1.1 Particle theory and bonding
An understanding of particle theory, including the structure of atoms and ions, and how they bond together to form compounds, helps to explain the properties of water and other substances important to marine life.
 

Learning outcomes
 

Candidates should be able to:
1.1.1 explain the changes of state in water, between solid, liquid and gas, in terms of the kinetic particle theory
 

1.1.2 describe the structure of the atom, including the nucleus containing protons and neutrons, surrounded by electrons arranged in shells
 

1.1.3 understand that sea water is a mixture of different elements and compounds
 

1.1.4 describe (including through the use of diagrams) the covalent bonding in a water molecule, limited to the sharing of electron pairs between atoms
 

1.1.5 identify (including from diagrams) covalent molecules, including water, carbon dioxide, oxygen, sulfur dioxide and glucose
 

1.1.6 describe (including through the use of diagrams) the ionic bonding in sodium chloride, limited to the loss and gain of electrons to form ions and the subsequent attraction between positive and negative ions
 

1.1.7 identify (including from diagrams) ionic substances, including sodium chloride and calcium carbonate
 

1.1.8 state the chemical name and formula of salts found in sea water, including sodium chloride (NaCl), magnesium sulfate (MgSO4) and calcium carbonate (CaCO3)
 

1.1.9 explain the formation of hydrogen bonds in water
 

1.1.10 explain how hydrogen bonding in water affects the properties of water, limited to solvent action, density, and specific heat capacity

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1.2 Solubility in water
Sea water is a solution made up of many different solutes dissolved in water. Various environmental factors affect the solubility of salts and gases in sea water. Hydrogen ion concentration is particularly important, as this affects pH.
 

Learning outcomes
Candidates should be able to:
1.2.1 explain the terms solute, solvent, solution and solubility
 

1.2.2 describe how soluble salts, such as sodium chloride, dissolve in water by the dissolution of ions
 

1.2.3 explain the effect of water temperature on the solubility of salts
 

1.2.4 define the term salinity as the concentration of dissolved salts in sea water (note that the unit for salinity used in this syllabus is parts per thousand (ppt))
 

1.2.5 (PA) investigate the effect of salinity on the freezing point of water
 

1.2.6 explain the effect of surface run-off, precipitation and evaporation on the salinity of sea water
 

1.2.7 describe the pH scale as a measure of the hydrogen ion concentration in water, including the terms acidic, neutral and alkaline (calculations relating to hydrogen ion concentration are not
required)
 

1.2.8 (PA) use litmus indicator, Universal Indicator and pH probes to measure the pH of water samples
 

1.2.9 state that oxygen has a low solubility in water
 

1.2.10 describe the effect of water temperature, water pressure (depth), atmospheric pressure and salinity on the solubility of gases in water and the implications this has for marine organisms
(knowledge of the gas laws is not expected)
 

1.3 Density and pressure

Density is a measure of the mass of a defined volume of water, and is affected by
temperature, pressure and salinity. Density differences help to maintain temperature and salinity gradients in the oceans, which affect the distribution of organisms.

Learning outcomes
Candidates should be able to:
1.3.1 explain how water temperature, water pressure and salinity affect the density of sea water
 

1.3.2 recall and apply the formula: density = mass ÷ volume, with units
of kg m–3, kg and m3 respectively
 

1.3.3 state that the density of ice is lower than sea water, causing ice to float
 

1.3.4 explain the importance of ice floating, limited to its action as a thermal insulator and as a habitat for marine organisms
 

1.3.5 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