Basic Chemistry Atoms, Elements & Molecules. Atoms Around Us “To understand the very large, we...

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 Negative charge

Protons Positive charge

Neutrons Neutral

Atomic Number

Each atom has electron orbitals (energy levels) 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:

1. Conduction

2. Reactivity

3. Chemical

4. Alloys

Happy Noble Gases

These elements are in Group VIIIA 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 & BasesSvante Arrhenius (1887)

ACIDS1. Turn indicator dye litmus

from blue to red

2. React with active metals such as zinc, iron, and tin, dissolving the metal and producing hydrogen gas

3. Taste sour, if diluted enough to be tasted safely

4. React with certain compounds called alkalis or bases to form water and compounds called salts

BASES1. Turn the indicator dye

litmus from red to blue

2. Feel slippery or soapy on the skin

3. Taste bitter

4. 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 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