• Review elements, bonding, properties of water, and the importance of Carbon in living things.

(In order to prepare for comparing the structure and function of bio-molecules)

Objective:

Can be found in the book: Starr Taggart: Pg. 22-37

Principles of Life: Pg. 17-22

• Matter – anything that has mass and occupies space (abiotic or biotic) – is made of substances called

elements.

ELEMENTS

• An element is a pure substance made only of one kind of atom. (it cannot be broken down into a simpler chemical substance)

• Elements differ in the number of protons (positively charged particles in it’s nucleus)

IMPORTANCE IN

BIOLO

GY!?!?!

These four elements are

major components

of ALL LIVING

THINGS.

• An atom is the smallest particle of an element that has the characteristics of that element.

• Atoms are the basic building blocks of all matter.

ATOMS

• All nuclei contain positively charged particles called protons (p+).

• The center of an atom is called the nucleus.

• Most contain particles that have no charge, called neutrons (n0).

ATOMS

• In the electron cloud there are extremely small, negatively charged particles called electrons (e-)

• There is a region of space that surrounds the nucleus called the electron cloud.

• Electrons exist around the nucleus in regions known as energy levels.

• The first energy level holds 2 electrons.

• The second and subsequent levels holds up to 8 electrons.

Nucleus8 protons (p+)8 neutrons (n0)

Oxygen atom

ATOMS

Animated Supplemental Tutorial

Chemical Bonding

Atoms can join together during chemical bonding to form

compounds

– A Compound is a substance made of the joined atoms of two or more different elements

– Compounds are represented by a chemical formula that shows the proportions of each element in the compound

• Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms.

• For many elements, an atom becomes stable when its outermost energy level is full.

ATOMIC BONDS

• The electrons that are in the outer most energy level for that atom are called

valence electrons.

ATOMS

Covalent bonds

• Covalent bonds occur when two or more atoms share electrons

(co = together, valence= outer electrons)

A compound made with covalent bonds is

called a molecule

Sharing the electrons

satisfies the outermost

energy level for both atoms

• Sometimes, when atoms form covalent bonds they do not share the electrons

equally. This is called a polar bond.

• One side of the molecule becomes positively charged…

while the other side is negatively charged.

Water is a Polar Molecule

• Water is an example of a polar molecule.

***Know why the Oxygen side is

negatively charged and the Hydrogen ends are positively

charged.

– Hydrogen bonds are a weak chemical attractions between polar molecules

that involve hydrogen atoms

Water molecules are attracted to each other by hydrogen bonds

Hydrogen bonds also found between

nitrogenous bases in DNA

Ionic bonds• An ion is an atom that

has gained or lost an electron.

– Ions have a charge due to the unequal number of protons and electrons

• The attractive force between two ions of opposite charge is known as an ionic bond.

• Chemical reactions occur when bonds are formed or broken, causing substances to recombine into

different substances.

CHEMICAL REACTIONS

Anabolic Reaction

Catabolic Reaction

Reactants

Reactants

Products

Products

• All of the chemical reactions (breaking down OR putting together) that occur within an organism are

referred to as that organism’s metabolism.

CHEMICAL REACTIONS

Sodium Chlorine Sodium Chloride

• It is as difficult to imagine life without carbon, as it is life without water.

Importance of Carbon

• Although a cell is mostly water, most of the rest of it consists of carbon-based

molecules.

• Proteins, DNA, carbohydrates, and other molecules that distinguish biotic matter from

abiotic are composed of carbon atoms bonded to one another and to atoms of other

elements.

Importance of Carbon

Importance of Carbon• The study of carbon compounds is called

organic chemistry.

• The term “organic” is used to describe molecules that have carbon skeletons

(backbones of carbon….also containing hydrogen).

Importance of Carbon

• The word “organic” is derived from the ability of living organisms to synthesize and use these molecules.

• Inorganic molecules include molecules that do not contain carbon, such as water.

Importance of Carbon• Carbon is very versatile.

• There are 4 valence electrons in a shell that holds 8

• In order for it to become stable, it must form 4 covalent bonds to fill the outer shell.

• Because carbon can use one or more of its bonds to attach to other carbon atoms, it can construct endless diversity of carbon skeletons, varying in size and branching pattern.

Carbon Skeletons

• They can form straight chains, branched chains, or rings.

Carbon Skeletons

• Isomers are compounds that are made of the same elements and have the same chemical formula, but because they are in a different order and shape, they have different properties.

Carbon Skeletons

• Water is perhaps the most important

compound in living organisms.

• Water makes up 70 to 95 percent

of most organisms.

The Importance of Water

Review: Remember Ions • An atom (or group of atoms) that gains or loses electrons has an electrical charge and is

called an ion.

• Polar water molecules attract ions as well as other polar molecules.

• Because of this attraction, water can dissolve many ionic compounds, such as salt, and many

other polar molecules, such as sugar.

•There is no “universal solvent”, but it is close…

Water is Polar

• Water molecules also attract other water molecules.

• Hydrogen bonds weak bonds formed between water

molecules.

• The positive ends are attracted to the negative ends.

Water is Polar

• Water molecules stick together due to the hydrogen bonds,

• But since hydrogen bonds are weak, the bond only lasts a few trillionths of a second…

• And then they quickly bond with other water molecules around them

Water is Polar

• The tendency of molecules to stick together, called cohesion, is much stronger in water than other liquids

Cohesion of Water • Hydrogen bonds also give water unusually high

surface tension, making it behave as though it were coated with an invisible film.

• Surface tension is a measure of how difficult it is to stretch or break the surface of a liquid.

Cohesion of Water • Adhesion is when water molecules

stick to other surfaces.

• Because of adhesion, water is able to creep up thin tubes.

• How is this property important for organisms?

• Water resists changes in temperature. Therefore, water requires more

heat to increase its temperature than do most other common liquids.

Water Resists Temperature Change

Water expands when it freezes • Water is one of the few substances that expands when it freezes.

• Ice is less dense than liquid water so it floats

as it forms in a body of water.

Liquid Water

Solid Water

Gas Water