5.3 NOTES Periodic Trends II. Classification of the Elements A. Organizing the Elements by Electron Configuration 1. Valence electrons outermost s and p electrons 2. Valence electrons and period energy level of an elements valence
e- indicates the period where the element can be found on the PT; 3. Valence electrons and group number representative Elements group # and # of valence e- are related - exception He only has 2 even though in group 8A atoms in the same group have similar properties b/c they have same # of valence electrons 1A has 1 so it must be an s1
B. The s, p, d, f block elements 1. s block elements 2. p block elements
3. d block elements 4. f block elements III. Periodic Trends Effective Nuclear Charge, Zeff:
Zeff = Z S, where Z = nuclear charge (at. no.) S = shielding (e- in inner shells) Relative strength of Nucleus; Higher Zeff values indicate stronger nuclear pull Within a group (family) of elements, Zeff is the same. Zeff for family 1 is 1, 2 is 2, 3 is 3, etc.
Li: 1s22s1 Zeff: 3-2 = 1 Cs: [Xe]6s1 Zeff: 55-54 = 1 Because shielding increases as the number of protons increase, Zeff stays the same. Even though Zeff is the same, attraction still slightly decreases because of the increased shielding.
Within a series (period) of elements, Zeff is increasing. Li: 1s22s1 Zeff: 3-2 = 1 F: 1s22s22p5 Zeff: 9-2 = 7 Li and F are in the same period and have the same shielding. Zeff is greater for F than Li. Fluorines nucleus has a stronger pull which affects its size and ability to attract electrons.
All other trends are based on Zeff! Examples - Indicate the Zeff of the following elements: Ca B S Ar K C He Atomic Radius
Atomic Radius: size of atom Trend within a family: Down a Family, Atomic Radius increases Principle Quantum Number (n) increases; valence electrons are farther from the nucleus Shielding Effect increases; additional inner core electrons prevent the nucleus from interacting with the valence electrons Examples: Choose the larger atom
B and Ga I and Cl Ar and Kr Ca and Ba K and Rb Atomic Radius Trend within a period: Across a Period, Atomic Radius decreases Zeff increase: nuclear pull gets stronger and therefore
attracts the valence electrons with greater force. Shielding stays the same: no additional shielding electrons allow the nucleus to exert additional power. Examples: Choose the smaller atom Mg and Cl Ne and C Sr and Xe
Al and S Te and Rb Atomic Radius In general, metals have large atomic radii and nonmetals have small radii.
The largest atom is Francium the smallest atom is Helium Ionic Radius Ionic Radius: size of ion (compared to its atom) Octet Rule: Atoms will gain, lose (or share) electrons to become stable (lower energy) Atom: a neutral particle
Ion: a charged particle Formed by the loss or gain of electrons Ionic Radius Cations: Positive Ions Formed by the loss of electrons Metal elements typically lose electrons
Cations are smaller than their atoms Valence shell becomes smaller Electron-electron repulsion is decreases With the loss of electrons, the shielding effect decreases, and electrons are pulled closer to the nucleus. Anions: Negative Ions Formed by the gain of electrons
Non-metal elements typically gain electrons Anions are larger than their atoms Electron-electron repulsion is increases With the gain of electrons, the shielding effect increases, and electrons are pushed farther from the nucleus. Examples: Choose the smaller particle
Ba+2 and Ba N and N-3 Cs and Cs+ Al+3 and Al Br- and Br
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