Periodic Trends: Periodic Periodic Trends: Periodic Properties Properties Certain physical and chemical properties recur at regular intervals, and/or vary in regular fashion, when the elements are arranged according to increasing atomic number. Melting point, boiling point, hardness, density, physical state, and chemical reactivity are periodic properties. We will examine several periodic properties that are readily explained using electron configurations.
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Periodic Trends: Periodic Properties Certain physical and chemical properties recur at regular intervals, and/or vary in regular fashion, when the elements.
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Certain physical and chemical properties recur at regular intervals, and/or vary in regular fashion, when the elements are arranged according to increasing atomic number.
Melting point, boiling point, hardness, density, physical state, and chemical reactivity are periodic properties.
We will examine several periodic properties that are readily explained using electron configurations.
Periodic Trends
• Atomic Size – – Group – increase in size down the group
• (addition of energy levels)
– Period – decrease in size across a period• (increase in the # protons in the nucleus
• Atomic radius decreases from left to right within a period.
• Why? The effective nuclear charge increases from left to right, increasing the attraction of the nucleus for the valence electrons, and making the atom smaller.
Mg has a greater effective nuclear charge than Na, and is smaller than Na.
Effective Nuclear Charge (Zeff): The nuclear charge actually felt by an electron.Zeff = Zactual - Electron shielding
Multielectron and ShieldingMultielectron and Shielding
Atomic Radii of the ElementsAtomic Radii of the Elements
ExampleExample
With reference only to a periodic table, arrange each set of elements in order of increasing atomic radius:
(a)Na, Al, P
(b) Te, S, Se
(c) Ge, Sb, Sn
Ionic RadiiIonic Radii
The ionic radius of each ion is the portion of the distance between the nuclei occupied by that ion.
Ionic Radii of CationsIonic Radii of Cations
• Cations are smaller than the atoms from which they are formed; the value of n usually decreases. Also, there is less electron–electron repulsion.
Ionic Radii of AnionsIonic Radii of Anions
• Anions are larger than the atoms from which they are formed.
• Effective nuclear charge is unchanged, but additional electron(s) increase electron–electron repulsion.
• Isoelectronic species have the same electron configuration; size decreases with effective nuclear charge.
Atomic Radii and the Periodic TableAtomic Radii and the Periodic Table
ExampleExample
Use the standard periodic table to arrange the following species in the expected order of increasing radius:
Certain __________________________recur at regular intervals, and/or vary in regular fashion, when the elements are arranged according to ______________________.
Melting point, boiling point, hardness, density, physical state, and chemical reactivity are periodic properties.
We will examine several periodic properties that are readily explained using electron configurations.
• Atomic radius __________ from left to right within a period.
• Why? The ________________________increases from left to right, increasing the attraction of the nucleus for the valence electrons, and making the atom smaller.
Mg has a greater effective nuclear charge than Na, and is smaller than Na.
Effective Nuclear Charge (Zeff): The nuclear charge actually felt by an electron.Zeff = Zactual - Electron shielding
Multielectron and ShieldingMultielectron and Shielding
Atomic Radii of the ElementsAtomic Radii of the Elements
ExampleExample
With reference only to a periodic table, arrange each set of elements in order of increasing atomic radius:
(a)Na, Al, P
(b) Te, S, Se
(c) Ge, Sb, Sn
Ionic RadiiIonic Radii
The ___________ of each ion is the portion of the distance between the nuclei occupied by that ion.
Ionic Radii of CationsIonic Radii of Cations
• __________ are _________ than the atoms from which they are formed; the value of n usually decreases. Also, there is less electron–electron repulsion.
Ionic Radii of AnionsIonic Radii of Anions
• ________ are _______than the atoms from which they are formed.
• Effective nuclear charge is unchanged, but additional electron(s) increase electron–electron repulsion.
• _____________ species have the same electron configuration; size decreases with effective nuclear charge.
Atomic Radii and the Periodic TableAtomic Radii and the Periodic Table
ExampleExample
Use the standard periodic table to arrange the following species in the expected order of increasing radius:
Sr2+, Ru3+, Rb+, I–, Br–
Periodic Trend• Ionization Energy –
– Group –
– Period –
Ionization EnergyIonization Energy
• ____________________(I) is the energy required to remove an electron from a ground-state gaseous atom.
• I is usually expressed in kJ per mole of atoms.
M(g) M+(g) + e– ΔH = I1
M+(g) M2+(g) + e– ΔH = I2
M2+(g) M3+(g) + e– ΔH = I3
Ionization Energy TrendsIonization Energy Trends
• I1 < I2 < I3– Removing an electron from a __________ is more difficult than
removing it from a ____________.
• A large jump in I occurs after valence electrons are completely removed (why?).
• I1 ____________ from top to bottom on the periodic table.– n increases; valence electron is farther from nucleus.
• I1 generally _________ from left to right, with exceptions.– Greater effective nuclear charge from left to right holds electrons