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Periodic Trends/Patterns
CH. 2
Periodic Trend
• Nuclear charge
• atomic size or radius
• ionization energy
• electron affinity
• electronegativity
• metallic character
• Reactivity
• bonding characteristics
• crystal configurations
• acidic properties
• densities
Quantum Mechanical Model
Effective Nuclear Charge: The s, p, d, and f orbitals within a given shell have slightly different energies.
The difference in energies between subshells result in electron–electron repulsion which shields outer electrons from the nucleus.
The net nuclear charge felt by an electron is called the effective nuclear charge ( Zeff ).
Zeff
Quantum Mechanical Model
Zeff is lower than actual nuclear charge.
Zeff increases toward nucleus ns > np > nd > nf
This explains certain periodic changes observed.
Z*
The effective nuclear charge in the actual
charge from the nucleus that an electron
feels due to attractive forces from the
nucleus but also repulsive forces from the
other electrons, mainly the core electrons.
Atomic radii
The Periodic Table 02
Periodic Properties 02
Atomic Radii 02:
Chapter 06 9
Ions and Ionic Radii02
Ions and Ionic Radii
Trend of ionic radii
The cation of an atom decreases in size while the
anion of an atom increases in size.
The trend can not be made according to the periodic
table, but by the isoelectronic series.
The more positive an ion is the smaller it is because
Zeff increases, while the more negative an ion, the
larger it is because Zeff decreases.
Ionization EnergyDefined as the amount of energy necessary to
remove the outermost electron from an isolated neutral atom in the gaseous state to infinity.
Abbreviation is Ei, it has units of kJ/mol.
IE
successive ionization energy
Ionization Energy
Minor irregularities in the Ei values are explained by looking at the electron configurations.
IE Trend
Ionization Energy
Ionization energies vary periodically, which is explained by the changes in Zeff .
Zeff
Electron Affinity 01
Electron Energy: Energy change that occurs when an electron is added to an isolated atom in the gaseous state.
Abbreviation is Eea, it has units of kJ/mol. Values are generally negative because energy is released.
Value of Eea results from interplay of nucleus electron attraction, and electron–electron repulsion.
EA
Electron Affinity 02
EA Trend
Periodic properties REACTIVITY - Li
Periodic properties - Na
Periodic properties - K
Metallic Character
• The metallic character of atoms can be
related to the desire to loose electrons
• On the periodic table, the metallic character
of the atoms increase down a family and
decreases from left to right across a period.
Periodic Trend Activities
• WebElements
• Periodicity and Properties of Elements and Compounds: An Internet Study
• Periodic Trends Lesson
• Periodic Table Exercises
• Our Favorite Element
• Structured Curriculum Lesson Plans
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