Chemical Foundations for Cells

Chapter 2

Chemical Benefits and Costs

•Chemical pollutants damage ecosystems

•Understanding of chemistry provides fertilizers, medicines, etc.

• Fundamental forms of _________

• Can’t be broken apart by normal

means

• ___ occur naturally on Earth

Elements

Most Common Elements in Living Organisms•________•________•___________•__________ The big fo

ur

What Are Atoms?• Smallest particles that retain properties of an element

• Made up of subatomic particles:

– ______ (+)

– __________(-)

– _________ (no charge)

HELIUM

electron

proton

neutron

Atomic Number

= Number of ___________Carbon= 6 protons

Mass Number= # of _______ + # of _______

= Atoms of an element with different numbers of ______(different mass numbers)

Isotopes

•Carbon 12 has 6 protons, 6 neutrons•Carbon 14 has 6 _____, 8 ________

Radioisotopes•Have an _____ nucleus that emits energy and particles•Decay occurs at a _____ rateRadiation therapy-

using radioisotopes to destroy _________cellsnormal thyroid enlarged cancerous

Thyroid Scan

What Determines Whether Atoms Will Interact?

Answer- The _____ and ________ of their electrons

• Carry a ______ charge• Repel one another • Are attracted to _______ in the

nucleus• Move in orbitals (shells)

Electrons

1st shell- ___electrons max

2nd, 3rd and 4th shells- ___electrons max

CALCIUM20p+ , 20e-

Only _______ electrons matter!

Hydrogen, carbon, oxygen, and nitrogen all have vacancies in their ____ shells- hence are ______

CARBON6p+ , 6e-

NITROGEN7p+ , 7e-

HYDROGEN1p+ , 1e-

•A bond is union between electron structures of atoms

Electron Vacancies make atoms reactive

What holds molecules together?

a._______b. __________c. ____________ Weak

Strong

•_________ Bonds= share electrons•________ Bonds= swipe or gain electrons•__________ Bonds= weak, opposite charge attraction

Three major bonds

_____________ Atoms share a pair or pairs of electrons to fill outermost shell

•Single covalent bond

•Double covalent bond

•Triple covalent bond_________ Covalent Bonds

• Atoms share electrons _______• Nuclei of atoms have same number of

______• Example: Hydrogen gas (H-H)

• ______ # of protons• Electrons near nucleus with most protons• Water - Electrons more attracted to O nucleus

than to H nuclei

________Covalent Bonds

• __________ –between two atoms are so unequal in their attraction for valence electrons that one atom strips an electron completely from the other.– Example- sodium (one valence electron) in its third

shell transfers this electron to chlorine with 7 valence electrons in its third shell.

– Now, sodium has a full valence shell (the second) and chlorine has a full valence shell (the third).

Fig. 2.14

These are now called ____

Na+ is a _______

Cl- is an _______

Cations and anions are attracted - form __________

• Example- ammonia molecules and water molecules link together with weak hydrogen

bonds.– Hydrogen atoms - partial ______ charges

– Nitrogen atom - partial ________ charge.

• Thus- ammonia forms hydrogen bonds with water

Fig. 2.16

• ___________ - a hydrogen atom that is already ________________ bonded to a strongly electronegative atom is attracted to another strongly electronegative atom.

The polarity of water molecules results from _____________ bonding

• Water molecule- two hydrogen atoms form ______ _______ bonds with an oxygen atom.– Partial negative

charge– Partial positive

charge

_______- because each share one electron_____- because O is more electronegative than H_______- because they each share electrons

The magic of water

• Water has unusual properties because of attractions between _____ molecules.– The slightly negative regions interact with

slightly positive regions of nearby molecules, forming a hydrogen bond.

– Each water molecule can form hydrogen bonds with up to ____ neighbors.

Fig. 3.1

• How? By _______ bonds• Water cohesion is key role in the ____

________in plants.– Water that evaporates from a leaf is replaced

by water from vessels in the leaf.• ________, clinging

of one substance to another, contributes too

Water adheres to itself- called _______

a.cohesionThe magic of water

• _____________, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.– Water has h igh _______________ – Why? __________ bonds resist breaking the

surface.– Water behaves as if

covered by an invisible ______.

b.Surface tensionThe magic of water

• Water _______ air temperatures by ___________ heat from warmer air and releasing heat to cooler air.

• Water can absorb or release relatively _________ of heat with only a slight change in its own temperature.

Water moderates temperatures on Earth

• Water resists changes in temperature – Why? ________________.– Heat must be absorbed to break __________________

and is released when hydrogen bonds form.

c.Temperature stabilizationThe magic of water

• As a liquid evaporates, the surface of the liquid that

remains behind cools - ___________________. – The most energetic molecules evaporate, leaving the

lower kinetic energy molecules behind.

• Evaporative cooling moderates ___________________ in lakes and ponds and prevents terrestrial organisms from overheating.– Evaporation of water from the leaves of plants

or the skin of humans removes excess heat.

The magic of water d. evaporative cooling

– At 0oC-water becomes a ______________________ with each molecule bonded to the maximum of ______ partners.

– Ice is about ___________ dense than water at 4oC, thus ice _____.

If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid.

e. Prevent lake freezing

• Water (unlike most liquids) is less dense as a solid than as a liquid.

The magic of water

• ________- A completely _______________ mixture of substances.

• ______ = dissolving agent

• _______ = agent being dissolved.– Example-water is a solvent and sugar the solute.

f. Powerful solventThe magic of water

Water dissolves almost anything polar or ionic

• Affinity for water = _________.– Substances with _______________ bonds.

• no affinity for water = _______________.– substances with ___________________

covalent bonds.• Example-Oils, such as vegetable oil, are non-polar • Hydrophobic molecules are major ingredients of ___

_________________.

Hydrophobic vs. hydrophilic

• How do we measure acidity? – Answer: In ____________.

• A water molecule dissociates into a hydrogen ion and a hydroxide ion:

• H2O <=> H+ + OH-

• At equilibrium the concentration of H+ or OH- is 10-7M (25°C) .

• Hydrogen and hydroxide ions are very reactive, and thus drastically affect the proteins and other molecules of a cell.

The pH Scale• Measures ___ concentration of fluid• Change of 1 on scale means ____

change in ____ concentration

Highest H+ Lowest H+

0---------------------7-------------------14______ Neutral _____

• How do we measure acidity? – Answer: In _______.

Examples of pH• Pure water is neutral with pH of ____

• Acidic- pH= < 7.0

– Stomach acid: pH ____________

– Lemon juice: pH ____

• Basic- pH= > 7.0

– Seawater: pH 7.8 - 8.3

– Baking soda: pH _____

• Weak acids- Reluctant H+ donors

– __________ acid (H2CO3)

• Strong acids- Completely give up H+ when dissolved

– HCl (hydrochloric acid)

Carbonic Acid-Bicarbonate Buffer System

• When blood pH rises, carbonic acid

dissociates to form ____________ and __

H2C03 -----> HC03- + H+

• When blood pH drops, bicarbonate binds H+

to form ________ acid

HC03- + H+ -----> H2C03

• ______________ (a product of the formation of carbonic acid from carbon dioxide and water) occurs when rain, snow, or fog has a pH that is more acidic than 5.6.

•caused primarily by _____________ and ______ ______ from burning of fossil fuels

Rain in the Adirondack Mountains of upstate New York averages a pH of ____Great impact on eggs and early developmental stages of _________ organismsThis has done major damage to forests in Europe and substantial damage of forests in North America

Isotope?

Radioactive isotope

Reactivity of an atom?

What is a valence shell?

Is this reactive? How many

valence electrons?