Chapter 2: The Chemistry of Life

Mr. Grivensky/Mr. Rutkoski

Elements and Atoms A chemical element is a substance that

cannot be broken down into another substance

The smallest unit of an element is an atom 1,000,000 atoms placed side by side would

only measure about 1 cm across

Parts of an Atom There are 3 main parts of an atom

Particle Location Charge

Proton Nucleus Positive (+)

Electron Orbits the Nucleus Negative (-)

Neutron Nucleus Neutral, No charge

Atoms Most of the mass (99.9%) of an atom is found in

the nucleus The mass of an electron is about 1/2000 that of a

Proton The opposite charges of the electrons and

protons keep the electrons orbiting the nucleus Atoms of different elements differ in the number of

protons, electrons, and neutrons

Bonds and Compounds There are 92 natural elements About 20 more have been created in

laboratory settings Atoms form chemical bonds with other

atoms to form compounds They bond in such as way as to create

stable arrangements

Ionic Bonds An ion is an atom that has gained or lost an

electron If an atom loses an electron, it has a

positive (+) charge Atoms that gain an electron have negative

(-) charges Two oppositely charged ions are attracted

to one another and may form a compound

Ionic Bond Example Sodium chloride (NaCl) Na loses an electron and becomes Na+

Cl gains an electron and becomes Cl-

These two are attracted to one another and form NaCl

Covalent Bonds Covalent bonds form when 2 or more

atoms share electrons These compounds are called molecules Molecules may contain few atoms (H2O) or

even millions (DNA) The more electrons the atoms share, the

stronger the bonds between the atoms

Chemical Formulas A chemical formula indicates the elements

present in a compound and the proportions in which they combine

Examples: H20 (water) 2 Hydrogen atoms and 1 Oxygen

C6H12O6 (glucose) 6 Carbon, 12 Hydrogen, and 6 Oxygen

Water Liquid water is found inside every cell and most

cells are surrounded by water Water is a polar molecule In a polar molecule the electrons are shared, but

they spend more time around one atom than another

Since the electrons in water spend more time around the Oxygen atom, that end of the molecule is slightly positive, while the Hydrogen side is slightly negative

Solutions When water dissolves a substance it forms a solution The compounds found in cells are often found in solutions

containing water and dissolved chemicals This is one of the reasons water is so important to living

things Parts of a solution

Solute: The part that is in the smaller amount Solvent: The part that is in the larger amount

Example: Salt water Water = greater amount = solvent Salt = smaller amount = solute

H+ and OH- ions Water has the ability to break down into

ions of its own This results in the formation of H+

(Hydrogen ions) and OH- (Hydroxide ions) The H+ and OH- ions are two of the most

reactive ions found in nature

H2O H+ + OH-

Acids and Bases Certain compounds dissociate in water to

form ions Acids are compounds that produce H+ ions

Example: Hydrochloric acid is formed in the stomach when it dissociates

HCl H+ + Cl-

Bases Bases are compounds that produce OH-

ions Example: Sodium hydroxide (NaOH)

NaOH Na+ + OH-

pH Scale The pH scale is used to indicate the

strength of an acid or base Acids have a pH of 0 to 6 Bases have a pH of 8 to 14 A pH of 7 is considered neutral

pH Scale pH is actually a measurement of the H+ ions

produced A substance that produces 10-3 H+ ions

10-3 = .0001 ions has a pH of 3 (acid)

A substance that produces 10-9 H+ ions 10-9 = .0000000001 ions has a pH of 9 (base)

Carbon Carbon is an especially important element to all

living things Organic compounds are compounds which

contain at least 2 Carbon atoms Carbon typically forms 4 covalent bonds to

become stable It has the ability to combine with many different

elements It also has the ability to form chains of Carbon

atoms

Macromolecules Macromolecules are very large polymers Polymers are large molecules which are

made up of many small molecules called monomers

There are 4 main groups of macromolecules which are important to living things; carbohydrates, lipids, proteins, and nucleic acids

Carbohydrates Sugars and starches are examples Carbohydrates are made up of Carbon,

Hydrogen, and Oxygen They usually contain 2x as many Hydrogen

atoms as Oxygen atoms Example: Glucose: C6H12O6

Carbohydrates Simple sugars make up most of the smallest of

the carbohydrates Examples include: Galactose (Milk), Fructose

(Fruits), and Glucose (in all cells) Each simple sugar has the same formula:

C6H12O6; they only differ in the arrangement of the atoms

Simple sugars are easy for the cells to produce and break down; they serve as the way for cells to store and release chemical energy

Carbohydrates Organisms can also use simple sugars to assemble larger

polymers 2 simple sugars joined together form a disaccharide

Table sugar (sucrose is an example) Simple sugars which contain only one sugar are called

monosaccharides Polysaccharides contain many sugars which can be broken

down when the cell needs a simple sugar or energy Plants store energy in the form of a polysaccharide known as

starch Animals store energy in the form of a polysaccharide known

as glycogen

Lipids Examples of lipids are waxes, fats, and oils Lipids are also a way to store energy but

they have other functions as well

Proteins Proteins are polymers that are made up of

monomers called amino acids There are 20 common amino acids which

make up the majority of proteins Amino acids share a common structure

Amino acid Structure

C C--N

OH

H

H

H O

R

--

- -

- --

Carboxyl Group (COOH)

Amino Group (NH2)

R Group

Varies from one amino acid to

another

In Glycine the R group is a Hydrogen atom

In alanine the R group is a Methyl group (CH3)

Amino Acids 2 or more amino acids can be joined

together by the reaction of the amino group (NH2) of one amino acid and the carboxyl group (COOH) of another

The bond formed is a chain and is called a peptide bond

A chain of amino acids is known as a polypeptide

Proteins A complete protein is made up of many

polypeptides and may contain other chemical groups

Proteins are the major components of many structures including skin, muscles, and feathers