A Brief Overview of Chemistry The Chemistry of Life A Brief Overview of Chemistry

Periodic Table

Element: Substance consisting entirely of one type of atom.

Atom: Basic Unit of Matter (smallest part of an element)

Parts of an Atom Protons, Neutrons, Electrons

Nucleus Nucleus: The central portion of an atom containing neutrons and protons

Outside nucleus Electrons

Atomic Number The number of protons in the nucleus of the atom. It is listed on the Periodic Table, in numeric order

Proton Proton: Positively charged particle(s) found in the nucleus of an atom Mass = 1

If you change the # of protons in an atom, you will have a different element…

Electron Electron: A negatively charged particle(s) found orbiting around the nucleus of an atom No mass Electron cloud Shells

Neutrons Neutron: Neutral (no charge) particles found in the nucleus of an atom. Mass = 1

# Protons = # Neutrons = # Electrons

Atomic Mass Atomic Mass: Includes the protons & neutrons in the nucleus of an element. #Protons + #Neutrons = Atomic Mass

Isotope Change in the “expected” number of neutrons The number of neutrons does NOT equal the number of protons

Isotope What is the atomic mass? What is the atomic number? How many protons? How many neutrons?

Radioactive Isotope Nuclei unstable Breaks down at a constant rate over time Radiation emitted can be dangerous Often used in determining the age of various things (i.e. fossils & rocks) The atomic mass is the average mass of all the known isotopes of the element

Atoms All atoms are neutral; they have the same number of electrons as protons. Example: An atom of 42He has an atomic number of 2 and a mass of 4. Therefore, it has 2 protons and 2 neutrons in its nucleus. Since it has 2 positive protons (neutrons are neutral) it must have 2 negative electrons to make the total charge neutral.

Chemical Compounds It is a substance formed by the chemical combination of 2 or more elements in definite proportions Atoms in compounds are held together by chemical bonds Examples: H2O, NaCl, C6 H12 O6

Chemical Compound Pure substance formed by two or more elements chemically combined. Ex: water: water (H2O), sodium chloride (NaCl)

Valence Electrons Electrons available to form bonds Located in outer shell

Subscript A subscript is a small lowered number after a symbol for an element. H2O: the 2 is lowered and considered a subscript. The 2 indicates how many atoms of the element are present in that compound.

Chemical Formula 6 12 6 States how many atoms are in each molecule. How many carbon atoms are in C6 H12 O6? How many hydrogen atoms? How many oxygen atoms? 6 12 6

Chemical Equations CO2 + H2O C6 H12 O6 + O2 REACTANTS PRODUCTS Let’s say I give you a chemical equation like— CO2 + H2O C6 H12 O6 + O2 What are the names of these compounds? Could you tell me which side are the reactants and which side are the products? REACTANTS PRODUCTS Carbon dioxide Water Sugar/glucose Oxygen Click for answers Click for answers

Ionic Bond When >/= 1 electron transfers from one atom to another Ions: charged either + or – (depending on whether they have lost or gained an electron) Ex: NaCl

Covalent Bond Electrons are shared between atoms Single bond: share 2 electrons Double bond: share 4 Triple bond (rare): share 6 Ex: H2O

Van der Waals forces When molecules are close together an attraction can develop between oppositely charged regions of nearby molecules Example: water molecules

Geckos and Van der Waals Geckos can stick to so many surfaces in a seemingly impossible manner. Specifically, the tiny hairs on the gecko's feet (called setae) are split at the microscopic level into as many as 1,000 branches. As a result, even though the Van der Waals forces acting on an individual tip is small, the adhesion of a billion or so tips adds up to enough force to let the gecko stick to basically anything.

Water (H2O) Most abundant compound in organisms Water is polar Unequally shares electrons between hydrogen & oxygen atoms Makes it possible for many other compounds to other compounds to dissolve in water

Water has Hydrogen Bonds Adhesion – the attraction of unlike molecules to one another Cohesion – the attraction of like molecules to one another Water “beads” because of cohesion Cohesion causes water to form drops, surface tension causes them to be nearly spherical, and adhesion keeps the drops in place.

Solvent-Solute Water is often called The Universal Solvent Solvent means to dissolve, or a dissolving agent. WATER is a SOLVENT! Solute is what is to be dissolved. Sugar and salt are solutes when they dissolve in water.

Mixture vs. Solution Mixture: >/= 2 elements physically mixed but not chemically combined (M & Ms) Solution: all components evenly distributed Solute: substance that is dissolved Solvent: substance in which solute dissolves Ex: Salt water: Salt = solute, Water = solvent

Suspension Mixture of water and non-dissolved material

Elements in the Human Body Most abundant element in our body Oxygen – 65% Carbon – 18.5% Hydrogen – 9.5% Nitrogen – 3.3% All of these equal 96.3%. The other 4% are trace elements: Calcium (1.5), Phosphorous (1.0), Potassium (0.4), & others. Water Most abundant compound in our body

pH Scale The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14 A pH of 7 is neutral A pH less than 7 is acidic A pH greater than 7 is basic

If #H ions > # OH ions : ACID If # OH ions > # H ions : BASE (alkaline) Each number on the pH scale represents an exponential change in strength Acids: the closer to 7 (neutral) on the pH scale… the weaker the acid Bases: the closer to 7 (neutral) on the pH scale… the weaker the base

Acids Acids taste sour Strong Acids are dangerous and can burn your skin Examples are: Vinegar, stomach acid, and citrus fruits

pH Scale 14 = Basic 0 = Acidic Oven cleaner Bleach Ammonia solution Increasingly Basic Soap Sea water Human blood 7 = Neutral Neutral Pure water Milk Normal rainfall Acid rain Tomato juice Increasingly Acidic Lemon juice Stomach acid 0 = Acidic

Bases Solutions containing bases are often called alkaline. Bases taste bitter Bases feel slippery Strong bases are very dangerous and can burn your skin Examples: Lye and ammonia

pH Question An ecologist is testing rainwater. She tests rainwater on the south side of town and finds that the pH is 6.2. Then she tests the north side of town and finds that the pH is 6.8. Which is more acidic? Click for answer 6.2 is correct!

Buffers Buffers are weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH.

Organic Compounds Carbohydrates Lipids Nucleic Acids Proteins