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Unit 2 – Electrons and Periodic Behavior
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Period The Periodic Table Group or Family Group or family Period
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Periodic Table Periodic table is divided into 3 classes Metals
Non metals Metalloids The horizontal rows are called periods while the vertical columns of the periodic table are called Groups or Families
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Properties of Metals Metals are good conductors of heat and electricity Metals are malleable Metals are ductile Metals have high tensile strength Metals have luster
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Examples of Metals Potassium, K reacts with water and must be stored in kerosene Copper, Cu, is a relatively soft metal, and a very good electrical conductor. Zinc, Zn, is more stable than potassium Mercury, Hg, is the only metal that exists as a liquid at room temperature
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Properties of Nonmetals
Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature
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Examples of Nonmetals Microspheres of phosphorus, P, a reactive nonmetal Sulfur, S, was once known as “brimstone” Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure
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Properties of Metalloids
Metalloids straddle the border between metals and nonmetals on the periodic table. They have properties of both metals and nonmetals. Metalloids are more brittle than metals, less brittle than most nonmetallic solids Metalloids are semiconductors of electricity Some metalloids possess metallic luster
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Silicon, Si – A Metalloid
Silicon has metallic luster Silicon is brittle like a nonmetal Silicon is a semiconductor of electricity Other metalloids include: Boron, B Germanium, Ge Arsenic, As Antimony, Sb Tellurium, Te
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The Properties of a Group: the Alkali Metals
Easily lose valence electron (Reducing agents) React violently with water Large hydration energy React with halogens to form salts (valence electrons are electrons in the outermost shell of an atom)
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Properties of Alkaline earth metals
They are the group II A elements Denser, harder and stronger than Group I A elements but less reactive Too reactive to be found pure in nature
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Halogens and Noble Gases
Halogens are the most reactive of the non metals. They are the group VII A elements The noble gases are the group VIII A elements. They are also called inert gases because they undergo very few reactions.
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Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
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The Bohr Model of the Atom
I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive. WRONG!!! Neils Bohr
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Electron Energy Level (Shell)
Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. Number of electrons that can fit in a shell: 2n2
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An orbital is a region within an energy level where there is a probability of finding an electron. This is a probability diagram for the s orbital in the first energy level… Orbital shapes are defined as the surface that contains 90% of the total electron probability.
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Energy Levels, Sublevels, Electrons
Sublevels in main energy level (n sublevels) Number of orbitals per sublevel Electrons per sublevel electrons per level (2n2) 1 s 2 p 3 6 8 d 5 10 18 4 f 7 14 32
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Orbital filling table
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Irregular conformations of Cr and Cu
Chromium steals a 4s electron to half fill its 3d sublevel Copper steals a 4s electron to FILL its 3d sublevel
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Periodic Trends How do properties of elements change as you go across a periodic table?
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Half of the distance between nuclei in
Determination of Atomic Radius: Half of the distance between nuclei in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius Radius decreases across a period Increased effective nuclear charge due to decreased shielding Radius increases down a group Addition of principal quantum levels
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Table of Atomic Radii
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ION An atom or a group of atoms that has a positive or negative charge are called ions. Atoms get a positive charge when they lose electrons Atoms get a negative charge when they gain electrons Ionization is the process that results in the formation of an ion.
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Increases for successive electrons taken from the same atom
Ionization Energy - the energy required to remove an electron from an atom Increases for successive electrons taken from the same atom Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove Tends to decrease down a group Outer electrons are farther from the nucleus
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Table of 1st Ionization Energies
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Electronegativity A measure of the ability of an atom in a chemical
compound to attract electrons Electronegativities tend to increase across a period Electronegativities tend to decrease down a group or remain the same
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Periodic Table of Electronegativities
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Summation of Periodic Trends
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Ionic Radii Cations Anions Positively charged ions formed when
an atom of a metal loses one or more electrons Cations Smaller than the corresponding atom Negatively charged ions formed when nonmetallic atoms gain one or more electrons Anions Larger than the corresponding atom
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