Elements of Life Flashcards
Isotope
Atoms of the same element (thus containing the same number of protons) with a different number of neutrons
Nuclear fission
A large nucleus (such as the Lanthanides and Actinides) splits into smaller nuclei, e.g. fission process used in nuclear power plants
Nuclear fusion
Smaller nuclei (such as hydrogen and helium) fuse to form a larger nucleus, e.g. creation of elements in stars
Alpha (α) radiation
A strongly ionising helium nucleus (2+ charge) with a short range (a few centimetres in air) in air. Very little deflection by a magnetic field; stopped by a sheet of paper
Beta (ß) radiation
Weakly ionising electrons (1- charge) emitted from the nucleus when a neutron decays into a proton and an electron. Travel a few metres in air; high deflection by a magnetic field; stopped by aluminium foil
Gamma (Ɣ)
Non-ionising electromagnetic radiation with a very long range in air. Not deflected by a magnetic field; stopped by a sheet of lead or several metres of concrete
α particle
4/2 He
ß particle
0/-1 e
Ɣ particle
Photons of high frequency electromagnetic radiation
Hydrogen fusion
The means by which stars release energy; in the early universe “clouds” of hydrogen nuclei fused together under a high temperature and pressure to form stars; continued fusion formed the “light” elements (up to iron). Heavier elements were formed in supernovae under conditions of huge temperature and pressure
Absorption and emission spectra
Under certain conditions elements emit or absorb electromagnetic radiation in a characteristic way. Absorption spectra appear as black lines on a bright background, while emission spectra are the inverse of this
Balmer series
A diagram showing how outermost electrons can be excited to unstable higher levels, only to emit photons to get back to ground level
Star structure
The photosphere, the glowing surface of a star that emits visible light, is surrounded by atoms and ions that absorb light from the photosphere, producing absorption spectra. The corona, an area of high temperature surrounds the star and contains ions such as Mg 11+ and Fe 15+
Light emission
The outermost electrons of an atom start in a stable “ground state”, and when heat, light or energy is applied the molecules transition into a higher, unstable state. When the electron goes back to ground state it emits energy as a photon of light or electromagnetic radiation
Wave-particle duality
Light can be imagined with two models: as a wave, equation c = f ƛ; and as a particle, equation E = h f. The energy of the light is a function of it’s wavelength, E = c h / ƛ
Bohr’s Theory
Atomic spectra are caused by electrons in atoms moving between different energy levels (shells and sub-shells)
Electron shells
Electrons are arranged in principal energy levels which contain overlapping sub shells
Electron sub-shells
S-orbital contains one orbital with two electrons; P-orbital contains three orbitals with six electrons; D-orbital contains five orbitals with ten electrons
Sub-shell order
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10
Electron configuration rules
The lowest energy sub-levels are occupied first (the Aufbau principle); single electrons fill empty orbitals before forming pairs (Hund’s rule); each orbital contains a maximum of two electrons (the Pauli exclusion principle)
Dative covalent bonds
In a dative covalent bond, one atom contributes both electrons to the covalent bond. The bond line is replaced by an arrow, demonstrating where the electrons come from
Electron Pair Repulsion theory
Areas of electron density repel each other as they are negatively charged, so they move as far apart as possible to reduce the repulsions
