Periodic Trends in Properties on the Periodic Table

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Periodic Trends in Properties on the Periodic Table

Periodic Trends in Properties on the Periodic Table

The Plan Essential Question: What causes the trends of the properties in the periodic

The Plan Essential Question: What causes the trends of the properties in the periodic table? l Discuss Some Properties of Atoms l Explore the Trends l Try to Explain the Trends

Effective Nuclear Charge - (Zeff) – the charge an electron “feels” from the nucleus

Effective Nuclear Charge - (Zeff) – the charge an electron “feels” from the nucleus l Zeff = Z – S, where Z is the atomic number and S is the shielding experienced by the outer electrons l The electrons in the outer energy levels don’t feel the full charge of the nucleus because the core electrons help shield them from the nucleus. l

Atomic Radius l l l Atomic radius – the radius of an atom Several

Atomic Radius l l l Atomic radius – the radius of an atom Several methods of determining the radius - usually measure the distance between two atoms Not all values are completely consistent with each other.

Ionization Energy l Ionization Energy – the energy required to remove one electron from

Ionization Energy l Ionization Energy – the energy required to remove one electron from an atom l Essentially this is the process of making a positive ion. X X+ + e -

Electronegativity l Electronegativity – the ability of an atom in a compound to attract

Electronegativity l Electronegativity – the ability of an atom in a compound to attract electrons to itself l Electrons in compounds spend the most time around atoms with high electronegativities. l Elements with high electronegativities have partial negative charges in compounds.

Periodic Trends Lab In your lab groups, predict what trends you think might occur

Periodic Trends Lab In your lab groups, predict what trends you think might occur down a family and across a period for each of the properties we discussed: Effective nuclear charge Atomic radius Ionization energy Electronegativity Record on the index card for discussion later

Effective Nuclear Charge l As you travel left to right across a period: l

Effective Nuclear Charge l As you travel left to right across a period: l Atomic number increases l Shielding stays roughly the same l Therefore Zeff increases significantly across a period l As you travel down a family l Atomic number increases sharply l Shielding increases sharply l Zeff does increase down a family but not as much as you might expect.

Atomic Radius l As you travel left to right across a period: l Effective

Atomic Radius l As you travel left to right across a period: l Effective nuclear charge increases l Electrons are being added to the same n shell l n values have somewhat to do with distance from the nucleus. l Size of atoms shrink as you move to the right. l As you travel down a family l Effective nuclear charge increases more slowly l Electrons are added to n shells farther away l Size of atoms increase down the family

Ionization Energy l As you travel left to right across a period l Effective

Ionization Energy l As you travel left to right across a period l Effective nuclear charge increases l Harder to remove an electron therefore… l Ionization Energy increases l As you travel down a family l Effective nuclear charge increases slowly l Outer electrons are farther away from the nucleus l Ionization Energy decreases

Ionization Energy

Ionization Energy

Ionization Energy

Ionization Energy

Electronegativity l As you travel left to right across a period: l Effective nuclear

Electronegativity l As you travel left to right across a period: l Effective nuclear charge increases strongly l Electronegativity increases l As you travel down a family l Effective nuclear charge increases slowly l Outer electrons are being added in shells farther and farther away l Electronegativity decreases

Electronegativity

Electronegativity

Ionic Radius l Ionic Radius – size of an ion l Consider two different

Ionic Radius l Ionic Radius – size of an ion l Consider two different relationships l Relationship between atom and ion l Relationship between ions and atoms with the same number of electrons l “isoelectronic series”

Ionic Radius

Ionic Radius

Ionic vs. Atomic Number of protons always stays the same l For negative ions

Ionic vs. Atomic Number of protons always stays the same l For negative ions (anions) l l Electrons are added to the same outer shell l Electron-electron repulsions increase l Anions are larger than their atoms l For positive ions (cations) l Electrons are removed to leave one less shell l n shells describe distance from nucleus l Cations are smaller than their atoms

Ionic Radius

Ionic Radius

Isoelectronic series All have the same number of electrons l Number of protons changes

Isoelectronic series All have the same number of electrons l Number of protons changes l Therefore effective nuclear charge increases l Electrons are pulled in tighter l The negative ions are larger than the positive ions with the same number of electrons. l

Practice Problems l Arrange the following elements in order of decreasing atomic radius: l

Practice Problems l Arrange the following elements in order of decreasing atomic radius: l As, l O, Sn, Ge, Ne, Ba, He Arrange the following elements in order of increasing electronegativity l Al, Mg, P, Sr, O, F, Rb

Ticket Out the Door l Arrange the following elements in order of increasing ionization

Ticket Out the Door l Arrange the following elements in order of increasing ionization energy: l Cs, Ba, Y, In, Ga, Si, P, F

Test Review Problem Challenge Problem l Place the following in order of increasing size:

Test Review Problem Challenge Problem l Place the following in order of increasing size: Ne, Cl-, Ar, Na+ l