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Chapter 6: The Periodic Table Elements Science has come a long way since Aristotle’s theory of Air, Water, Fire, and Earth Scientists have identified 90 naturally occurring elements, and created about 28 others A Little Bit of the History.. He originally organized the periodic table by atomic mass Dmitri Mendeleev Could not make a complete table, only had 63 elements leaving many spaces between elements Used properties of other elements to predict undiscovered elements properties A Little Bit of the History.. Mendeleev’s original Periodic Table The Periodic Law • In the modern periodic table, elements are arranged in order of increasing atomic number. • Organized into columns and rows. • 7 horizontal rows correspond to the energy levels found outside an atom’s nucleus. The Periodic Law • Horizontal rows called periods • Maximum of 7 periods that represent the energy levels of the atom • Every element in the first period has ONE energy level • Second period – TWO energy levels • Third period – THREE energy levels The Periodic Law • • • • Columns known Groups or Families Elements in the same column have similar properties Group 1 Alkali Metals, 1 valence electron, very reactive Group 2 Alkaline Earth Metals, 2 valence electrons The Periodic Law • Farthest column to right: Noble Gases • Each element has 8 valence electrons • The elements that are truly inert: Helium and Neon The Periodic Law • • • • Column to the left of noble gases: Halogens Each element has 7 valence electrons Transition metals: in the “d block” Rare Earth metals: in the “f block” How are Elements Classified? Three Regions How are Elements Classified? Three Regions: Representative, Transition, and Rare Earth Properties of Metals Metals are: Good conductors of heat and electricity Shiny Ductile (can be stretched into thin wires) Malleable (can be pounded into thin sheets) Mostly solid at room temp (except Hg) Properties of Metals Metals are not found in their pure form in nature Found in ore, mixed with other elements. Must be refined to get the pure metal. Let’s Look at the Families • • • • Alkali Alkali Earth Halogen Noble Gases Alkali Metals Group 1A (Not including hydrogen) Very reactive metals Always combined with something else in nature (like salt) 1 valence electron Malleable, ductile, good conductors of electricity Soft enough to cut with a butter knife Two most reactive elements: Cs and Fr Explodes in water http://www.youtube.com/watch?v=92Mfric7JUc Li Na K Rb Cs Fr Alkaline Earth Metals Be Group 2A Mg Reactive metals that are always combined with nonmetals in nature Ca 2 valence electrons Ba Several of these are important mineral nutrients (Mg and Ca) Ra Sr Transition Metals 38 elements Valence electrons: The electrons used to combine with other elements. Valence electrons present in more than one shell. We’ll deal with oxidation states next chapter. Iron, Cobalt and Nickel produce magnetic fields d block Other Metals (We won’t include this as a separate category) 7 elements (Al, Ga, In Sn, Th, Pb, Bi) Similar to transition metals – Ductile and malleable Different than transition metals – valence electrons only present in outer shell 3 physical properties – solid, high density, opaque Metalloids Have properties of both metals and non-metals Semi-conductor: Can carry an electric charge better than non-metals but not as well as metals Silicon and Germanium Useful in computers and calculators Silicon Properties of Non-Metals Poor conductors of heat and electricity, are not ductile or malleable and are brittle 3 states of matter at room temperature: Gas, solid or liquid Have no luster and do not reflect light Sulfur Halogens F Cl Are non-metals “Halogen” means salt former. Compounds containing halogens are called salts NaCl – table salt 7 valence electrons Liquid (Br), Gas (F, Cl), Solid (I, At) Br I At The Noble Gases He Ne Ar VERY stable gases because they have the maximum number of electrons in their outer shell Helium – 2 valence electrons All others – 8 valence electrons Used in lighted “neon” signs Used in blimps to fix the Hindenberg problem Kr Xe Rn Rare Earth Metals 30 elements in the f- block Trans-uranium means Man-Made or Synthetic One element in Lanthanides and most of Actinides are man-made In periods 6 and 7 f block lanthanides actinides OK, Let’s Review… What are some examples of metals? Gold, silver, magnesium, lead, aluminum What is a metal that is liquid at room temp? Mercury What are some examples of non-metals? Oxygen, fluorine, nitrogen, sulfur What are some of the characteristics of the metalloids ? Better conductors than non-metals, are shiny or dull, etc. Periodic Trends • So – we’ve learned about how the periodic table is organized by…. – PERIODS (Rows): • Each period represents elements with electrons in a different energy level. • Properties of elements change as you move across a period – GROUPS/FAMILIES (Columns): • Elements in the same group have similar properties • For representative elements, group number (1A – 8A) = the number of valence electrons (electrons in the s & p sublevels in the highest energy level) Periodic Trends • Now we’re going to look at how element properties change across a period or down a group: “PERIODIC TRENDS” • The periodic trends of properties that we will look at are: – – – – atomic size or atomic radius ionic size or ionic radius ionization energy electronegativity Trends in Atomic Size • The atomic radius is the distance between the nucleus and the outer edge of the electron cloud. Trends in Atomic Size • In general, atomic size: – increases from top to bottom within a group and – increases from right to left across a period. Atomic radius vs. atomic number Atomic Radius (pm) 250 K 200 Na Li 150 Mg Al Si Be 100 Ca P S Cl B C N O F Ar Ne 50 H 0 0 He 2 4 6 8 10 12 Element 14 16 18 20 Trends in Atomic Size Ions • Ions form when electrons are transferred between atoms. • If an atom loses an electron: cation (positive charge) • METALS ALWAYS LOSE (electrons) Ions • If an atom gains an electron: anion (negative charge) • Non-metals always gain electrons Trends in Ionic Size • The size of ions: – Cations (LOSE ELECTRONS) are always smaller than the original atoms. – Anions (GAIN ELECTRONS) are always larger than the original atoms. Trends in Ionic Size • Trends in Ionic Size: Size of anions and cations increase from right to left Size generally increases Positive Ions (cations) Negative Ions (anions) Trends in Ionization Energy • Atoms hold onto its electrons with different “strengths” • The energy required to remove an electron from an atom is called ionization energy. – Energy required to remove the first electron is called the first ionization energy. – Energy required to remove an electron from an ion with a 1+ charge is called the second ionization energy. Trends in Ionization Energy • First ionization energy: – increases from bottom to top within a group, and – increases from left to right across a period. Ionization energy vs. atomic number He Ionization energy (kJ/mol) 2500 Ne 2000 Ar F 1500 N H Cl C Be 1000 O P S B 500 Mg Si Al Li Ca Na K 0 0 2 4 6 8 10 12 Element 14 16 18 20 Trends in Electronegativity Electronegativity is the ability of an atom to attract electrons when the atom is in a compound * * Fluorine has the highest electronegativity Trends in Electronegativity • Electronegativity is the ability of an atom to attract electrons when the atom is in a compound. • Fluorine has the highest electronegativity. • Noble gases have zero electronegativity (they already have a full valence shell) Periodic Trends 1. How is the atomic radius measured? 2. What is the ionization energy? 3. Do cations gain or lose electrons? Periodic Trends 4. What is the ionic size? 5. What is electronegativity? 6. Which element has the highest electronegativity?