1.2 - atom

• Absorption spectra


  A spectrum of frequencies of electromagnetic radiation that has been transmitted through an atom or molecule, that shows dark bands due to the absorption of the radiation at those specific wavelengths
• Alpha-decay


  A type of radioactive decay, during which an atomic nucleus loses two protons and two neutrons. An alpha particle is equivalent to a helium nucleus. It reduces the atomic number by two and the mass number by four, making the element more stable
• Beta-decay


  A type of radioactive decay, during which a beta particle is lost, which is equivalent to an electron and a neutron turns into a proton or a proton turns into a neutron. This changes the atomic number by one, but the mass number remains the same
• Electromagnetic spectrum


  The range of frequencies of electromagnetic radiation and the respective wavelengths
• Electron transition


  When an electron absorbs energy and moves from a low energy orbital to a vacant higher energy orbital
• Electronic configuration


  The arrangement of electrons into orbitals and energy levels around the nucleus of an atom/ion. E.g. Ca: 1s22s22p63s23p64s2
• Emission spectra


  A spectrum of frequencies of electromagnetic radiation that has been emitted by an atom or molecule undergoing a transition from a state with higher energy to a state with lower energy
• Energy level


  The shell that an electron is in
• First ionisation energy


  The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions. For example, O(g)→ O+(g) +e-
• Frequency


  The number of wave oscillations per second. E = hf, f = c / λ (E = energy, h = Planck's constant, f = frequency, c = speed of light, λ = wavelength)
• Gamma radiation


  A type of electromagnetic wave that can be emitted when a nucleus undergoes radioactive decay
• Half-life (t1/2)


  The time taken for the number of radioactive nuclei in a sample to decrease by half
• Isotope


  Atoms of the same element with the same number of protons but different numbers of neutrons in the nucleus, e.g. 35Cl and 37Cl
• Infrared


  The part of the electromagnetic spectrum that has wavelengths between 780 nm and 1 mm
• Lyman series


  A group of lines present in the ultra-violet spectrum. The lines converge as frequency increases
• Orbital


  A cloud of negative charge that can hold up to two electrons. Different orbitals have different shapes
• p orbital


  A dumbbell shaped region in which up to two electrons can be found. There are three p orbitals at right angles to each other, so in total, the p subshell can hold up to 6 electrons
• Radioactive decay


  A random process in which a radioactive nuclei loses energy by emitting radiation
• s orbital


  s orbitals are spherical and symmetrical regions around the nucleus, they can each hold up to two electrons
• Second ionisation energy


  The energy required to remove 1 mole of electrons from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions (could be asked for any successive ionisation energy)
• Shell


  The energy level that an orbital is in around the nucleus of an atom. The shell closest to the nucleus is the first shell. The outermost shell that is occupied by electrons is the valence shell
• Shielding


  A decrease in the nuclear attraction experienced by an outer shell electron caused by electron-electron repulsion between the outer shell electron and electrons from adjacent quantum shells
• Third ionisation energy


  The energy required to remove 1 mole of electrons from each ion in 1 mole of gaseous 2+ ions to form 1 mole of gaseous 3+ ions (could be asked for any successive ionisation energy)
• Ultra-Violet


  The part of the electromagnetic spectrum that has wavelengths between 10 nm and 400 nm
• Visible light


  The part of the electromagnetic spectrum that has wavelengths between 380 and 700 nm
• Wavelength


  The distance between two successive points on a wave, such as two troughs or two crests. Inversely proportional to frequency
• Atom


  Made up of three particles: protons, neutrons, electrons
• Proton


  • Relative mass 1, relative charge +1
• Neutron


  • Relative mass 1, relative charge 0
• Electron


  • Relative mass 1/1840, relative charge -1
• Atomic number


  Number of protons
• Atoms of the same element have the same number of protons
• Mass number


  Sum of protons and neutrons
• Atoms of the same element can have different numbers of neutrons. These are called isotopes
• Radioactive isotopes


  • Unstable, usually heavy nuclei like uranium and plutonium, spontaneously disintegrate and can emit alpha, beta, and gamma radiation
• Alpha (α) particles


  Positively charged helium nuclei, mass of four units, stopped by a piece of paper, strongly ionising
• Beta (β) particles


  Negatively charged electrons, negligible mass, stopped by 0.5 cm of aluminium
• Gamma (γ) radiation


  Very high energy electromagnetic radiation, > 2cm of lead required to stop it, weakly ionising
• Radioactive decay


  1. Alpha decay

  2. Beta decay

  3. Positron emission

  4. Electron capture

  5. Gamma emission
• Half-life


  The time taken for the radioactivity of a radioactive isotope to fall to half of its initial value, or the time taken for half the atoms in a radioactive isotope to decay