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Atomic RadiusBy: Shourik, Holly, Zach, and Elizabeth

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Defined as the measure of the size of an atom; themean distance from the nucleus to the boundary of thesurrounding electron cloud

The radius is dependent on the type of bond present, ifthere is one, whether that be covalent, ionic, metallic, orVan der Waals these bonds affect how far our the valence electron

shell extends

Atomic radius is variable due to the fact that effectivenuclear charge changes among individual elements this affects the attraction of the electrons in the

valence shell. Thus the effective nuclear chargedetermines how "tightly packed" the valence electron

cloud is.

The Property of Atomic Radius

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The atomic radius increases as the atomicnumber increases, moving down a column.

What is the trend as you go down acolumn?

Group 13 Group 14 Group 15

Smaller

Small

Big

Bigger

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Moving down the group of elements, the atoms increase inmass. They have more protons and also more electrons.The radius increases not only because there is more massto the atom, but also because there are more electrons that

will be undergoing electron-electron repulsion. The radiusis determined by the valence electrons and the valenceelectrons will be on higher shell levels as we go down agroup, meaning that a greater amount of electrons willconsequently be below the valence electrons, shielding

them from the nucleus and at the same time causing thevalence electrons to be pushed out to further reaches of theatom, thus extending the radius.

Why do atomic radii increase as yougo down a group of elements?

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What is the trend as you go across arow?

Not including the noble gases, atomic radii getsmaller as you move across a period.

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Why do atomic radii decrease as yougo across a period?

As you go across a period, the number ofprotons in the nucleus increases. This causesthe electrons to experience a greater effective

nuclear charge, which pulls the electrons inmore tightly, thus causing the radius todecrease. While electrons are being added asyou move across a period, they are all in thesame shell at about the same distance from thenucleus, so the shielding effect does not affectthe radius size as you go across a period.

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How is atomic radius measured?

The radius of an atom is dependent on thedistance from the nucleus to the outermostboundary of its probability cloud. Therefore,

the atomic radius of an atom is not a fixedamount. The only way to determine the radiusis to find the distance between the nuclei of twobonded similar atoms and dividing the distanceby 2.

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Exceptions to This Trend

Transition metals Across a period: decreases initially from left to right, changes

very little in the middle, and ends with a small increase ub

suze at end of row Down a column: maintains pattern of increasing uniformly Rationale for irregularity

electron-electron repulsion cancels this decrease out halfway throughthe period

the 'additional' electron for each successive element enters the theinner 3d sub shell where it provides a more effective shield betweenthe nucleus and the outer 4s sub shell.

although each successive nucleus has one more proton, the extrapositive charge is partly shielded by the extra electron in an underlying

3d sub shell; this is why halfway through, we see an increase in radii

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Questions???