X Unit 11: The Periodic Table

History of the Periodic Table Antoine Lavoisier (1743 – 1794) Published Elements of Chemistry in 1789 Included a list of “simple substances” (which we now know to be elements) Formed the basis for the modern list of elements Only classified substances as metals or nonmetals

History of the Periodic Table Johann Döbereiner (1780 – 1849) Classified elements into “triads” Groups of three elements with related properties and weights Began in 1817 when he realized Sr was halfway between the weights of Ca and Ba and they all possessed similar traits Döbereiner’s triads: Cl, Br, I  S, Se, Te Ca, Sr, Ba  Li, Na, K

History of the Periodic Table John Newlands (1837 – 1898) Law of Octaves (1863) Stated that elements repeated their chemical properties every eighth element Similar to the idea of octaves in music

History of the Periodic Table Dmitri Mendeleev (1834 – 1907) Russian chemist (“The father of the periodic table”) Arranged elements based on accepted atomic masses and properties that he observed Listed elements with similar characteristics in the same family/group Left blank spots for predicted elements which would be discovered later

Dmitri Mendeleev (1834 – 1907)

Dmitri Mendeleev (1834 – 1907) Property Mendeleev’s Prediction for “eka-silicon” in 1871 Observed Properties of Germanium (discovered in 1886) Atomic Weight 72 72.59 Density (g/cm3) 5.5 5.35 Melting Point (°C) High 947 Color Dark gray Grayish white Formula of oxide XO2 GeO2

History of the Periodic Table Henry Moseley (1887 – 1915) English physicist Arranged elements based on increasing atomic number Remember: atomic number = # of p+ in nucleus Periodic table looked similar to Mendeleev’s design since as atomic number increases, so does the atomic mass

Periodic Law Periodic – occurring at regular intervals Relates to trends on the periodic table of elements Modern Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their properties Just like Mendeleev suspected!!

Reading the Periodic Table Periods “Horizontal Rows” on the periodic table Groups (or Families) “Vertical Columns” on the periodic table

Reading the Periodic Table Metalloids – elements having properties of both metals and nonmetals

Properties of Metals/Non-metals/Metalloids Metals - shiny, smooth, solid at room temperature, good conductors of heat and electricity, malleable and ductile. Metalloids (along stair step line) physical and chemical properties of both metals and nonmetals- B, Si, Ge, As, Sb, Te Nonmetals – low melting and boiling points, brittle, dull-looking solids, poor conductors of heat and electricity.

Reading the Periodic Table Valence e- are periodic! Notice the similarities Ex.) Write the noble gas configurations for: F Cl Br I GROUPS have similar valence electron configurations!

Groups of Elements Group 1 = Alkali Metals Located in Group 1 (except Hydrogen) Extremely reactive Want to lose 1 e- to become “noble gas-like” Group 2 = Alkaline Earth Metals Also very reactive Both Group 1 & 2 occur naturally as compounds not elements

Group 1: Alkali Metals Li, Na, K, Rb, Cs Reaction of potassium + H2O Potassium & Water Explanation Reaction of Potassium & Water (Larger Scale) Cutting sodium metal

Group 2: Alkaline Earth Metals Be, Mg, Ca, Sr, Ba, Ra Magnesium Magnesium oxide Burning Mg Ribbon

Groups of Elements Group 17 = Halogens Very active nonmetals Want to gain 1 e- to become like a noble gas

Mythbusters Noble Gas Demo Groups of Elements Group 18 = Noble Gases Sometimes called “inert gases” since they generally don’t react Mainly true, but not always (Kr, Xe will react sometimes) Have a full valence shell (8 e-) Mythbusters Noble Gas Demo

Groups of Elements Transition Metals Lanthanides and Actinides Located in the center of the Periodic Table 10 elements wide (“d” orbitals) Semi-reactive, valuable, crucial to many life processes Lanthanides and Actinides Located at the bottom of the Periodic Table 14 elements wide (“f” orbitals) Some are radioactive, though not all Lanthanides = Period 6 Actinides = Period 7

Alkali Metals = Alkaline Earth Metals = Transition metals = Metalloids = Lanthanides = Halogens = Actinides = Noble Gases =

Periodic Properties & Trends Electronegativity Ability of an atom to pull e- towards itself Linus Pauling: developed scale to demonstrate different electronegativity strengths Increases going up and to the right Across a period  more protons in nucleus = more positive charge to pull electrons closer Down a group  more electrons to hold onto = element can’t pull e- as closely

Periodic Properties & Trends Electronegativity Ability of an atom to pull e- towards itself Across a period  more protons in nucleus = more positive charge to pull electrons closer Down a group  more electrons to hold onto = protons in nucleus can’t pull e- as closely

Periodic Properties & Trends Atomic Radius Distance between the nucleus and the furthest electron in the valence shell Increases going down and to the left Down a group  more e- = larger radius Across a period  elements on the right can pull e- closer to the nucleus (more electronegative) = smaller radius *Remember* LLLL  Lower, Left, Large, Loose

Periodic Properties & Trends Atomic Radius Increases going down and to the left *Remember* LLLL  Lower, Left, Large, Loose

LLLL: Lower Left, Larger Atoms Memory Device LLLL: Lower Left, Larger Atoms

Periodic Properties & Trends Ionization Energy Energy required to remove an e- from the ground state 1st I.E. = removing 1 e-, easiest 2nd I.E. = removing 2 e-, more difficult 3rd I.E. = removing 3 e-, even more difficult Ex.) B --> B+ + e- I.E. = 801 kJ/mol Ex.) B+ --> B+2 + e- I.E.2 = 2427 kJ/mol Ex.) B+2 --> B+3 + e- I.E.3 = 3660 kJ/mol

Periodic Properties & Trends Ionization Energy Increases going up and to the right Down a group  more e- for the nucleus to keep track of = easier to rip an e- off Across a period  elements on the right can hold electrons closer (more electronegative) = harder to rip an e- off

Periodic Properties & Trends Metallic Character How “metal-like” an element is Metals lose e- Most Metallic: Cs, Fr Least: F, O Increases going down and to the left Think about where the metals & nonmetals are located on the periodic table to help you remember!

Periodic Properties & Trends Ionic Radius Radius of an atom when e- are lost or gained different from atomic radius Ionic Radius of Cations Decreases when e- are removed Ionic Radius of Anions Increases when e- are added

Sizes of Ions Li + , 78 pm 2e and 3 p Li,152 pm 3e and 3p CATIONS are SMALLER than the atoms from which they are formed. Size decreases due to increasing he electron/proton attraction.

Sizes of Ions F - , 133 pm 10 e and 9 p F, 71 pm 9e and 9p ANIONS are LARGER than the atoms from which they are formed. Size increases due to more electrons in shell.

Overall Periodic Trends Property Group Trend Period Trend Atomic Radius Increases going down Increases to the left Ionization Energy Increases going up Increases to the right Electronegativity Metallic Character

Summary of Periodic Trends