Chemical Periodicity? What?

Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities. Elements in the same group have similar chemical properties.

Periodicity When elements are organized in order of  atomic mass, and grouped by similarities of chemical properties, a certain “pattern” or periodicity of properties becomes evident Draft for first version of Mendeleev's periodic table (17 February 1869).

Review of the Periodic Table Group IA – alkali metals Review of the Periodic Table

Group IA – alkali metals H1 - 1s1 Li3 - 1s22s1 Na11 - 1s22s22p63s1 K19 - 1s22s22p63s23p64s1 Rb37 - 1s22s22p63s23p63d104s24p65s1 Cs55 - 1s22s22p63s23p63d104s24p64d105s25p66s1 Fr87 - 1s22s22p63s23p63d104s24p64d104f145s25p65 d106s26p67s1

Review of the Periodic Table Group IIA – alkaline earth metals Review of the Periodic Table

Group IIA – alkaline earth metals Be4 - 1s2 2s2 Mg12 - 1s22s22p63s2 Ca20 - 1s22s22p63s23p64s2 Rb38 - 1s22s22p63s23p63d104s24p65s2 Cs55 - 1s22s22p63s23p63d104s24p64d105s25p66s2 Fr87 - 1s22s22p63s23p63d104s24p64d104f145s25p65 d106s26p67s2

Review of the Periodic Table Group VIII – Noble Gases Review of the Periodic Table

Group VIII – Noble Gases He2 - 1s2 Ne10 - 1s22s22p6 Ar18 - 1s22s22p63s23p6 Kr36 - 1s22s22p63s23p63d104s24p6 Cs54 - 1s22s22p63s23p63d104s24p64d105s25p6 Rn86 - 1s22s22p63s23p63d104s24p64d104f145s25p65 d106s26p6

Review of the Periodic Table Group VII – Halogens Review of the Periodic Table

Group VII – Halogens F9 - 1s22s22p5 Cl17 - 1s22s22p63s23p5 Br35 - 1s22s22p63s23p63d104s24p5 I53 - 1s22s22p63s23p63d104s24p64d105s25p5 At85 - 1s22s22p63s23p63d104s24p64d104f145s25p65 d106s26p5

Review of the Periodic Table Group VI

Group VI O8 - 1s22s22p4 S16 - 1s22s22p63s23p4 Se34 - 1s22s22p63s23p63d104s24p4 Te52 - 1s22s22p63s23p63d104s24p64d105s25p4 Po84 - 1s22s22p63s23p63d104s24p64d104f145s25p65 d106s26p4

Atomic Radii

Group trends As you go down a group, first IE decreases because... The electron is further away. More shielding. The electron in the outermost energy level experiences more inter-electron repulsion (shielding).

Group trends As we go down a group... H As we go down a group... each atom has another energy level, so the atoms get bigger. Li Na K Rb

Periodic trends All the atoms in the same period have the same energy level. Same shielding. But, increasing nuclear charge So IE generally increases from left to right. Exceptions at full and 1/2 full orbitals.

Periodic Trends As you go across a period, the radius gets smaller. Electrons are in same energy level. More nuclear charge. Outermost electrons are closer. Na Mg Al Si P S Cl Ar

Ionization Energy Energy needed to remove an electron from a gaseous atom: M(g) + I  M+(g) + e-; (I = ionization energy)

The Periodic Trend of Ionization Energy

He has a greater IE than H. same shielding greater nuclear charge First Ionization energy Atomic number

Outer electron further away outweighs greater nuclear charge Li has lower IE than H Outer electron further away outweighs greater nuclear charge H First Ionization energy Li Atomic number

greater nuclear charge He Be has higher IE than Li same shielding greater nuclear charge First Ionization energy H Be Li Atomic number

greater nuclear charge He B has lower IE than Be same shielding greater nuclear charge p orbital is slightly more energy and its electron easier to remove First Ionization energy H Be B Li Atomic number

First Ionization energy He First Ionization energy H C Be B Li Atomic number

First Ionization energy He N First Ionization energy H C Be B Li Atomic number

First Ionization energy He Breaks the pattern, because the outer electron is paired in a p orbital and experiences inter-electron repulsion. N First Ionization energy H C O Be B Li Atomic number

First Ionization energy He F N First Ionization energy H C O Be B Li Atomic number

Ne has a lower IE than He Both are full, Ne has more shielding Greater distance F N First Ionization energy H C O Be B Li Atomic number

Na has a lower IE than Li Both are s1 Na has more shielding He Ne Na has a lower IE than Li Both are s1 Na has more shielding Greater distance F N First Ionization energy H C O Be B Li Na Atomic number

Periodic Patterns and Ionization Energy In group: ionization energy  as you move down the column Across period: Ionization energy  as you move from left to right Rationale: group –outermost shell electrons farther away from nucleus row – outermost electron more tightly held

Ions When atoms lose or gain electrons, they become ions. Cations are positive and are formed by elements on the left side of the periodic chart. Anions are negative and are formed by elements on the right side of the periodic chart.

Ionic Radius Cations form by losing electrons. 190pm vs 102pm 97pm vs 181pm Cations form by losing electrons. Cations are smaller that the atom they come from. Metals form cations. Anions form by gaining electrons. Anions are bigger that the atom they come from. Nonmetals form anions

The Periodic Table Always remove electrons from the highest n value? Na is: 1s22s22p63s1 Forms a 1+ ion: 1s22s22p6 Same configuration as neon (isoelectronic with NEON. Ions have noble gas configurations (not transition metals)

Size of Isoelectronic ions Iso- means the same Iso electronic ions have the same # of electrons Al3+ Mg2+ Na1+ Ne F1- O2- and N3- all have 10 electrons all have the configuration: 1s22s22p6

Size of Isoelectronic ions Positive ions that have more protons would be smaller. N3- O2- F1- Ne Na1+ Al3+ Mg2+

Periodicity and Electronegativity Electronegativity ≡ a measure of how tightly held an electron is.

Periodicity and Electronegativity In group: electronegativity  as you move down the column Across period: Electronegativity  as you move from left to right Rationale: group –atoms more willing to accept another electrons due to  nuclear charge

Periodic Trends – Summary Decreasing Atomic Radii Decreasing Ionic Size Increasing Ionization Energy Increasing Electronegativity Decreasing Ionization Energy Decreasing Electronegativity Increasing Atomic Radii Increasing Ionic Radius