Reactions

Review 5 Main Types of Reactions: Synthesis Decomposition Single Replacement Double Replacement Combustion

Subcategories of Reactions Precipitation Acid-Base Oxidation-Reduction (Redox)

Redox Reactions Chemical reactions in which electrons are ____________ from one chemical species to another. One species will give away electrons (____________). Another species must take electrons (____________). A redox reaction must have reduction AND oxidation; one cannot occur without the other. Li + Cl

Electrically Neutral Every element on the Periodic Table is electrically _________. This means that they have ________ numbers of protons and electrons. The atomic # determines how many protons/electrons an element has. Electrons are found outside the nucleus and each electron contributes a 1- charge to the element. Protons are found in the nucleus and each proton contributes a 1+ charge to the element. Al = 13 Electrons + 13 Protons Al = (-13) + (13) = 0

Affect on Charge: Gaining Electrons Nonmetals tend to gain electrons. Let’s see what affect that has on the overall charge of the atom. Initially there are 17 electrons and 17 protons causing the element to be neutral. Then, 1 more electron is gained to get 8 valence electrons... What overall effect does this have on the charge?

Affect on Charge: Losing Electrons Metals tend to lose electrons. Let’s see what affect that has on the overall charge of the atom. Initially there are 13 electrons and 13 protons causing the element to be neutral. Then, 3 electrons are removed to get 8 valence electrons... What overall effect does this have on the charge?

+ - Li Li + Cl Cl Redox Reactions, cont. One species will ___________ electrons (oxidation). Another species ____________ the electrons (reduction). + - Li Li + Cl Cl

Recall: In order to obtain an octet, metals tend to __________ electrons. Likewise, non-metals tend to __________ electrons to obtain an octet. All atoms want to have a stable electron configuration with _____ valence electrons. The group # determines how many valence electrons an element has.

1+ 2+ Metals vs. Non-metals Metals Non-metals Notice that all the metals are positively charged and all the nonmetals (except H) are negatively charged. Metals Non-metals 1+ 2+ The charges of this middle section vary, but they are all positive.

Most Likely Oxidation #s Noble Gases have 8 valence electrons and thus do not want to gain or lose electrons Metals Non-metals Group 4A elements are able to gain 4 OR lose 4 electrons 1+ 4+/- 2+ 3+ 3- 2- 1-

Rules for assigning oxidation numbers: All ___________ are zero. 2. Charges of ______ are their oxidation numbers. 3. All ________ without a net charge are zero. 4. Hydrogen is almost always _______ when found in a compound. 5. Oxygen is almost always ________ when found in a compound. 6. If a compound has a net charge, the sum of its atoms’ charges _____________ the net charge.

Assigning oxidation numbers: Rule 1 1. Charges of elements are zero. Zn (s) + HCl(aq)  ZnCl2(aq) + H2(g) elements

Assigning oxidation numbers: Rule 2 Charges of ions are their oxidation numbers. 2+ Zn2+(aq) + HCl(aq)  ZnCl2(aq) + H2(g) ion

Assigning oxidation numbers: Rule 3 All compounds without a net charge are zero. Zn2+(aq) + Cl2(g)  ZnCl2(aq) Compound with a net charge of zero Zn + 2Cl = 0

Assigning oxidation numbers: Rule 4 Hydrogen is almost always 1+. 1+ H2O(l) 1+ when paired with _____________. . 1- when paired with ______________. 1- LiH(aq)

Assigning oxidation numbers: Rule 5 Oxygen is almost always 2- when found in a compound. 2- H2O(l) 2- in almost all ____________. 1- in _________________. 1- H2O2(aq) (exception)

Zn2+(aq) + Cl2(g)  ZnCl2(aq) Recall Rule 3: All compounds without a net charge are zero. - we can apply this rule along with rules 4 and 5 and our expected oxidation numbers from the periodic table to assign oxidation numbers to elements other than oxygen and hydrogen that are found in compounds Zn2+(aq) + Cl2(g)  ZnCl2(aq)

Calculate Oxidation Numbers for: H2SO4 Net Charge = (# of atoms x Charge) + (# of atoms x Charge)… 0 = (2 x Hydrogen) + (Sulfur) + (4 x Oxygen) 0 = (2H) + (S) + (4O)

Assigning oxidation numbers: Rule 6 6. If a compound has a net charge, the sum of its atoms’ charges must equal the net charge. - we can apply this rule along with rules 4 and 5 and our expected oxidation numbers from the periodic table to assign oxidation numbers to elements other than oxygen and hydrogen that are found in compounds S(s) + O2(g)  S2O32-(aq)

Calculate Oxidation Numbers for: SO42- Net Charge = (# of atoms x Charge) + (# of atoms x Charge)… -2 = (Sulfur) + (4 x Oxygen) -2 = (S) + (4O)

Calculate Oxidation Numbers for: ClO3- Net Charge = (# of atoms x Charge) + (# of atoms x Charge)…

Calculate Oxidation Numbers for: NO3- Net Charge = (# of atoms x Charge) + (# of atoms x Charge)…

Why are Oxidation numbers important? L R G They help us determine which chemical species is oxidized and which chemical species is reduced. O_________ I_____ L__________ R__________ G__________ Oxidation = Charge ________ Reduction = Charge ________

Redox Reactions: Electron Transfer electrons are ___________ from one species to another (redox). assign oxidation numbers to identify which loses e– and which gains e– .

Redox Reaction: Oxidation Numbers Oxidation #s help us determine which chemical species is oxidized and which chemical species is reduced. Zn(s) + O2(g)  ZnO(aq) Oxidation = Charge Increases Reduction = Charge Decreases

Try This #1: Redox Reactions Assign oxidation #s and determine which chemical species is oxidized and which chemical species is reduced. Ag(s) + Cl2(g)  AgCl(aq) Oxidation = Charge Increases Reduction = Charge Decreases

Try This #2: Redox Reactions Assign oxidation #s and determine which chemical species is oxidized and which chemical species is reduced. N2(g) + 3 H2(g)  2 NH3(aq) Oxidation = Charge Increases Reduction = Charge Decreases