Ch 4 The periodic table

1. Ch 4The periodic table Element organizations: Patterns in element properties, groups of elements that share properties

2. Contribution to the periodic table • John Newland • Arranged elements by properties and increase atomic mass. • Rows of similar chemical and physical properties repeated every 8th element. (law of octaves. • Dmitric Mendeleev: • 63 elements in a table to show similarities & periodic trends by increase atomic mass. • Chemical & physical properties w/ symbols of each element on cards. • Gaps in table, predicted properties of missing elements (Ga, Sc & Ge) • Not all fit by increasing atomic mass (Te & I), needed to switch but did not understand why.

3. Periodic law • Mosley: • Identified element & atomic number. • Arrange elements by increasing atomic number, fix some of the problems with Mendeleev’s PT • Ramsey: • Discovered noble gases • Periodic law: • Repeating physical & chemical properties of elements change periodically with their atomic number.

4. Periodic table organization (pg 120-121) • By element’s valence electrons (outer most electrons) determines chemical properties • s and p block electrons • Groups: • Vertical column of elements in the periodic table. • Elements share chemical & physical properties, same number valance elements. • Periods: • Horizontal row (same # of occupied energy levels • Period # = occupied energy level • Systematic change properties (metal -> nonmetal)

5. Regions Periodic table • Main group elements (representative elements): • Elements in s-block or p-block of the periodic table. • Elements in each group have the same # of valance electrons. • Alkali metals (G1): • Name from metals that react with water to form alkaline solutions. • Very reactive (1 valence electrons) • Stored in oil, not found free in nature, soft, good conductors of electricity. • Alkaline-earth metals (G2): • Highly reactive, not found free in nature • 2 valence electrons, harder & higher melting point than G1

6. Continue • Halogens G17 • Most reactive nonmetal, “salt maker” • 7 valence electrons, gain 1 electron • Noble gases G18 • Inert gases, 8 valence electrons, non reactive. • Hydrogen • Most common element in the universe • Unique properties, separate classification. • Metals (most elements) • Shinny appearance, durable, conductors, ductile, malleable. • d-block called transition metals G3-G12, sum of outer s&d electrons = group # • Less reactive metal, nonreactive --> free in nature Au, Pt, Pd.

7. Continue • Lanthanides & actinides • f-block, rare-earth • Additional metal properties • Alloys: mixing 2 or more metals-> different properties than each metal. (brass Cu&Zn harder and corrosion resistant, sterling silver Ag&Cu used in jewelry, steel Fe&C)

8. Periodic table trends • Trend: predicable change in a particular directions. • Make predictions about the chemical behavior of the elements • Based on electron configuration. • Ionization energy: • Energy required to remove an electron from an atom or ion. • Overcome attractive force between protons and electrons. • Become positive charge (cation) • Atom + IE --> Cation (+) + electron • Trend: IE decrease down group, valence electrons further from nucleus and electron shielding -> decrease attractive force between nucleus and valance electrons • IE increases across a period, # of protons and electrons increase, higher nuclear charge and attractive forces -> decrease size

9. PT Trends continue • Atomic radius: • Volume occupied by electrons • Measured using bond radius. 1/2 distance from the center to center of two like atoms that are bonded together. • Trend: increases down group, increase energy levels and shielding decreases effective nuclear charged “felt” by valance electrons. • Decreases across period: across period increase # protons and electrons, shielding does not play a major role. Increase nuclear charge and attraction to electrons.

10. PT trends continue • Electronegativity: • Measure of the ability of an atom in a chemical compound to attract electrons. • Know the strength of attraction -> predict chemical and physical properties. • Linus Pauling: scale of values, reflect how much an atom attract electrons. Increase value, increase attraction. • Trend: decrease down groups, electron shielding decreases attraction between valence electrons & effective nuclear charge, increase size and decrease attraction. • Increases across periods, increase # protons & electrons (electron shielding no change) -> increase effective nuclear charge -> electron attracted greater.

11. PT trend continue • Ionic size: • Increase effective nuclear charge and attraction. • Cation decrease across period, anions decrease across period. • Electron affinity: • Gain electrons from neutral atom. • Increase from low left to upper right of the periodic table • Due to electron shielding and effective nuclear charge.

12. Melting & boiling pt trends • Across period: • 2 peaks as d&p orbital fill • Increase # electrons -> stronger bonds between atoms -> more energy to melt or boil. • 1st peak in d-block when orbital about 1/2 filled. • As decrease # of unpaired electrons-> decrease attraction. • 2nd peak in p-block when orbital about 1/2 filled. • Arrange the following atoms by increasing atomic size, electronegativity, ionization energy and electron affinity. • Si, Ba, O, and Ge

13. Elements come from? • 93 naturally occurring elements • Tc (technetium, Pm (promethium) & Np (neptunium) not found on earth but detected in spectrum of stars. • Most atoms in living things contain 6 elements • C,H,O,N,P and S • All (93) created in center of stars billions of years ago. • Hydrogen & helium formed after big bang. • Big bang -> all energy. As cooled & expanded energy -->matter. • Electrons, protons & neutrons -> form hydrogen -> fusion to form helium. • Hydrogen clouds condense • Form stars, center of stars nuclear reactions to form heavier elements.

14. Mass  to energy • E=mc2 --> gamma rays • Depended on size of star collapsed • Supernovas explode and spread out heavier elements. • Transmutations •  one element to another, nuclear reactions. • Synthetic elements: transuranium elements with more than 92 protons. • Particle accelerators (cyclotron) make super heavy elements.

15. Nuclear Stability • Nucleon: proton or neutron • Nuclide: isotope of a specific element identifed by the number of protons and neutrons. • Strong nuclear force: interaction that binds nucleons together in the nucleus of a nuclide. • Binding energy determines nuclear stability. • Mass defect due to the difference between the mass of an atom and the sum of the mass of atom’s protons, neutrons and electrons and is equal to the binding energy. A, mass number, = # P & N Z, atomic number, = #P X is symbol of the element AX Z

16. Nuclear Stability • Predicted by the amount of binding energy. • Ratio of # of neutrons to protons. Band of stability. • Stable nucleus: equal or more neutrons to protons • Even number of protons and neutrons. • Magic numbers : 2,8,20,28,50,82 and 126 of protons or neutrons. • Isotopes atomic number greater than 83 and mass number greater than 209 are unstable.

17. Radioactivity decay • Process by which an unstable nucleus emits one or more particles or energy. (pg 648 table 1) • Decay particles ( involve the isotope’s nucleus): • Alpha (): helium nucleus (4He). • Beta (): charged electron emitted from a neutron (0e-). • Gamma ray (): high energy photon. Mass convert to energy. • Electron capture: proton convert to a neutron (0e-). • Positron emission: positive particle emitted from a proton to form a neutron (0e+). • During nuclear decay total number of nucleons is conserved,

18. Nuclear decay reactions • Complete the following: • 222Rn --> 218Po + ? • 87Rb --> 87Sr + ? • 37Ar + 0e- --> ? • 243Am --> ? + 4He • ? + 0e- --> 82Rb • ? --> 61Ni + 0e+

19. Nuclear fission • Splitting the nucleus of a large atom into two or more fragments, produces additional neutrons and energy (nuclear power plants). • 235U + 1n ---> 93Kr + 140Ba + 3 1n • Chain reaction: change in a single molecule makes many molecules change until stable. • Critical mass: minimum mass of a fissionable isotope that provides the number of neutrons needed to sustain a change reaction. Control rods help control the chain reaction. • Energy released is used to convert water into steam a drive a steam turbine. • Waste is radioactive and difficult to store.

20. Nuclear fusion • Combination of the nuclei of small atoms to form a large nucleus, releases energy (mass loss convert into energy E = mc2). • Process occurs in the cores of stars (high temperature 1million K and pressure) • 4 1H --> 4He + 2 0e+ • No radioactive waste yet hard to maintain process.

21. Half-life • Time require for half of a radioactive substance to decay. • Is constant for specific isotopes (pg659 table 2) • Can be used to determine the age of a substance. • Practice: • A fossil of an unknown age is found. Scientists determine that the C-14/C-12 ratio in the fossil is 1/32 of the ratio found in living substance today. Calculate the age of the fossil.

22. Uses of nuclear chemistry • Geologic dating • Smoke detectors • Detecting art forgeries • Nuclear medicine • Important to minimize daily exposure of living organisms