2The Periodic Table-Key Questions What is the periodic table ?What information is obtained from the table ?How can elemental properties be predicted based on the Periodic Table?
3Periodic TableThe development of the periodic table brought a system of order to what was otherwise an collection of thousands of pieces of informationThe periodic table is a milestone in the development of modern chemistry. It not only brought order to the elements but it also enabled scientists to predict the existence of yet undiscoveredelements.
4Early Attempts to Classify Elements Dobreiner’s Triads (1827)Classified elements in sets of three having similar properties.Found that the properties of the middle element were approximately an average of the other two elements in the triad.
5Dobreiner’s Triads Cl Br I 35.5 79.9 126.9 81.2 1.56 3.12 4.95 3.25 Ca ElementAtomic MassAverageDensityClBrI35.579.9126.981.21.563.124.953.25CaSrBa40.187.6137.388.71.522.214.171.124Note: In each case, the numerical values for the atomic mass and density of the middle element are close to the averages of the other two elements
6Newland’s Octaves -1863John Newland attempted to classify the then 62 known elements of his day.He observed that when classified according to atomic mass, similar properties appeared to repeat for about every eighth elementHis Attempt to correlate the properties of elements with musical scales subjected him to ridicule.In the end his work was acknowledged and he was vindicated with the award of the Davy Medal in 1887 for his work.
7Dmitri MendeleevDmitri Mendeleev is credited with creating the modern periodic table of the elements.He gets the credit because he not only arranged the atoms, but he made predictions based on his arrangement which were shown to be quite accurate.
8Mendeleev’s Periodic Table Mendeleev organized all of the elements into one comprehensive table.Elements were arranged in order of increasing mass.Elements with similar properties were placed in the same row.
10Mendeleev’s Periodic Table Mendeleev left some blank spaces in his periodic table. At the time the elements gallium and germanium were not known. He predicted their discovery and estimated their properties
11Periodic TableThe Periodic Table has undergone several modifications before it evolved in its present form. The current form is usually attributed to Glenn Seaborg in 1945
12Periodic Table Expanded View The Periodic Table can be arranged by energy sub levels The s-block is Group IA and & IIA, the p-block is Group IIIA - VIIIA. The d-block is the transition metals, and the f-block are the Lanthanides and Actinide metalsThe way the periodic table usually shown is a compressed view. The Lanthanides and actinides (F block)are cut out and placed at the bottom of the table.
13Periodic Table: Metallic Arrangement Layout of the Periodic Table: Metals vs. nonmetalsNonmetalsMetals
14The Three Broad Classes Are Main, Transition, Rare Earth Main (Representative), Transition metals,lanthanides and actinides (rare earth)
15Reading the Periodic Table: Classification Nonmetals, Metals, Metalloids, Noble gases
17Periodic Table: The electron configurations are inherent in the periodic table Li2s1Be2s2B2p1C2p2N2p3O2p4F2p5Ne2p6Na3s1Mg3s2Al3p1Si3p2P3p3S3p4Cl3p5Ar3p6K4s1Ca4s2Sc3d1Ti3d2V3d3Cr4s13d5Mn3d5Fe3d6Co3d7Ni3d8Cu4s13d10Zn3d10Ga4p1Ge4p2As4p3Se4p4Be4p5Kr4p6Rb5s1Sr5s2Y4d1Zr4d2Nb4d3Mo5s14d5Tc4d5Ru4d6Rh4d7Ni4d8Ag5s14d10Cd4d10In5p1Sn5p2Sb5p3Te5p4I5p5Xe5p6Cs6s1Ba6s2La5d1Hf5d2Ta5d3W6s15d5Re5d5Os5d6Ir5d7Ni5d8Au6s15d10Hg5d10Tl6p1Pb6p2Bi6p3Po6p4At6p5Rn6p6Fr7s1Ra7s2Ac6d1Rf6d2Db6d3Sg7s16d5Bh6d5Hs6d6Mt6d7
18Periodic Table Organization------ Groups or Families Vertical columns in the periodic table are known as groups or families The elements in a group have similar electron configurations
19Periodic Table Organization ---- Periods Horizontal Rows in the periodic table are known as Periods The Elements in a period undergo a gradual change in properties as one proceeds from left to right
20Periodic PropertiesElements show gradual changes in certain physical properties as one moves across a period or down a group in the periodic table. These properties repeat after certain intervals. In other words they are PERIODICPeriodic properties include:-- Ionization Energy-- Electronegativity-- Electron Affinity-- Atomic Radius-- Ionic Radius
21Trends in Ionization Energy Ionization energy is the energy required toRemove an electron from an atomIonization energy increases across a period because the positive charge increases.Metals lose electrons more easily than nonmetals.Nonmetals lose electrons with difficulty (they like to GAIN electrons).
22Trends in Ionization Energy The ionization energy increases UP a groupBecause size increases due to an effect known as the Shielding Effect
25ElectronegativityElectronegativity is a measure of the ability of an atom in a molecule to attract electrons to itself.This concept was first proposed by Linus Pauling ( ). He later won the Nobel Prize for his efforts
26Periodic Trends: Electronegativity In a group: Atoms with fewer energy levels can attract electrons better (less shielding). So, electronegativity increases UP a group of elements.In a period: More protons, while the energy levels are the same, means atoms can better attract electrons. So, electronegativity increases RIGHT in a period of elements.
31Electron Affinities Are Periodic Electron Affinity v Atomic Number
32The Electron Shielding Effect Electrons between the nucleus and the valence electrons repel each other making the atom larger.
33Atomic Radius The radius increases on going down a group. Because electrons are added further from the nucleus, there is less attraction. This is due to additional energy levels and the shielding effect. Each additional energy level “shields” the electrons from being pulled in toward the nucleus.The radius decreases on going across a period.
34Atomic RadiusThe radius decreases across a period owing to increase in the positive charge from the protons. Each added electron feels a greater and greater + charge because the protons are pulling in the same direction, where the electrons are scattered.LargeSmall
38CationsCations (positive ions) are smaller than their corresponding atoms
39Ion SizesDoes the size go up or down when gaining an electron to form an anion?
40Ionic Radius CATIONS are SMALLER than the atoms from which they come. Li+, 78 pm2e and 3 pForming a cation.Li,152 pm3e and 3pCATIONS are SMALLER than the atoms from which they come.The electron/proton attraction has gone UP and so the radius DECREASES.
41Ionic Radius for Cations Positve ions or cations are smaller than the corresponding atoms.Cations like atoms increase as one moves from top to bottom in a group.
42AnionsAnions (negative ions) are larger than their corresponding atoms
43Ionic Radius-Anions Forming an anion. , 133 pm10 e- and 9 p+F pm9e- and 9p+Forming an anion.ANIONS are LARGER than the atoms from which they come.The electron/proton attraction has gone DOWN and so size INCREASES.Trends in ion sizes are the same as atom sizes.
44Ionic Radii for Anions Negative ions or anions are larger than the corresponding atoms.Anions like atoms increase as one moves from top to bottom in a group.
45Ionic Radius for an Isoelectronic Group Isoelectronic ions have the same number of electrons.The more negative an ion is the larger it is and vice versa.
49The D Block ElementsThe d block elements fall between the s block and the p block.They share common characteristics since the orbitals of d sublevel of the atom are being filled.
50The D Block ElementsThe D block elements include the transition metals. The transition metals are those d block elements with a partially filled d sublevel in one of its oxidation states.Since the s and d sublevels are very close in energy, the d block elements show certain special characteristics including:Multiple oxidation statesThe ability to form complex ionsColored compoundsCatalytic behaviorMagnetic properties
51Some common D block oxidation states The D Block ElementsThe d electrons are close in energy to the s electrons.D block elements may lose 1 or more d electrons as well as s electrons. Hence they often have multiple oxidation statesSome common D block oxidation states
52Multiple Oxidation States There is no sudden sharp increase in ionization energy as one proceed through the d electrons as there would be with the s block.D block elements can lose or share d electrons as well as s electrons, allowing for multiple oxidation states.Most d Block elements have a +2 oxidation State which corresponds to the loss of the two s electrons.This is especially true on the right side of the d block, but less true on the left.---- For example Sc+2 does not exist, andTi+2 is unstable, oxidizingin the presence of anywater to the +4 state.
53Complex IonsThe ions of the d block and the lower p block have unfilled d or p orbitals.These orbitals can accept electrons either an ion or polar molecule, to form a dative bond. This attraction results in the formation of a complex ion.A complex ion is made up of two or more ions or polar molecules joined together.The molecules or ions that surround the metal ion donating the electrons to form the complex ion are called ligands.
54Complex Ions K3Fe(CN)6 Cu(NH3)42+ Compounds that are formed with complex ions are called coordination compoundsCommon ligandsComplex ions usually have either 4 or 6 ligands.K3Fe(CN) Cu(NH3)42+
55Complex IonsThe formation of complex ions stabilizes the oxidations states of the metal ion and they also affect the solubility of the complex ion.The formation of acomplex ion often hasa major effect on thecolor of the solution ofa metal ion.
56The D Block Colored Compounds In an isolated atom all of the d sublevel electrons have the same energy.When an atom is surrounded by charged ions or polar molecules, the electric field from these ions or molecules has a unequal effect on the energies of the various d orbitals and d electrons.The colors of the ions and complex ions of d block elements depends on a variety of factors including:The particular elementThe oxidation stateThe kind of ligands bound to the elementVarious oxidationstates of Nickel (II)
57Colors in the D BlockThe presence of a partially filled d sublevels in a transition element results in colored compounds.Elements with completely full or completely empty subshells are colorless,For example Zinc which has a full d subshell. Its compounds are whiteA transition metal ion is colored, if it absorbs light in the visible range (nanometers).If the compound absorbs aparticular wavelength of light itscolor will be the composite of thosewavelengths that it does not absorb.In other words it shows itscomplimentary color.
58Colors and d Electron Transitions When ligands are attached to transition metal ions, the d orbitals may split into two groups. Some of the orbitals are at a lower energy than the othersThe difference in energy of these orbitals varies slightly with the nature of the ligand or ion surrounding the metal ionThe energy of the transition: ∆E =hn may occur in the visible region.When white light passes through a compound of a transition metal, light of a particular frequency is absorbed as an electron is promoted from a lower energy d orbital to a higher one.The result is a colored compound
59Magnetic PropertiesParamagnetism --- Molecules with one or more unpaired electrons are attracted to a magnetic field. The more unpaired electrons in the molecule the stronger the attraction. This type of behavior is calledDiamagnetism --- Substances with no unpaired electrons are weakly repelled by a magnetic field.Transition metal complexes with unpaired electrons exhibit simple paramagnetism.The degree of paramagnetism depends on the number of unpaired electrons
60Catalytic BehaviorMany D block elements are catalysts for various chemical reactionsCatalysts speed up the rate of a reaction with out being consumed.The transition metals form complex ions with ligands that can donate lone pairs of electrons.This results in close contact between the metal ion and the ligand.Transition metals also have a wide variety of oxidation states so they gain and lose electrons in oxidation- reduction reactions
61Some Common D Block Catalysts Examples of D block elements that are used as catalysts:Platnium orrhodium in acatalytic converterMnO2 decompositionof hydrogen peroxideV2O5 in the contactprocessFe in Haber processNi in conversion ofalkenes to alkanes
62The Periodic Table--Summary The periodic table is a classification system. Although we are most familiar with the periodic table that Seaborg proposed more than 60 years ago, several alternate designs have been proposed.