Water

PARTICLE THEORY AND BONDING

Kinetic particle theory states that all matter is a collection of particles that are in constant, random motion.

• Freezing (Liquid to Solid):

  • When water cools, molecules slow down.

  • They lock into a fixed lattice, forming ice.

  • Ice grows as more molecules join the lattice.

• Melting (Solid to Liquid):

  • Heating ice gives energy to the molecules.

  • They vibrate faster, breaking free from the lattice.

  • Molecules can now move past each other, forming liquid water.

• Evaporation (Liquid to Gas):

  • Heating liquid water gives molecules energy.

  • Some surface molecules gain enough energy to escape into the air as vapor.

  • Faster at higher temperatures (important in the water cycle).

• Boiling (Rapid Liquid to Gas):

  • At 100°C (1 atmosphere), all molecules gain enough energy to break free.

  • Rapid evaporation happens everywhere in the liquid, forming water vapor.

• Condensation (Gas to Liquid):

  • Cooling water vapor slows the molecules.

  • They come closer, forming liquid droplets.

  ATOMS

  Protons are positively charged

  Neutrons have no charge

  Electrons are negatively charged

  The nucleus contains neutrons and protons surrounded by orbitals containing electrons called shells.

  first shell holds 2 electrons and other valance shells hold a maximum of 8 electrons

  A covalent bond is strong electrostatic forces between nonmetals by sharing electrons. Hydrogen needs 2 electrons to be stable and Oxygen needs 2 electrons, so they form a bond by sharing electrons.

CO2 CARBON DIOXIDE

O2 OXYGEN

SO2 SULPHUR DIOXIDE

Ionic Bond

Sodium losses an electron and Chlorine gains an electrons to form Na+ and Cl- ions and the subsequent attraction between positive and negative ions

Salts found in the Ocean NACl (sodium Chloride), MgSO4 (magnesium sulphate) and Calcium Carbonate (CACO3)

Hydrogen Bonds are weak bonds

This can be seen in water; the oxygen has a greater pull on electrons than the hydrogen making the oxygen slightly negative and the oxygen slightly positive creating a dipole.

Due to this partial positive charge the hydrogen forms hydrogen bonds with partially negative oxygens of adjacent water molecules.

Because water is polar it is a great universal solvent because polar solutes can dissolve in it.

Density is also affected by hydrogen bonds

Water molecules move closer strengthening hydrogen bonds. Molecules are spread apart making solid ice less dense than liquid water.

Water has a high specific heat capacity due to many hydrogen bonds making it a great temperature buffer.

SOLUBILITY IN WATER

Solute- Something that dissolves in a solvent

Solvent- something that dissolves a solute

Dissolution- the process of being dissolved

Solution- a mixture of solute dissolved in solvent

Soluble salts can dissolve easily in water through dissolution of ions this is because water is a polar substance that interacts with ions in ionic compounds.

The positive ions are attracted to the partially negative oxygen molecule and the negative ions are attracted to the partially positive hydrogens.

As temperature increases so does the rate of dissolution of salts, this is because water molecules move faster and can mix and break ionic bonds quicker.

salinity is the concentration of dissolved salts in sea water (the unit for salinity used in this syllabus parts per thousand (ppt)

INCREASED SALINITY WILL LOWER THE FREEZING POINT FROM THE NORMAL FREEZING POINT OF 0 TO MORE NEGATIVE NUMEBER.

Pure runoff adds water to the ocean decreasing salt concentration (salinity).

Precipitation adds water to the ocean which decreases salinity.

Evapouration removes water from the ocean increasing salt concentration (salinity).

The pH scale is a measure of the hydrogen ion concentration in water, acidic under 7, neutral is 7 and alkaline above 7.

Oxygen has a low solubility in water this is because oxygen does not chemically combine with water molecules.

DISSOLVED OXYGEN (DO)

Temperature increase of water causes increased vaporization of gases, decreasing temperatures= increased DO.

Solubility of gases increase with atmospheric pressure. Higher pressure pushes more gas molecules into seawater increasing DO. During tropical cyclone equilibrium shifts more DO escapes into atmosphere.

As ocean depth increases, water pressure increases due to mass of water above increasing gas solubility. (USE DEEPER, SHALLOWER NOT HIGHER, LOWER)

Implications on Marine organisms

DENSITY AND PRESSURE

TEMPERATURE

As temperatures of water increase density decreases this causes warmer waters heated by the sun to float near the surface and cold waters deeper. This also forms a thermocline (a layer between two layers of different temperatures).

PRESSURE.

Pressure increasing with depth so does the density. with increased pressure the molecules are pushed together forcing more molecules into smaller volumes. forms a pycnocline an area where the density changes quickly with depth.

SALINITY

As salinity increases so does density. Fresher water floats on saltier/denser water. Halocline, an area where salinity changes drastically with depth.

density = mass ÷ volume, with units of kg m–3, kg and m3 respectively

The density of ice is lower than sea water, causing ice to float. Hydrogen bond push water molecules apart.

The importance of ice floating, to be a thermal insulator and as a habitat for marine organisms

SYLLABUS QUESTION

describe how temperature and salinity gradients form in water columns to produce ocean layers, including the surface layer, thermocline, halocline and deep ocean, and how subsequent mixing of these layers may occur.

MIXING OF LAYERS

Upwelling- cold nutrient rich waters being brought to the surface

Turbulence- waves by tides and currents can lead to mixing at the thermocline and halocline.

Convection currents- move mantle causing plates to move?