Oxidation – Reduction

Redox reactions Also known as electron transfer reactions

One substance gets oxidized Redox reactions One substance gets oxidized loses electrons - Known as the REDUCING agent One substance gets reduced Gains electrons Known as the oxidizing agent

Ex: 4 Fe (s) + 3 O2 → 2 Fe2O3 (s) when the iron reacts with the oxygen, it transfers 3 electrons to oxygen – iron is oxidized, oxygen is reduced

LEO says GER Redox reactions

Ex: A piece of copper is immersed in a solution of copper(II) sulfate Fe(s) + CuSO4(aq)  Cu + FeSO4 Just looking at the metals (they are the only ones change oxidation state….. Redox reactions

Rules for determining oxidation numbers 1. For an atom in it’s elemental form the oxidation number is 0 ex: Mg, Fe, Cu, H2, O2 Redox reactions

Redox reactions Rules for determining oxidation numbers 2. For a monatomic ion, it’s oxidation number is equal to its charge ex: Mg 2+ oxidation number = +2 Cl1- oxidation number = -1

Rules for determining oxidation numbers 3. The oxidation number for oxygen in a MOLECULAR compound is -2 ex: H2O, CO2 Redox reactions

Rules for determining oxidation numbers 4. Hydrogen +1 when it is bonded to a nonmetal ex: HCl -1 when it is bonded to a metal ex: MgH2

Rules for determining oxidation numbers 5. For other covalent compounds not containing oxygen or hydrogen, the most electronegative element has an oxidation number equal to its charge as an ion ex: BF3 ; the oxidation number for fluorine is -1

Rules for determining oxidation numbers 6. The sum of all the oxidation numbers for all of the atoms in a compound must equal the overall charge of the compound ex: H2O oxidation number of H = +1(2) = +2 oxidation number of O = -2 Sum of oxidation numbers = 0

7. For a polyatomic ion, the sum of the oxidation numbers for each of the atoms in the compound is equal to the ionic charge on the polyatomic ion.

Ex: ClO3- oxidation number of O = -2(3) = +6 oxidation number of Cl must be +5 so that the overall charge = -1

Sample problems Calculate the oxidation number for sulfur in each of the following ions: Sulfide ion, S-2 sulfite ion, SO3-2 sulfate ion, SO4-2 Thiosulfate ion, S2O3-2

Sample problems Sulfide ion, S-2 Oxidation number would be -2 because For a monatomic ion, it’s oxidation number is equal to its charge

Sample problems sulfite ion, SO3-2 Oxidation number would be +4 because Oxygen is assigned a -2 charge x 3 = -6 So then S has to be +4 so that the overall charge is -2

Sample problems sulfite ion, SO4-2 Oxidation number would be +4 because Oxygen is assigned a -2 charge x 3 = -6 So then S has to be +6 so that the overall charge is -2

Sample problems sulfite ion, S2O3-2 Oxidation number would be +2 x 2 = +4 because Oxygen is assigned a -2 charge x 3 = -6 So then S has to be +6 so that the overall charge is -2

Calcium metal gets oxidized (loses electrons) Redox reactions How can you tell what gets oxidized and what gets reduced? 2Ca(s) + O2(g)  2CaO(s) 0 0 +2 -2 Calcium metal gets oxidized (loses electrons) Oxygen gas gets reduced (gains electrons)

Oxidizing and reducing agents Oxidizing agent is a substance that accepts the electrons Reducing agent is a substance that transfers the electrons

Oxidizing and reducing agents Fe(s) + S(s) → FeS(s) Fe = 0 Fe = +2 S = 0 S = -2 Iron is oxidized and sulfur is reduced So iron is the reducing agent and sulfur is the oxidizing agent

Molecular equation – represents the complete formulas of all the reactants and products K2CrO4 (aq) + Ba(NO3)2  BaCrO4 + KNO3 Complete ionic equation- includes all ions K+(aq) + CrO4 2-(aq)+ Ba2+(aq) + NO31-(aq)+ K+(aq)  BaCrO4 + K+(aq)+ NO31-(aq) K+ and NO31- are called spectator ions- they do not participate in the reaction

Nuclear Chemistry

Chemical vs. Nuclear Reactions Chemical Reactions- A rearrangement of atoms and molecules by breaking and forming bonds -involves electrons Nuclear Reactions- Combining, splitting or decay the nuclei of atoms.

Nuclear Chemistry involves the NUCLEUS of the atom. That means…. the protons and neutrons will undergo a change (nuclear reactions) Nuclear reactions usually involve radioactive elements

Radioactive Elements are NOT stable…. …because of the proton to neutron ratio.

Radioactive elements will give off particles and energy until they become stable (non-radioactive)

Radioactive elements change by themselves Of the 119+ different atoms…. …there are more than 1500 different nuclei, only 264 are stable

Discovery of Radioactivity Professor Roentgen – 1895- found that certain elements gave off X-rays but didn’t know what caused them.

Two Kinds of Nuclear Reactions 1. Fission- Splitting the nucleus 2. Fusion- Combining nuclei

Transuranium Elements The elements past uranium (#92) All radioactive

Showing Radioactive Atoms. Use Isotope Notation C-12 C-14 Mass number 12 14 C C 6 6 Atomic number

Types of Radiation Alpha Particle: α Beta Particle: β Gamma Ray: γ

Alpha Decay -when an atom gives off an alpha particle (helium nucleus) Alpha Particle = 2p and 2n -atomic # goes down 2 and atomic mass goes down 4

Written as: 4 He (in nuclear equations) 2 or a (in decay series)

-U-238 turns into Th-234 when it gives off an alpha particle Ex. (nuclear equation) 238 4 234 U Th He + 90 92 2

Alpha Particles -weakest radiation -can be stopped by a piece of paper. -can burn flesh

Affects of Alpha Particles on Body will not penetrate the outer layer of skin dangerous if inhaled or swallowed. Cells in lining of the lungs or internal organs will be changed (mutated) or killed lung cancer cases among uranium miners from inhaled and ingested alpha sources is much higher than those of the public at large.

Radon Radon gas produced by the decay of radium-226 emits alpha particles poses a hazard to lungs and airways when inhaled.

e e -1 +1 Beta Decay Two types: Beta minus decay Beta plus decay - Written as b- Written as β+ or e e -1 +1

A. BETA MINUS DECAY: Neutron decays into a proton, an electron and an antineutrino Mass number remains the same but atomic # increases by 1

B. BETA PLUS (positron) DECAY A proton decays into a neutron, a neutrino and a positron Positron has the mass of an electron but is positively charged Mass number remains the same Atomic Number decreases by 1

-100x more penetrating than an alpha particle Beta Particles -100x more penetrating than an alpha particle -can be stopped by clothing or wood -travel at the speed of light -usually accompanies other modes of radioactive decay

Gamma Decay -gives off a gamma ray (γ ) - a release of high energy electromagnetic radiation from nucleus -it’s pure energy not a particle -Atomic # and mass stay the same, just changes to an atom with less energy - needs thick walls of concrete or lead to stop it.

Nuclear equations Alpha decay equation Show one transformation of a decay series Must be equal on both sides. !!!!!!!!! Alpha decay equation 237 Np 93

Beta minus decay equation 32 P 15 Beta plus decay equation (positron decay) 15 O 8