periodic trends: atomic radius

atomic radius

*The Atomic Radius of an element is an estimate of the size of an atom is nucleus to its outer shell:

• Atomic radius is usually measured in angstroms (A), An angstroms 1x10-10m

trends of atomic radius

• Atomic radius gets smaller as you move left to right on an the periodic table

why does the atomic radius get smaller as u move left to right on periodic table

• The number of protons and electrons increases

• The number of attractions between opposite charges increases → The last shell is pulled closer to the nucleus (Shrinking effect)

-Atomic radius gets larger as you go from top to bottom on the periodic table

Li< Na<K

why ?

The number of shells increase (distance from nucleus to last she’ll)

1 The attraction force exerted by the nucleus decrease)

electrons inner Shells repel each other (shielding effect)

nuclear charge

positive charge of the nucleus

strength of nuclear charge depends on __

number of protons

what happens when number of protons increase

nuclear charge increases

what happens when nuclear charge increases

electrostatic force of attraction also increases which makes atomic radius smaller

what causes atomic radius to get bigger

shipping effect because electrons in inner shell repel electrons in outer shell which prevents electrons in outer shell from fully experiencing the nuclear charge

effective nuclear charge

the net positive pull that an electron actually feels from the nucleus after you subtract the “shielding” effect of the other electrons

effective nuclear charge formula

nuclear charge - shielding effect

what happens if nuclear charge is greater than shielding effect

effective nuclear charge increases and there will be a net inward force of attraction between nucleus and valence electrons as it is stronger than the shielding effect between the electron shells

• Which has a larger radius: a neutral atom or its cation/anion? Explain.

• Neutral atom > cation radius (cation loses shell, stronger pull). Anion > neutral atom (extra electron repulsion expands shell)

• Explain why atomic radius increases down a group (top → bottom).

• Increases top → bottom down a group (more shells = bigger atom).