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Chemical Bonds

Chemical Bonds. A chemical bond forms between two atoms when valence electrons move between them Two main types of chemical bonds Covalent Bonds : occur between atoms when valence electrons are shared . Ionic Bonds : occur when valence electrons are transferred ( stolen ) between atoms

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Chemical Bonds

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  1. Chemical Bonds • A chemical bond forms between two atoms when valence electrons move between them • Two main types of chemical bonds • Covalent Bonds: occur between atoms when valence electrons are shared. • Ionic Bonds: occur when valence electrons are transferred (stolen) between atoms • A third type of bond between atoms are hydrogen bonds

  2. Ding-a-Ling! Ding-a-Ling! A metal and a nonmetal will form Ionic Bonds when chemically bonded together!! Ionic Bonding • When an atom gains or loses and electron or two they no longer have a neutral charge. A charged atom is called an “Ion” • An Ion w/ extra electrons makes it negatively charged, this an Anion • An Ion w/ more protons than electrons makes it positively charged & is called a Cation. • A “+” ion (cation) is attracted to a (-) ion (anion) just like two magnets are attracted to each other • When ions get close enough together they form an chemical bond – an Ionic Bond! • Naming Ionic compounds • The metal is named first • If the anion is an element, the end of its name is changed ti “ide” • Polyatomic ions usually keep their names NTK - “Polyatomic” ions HCO3-1 Bicarbonate NO3-1 Nitrate O-2 Oxide SO4-2 Sulfate CO3-2 Carbonate

  3. Writing Binary Formulas • Ions build strong bonds that have a net electrical charge of 0 (zero) • Remember the Cation (+ ion) is listed 1st, the Anion (- ion) is 2nd • You write how many of the ions you need as subscripts. • A Sodium ion, Na+will bond with a Chlorine ion, Cl- NaCl • A Barium ion, Ba+2, will bond with a Flourine ion, F- BaF2 • How many Flourine ions do you need to balance the +2 charge on the Ba ion? … you need 2 and you write the formula as a subscript on the Flourine ion. • A Silver ion, Ag+ will bond with an Oxygen ion, O-2 Ag2O • You need 2 Ag+ to balance the O-2 charge • A Nickel ion, Ni+3will bond with an Oxygen ion, O-2 Ni2O3 • With this bond you need 2 Nickel+3’s that have a total of a +6 electrical charge to balance 3 Oxygen-2’s that will have a total of -6 electrical charge. A +6 added to a -6 = 0

  4. Covalent Bonding • When valence electrons are “shared”, covalent bonds are formed • They are generally weaker than Ionic bonds • The number of bonds an atom can form is equal to the number of electrons needed to reach the required 8 valence electrons • Hydrogen needs only 1 to be like Helium that has 2 and fills its “S” orbit. Carbon can form 4 bonds Chlorine can form 1 bond Oxygen can form 2 bonds Ding-a-Ling! Ding-a-Ling! Two or more nonmetals will form Covalent Bonds when chemically bonded together!!

  5. Polar or Nonpolar Covalent Bonding Carbon Tetrachloride • Nonpolar Covalent Bonds - Equal sharing of electrons • Polar Covalent Bonds – an unequal sharing of electrons • Some atoms pull stronger on the “shared” electrons than other atoms • These electrons move closer to these atoms and they become more negatively charged • The atom that the shared electrons move away from become slightly positively charged

  6. Changes in Matter • Physical Change -A change that alters the form of a substance but not the chemical makeup of the substance, a change of state • Words like: crush, smash, tear, evaporate, slice, breakdown, dissolve, absorb, swell, burst • Chemical Change - One or more substances combine or decompose to form a chemically different substance • Words like: react, burns, forms, decomposed, rusting, sours, rotting, digesting, cooked, molecular change

  7. Observing Chemical Reactions • Chemical reactions produce new substances that can usually be detected by observing the evidence: • Color change • Precipitation • Temperature change • Property change • Gas produced

  8. Chemical Reactions • Chemical reactions occur when chemical bonds are formed or broken • 2. Strong chemical bonds resist change: glass • 3. Weak chemical bonds breakdown easily: wood

  9. Writing Chemical Reactions • Elements are represented by a one or two letter symbol • a. When symbol is a single letter: always capitalize: Hydrogen=H • b. When symbol is two letters, capitalize first letter & lower case second letter: Sodium = Na

  10. Writing Chemical Reactions • Chemical formulas show the ratio of elements found in molecules and compounds • a. Subscript numbers designate how many atoms of each element are present: H2O2 ; 2 Hydrogen atoms and 2 Oxygen atoms are present in this molecule • b. When no subscript number is shown: it is understood that there is only one atom present: H2O = 2 Hydrogen atoms and only one Oxygen atom are present in this molecule C2H6 H2O C2H4 C2H2

  11. Structure of an Chemical Equation: • Conservation of Mass - Matter cannot be created nor destroyed so there must be the same number of atoms on each side of the equation • Beginning materials are reactants • Ending materials are products • Example of Chemical reaction: Reactant + Reactant Product + Product

  12. Structure of an Equation: yields

  13. Counting Atoms in an Equation • If no subscript present it is assumed to be 1 atom • If elements in brackets or parenthesis, treat same as in math. • Coefficients multiple the entire molecule atoms • You must add all reactant molecules together & compare w/ all molecules in the products CaCl2 Ca=1 Cl=2 Ca3(PO4)2 Ca=3 P=2 O=8 2Ca3(PO4)2 Ca=6 P=4 O=16 It’s best to list the # of atoms under the molecules as we are doing in these examples

  14. Balancing Equations • Remember matter cannot be created or destroyed • Therefore the # of reactant atoms must equal the # of product atoms This reaction IS NOT balanced 4 Reactant Hydrogens = 4 Product Hydrogens 2 Reactant Oxygens = 2 Product Oxygens This reaction is balanced!

  15. Balance this… Step 1: Count the atoms on both sides of the equation & compare ** you can only add or change whole # coefficients to balance equations. Never change subscripts Step 2: apply a coefficient to a molecule to balance an “easy” atom (in this case, we can add a 2 coefficient to the product water to balance the H’s) Step 3: Recount

  16. Balance this… (continued) Step 4: apply a coefficient to a molecule to balance the next off balanced atom (in this case, the oxygens are not yet balanced. We can add a coefficient of 2 in front of the reactant oxygen to correct this) Step 5: Recount Step 6: Continue doing this until all atoms are balanced BALANCED!!

  17. Classifying Chemical Reactions • Synthesis: When two or more substances combine to form a more complex substance 2H2 + O2 2H2O • Decomposition: When a complex substance is broken into two or more simpler substances: 2H2O 2H2 + O2 • Single Replacement: When one element replaces another 2CuO + C 2Cu + CO2 • Double Replacement: two elements in different compounds change places NaCl + Pb(NO3)2 NaNO3 + PbCl2

  18. Synthesis Reactions

  19. Decomposition Reactions

  20. Replacement Reactions • 2 types: • Single Replacement • Double Replacement

  21. Controlling Chemical Reactions • Every chemical reaction involves a change in energy. • Some reactions release energy in the form of heat (exothermic) • Some reactions absorb energy & the container holding the reaction gets colder to the touch (endothermic)

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