Atoms, Elements & Molecules Basic Chemistry Atoms, Elements & Molecules

Atoms Around Us “To understand the very large, we must understand the very small” Democritus Atoms Atomos (indivisible)

Atom Anatomy Electrons Protons Neutrons Negative charge Positive charge Neutrons Neutral

Atomic Number Each atom has electron orbitals (energy levels) 2n2 If completely filled, the atom is stable If not completely filled, the atom is unstable 2n2 Elements are arranged according to their atomic number.

Electron Dot Diagrams

Periodic Table Dimitri Ivanovich Mendelèev (1834 – 1907) Organized elements in order of increasing atomic weight Atomic weight is the average mass of the atoms in a representative sample of an element. Isotopes Atoms with the same number of protons, but different number of neutrons

Periodic Table Groups (families) Periods

Periodic Table Metals Nonmetals Group IA = Alkali metals Group IIA = Alkaline earth metals Group VIIA = Halogens Extreme right = Noble gases Group B = Transition metals

Metals Four characteristics: Conduction Reactivity Chemical Alloys

Happy Noble Gases These elements are in Group VIIIA Helium Neon Argon 8 electrons in the outer orbital The fact that their outer orbitals are full means they are quite happy not reacting with other elements Helium Neon Argon Xenon

Transition Metals Advanced orbital rules In general, they are elements in which the inner electron energy levels are being filled. In other words, they are able to use the two outermost orbitals to bond with other elements.

Ions Ions are atoms with either extra electrons, or missing electrons In other words, the number of electrons are not equal to the number of protons. Cations sodium Anions chloride

Ionic Bonds Generally speaking, those elements on the left hand side of the table react with those elements on the far right (excluding the noble gases) to form stable crystalline solids. Metals give up electrons to elements on the right (nonmetals).

Covalent Bonds Shared pairs of electrons Many elements are diatomic Meaning that they can attach to each other For example, chlorine atoms: Cl

Chemical Reactions Chemical change must occur. A reaction could include ions, molecules, or pure atoms. Reaction Rate & Collision Theory Concentration Temperature Pressure

Chemical Equations Law of Conservation of Mass Reactants Products Catalysts Inhibitors

Balancing Chemical Equations A silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, the black material we call tarnish: ___ Ag + ___S → ___Ag2S

Types of Chemical Reactions Composition (Synthesis) A + B → AB Decomposition (Desynthesis) XY → X + Y Single Replacement AB + C → CB + A Double Replacement AB + CD → AD + BC Endothermic Requires heat energy Exothermic Releases heat energy Formation of a Precipitate

Chemical Reaction Properties Reversible Equilibrium

Acids & Bases Svante Arrhenius (1887) Turn indicator dye litmus from blue to red React with active metals such as zinc, iron, and tin, dissolving the metal and producing hydrogen gas Taste sour, if diluted enough to be tasted safely React with certain compounds called alkalis or bases to form water and compounds called salts BASES Turn the indicator dye litmus from red to blue Feel slippery or soapy on the skin Taste bitter React with acids to form water and salts

Acids Arrhenius proposed that these characteristic properties of acids are actually properties of the hydrogen ion (H+), and that acids are compounds that yield H+ in aqueous solutions. Slightly modified today Hydronium ion (H3O+) For simplification, we’ll stick with the H+ terminology.

Acids Monoprotic Diprotic Triprotic Polyprotic Strong Acids Weak Acids One H+ Diprotic Two H+ Triprotic Three H+ Polyprotic General term for acids that give up more than one H+ Strong Acids Ionize completely (or nearly completely) in water HCl (hydrochloric acid) Weak Acids Ionize only slightly in water CH3COOH (acetic acid)

Bases Yield hydroxide ions (OH-) in aqueous solutions Monobasic One hydroxyl anion Dibasic Two hydroxyl anions Tribasic Three hydroxyl anions Polybasic General term for bases that give up more than one OH- Strong Bases Completely ionize NaOH (sodium hydroxide; lye) All the bases of Group I and Group II are strong bases Weak Bases NH3 (ammonia)

pH Scale pH = -log [H+]

Brønsted-Lowry Acid-Base Theory By the 1920’s chemists were working with solvents other than water. Acid Proton (H+) donor Base Proton (H+) acceptor

Acid-Base Titrations Method used to determine just how much acid (or base) there is in a solution of unknown concentration Buret A piece of laboratory glassware designed to deliver known amounts of liquid into another container

A Word About Moles…. A mole used in chemistry is something like the dozen we use every day. A mole simply means that you have 6.02 x 1023 of whatever you’re talking about. Avogardo’s number Molarity is defined as the number of moles of solute divided by the number of liters of solution Molarity (M) = moles of solute liters of solution

Lab Prep (Tomorrow) Salinity & Conductivity SPM filter prep. Glassware Use Pipettes Dilutions of copper II sulfate Burets Acids & Base Titration Nutrients Prep. of standards for nutrient analysis

Lab Prep (Next Week - Sierra) Field Trip to collect water for nutrient analyses Salinity, DO, and pH will be recorded on site Nutrients measured the week after in the lab Watershed Readings North Carolina Division of Water Quality