Chemistry scares people, but it doesn’t have to!

Understanding chemistry is very important for understanding aspects of oceanography and the living organisms that inhabit the oceans

Basic chemistry○ Atomic structure

Nucleus = protons (positive) + neutrons (neutral)

Electrons in orbitals around nucleus (negative)

http://www.rstp.uwaterloo.ca/manual/matter/graphic/atom.jpg

Chemical bonds Attractive force that holds atoms together,

interaction of those electrons Three major types

○ Ionic bonds ○ Covalent bonds○ Hydrogen bonds

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○ Ionic bonds Atoms “exchange” electrons to fill outer shell

becomes positive ion if lose electron becomes negative ion if gain electron + & – ions attracted to each other NaCl Na+ + Cl-

http://www.physicalgeography.net/fundamentals/images

http://www.msnucleus.org/membership/html/k-6/rc/minerals/3

Covalent bonds Atoms “share” electrons to fill outer shell For example:

H (hydrogen) has one electron, needs 1 more O (oxygen) has 6 electrons in outer shell, needs two electrons

Therefore, oxygen and 2 hydrogens bond to form water

Covalent bonds are stronger because there is sharing of the electrons

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Polar covalent bonds○ Electrons not equally distributed in molecule○ Water is a polar molecule

O strongly attracts electrons slightly negative H slightly positive

- Think of oxygen as being the “bully” – it’s larger so it pulls the electrons towards it’s nucleus more often

○ Allows formation of H-bonding between water molecules

http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig

H2O molecule Two hydrogen H and one oxygen O

atoms bonded by sharing electrons Polar covalent bondPolar covalent bond

Hydrogen bonding as a result of polar covalent bonds

Polarity small negative

charge at O endsmall positive

charge at H endAttraction between

+ and – ends of water molecules to each other or other ions

Happens because of the polar covalent bondFig.

5.3

Hydrogen bonds are weak bonds between +/- ends of poles causes water molecules to "stick" together – cohesion

Gives water important distinct properties H2O molecule forms H-bonds w/ up to four

other water molecules, depending on temperature

http://www.nyu.edu/pages/mathmol/modules/water

Hydrogen bonding and water Hydrogen bonds are

weaker than covalent bonds but still strong enough to result in unique properties of water Cohesion = sticks to

other water molecules Adhesion = sticks to

other types of molecules High surface tension

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Hydrogen bonding and waterH-bonds absorb red light,

reflect blue light blue color

High solubility of chemical compounds in water

Solid, liquid, gas at Earth’s surface, not all substances can say the same

Unusual thermal properties

Unusual density

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Water exists naturally in all 3 states on Earth’s surface

Changes of state due to adding or subtracting heat

Heat is energy of moving molecules calorie is amount of heat needed to raise

the temperature of 1 gram of water by 1o C

Temperature is measurement of average kinetic energy

Unusual thermal properties of H2O H2O has high boiling point

H2O has high freezing point

Most H2O is in liquid form of water on Earth’s surface VERY important for life

Unusual thermal properties of H2O High latent (hidden) heatslatent (hidden) heats of

Vaporization Melting/freezing

H-bonds holding water together require extra energy (heat) to break bonds change states without change in

temperature (a to b, c to d in figure)

Fig. 5.6

Unusual thermal properties of H2O

Water high heat capacity (specific heat capacity (specific heat)heat)Amount of heat required to raise

temperature of 1 gram of any substance 1o C

Water can take in/lose lots of heat without changing temperature – must break H-bonds

On the other hand, rocks have low heat capacity○ Rocks quickly change temperature as they

gain/lose heat

Global thermostatic effects Moderates temperature on

Earth’s surface – water temp less variable and less extreme than air temperaturesEquatorial oceans (hot) don’t

boilPolar oceans (cold) don’t

freeze solid

http://www.goredsea.com/media/images/EN

Global thermostatic effects Marine effectMarine effect

Oceans moderate temperature changes day/night; different seasons

Continental effectContinental effectLand areas have greater range of temperatures

day/night and during different seasons

Look at the differences between coastal Florida compared to Orlando

Density of water Density of water increases as

temperature decreases down to 4oC From 4oC to 0oC density of water

decreases as temperature decreases Density of ice is less than density of

waterVERY unique propertyThink about it – most solids are MORE dense

then their liquids

Density of water

Fig. 5.10

Density of water Dissolved solids reduce freezing point of

waterAs water freezes, the crystalline structure

“pushes out” much of the dissolved solidsCreates icy “slush” and surrounding waters

become saltierPutting salt on icy roads melts ice

○ Salt lowers freezing point of water on roads allowing it to remain liquid at colder temps

Water = Life• Summary:

• Unique properties of water that make life possible• High heat capacity and specific heat

• Moderates climates• Keeps equatorial regions from boiling and pole

regions from freezing solid• High latent heat – when undergoing change of state,

large amount of heat is absorbed or released• Sweat evaporating from your skin draws heat from

your body, keep you cool• Ice is less dense than liquid water• Cohesion

• Water moving up xylem in plants• Surface tension – allows plankton to stay near

surface of water

Salinity Six elements make up 99% of dissolved

solids in seawater – from erosion of land, volcanism

Total amount of solid material dissolved in water- Traditional definition

Typical salinity is 3.5% or 35o/ooo/oo or parts per thousand (ppt) = grams of salt per

kilogram of water (g/Kg )

Adding salts changes many properties of water

Fig. 5.12

Measuring salinity EvaporationEvaporation Chemical analysis - Chemical analysis - titrationtitration

Principle of constant proportions Major dissolved constituents in same

proportion regardless of total salinity Measure amount of halogens (Cl, Br, I,

F) (chlorinity) Salinity = 1.80655 * Chlorinity (ppt)

Specific gravity (1.028 g/ml)Specific gravity (1.028 g/ml) Hydrometer

Electrical conductivity Electrical conductivity Salinometer

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Pure water vs. seawater

Salinity variations Open ocean salinity 33 to 38

o/oo However, coastal areas

salinity varies more widelyInflux of freshwater lowers

salinity or creates brackishbrackish conditions

Greater rate of evaporation raises salinity or creates hypersalinehypersaline conditions

Salinity may vary with seasons (dry/rain)

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How to change salinity

Add/remove water Add/remove

dissolved substances

Processes that add/subtract salinity from oceans

Precipitation (rain or snow)

Runoff (river flow)

Melting icebergs Melting sea ice

Evaporation Formation of sea

ice

Salinity decreases through:

Salinity increases through:

Floating in the Dead Sea

Hydrologic cycle describes recycling of water near Earth’s surface

Fig. 5.15

Processes that add/subtract dissolved substances

River flow Volcanic eruptions Atmosphere Biologic

interactions

Salt spray Chemical reactions at

seawater-sea floor interface

Biologic interactions Evaporite formation Adsorption

Physical attachment to sinking clay or biological particles

Dissolved substances increases through:

Decreases through:

Residence time Average length of time a substance remains

dissolved in seawaterIons with long residence time are in high

concentration in seawater (Na+, Cl-)Ions with short residence time are in low

concentration in seawater percipitate out (K+, Ca2+ )

Steady state condition

Residence time and steady state

Fig. 5.16

pH – concentration of H+ ions Acid releases H+ when dissolved in

water (HCl, H2SO4) Alkaline (or base) releases OH- (NaOH) pH scale measures the hydrogen ion

concentration, logarithmic scale 0-14Low pH value, acidHigh pH value, alkaline (basic)pH 7 = neutral

Figure 5.17

Carbonate buffering

Keeps ocean pH about same (8.1, slightly alkaline)pH too high, carbonic acid releases H+pH too low, bicarbonate combines with H+

Precipitation/dissolution of calcium carbonate CaCO3 buffers ocean pH (CaCO3 Ca+ + CO3

-)CO3

- bonds with H ions created when CO2 interacts with H2O

Oceans can absorb CO2 from atmosphere without much change in pH

Fig. 5.18

Carbonate bufferingCarbonate buffering

Too acidic removes H+

Too basic adds H+

Surface ocean variation of salinity Surface salinity varies primarily with latitude Polar regions: salinity lower

lots of rain/snow and runoff

Low temps, not a lot of evaporation

Mid-latitudes: higher salinity

because of evaporation (dry areas)

Equator: salinity slightly lower than mid-latitudes

due to lots of rain despite high evaporation

Deep ocean variation of salinity

Surface ocean salinity is variable

○ Due to occurrences at surface – rain, evaporation, etc

Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water)

HaloclineHalocline, rapid change of salinity with depth

Density of seawater 1.022 to 1.030 g/cm3 surface seawater Saltwater more dense than pure water

That is why you can float better in saltwater

Ocean layered according to density Density seawater controlled by

temperature, salinity, and pressureMost important influence is temperatureDensity increases with decreasing

temperature

Density of seawater Overall, temp has greatest

effect on density However, salinity greatest

influence on density in polar oceans polar ocean is isothermal

(same temperature as depth increases)

Currents from lower latitudes bring higher salinity water into polar areas

But polar waters are overall isothermal AND isopycnal

http://www.waterencyclopedia.com/images/wsci_03_img0394.jpg

Density versus depth

PycnoclinePycnocline, abrupt change of density with depth

ThermoclineThermocline, abrupt change of temperature with depth

Density differences cause a layered ocean

Mixed surface water Pycnocline and thermocline Deep water

Desalination processes Remove salt from seawater Distillation Distillation – most common process,

but energetically costly Reverse osmosis Reverse osmosis – flimsy

membranes

Misconceptions – What have we learned that make these statement false? Increases in global temperatures in the

atmosphere and the consequent warming of the oceans will only create a problem for people living along the coast.

Water exists in the ground in actual rivers or lakes that are constantly renewed.

People drink bottle water because it is better for our health; the safety of tap water is below consumption standards.

Ocean Literacy Principles 1e - Most of Earth’s water (97%) is in the ocean. Seawater has unique properties: it is saline, its

freezing point is slightly lower than fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. The salt in seawater comes from eroding land, volcanic emissions, reactions at the seafloor, and atmospheric deposition.

1g - The ocean is connected to major lakes, watersheds and waterways because all major watersheds on Earth drain to the ocean. Rivers and streams transport nutrients, salts, sediments and pollutants from watersheds to estuaries and to the ocean.

3a - The ocean controls weather and climate by dominating the Earth’s energy, water and carbon systems.

Sunshine State Standards SC.6.E.7.1 Differentiate among radiation, conduction, and convection, the three mechanisms by

which heat is transferred through Earth's system. SC.6.E.7.6 Differentiate between weather and climate. SC.8.P.8.1 Explore the scientific theory of atoms (also known as atomic theory) by using models to

explain the motion of particles in solids, liquids, and gases. SC.8.P.8.4 Classify and compare substances on the basis of characteristic physical properties that

can be demonstrated or measured; for example, density, thermal or electrical conductivity, solubility, magnetic properties, melting and boiling points, and know that these properties are independent of the amount of the sample.

SC.8.P.8.6 Recognize that elements are grouped in the periodic table according to similarities of their properties.

SC.8.P.8.8 Identify basic examples of and compare and classify the properties of compounds, including acids, bases, and salts.

SC.912.E.7.9 Cite evidence that the ocean has had a significant influence on climate change by absorbing, storing, and moving heat, carbon, and water.

SC.912.P.8.4 Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom

SC.912.P.8.5 Relate properties of atoms and their position in the periodic table to the arrangement of their electrons.