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

The World of Elements

C

Different kinds of atoms = elementsDifferent kinds of atoms = elements

H

ON

P SNa

K

Mg

Ca

Elements6

CCarbon

12.011

Atomic Number

Symbol

Name

Atomic Mass

AtomThe smallest portion of an

element that retains its chemical properties

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.

Structure of the Atom

Atomic mass – add up the number of protons and neutrons

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

Isotopes: Atom with an altered number of neutrons

Molecules: Two or more elements bonded covalently

Compounds: Two or more elements bonded ionically  Chemical Reactions

Reactants Products

– carbon dioxide (CO2)

• A compound is made of atoms of different elements bonded together.

– water (H2O)

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

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

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

Ionic bonding

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 )

Covalent Bonds– Share electrons between atoms– Bond can be single, double, or triple

Covalent bonds

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.

Covalent bonds can be Polar or Nonpolar

Polar Covalent Bonds – Electrons are not shared

equally

Nonpolar Covalent Bonds

Electrons shared equallyNo areas of partial charge

Water

O

HH

_

++

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.

OH

H

_

+

+

OH H

_

+ +

Hydrogen Bonds

OH

H

_

++

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

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

Cohesion: Water molecules sticking together. Held together by weak hydrogen bonds.

Adhesion: Water molecules stickingto other molecules by weak hydrogen bonds.

  

Capillary action:As water molecules stick to different surfaces, they pull other water molecules along with them

Hydrophobic: “water fearing” molecules repel water molecules because they are non-polar while water is polar. Examples: wax, oils, and fats

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

Amphipathic: Polar at one end non polar at the other.

Detergents Phospholipid Bilayer

The Cell Membrane

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

• “Like dissolves like.”

– Polar solvents dissolve polar solutes.

– Nonpolar solvents dissolve nonpolar solutes.

– Polar substances and nonpolar substances generally remain separate.

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

• A base removes hydrogen ions from a solution.

– low H+ concentration

– pH greater than 7

bile pH between 8 and 9

more basic

• A neutral solution has a pH of 7.

pure water pH 7

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.

  

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

Acids•Definition – Any substance that produces _______________ when mixed with water•Properties:

•Taste sour•Corrosive•Conduct electricity•Produce Hydrogen gas when exposed to metals

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

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