Chemical bonds
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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
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

Ionic bonding

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

Writing binary formulas
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

  • Covalent bonding
    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!!

    Polar or nonpolar covalent bonding
    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

    Changes in matter
    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

    Observing chemical reactions
    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

    Chemical reactions
    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

    Writing chemical reactions
    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

    Writing chemical reactions1
    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





    Structure of an chemical equation
    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

    Counting atoms in an equation
    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












    It’s best to list the # of atoms under the molecules as we are doing in these examples

    Balancing equations
    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!

    Balance this
    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

    Balance this continued
    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


    Classifying chemical reactions
    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

    Synthesis reactions
    Synthesis Reactions

    Replacement reactions
    Replacement Reactions

    • 2 types:

      • Single Replacement

      • Double Replacement

    Controlling chemical reactions
    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)