Chapter 02 AP

8/3/2019 Chapter 02 AP

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Chapter 2: The Chemical Context of Life


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Word roots to know for this

chapter:

an- = not

co- = together

-valent = strength

electro- = electricity

iso- = equal

neutr- = neither

pro- = before

Covalentstrength togethera bond

formed by sharing the electrons between

the two atoms.


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Matteranything that has

mass and takes up space.

Elementthe simplest form of

matter. A substance that cannot

be broken down into anothersubstance by chemical means.

Compounda substance

consisting of two or more different

elements combined in a fixed ratio.


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About 25 of the 92 naturally

occurring elements are

essential to life.

Of these, carbon (C),

oxygen (O), hydrogen (H),

and nitrogen (N) make up

about 96% of living matter.

Phosphorous (P), sulfur

(S), calcium (Ca),

potassium (K), and a fewother trace elements make

up the remaining 4%.

Trace elementsrequired only in minute quantities: Iron (Fe), Iodine (I)


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Atomthe smallest unit of

matter that still retains the

properties of the element

electron

neutron

proton

Subatomic particles

building block of an

atom.

Protonspositively charged

Neutrons - neutral

Electronsnegatively charged

Protons and neutrons make up the nucleus of the atom. The nucleus is

therefore positively charged. Electrons remain outside the nucleus in a

cloud. The cloud remains near the nucleus because of the attractions

of opposite charge.


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C

62

4

Carbon

12.011

Atomic numberthe

number of protonsunique

to each element

Electron configuration

placement of electrons

in energy levels

Atomic symbol

used to represent

both the element andone atom of that

element

Atomic massthe total mass of

the atomsum of the mass of the

protons and neutrons

12

Mass number

number of protons

plus the number of

neutrons


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Each proton and each neutron have a mass of about 1 dalton.

A dalton is equivalent to 1 amu or 1.7X10-24 grams.

Because electrons are so small, their mass is negligible and notused in the atomic mass.

You can determine the number

of neutrons an atom has bysubtracting the atomic number

from the mass number.

Carbons atomic number is 6 and

mass number is 12.

Therefore, it has 6 neutrons.


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Isotopeforms of an element that contain the same number

of protons but different numbers of neutrons

Carbon has 3 isotopes.

14

6 C13

6 C12

6 C

Carbon-12 is the most

commonly found isotope

of carbon.

Both carbon-12 and carbon-13

are stable isotopes

Carbon-14 is a radioactive

isotopethe nucleusdecays spontaneously ,

giving off particles and

energy.

Atomic # is the same.


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Uses for radioactive isotopes

Radioactive isotopes can be

used as tracers to follow atoms

through metabolism.

Here radioactive hydrogen-3

is used to label and trace the

production of DNA molecules.

Radioactive isotopes function the same chemically in these molecules.

Tracers


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Positron-Emission Tomography

(PET Scan)

When radioactive tracers

are used in conjunction

with detection and

imaging systems, theycan be used to detect hot

spots of chemical

activity, here in cancer

cells.


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Energy Levels and Electrons

Energy(E) - the capacity tocause changeperforming

work.

Potential Energy (PE)

the energy matterposses because of

location or structure.

Kinetic Energy

(KE)the energy of

motion or action.


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The different states of PE

that electrons have are

called energy levels.

The electrons energy level

correlates with the average

distance from the nucleusand is represented by

electron shells.

An electron can change the shell it occupies by

either gaining or losing a specific amount of PE.

Lost energy is usually released to the environment

as light and heat.


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These atoms are arranged in periods according to the

number of electron shells they possess.


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Electrons tend to exist in the lowest available state of potential

energy.

Things to Remember

The chemical behavior of an atom depends mostly on the

electrons found in the outermost shell.

The outermost electrons are called valence electrons and theoutermost shell is called the valence shell.

Atoms with the same number of valence electrons exhibit

similar chemical properties.


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Atoms with their outer most shell filled (total of 8

valence electrons) are inert or non-reactive.

These elements, plus

Xenon (Xe), are

called the noble or

inert gases.


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Electron Orbitals

The 3-dimensional space where an electron can be found 90% of the

time is called an orbital.

There are 4 types of orbitals, with different theoretical shapess, p,

d, f.

Each orbital can hold only 2 electrons.


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Dont Forget

The first electron shell has only one orbitalan s-orbitalthat can

hold only 2 electrons.

The next electron shell has 4 orbitals, 1 s and 3 p orbitalsthat

can hold a total of 8 electrons.

Orbitals are filled with electrons singly; only when all of theorbitals in a shell have one electron will they begin to pair.

The reactivity of atoms arises from the presence of unpaired

electrons in the orbitals of the valence shells.

When atoms react and form bonds, they are completing their

valence shells, which means they contain 8 electrons.

The unpaired electrons are the ones involved in forming bonds.


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The name is BondCovalent Bond

Covalent bonds result from the

sharing or electrons between two

atoms.

Two or more elements held

together by covalent bonds are

called molecules.

One shared pair between two

atoms is a single bond, two

shared pairs are a double bond,

and three shared pairs are atriple bond.

H-H is the structural formula

and H2 is the molecular formula.


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Not all bonds are created equal!!!

Electronegativitythe measure of the affinity of an atom for

electrons. The more electronegative an atom, the higher the electron

affinity.

A bond where the electrons

are shared equally is a non-polar covalent bondH2 or

H-H.

A bond where the electrons are

not shared equally is a polar

covalent bondH2O.

O i l i h h d i k h


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Oxygen is more electronegative than hydrogen so it keeps the

valence electrons of the entire molecule closer to it.

This gives the molecule an uneven charge distribution and makes it

a polar molecule.

The Greek

symbol for

delta ( )represents

the unequal

charges.

This water molecule has polar bonds and is a polar molecule.

Are all molecules that have polar bonds polar?


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All of the bonds in this

methane (CH4) molecule are

also polar because carbon is

more electronegative than

hydrogen.

However, because the

uneven charges are evenly

distributed around the center

of the molecule methane is a

non-polar molecule.

No!!!

Another example of a non-polar molecule with polar bonds is

carbon dioxide, structural formula: O=C=O.


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Ionic Bonds

When the electronegativity of one atom far exceeds that

of another atom, the more electronegative atom will stripaway the electron(s) and add them permanently to their

valance shell.


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This results in two ions or charged particles.

Na has lost one

electron, giving

it a +1 charge.

When an ion is

positive it is

called a cation.

Cl has gained one

electron, giving it

a1 charge.

When an ion is

negative it is

called an anion.

Oppositely charge particles attract each other and an ionic bond

is formed.

Compounds formed by ionic bonds are called ionic compounds

or salts.

NaCl is sodium chloride, or table salt.


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Ionic compounds are often

found as crystalline

structures, which areaggregates of cations and

anions arranged in a three-

dimensional lattice.

These structures areextremely strong when in

their solid state but when

mixed with a solvent, like

water, the ionic attractionbetween the atoms greatly

decreases and the salt will

dissolve readily.


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Other Molecular Attractions

Most of the chemical bonds in living things are covalent ones.

The sharing of electrons, either equally or not, gives covalent

molecules the ability to form weak attractions between themselves.

These weak attractions are critical to the formation of many of the

molecules that we will be studying.


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Hydrogen Bondsa crucial attraction in living chemistry.

Hydrogen is less electronegative

than all the other atoms with which

it bonds.

Because of this, it frequently

has a partial positive charge

when in a covalent

molecule.

The partial positive of the

hydrogen attracts and holds

partial negative charges

from other polar molecules

thus creating a hydrogen

bond.


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Van der Waals Interactions

Even a molecule that is not polar can have regions of variable

charge.

These positive and negative zones move throughout the molecule

but they exist with enough frequency and duration to create

attractions between molecules.

Van der Waals forces are very weak and only happen when atoms

and molecules are very close together.

Attractions like these do not just have to happen between separate

molecules, they can happen within molecules as well. Ex: proteins.


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Molecular Shape and Function

A very important concept

that will become evident in

many of our topics is thatform defines function.

This is especially true in

biological molecules.


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Molecular shapes determines how molecules recognize and

respond to each other.

Only molecules with complimentary shapes can get close enoughto each other to interact.

Proteins of all types work because of their specific conformations.

Enzymes

Hormones

Cell surface receptors


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The making and breaking of

chemical bonds, leading to a

change in the composition of

matter, are called chemicalreactions.


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An arrow indicates the direction that the reaction occurs.

Raw materials are called reactants.

End materials are called products.

Coefficients show the number of molecules or atoms involved.

Matter is conserved during a chemical reaction.


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Some reactions go to completionall reactants are converted to

products.

C3H8 + 5O2 3CO2 + 4H2O

Most reactions are reversiblethe products of the forward reaction

become the reactants of the reverse reaction.3H2 + N2 2NH3

When the forward and reverse reactions are occurring at the samerate the system has reached dynamic equilibrium.

The reactions does not cease to occur, rather the ratio of products to

reactants remains constant.

1) Which four elements make up approximately 96% of living matter?A) b di hl i it


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A) carbon, sodium, chlorine, nitrogenB) carbon, sulfur, phosphorus, hydrogenC) oxygen, hydrogen, calcium, sodiumD) carbon, hydrogen, nitrogen, oxygenE) carbon, oxygen, sulfur, calcium

2) Each element is unique and different from other elements because of itsA) atomic mass.

B) atomic weight.C) atomic number.D) mass weight.E) mass number.

3) Nitrogen (N) is much more electronegative than hydrogen (H). Which of the following statements is correct about theatoms in ammonia (NH3)?A) Each hydrogen atom has a partial positive charge.B) The nitrogen atom has a strong positive charge.C) Each hydrogen atom has a slight negative charge.

D) The nitrogen atom has a partial positive charge.E) There are covalent bonds between the hydrogen atoms.

4) What explains most specifically the attraction of water molecules to one another.A) nonpolar covalent bondB) polar covalent bondC) ionic bondD) hydrogen bondE) hydrophobic interaction

5) Which of the following best describes chemical equilibrium?A) Forward and reverse reactions continue with no effect on the concentrations of the reactants and products. B) Concentrations of the products are higher than the concentrations of the reactants. C) Forward and reverse reactions have stopped so that the concentration of the reactants equals the concentration of theproducts.D) Reactions stop only when all reactants have been converted to products.E) There are equal concentrations of reactants and products and the reactions have stopped.

D

C

A

D

A


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Chapter 02 AP

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