their corresponding neutral atoms.
spiderflower

## Homework Statement

Order each of the following sets of five atoms and ions according to decreasing size.
(i.e. "1" largest and "5" smallest)

N, Br-, Cs, P, Mg2+

## Homework Equations

When an atom loses electrons (becomes more +), its size decreases. Conversely, when an atom gains electrons (becomes more -), its size increases.

## The Attempt at a Solution

I know that Br- will be the largest, and Mg2+ will be the smallest. Then Cs will probably be the second largest considering its position on the periodic table. But for N and P I'm not entirely sure. So my best bet is: Br- > Cs > P > N > Mg2+
Or should I switch the P and N around?

One little problem... simply by adding one electron to Br will increase its size so much that it'll be larger than Cs? I find it a little unreasonable... but my teacher says that if there is a negatively charged ion, whatever the other ones, the anion will be the largest. How come?

Thank you very much in advance. :)

spiderflower said:
One little problem... simply by adding one electron to Br will increase its size so much that it'll be larger than Cs? I find it a little unreasonable...
As you move along a row in the periodic table, the radius of a neutral atom and equivalent ions decreases. As you move down the periodic table, the radius increases. Like you said, as you lose electrons---your radius also decreases (and therefore, gaining electrons increases the radius). So you are at least on the right track...

spiderflower said:
but my teacher says that if there is a negatively charged ion, whatever the other ones, the anion will be the largest. How come?
That's not true. I.e. Br- is most certainly larger than H, or He, or most other low atomic number elements. Anions are always larger than the neutral version of the same element. Thus I'm not familiar with any immediate way of knowing which is bigger, Cs or Br-

## 1. What is the difference between relative atom and ion sizes?

The size of an atom is determined by its electron cloud, while the size of an ion is determined by the number of protons and electrons it has. Atoms are neutral, meaning they have the same number of protons and electrons, while ions have a different number of protons and electrons, giving them a different size.

## 2. How do relative atom and ion sizes change across the periodic table?

Across the periodic table, atom and ion sizes generally decrease as you move from left to right and increase as you move down a group. This is due to the increasing number of protons and electrons, which results in a stronger pull on the electron cloud and a smaller size.

## 3. Why do ions have different sizes even if they have the same number of electrons?

Ions can have different sizes even if they have the same number of electrons because the number of protons also plays a role in determining the size. The more protons an ion has, the stronger the pull on the electron cloud, resulting in a smaller size.

## 4. How do relative atom and ion sizes affect chemical reactions?

The size of an atom or ion can affect how it interacts with other atoms or ions in a chemical reaction. For example, smaller atoms or ions can fit into smaller spaces or form tighter bonds, while larger atoms or ions may have trouble fitting together or have weaker bonds.

## 5. Can relative atom and ion sizes be measured?

Yes, relative atom and ion sizes can be measured using techniques such as X-ray crystallography or electron microscopy. These methods can provide information about the size and arrangement of atoms and ions in a substance.

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