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The periodic table: Reading the periodic table: Atomic Mass Atomic Number Symbol Name Reading the periodic table: Number of Protons + Neutrons Number of protons (or electrons if neutral) How do you know the number of protons? • The number of protons always = the atomic number. • In a neutral atom, number of protons = the number of electrons. How do you know the number of neutrons? • The atomic mass = # protons + # neutronsso, if you know the protons and the mass, you can determine the # of neutrons. • Practice. Hydrogen has atomic #1, and atomic mass 1amu. How many neutrons. • Carbon has atomic #6, and atomic mass 14amu. How many neutrons. How do you know the # of e-? • • • • We will consider neutral atoms. So the charges will amount to 0. Every proton will be balanced by an e-. So, # of protons = # of e-. Practice What is the atomic #? What is the atomic mass? How many protons, neutrons, and electrons? How do we draw atoms again? Indicate the # of protons and neutrons in the nucleus Indicate the location of electrons in the orbitals: 2 in the first, and up to 8 in every other. Practice Drawing atoms: Chemical Bonding • The rearrangement of atoms, driven by e-s . • There are 2 major classes of bonds, covalent and ionic Why bond? • 1. All atoms want to get to the lowest energy state possible • 2. All atoms want to fill their valence shell. Valence shell • Valence shell = The outermost shell of e- . • The first e- orbital only holds 2. • All of the others we will consider hold UP TO 8. • (There are energy levels that hold more than 8 e- , but you’ll get to that in chemistry). Octet Rule • Octet = 8. In general, atoms bond in order to fill their valence shell with 8 e• Noble Gasses are the elements on the far right of the periodic table. These have a full valence shell. Will they bond? How many total electrons does each have? How many valence electrons? How many bonds will each make? Representing the Valence Shell in Electron-Dot format • 1. Use the atomic symbol • 2. Determine the # of valence electrons • 3. Begin above the symbol, and place a dot moving clockwise for each electron. Representing Bonds with Electron dot Structures 1. Count the number of dots around each atom (needs to add up to 8 or 2) 2. If atoms are sharing 1 pair of electrons, draw 3. If atoms are sharing 2 pairs of electrons, draw = 4. If atoms are sharing 3 pairs of electrons (Carbon and Silicon), draw a triple bond. Draw each element bonded with enough Hydrogen atoms to fill the valence shell. • What do you do with Li, Be, or B? Covalent Bonding • “Co” means together. Atoms that share e-s together are covalently bonded. • There are 2 types of covalent bonds 1. Non-polar bonds share e- equally 2. Polar bonds don’t share e- equally Non-polar bonds • When two atoms have very similar electronegativies they will have similar pulls or affinities for the e-s they share. • As a result of equal sharing, the charges of the electrons will be equally distributed. • This happens whenever Carbon and Hydrogen bond together. • This also happens when two identical atoms bond together as in O2 or Cl2, etc. Nonpolar bonds exist in things like oils and waxes. • Oils are made of H and C, they are called Hydrocarbons • Waxes too are Hydrocarbons Polar Bonds • In Polar bonds the atoms have different electronegativities. On atom will have a stronger affinity or pull on the e-s than the other(s). • This results in one “pole” where the e-s spend more time (negative), and another “pole” where the e-s spend less time (positive). Example of Polar Bonds • Water is the classic example of a polar molecule. The Oxygen atom has a much greater electronegativity than either Hydrogen atom. • The Oxygen takes on a slight negative charge • The Hydrogen atoms take on a slight positive charge. • This creates two poles - a dipole. Ionic Bonds • Sometimes different atoms have such different electronegativities that one atom will end up “stripping” e-s from the other(s). • The atoms are now called ions (either positive or negative). • The resulting ionic compounds are called salts. Practice Drawing Bonds • • • • • • • • • C2H6 C2H4 C2H2 O2 H2 H2O CH3OH LiOH H2O2 Ions • After stipping (or being stripped of) an e-, an atom takes on a permanent charge. • NaCl Na+ and Cl- (Chlorine has one more e- than +, and Na has one more + than e-). • Predict, HF or H2O or MgCl Ions • How many +s and e-s does each atom have? • Li+ Be-2 Al +3 • BrK+ Ca+2 Isotopes • Atoms with the same number of protons, but different numbers of neutrons (different atomic masses) • i.e. C12 & C14 • The atoms have the same properties, but different masses. Practice: (Ions, Isotopes, Different Elements, or Neutral Atoms) Atom 1 Protons Neutrons Electrons Atom 2 Protons Neutrons Electrons He 2 2 2 He 2 4 2 O 8 8 8 O 8 8 8 Cl 17 18 18 Cl 17 18 18 N 7 7 7 N 8 7 8 F 9 9 9 F 9 7 9 Na 23 22 22 Na 23 22 22 Li 3 2 2 Li 2 2 2 Answers Atom 1 Protons Isotopes Neutrons Electrons Atom 2 Protons 2 O Neutral Ions 17 Different 7 Isotopes Atoms Neutral O Different Atoms 23 Different 3 Elements 8 Atoms 18 Different Elements 7 22 Elements Neutral 17 9 Ions Electrons 4 18 Elements Neutrons Different 23 Elements 2 22 Different Elements Practice Bonding • • • • • • • H2 H 2O O2 H 2O 2 C 2H 6 C 2H 4 C2H2 PH3 SO NaOH S2 Cl2 NH3 Si2H2 Lab: Build & Draw • • • • • • • Represent the elements by this color scheme: C=Black N=Red O=Blue H=White Cl=Purple S=Yellow Si=Brown H2 H2O SO C2H2 O2 Si2H2 H2O2 S2 C2H6 Cl2 C2H4 NH3