The Chemistry of Living Things. An introduction to atoms, elements, compounds and mixtures.
Living things are highly ordered. There are approximately 25 elements that are essential to all...
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Living things are highly ordered. There are approximately 25 elements that are essential to all living things. Four elements – carbon, hydrogen, oxygen and nitrogen make up about 96% of living matter. The other 4% include trace elements.
Basic Chemistry for the Biologist
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The World of Elements
C
Different kinds of atoms = elementsDifferent kinds of atoms = elements
H
ON
P SNa
K
Mg
Ca
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Elements6
CCarbon
12.011
Atomic Number
Symbol
Name
Atomic Mass
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AtomThe smallest portion of an
element that retains its chemical properties
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Element: A pure substance that cannot be broken down into other substances by chemical means.
Atom: The smallest possible particle of an element.
• Nucleus: protons and neutrons tightly packed together in the center of the atom.
• Protons: Positive (+) electrical charge.
• Neutrons: No ( ) electrical charge.
• Shells: energy levels surrounding the nucleus in which electrons move around at a great speed.
• Electrons Negative (-) electrical charge.
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Structure of the Atom
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Atomic mass – add up the number of protons and neutrons
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Ionic Bonds– Formed due to attraction between a cation and
an anion– An ionic compound is a substance consisting of
cations and anions bonded together– An example of ionic bond is the attraction
between sodium ions and chloride ions
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Isotopes: Atom with an altered number of neutrons
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Molecules: Two or more elements bonded covalently
Compounds: Two or more elements bonded ionically Chemical Reactions
Reactants Products
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– carbon dioxide (CO2)
• A compound is made of atoms of different elements bonded together.
– water (H2O)
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Bonds : Forces between elements that hold them together.
Ionic Bond: A transfer of electrons from one element to the other. One becomes (+) the other (-).
Na + Cl NaCl
Covalent Bond: Sharing of electrons in the outer most shell.
H2 + O2 H2O
Bonding song
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Ions– Particle with one or more units of electrical charge– Results when an atom gains or loses electrons
• Cations—positively charged ions
• Anions—negatively charged ions
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Ionic Bond• Formed when atoms gain or lose (transfer) electrons
• Forms between a metal and a nonmetal
• Forms an ion with a charge– Positive ions and negative ions
Sodium atom (Na)
Chlorine atom (CI)
Sodium ion (Na+)
Chloride ion (CI-)
Na loses anelectron to CI ionic bond
gained electron
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Ionic bonding
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Covalent Bond• Sharing of pairs of electrons
• Forms between 2 nonmetals• Each atom has a filled valence shell
covalent bonds
Oxygen atom (O) Carbon atom (C) Oxygen atom (O)
Carbon dioxide (CO2 )
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Covalent Bonds– Share electrons between atoms– Bond can be single, double, or triple
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Covalent bonds
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Carbon can form upto 4 covalent bonds!
This lets it bond with lots of different elements, and make cool structures that all living things need.
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Covalent bonds can be Polar or Nonpolar
Polar Covalent Bonds – Electrons are not shared
equally
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Nonpolar Covalent Bonds
Electrons shared equallyNo areas of partial charge
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Water
O
HH
_
++
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OHH
_
++
Life depends on hydrogen bonds in water.
• Water is a polar molecule.– Polar molecules have slightly charged regions.
– Nonpolar molecules do not have charged regions.
– Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.
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OH
H
_
+
+
OH H
_
+ +
Hydrogen Bonds
OH
H
_
++
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Hydrogen bonds– Tend to form between an atom with partial
negative charge and a hydrogen atom covalently bonded to oxygen or nitrogen
– Readily formed and broken– While individually weak, hydrogen bonds are
strong when present in large numbers
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Hydrogen bonding
What does this mean for life?•Ice is less dense than water•Ice floats on top of water•Lakes freeze from top down
•Animals/plants can live through the winter under the ice
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Cohesion: Water molecules sticking together. Held together by weak hydrogen bonds.
Adhesion: Water molecules stickingto other molecules by weak hydrogen bonds.
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Capillary action:As water molecules stick to different surfaces, they pull other water molecules along with them
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Hydrophobic: “water fearing” molecules repel water molecules because they are non-polar while water is polar. Examples: wax, oils, and fats
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Hydrophilic: “water loving” Molecules are attracted to water molecules because both molecules are polar molecules. Solution: A uniform mixture of a solvent and a solute.
Solvent: something that dissolves
Solute: something that is dissolved
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Amphipathic: Polar at one end non polar at the other.
Detergents Phospholipid Bilayer
The Cell Membrane
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Many compounds dissolve in water.
• A solution is formed when one substance dissolves in another.
– A solution is a homogeneous mixture.
– Solvents dissolve other substances.
– Solutes dissolve in a solvent.
solution
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• “Like dissolves like.”
– Polar solvents dissolve polar solutes.
– Nonpolar solvents dissolve nonpolar solutes.
– Polar substances and nonpolar substances generally remain separate.
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Some compounds form acids or bases.
• An acid releases a hydrogen ion when it dissolves in water.– high H+ concentration
– pH less than 7
more acidic
stomach acid pH between 1 and 3
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• A base removes hydrogen ions from a solution.
– low H+ concentration
– pH greater than 7
bile pH between 8 and 9
more basic
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• A neutral solution has a pH of 7.
pure water pH 7
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pH Scale: Describes how acidic or basic a solution is.
Acid: Gives off excess H+ (Hydrogen Ions) when added to water. Example - HCl Base: Gives off excess OH- (Hydroxyl Ions) when added to water. Example - NaOH
Buffer: Maintains pH in an acidic and alkaline environment.Natural buffers enable living organisms to maintain homeostasis.
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Common Acids
Name Formula Uses
Acetic acid CH3COOH Vinegar
Carbonic acid H2CO3 Carbonated beverages
Hydrochloric acid
HCl Digestive juices in stomach
Nitric acid HNO3 Fertilizer production
Phosphoric acid H3PO4 Fertilizer production
Sulfuric acid H2SO4 Car batteries
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Acids•Definition – Any substance that produces _______________ when mixed with water•Properties:
•Taste sour•Corrosive•Conduct electricity•Produce Hydrogen gas when exposed to metals
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Common Bases
Name Formula UsesAluminum hydroxide
Al(OH)3 Deodorant, antacid
Calcium hydroxide
Ca(OH)2 Concrete, plaster
Magnesium hydroxide
Mg(OH)2 Antacid, laxative
Sodium hydroxide
NaOH Drain cleaner, soap products
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Bases
•Definition – any substance that produces hydroxide ions (OH) or bonds with Hydrogen ions when mixed with water•Properties
•Tasts bitter•Feel slippery•Dissolve oils and fats