chemical+activity


 * Periodic Trends: Chemical Activity**

An element's chemical activity is defined as how stable it is relative to the others around it on the table of the elements. For example, we know that oxygen gas is stable in air - it does not spontaneously react with most materials around us. We do know, however, that oxygen gas will spontaneously react in the presence of some elements, such as hydrogen, chlorine, and metals such as sodium or iron.

Fluorine gas, which lies right beside oxygen on the table, is extremely reactive (highly chemically active) to most substances it comes in contact with. Therefore, fluorine is more chemically active than oxygen.



In general, the group of elements including copper, silver, and gold are the least chemically active metals. As you move from this group towards the left side of the table, elements generally become more chemically active. As you move from the copper group to the right, elements generally become more chemically active.

Moving vertically within the metals, chemical activity increases as you approach the bottom of the table (francium is more reactive than potassium, for example).

The opposite is true for nonmetals - moving down the groups, you encounter more stable (less chemically active) elements. Of course, the last group, the noble gases, are chemically inert due to their valence shell being full (8 electrons).

The trends in chemical activity are controlled by the following factors:
 * atomic size
 * valence electron configuration
 * electronegativity
 * effective nuclear charge

Effective Nuclear Charge
To understand //effective nuclear charge (Z// eff //)//, Let's compare lithium metal to potassium metal.

First, lithium is reactive to water, but it fizzes like an alka-seltzer tablet.

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Here is the structure of Li:



Note the outer lone electron, that is the one that will be leaving lithium when it undergoes a chemical reaction.

It has only two other electrons between it and the nucleus (it only "sees" two electrons), thus the **effective nuclear charge** is strong.

Now, watch potassium react with water:

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Here is the atomic structure of potassium:

Now, potassium also has one lone electron in its outer shell, and again, it is the one that will leave in a reaction.

However, note that there are now 18 other electrons between it and the nucleus! This really weakens the effective nuclear charge for this valence electron, and it will have a much easier time leaving than lithium's valence electron would.

This is why potassium is more chemically active than lithium.

Of course, for nonmetals, the same thing is happening, but for the opposite affect - the stronger the effective nuclear charge, the more likely these elements will grab electrons and hold on to them in reactions.

Here is the overall trend: