2.2 (Topic 2) Flashcards
Describe the structure of an atom
- Atoms are composed of protons, neutrons and electrons. Protons have a positive charge, neutrons have no charge and electrons have a negative charge.
- Protons and neutrons are found in the atomic nucleus. Electrons are found in a cloud surrounding the nucleus.
Contrast ion with atom.
Atoms have no net charge because the have equal numbers of protons (+) and electrons (-). If an atom gains or loses an electron it will have a net charge and be called an ion.
Define anion and cation.
- A negatively charged ion because it has gained electrons
- A positively charged ion because it has lost electrons.
Contrast covalent, ionic and hydrogen bonds.
- All bonding involves electrons or the charges that result from the giving/taking of electrons.
- Covalent bond: electrons are shared between two atoms
- Ionic bond: attraction between cation and anion (no sharing of electrons)
- Hydrogen bond: an attraction (not a true bond) between two polar molecules.
Write the molecular formula for water and draw the atomic structure of the molecule.
H2O
Describe the cause and effect of the polar nature of water.
- In water, the oxygen has a greater “pull” on the shared electrons than the hydrogen atoms. As a result, there is unequal sharing of the electrons, with the electrons drawn closer to the oxygen.
- As a result, the oxygen has a slightly negative charge and the hydrogens have a slightly positive charge.
Describe where and how water is able to form hydrogen bonds.
- Water forms hydrogen bonds between the partial positive hydrogen of one water molecule and the partial negative oxygen of ANOTHER water molecule.
- One water molecule is capable of forming up to four hydrogen bonds with other water molecules.
Contrast adhesion with cohesion.
- Adhesion: Water molecules bonding to non-water molecules through hydrogen bonding or attraction to an ionic charge.
- Cohesion: Water molecules attach to other water molecules through hydrogen bonding.
Outline an example of the cohesive property of water being of benefit to life.
- Water cohesion allows for surface tension, allowing some insects to stay on the surface of the water.
- Water cohesion creates a chain of water molecules that allows for the transport of water from the roots to the leaves of plants.
- Water cohesion is responsible for the high heat capacity of water, maintaining a relatively stable internal temperature and external environment for living organisms
Outline an example of the adhesive property of water being of benefit to life.
Adhesion is needed for water to move from the roots to the leaves of plants. Water sticks to the sides of the xylem wall through adhesion.
Explain three thermal properties of water that are useful to living organisms.
- This means water absorbs more heat before changing state (each H-bond has an average energy of 20 kJ/mol)
- Water has a significantly higher melting and boiling point
- Water has a higher specific heat capacity (energy required to raise the
temperature of 1 g of substance by 1ºC) - Water has a higher heat of vaporization (energy absorbed per gram as it
changes from a liquid to a gas / vapour) - Water as a higher heat of fusion (energy required to be lost to change 1 g
of liquid to 1 g of solid at 0ºC)
Outline a benefit to life of water’s high specific heat capacity.
It takes a relatively large amount of heat energy to raise the temperature of water. This is a benefit because the temperature of large bodies of water remains relatively constant, protecting life from potentially lethal temperature fluctuations.
Outline a benefit to life of water’s high latent heat of vaporization.
- It takes a relatively high amount of heat energy to vaporize water (convert from liquid to gas) because hydrogen bonds must be broken.
- As the water evaporates, the surface it leaves becomes cooler. This is called evaporative cooling and allows organisms to cool with sweating
Outline a benefit to life of water’s high boiling point.
- Water boils at a relatively high temperature for a compound made of such light elements; this is due to the hydrogen bonding between water molecules causing them to resist being pulled apart (which is what happens when water boils to become a gas).
- Without this, water would not be a liquid over much of the surface of the Earth and we would not have a liquid ocean
Explain why water is such a good solvent.
Water is a good solvent because it can form hydrogen bonds with a variety of different substances. Water is called the “universal solvent” because it dissolves more substances than any other liquid.