Chap7 - Dr. Saidane Chem 200 Lecture Notes Chapter 7...

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Chem 200 Dr. Saidane Lecture Notes Chapter 7 Periodic Properties of the Elements PERIODIC TRENDS Atomic Radius It is defined as half the distance between the centers of neighboring atoms . There are two factors that affect the atomic radius: the pull effect of the nucleus and the shielding effect of the inner shell electrons. Within a period, all atoms have the same number of shielding electron (inner shells electrons), but have different number of valence electrons, and therefore have same shielding effects but different pull effect. The more protons in the nucleus, the stronger the pull effect, and therefore the smaller the atom. The number of protons increases from left to right within a period, and therefore, the pull effect increases. The Radii decreases from left to right within a period . Down a group, atoms have increasing shielding effect and therefore less pull from the nucleus, which increases the atomic size. The Radii increases down a group . Ionic Radius Metals lose electrons to have their valence shell filled, and become cations. In cations there are more protons than electrons, which produces a strong pull effect from the protons in the nucleus Cations are smaller than their parent atoms . The higher the charge of the cation, the stronger the pull, and the smaller the ion A + > A 2+ > A 3+ > A Non-metals gain electrons to fill their valence shell, and become anions. Anions have more electrons than protons, which create less pull effect from the protons in the nucleus Anions are larger than their parent atoms . The higher the charge of the anion, the weaker the pull, and the larger the ion. A 3- > A 2- > A - > A
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Ionic radii increase down a group (increasing shielding effect) and decrease across a period (stronger pull). Ionization Energy
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This note was uploaded on 09/09/2011 for the course CHEM 200 taught by Professor Saidane during the Spring '11 term at Mesa CC.

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Chap7 - Dr. Saidane Chem 200 Lecture Notes Chapter 7...

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