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CHAPTER 2

Community

Ecosystem

Population

BIOSPHERE

Organelles

Subatomic particles

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STATES OF MATTER

Solid Liquid Gas

• Definite shape Shape of container No definite shape

• Definite volume Volume of container No def. volume

• Tightly packed May overlap Very spread out

• Vibrate in place Move faster Very fast

• A chemical element is a substance that cannot be broken down to other substances by ordinary chemical means

• About 25 different chemical elements are essential to life

Life requires about 25 chemical elements but four are most important

• Goiters are caused by iodine deficiency

Figure 2.2

Atomssmallest unit of an element

How are the protons, neutrons, and electrons determined?

How is the shorthand version written?

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DIATOMIC ELEMENTS

• Elements that must exist naturally as 2 atoms bonded together (until it forms a chemical bond with any other element)

• Br I N Cl H O F

H2 N2 O2 F2 Cl2 Br2 I2

Atom vs. Elementatoms are the individual units of an

element

An example is hydrogen. Hydrogen exists as 2 atoms of the element bonded together.

• Atoms of each element are distinguished by a specific number of protons

Table 2.4

– The number of neutrons may vary – Variant forms of an element are called

isotopes– Some isotopes are radioactive

Isotopes

Isotope of???

• Radioactive isotopes can be useful tracers for studying biological processes

• PET scanners use radioactive isotopes to create anatomical images

Connection: Radioactive isotopes can help or harm us

Figure 2.5BFigure 2.5A

Atomic Structure

ELECTRON ENERGY LEVELS

• Atomic structure demonstrates the 2, 8, 8 rule.

• The farther the electron is from the nucleus, the greater the potential energy (energy due to its location….farther from the opposing positive protons).

NobleGases“Inert”

• Electrons are arranged in shells– The outermost shell determines the

chemical properties of an atom. Unpaired electrons are involved in bonding.

Electron arrangement determines the chemical properties of an atom

HYDROGEN (H)Atomic number = 1

CARBON (C)Atomic number = 6

NITROGEN (N)Atomic number = 7

OXYGEN (O)Atomic number = 8

Electron

Outermost electron shell (can hold 8 electrons)

First electron shell (can hold 2 electrons)

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CHEMICAL BONDING

Elements forming Compounds

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+ =

Sodium is a silver-colored metal that reacts so violently with water that flames are produced when sodium gets wet.  Chlorine is a greenish-colored gas that is so poisonous that

it was used as a weapon in World War I. When chemically bonded together, these two dangerous substances form sodium chloride, a compound so safe that we eat it every day - common table salt!

Compound vs. Molecule

• A compound is a result of 2 or more different elements combined in a fixed ratio.

• Water is a compound formed when 2 hydrogen bond with one oxygen.

• Imagine a waterfall……explain compound vs molecule with this example.

• When atoms gain or lose electrons, charged atoms called ions are created– An electrical attraction between ions with

opposite charges results in an ionic bond

Ionic bonds are attractions between ions of opposite charge

Figure 2.7A

NaSodium atom

ClChlorine atom

Na+

Sodium ionCl–

Chloride ion

Sodium chloride (NaCl)

Na Cl Na Cl

+–

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Bohr Model Method:

Step 1: Draw the energy levels for each element

Step 2: Show the arrow of transfer. There should be an arrow showing transfer for EACH electron given away. (Just like the top picture)

Step 3: State the ions below each atomic structure to indicate that electrons have been gained or lost.

IONIC BOND:Bohr Method

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IONIC BOND:Lewis Dot Structure

NaCl

MgO

Lewis Dot Method:

Step 1: Write the symbol for each atom separately and show valence electrons (evenly spread out )

Step 2: No arrows. Write ions once transfer has taken place. Show electrons for the ORIGINAL outer shell (the one that gained will show electrons).

Remember that ions are written as symbol with superscript.

REDOX REACTIONSReduction = gain electronsOxidation = lose electrons

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COVALENT BOND:Bohr ModelBohr Model Method:

Step 1: Draw the energylevels for each element separately.

Step 2: Show the energy levels joined (similar to the top picture)

All diatomic elementsDemonstrate a Covalent bondRemember: BrINClHOF(Chlorine isshown to the right)

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Mole

cula

r form

ula

COVALENT BOND:Lewis Dot Structure

Lewis Dot:

Step 1: Draw the dot diagram for each element individually (use X and • for different atoms)

Step 2: Draw the dot diagram for the compound

Step 3: Show the molecular formula (including lone electrons)

Electronegativity ChartIn a covalent compound, the more electronegative an atom, the greater the pull on the electrons that are being shared. Therefore, it is an unequal tug of war.Nonpolar covalent = equal sharingPolar covalent = unequal sharing

Polar covalent bonds in a water molecule

This results in a partial negative charge on theoxygen and apartial positivecharge onthe hydrogens.

H2O

δ–

O

H Hδ+ δ+

Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen.

A hydrogen bond

Water(H2O)

Ammonia(NH3)

δ– δ+

OH

Hδ+

δ–

N

HH H

A hydrogenbond results from the attraction between thepartial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia.

δ+

δ+

δ+

Van der WaalsWeak, temporary attraction

• Due to the constant motion of electrons in the orbitals, all atoms may be attracted to one another just because they are close and exhibit a positive or negative region at the right moment. Look at Neon to the right…..Neon is a noble gas and will never bond.

• In a chemical reaction:– reactants interact– atoms rearrange– products result

Chemical reactions rearrange matter

REARRANGEMENTS OF ATOMS

2 H2+ O2

→2 H2O

Figure 2.17A

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CHANGES IN STATE

Latent Heat = energy absorbed (stored) or releasedHeat of fusion = energy released; Gas to Liquid to SolidHeat of Vaporization = energy absorbed; Solid to Liquid to Gas

Hydrogen bonds between water molecules

Hydrogenbonds

δ +

δ+

H

Hδ+

δ+

δ–

δ–

δ–

δ–

The polarity of water iscrucial to understanding itsunique properties.

Explain how electronegativity plays a role in the attraction of water molecules.

Why water allows for life to exist on Earth…..

– Cohesion and Adhesion increase surface tension

– Ice is less dense than liquid water

– Moderates temperature– Universal Solvent

Water transport in plantsWater conducting cells

100 µm

Hydrogen bondsbetween neighboring water molecules hold the substance together, resulting in a cohesive property of water.

Adhesion, the “sticking”of one substance to another, also contributesto the transport of water from roots to shoots.

The collective strength of water’s hydrogen bonds results in surface tension.

• Due to hydrogen bonding, water molecules can move from a plant’s roots to its leaves

• Insects can walk on water due to surface tension created by cohesive water molecules

Hydrogen bonds make liquid water cohesive

• Molecules in ice are farther apart than those in liquid water

Ice is less dense than liquid water

Hydrogen bond

ICEHydrogen bonds are stable

LIQUID WATERHydrogen bonds constantly break and re-form

Ice: crystalline structure and floating barrier

Liquid water

Hydrogen bonds constantly break and re-form

Ice

Hydrogen bonds are stable

Hydrogen bond Floating ice protects the

Liquid water below from theColder air.

If ice sank, it would seldom have a chance to thaw

Ponds, lakes, and oceans would eventually freeze solid

Water can absorb high amounts of energy with little change in its temperature….SPECIFIC HEAT

Temperature Moderation

Specific Heat of Water compared to……….

Imagine the beach……..

An importance of Water in terms of air temp….

Now imagine if our planet did not have water……

Imagine a desert-like condition……

• Solutes whose charges or polarity allow them to stick to water molecules dissolve in water– They form

aqueous solutions

– Solutes may dissolve in a solvent until saturation is reached

Water is a versatile solvent

Ions in solution

Salt crystal

Cl–

Na+

Cl–

–

– –

–

–Na+

+

+

+

+

A crystal of table salt dissolving in waterNegative

Oxygen regions of polar water molecules are

attracted to sodium cations (Na+).

+

+

+

+Cl –

–

–

–

–

Na+

Positive hydrogen regions

of water molecules cling to chloride

anions (Cl–).

+

+

+

+

–

–

–

–

–

–

Na+

Cl–

Acids and Bases• Substances that breakdown to produce

more hydrogen ions than hydroxide ions are……

• Substances that breakdown to produce more hydroxide ions than hydrogen ions are……

• Substances that breakdown to produce equal amounts of hydrogen ions than hydroxide ions are……

pH = “potential Hydrogen”

Aqueous solutions have the total concentration of H+ ions and OH- is a constant….10-14

• Cells are kept close to pH 7 by buffers

• Buffers are substances that resist pH change

– They accept H+ ions when they are in excess and donate H+ ions when they are depleted

– Buffers are not foolproof

• Some ecosystems are threatened by acid precipitation

• Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids

Connection: Acid precipitation threatens the environment

Figure 3.9 Acid precipitation and its effects on a forest

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Moreacidic

Acidrain

Normalrain

Morebasic