6 Chapter 5The Periodic Law5.1 History of the Periodic Table
7 Predecessors to the Modern Periodic Table Dobereiner’s TriadsJ.W. Dobereiner classified some elements into groups of three, which he called triads.similar chemical propertiesphysical properties varied in an orderly way according to their atomic masses.
9 Predecessors to the Modern Periodic Table Mendeleev’s Periodic TableDmitri Mendeleev realized that the chemical and physical properties of the elements repeated in an orderly way when he organized the elements according to increasing atomic mass.In 1869, Mendeleev published a table of the elements organized by increasing atomic mass.Mendeleev was a Russian scientist and is often referred to as the “Father” of the Periodic Table.Periodicity is the tendency to recur at regular intervals.
10 Mendeleev’s Table "The chemical properties of the elements are a periodic function of their atomic weights"
11 Mendeleev's Periodic Table Vertical columns in atomic weight orderHorizontal rows have similar chemical propertiesMendeleev made some exceptions toplace elements in rows with similarproperties (tellurium & iodine's places were switched)Missing Elements: gaps existed in Mendeleev’s tableMendeleev predicted the properties of the “yet to be discovered” elements(scandium, germanium and gallium)
12 Problems with Mendeleev’s Table Why didn't some elements fit in order of increasing atomic mass?Moseley helped to clarify some of the problems…Why did elements exhibit periodic behavior?
13 Henry MoseleyEnglish physicist who determined the number of positive charges in the nucleus (protons) by measuring the wavelength of the x-rays given off by certain metals in 1913.He was killed by a sniper in Turkey in August 1915 during WWI. Many people think that Britain lost a future Nobel Prize winner. This is because Nobel Prizes, the most prestigious awards for scientific achievement are awarded only to living people.
14 Moseley and the Periodic Table Protons and Atomic Number:X-ray experiments revealed a way to determine the number of protons in the nucleus of an atomThe periodic table was found to be in atomic number order, not atomic mass order!!!This explained tellurium-iodine anomaly***Moseley was killed in battle in 1915, during WWI. He was 28 years oldThe Periodic LawThe physical and chemical properties of the elements are periodic functions of their atomic numbers
15 Discovery of the Noble Gases William Ramsay discovers argonRamsay discovers krypton and xenonHelium discovered as a component of the sun, based on the emission spectrum of sunlightRamsay finds helium on EarthFreidrich Dorn discovers radon18681894189518981900Sir William Ramsay
16 The LanthanidesEarly 1900's the elements from cerium (#58) to lutetium (#71) are separated and identified. Also known as the rare earth elements, less than 0.01% naturally occurring.The ActinidesDiscovery (or synthesis) of thorium, # 90 to lawrencium #103Both groups pulled out of the table for space reasons.Periodicity:Elements with similar properties are found at regular intervals within the "periodic" table
18 5.2 Electron Configuration & The Periodic Table Chapter 5The Periodic Law5.2 Electron Configuration & The Periodic Table
19 Sublevel Blocks on the Periodic Table 123456789101112131415161718Sublevel Blocks on the Periodic Table
20 The Properties of a Group: the Alkali Metals Easily lose 1 valence electron(Reducing agents)React violently with waterReact with halogens to form salts
21 The Properties of a Group: the Alkali Earth Metals Easily loses 2 valence electron(Reducing agents)Harder, denser, stronger than Group 1 metalsHigher melting pointsLess reactive than Group 1, but too reactive to be found free in nature
22 5.3 Electron Configuration & Periodic Properties Chapter 5The Periodic Law5.3 Electron Configuration & Periodic Properties
23 Determination of Atomic Radius: Half of the distance between nuclei incovalently bonded diatomic molecule"covalent atomic radii"Periodic Trends in Atomic Radius:Radius decreases across a periodIncreased effective nuclear charge dueto decreased shieldingRadius increases down a groupAddition of principal quantum levels
25 How to Achieve an Octet… Atoms can form ions by gaining or losing electrons to obtain a stable outer configurationCation- Positive ion (+) ionAnion- Negative ion (-) ionIons attract (opposites attract)
26 Predicting Ionization Metals tend to lose electronsThey form cations.Ex: Na, 1s22s22p63s1 becomes Na+1,1s22s22p6Nonmetals tend to gain electrons.They form anions.Ex: O, 1s22s22p4 becomes O-2, 1s22s22p6
27 Electron Transfer: Anions When an atom gains electrons it increases its negative charge so it becomes negatively charged. There are now more electrons than protons.X + e- = X –Ex: Nitrogen Atom + 7 protons- 7 electronsNitrogen Ion +7 protons- 10 electronsNeutral-3 charge
28 Electron Transfer: Cations When an atom loses electrons, it loses negative charges so it becomes more positively charged. There are now more protons than electrons.X - (e-) = X +Ex: Potassium Atom protons- 19 electronsPotassium Ion +19 protons-18 electronsNeutral+1 charge
29 Ionization Energy - the energy required to remove an electron from an atom Increases for successive electrons taken fromthe same atomTends to increase across a periodElectrons in the same quantum level do not shield as effectively as electrons in inner levelsIrregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to removeTends to decrease down a groupOuter electrons are farther from the nucleus
33 Electron Affinity - the energy change associated with the addition of an electron Affinity tends to increase across a periodAffinity tends to decrease down a groupElectrons farther from the nucleusexperience less nuclear attractionSome irregularities due to repulsiveforces in the relatively small p orbitals
39 Electronegativity A measure of the ability of an atom in a chemical compound to attract electronsElectronegativities tend to increase acrossa periodElectronegativities tend to decrease down agroup or remain the same