X Unit 10: 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 (Ted-Ed Video)Ted-Ed Video

Dmitri Mendeleev (1834 – 1907)

PropertyMendeleev’s Prediction for “eka- silicon” in 1871 Observed Properties of Germanium (discovered in 1886) Atomic Weight Density (g/cm 3 ) Melting Point (°C) High947 ColorDark grayGrayish white Formula of oxide XO 2 GeO 2

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” Groups (or Families) - “Vertical Columns”

Reading the Periodic Table Valence electrons are periodic! Notice the similarities –Ex.) Write the noble gas configurations for: F [He]2s 2 2p 5 7 valence electrons Cl [Ne]3s 2 3p 5 7 valence electrons Br [Ar]4s 2 3d 10 4p 5 7 valence electrons I [Kr]5s 2 4d 10 5p 5 7 valence electrons –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

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

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 –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 (4f) –Actinides = Period 7 (5f)

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

Electronegativity –Ability of an atom to pull e - towards itself –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

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 Ionization Energy –Energy required to remove an e- from the ground state –1 st I.E. = removing 1 e -, easiest –2 nd I.E. = removing 2 e -, more difficult –3 rd 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 CATIONS are SMALLER than the atoms from which they are formed. Size decreases due to increasing he electron/proton attraction. Li,152 pm 3e and 3p Li +, 78 pm 2e and 3 p +

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

Overall Periodic Trends PropertyGroup TrendPeriod Trend Atomic Radius Increases going down Increases to the left Ionization Energy Increases going upIncreases to the right Electronegativity Increases going upIncreases to the right Metallic Character Increases going down Increases to the left

Practice: Rank the elements from lowest to highest… Electronegativity - C, F, Mg Atomic Radius - Ir, Re, Bi Metallic Character - Rb, Mn, P Ionization Energy - B, Ga, In

Summary of Periodic Trends