Chapter 1 - The Chemical Basis of Life (1) Flashcards
Isotopes
atoms of an element with different mass, due to a differing number of neutrons
isotopes have the same chemical properties but slightly different physical properties
Radioisotopes
unstable isotopes that emit alpha, beta particles or gamma rays
each emission converts the unstable isotope into an atom of a different element
the resulting product will give off emissions until it is stable
these are often used to make DNA probes and tracers
Half-life
period of time required for half the radioisotopes to decay
every radioisotope has a unique half-life
ratio of isotopes in a sample can be used to date an object (radiometric dating)
Nuclear medicine
radioisotopes are used to diagnose or treat disease
these radioisotopes must have a very short half-life so that they aren’t radioactive for too long
PET scanning
positron emission tomography
positrons are antimatter electrons
when positrons and electrons come in contact, they produce a gamma ray
a patient will drink a solution of positron emitting glucose, which is then absorbed and carried by the blood to tissues
the PET scanner can then detect the position of gamma ray formation (active = coloured, dead = dark)
Hyperthyroidism therapy
a disease where the thyroid produces too much thyroxine, raising the metabolic rate
iodine-131 is absorbed by the thyroid gland, killing some of the tissue and reducing thyroxine production
very few side effects
Chemical bonding
electronegativity is the tendency of an element to attract valence electrons
EN increases across a row, as number of protons increases
EN increases up a column, as number of valence shells decreases
the difference in EN determines the type of bonding
Ionic bonding
non-metal atoms take valence electrons from metal atoms, forming ions
the ions are held together as crystals
they do not have a molecular formula, but a formula unit
Polar covalent bonding
atoms of different non-metals share pairs of valence electrons
the higher EN atoms unequally share electrons with lower EN atoms
the uneven distribution leads to polar molecules, unless there is 3D symmetry
Covalent bonding
when non-metal atoms have similar EN, they share pairs of valence electrons equally
this leads to non-polar molecules
London dispersion forces
spontaneous temporary induced dipoles
occurs when the electron cloud temporarily shifts to one side of a molecules
these attractions become more important for massive or longer molecules
as carbon chains increase, and the number of electrons increase, it is more likely to becomes liquid or solid
Dipole-dipole forces
weak attractions between permanent dipoles
polar molecules have uneven electron sharing and lack symmetry
neutral overall, but there is a slightly negative end, and a slightly positive end
these charged ends attract the oppositely charged ends of the surrounding molecules
Hydrogen bonding
strong examples of dipole-dipole forces that occur between HF, HO, or HN of an adjacent polar molecule
they are important since they give water many of its interesting properties and hold some proteins into their characteristic shape
pH scale
ranges from 0 - 14
7 is neutral
anything less than 7 is acidic, anything more is basic
it is a logarithmic scale, so each consecutive pH unit is a 10x increase or decrease in acidity
Acids
increase the hydrogen ion or hydronium ion concentration in water
strong acids
all molecules ionize in water
most common examples are HCl, HNO3, H2SO4
weak acids
few molecules ionize in water, and the reaction is reversible
common examples are H3PO4, CH3COOH
