Atoms, Ions and Compounds

Atoms, Ions and Compounds

1. Atomic Structure and Isotopes

   • Atoms = contain a nucleus w/ protons and neutrons
   • Atoms = Surrounded by electrons in shells
   • No. of protons = no. of electrons in an ATOM (no overal charge)
   • Neutrons = charge 0, mass 1
   • Protons = charge +1, mass 1
   • Electrons = charge -1, mass 1/1836 (0)
   • Isotopes = atoms of the same element with different no.s of neutrons (so, different masses)
   • Ions = charged particles. Atoms that have lost/gained electrons
   • +vely charged ion = LOST ELECTRONS, CATIONS
   • -vely charged ion = GAINED ELECTRONS, ANIONS
   • Subatomic particles = protons, neutrons, electrons
   • Mass number = protons + neutrons
   • Atomic number = number of protons. The periodic table is arranged in order of atomic number
   • Every atom of the same element has the same np. of protons
   • Isotopes of the same element react in the SAME way (reactivity depends on electrons), small differences in PHYSICAL properties

2. Relative Mass

   • RAM = the weighted mean mass of one atom of an element, compared with 1/12th of the mass of an atom of carbon-12
   • Relative Isotopic Mass = the average mass of one isotope of an element, compared with 1/12th of the mass of an atom of carbon-12
   • RAM (Ar) = (% x mass)+(% x mass)/ total abundances (%'s)
   • Mass spectrometry = measures the % abundances of each isotope present in an element (what proportion of the element is in each isotope) The ions are detected on a MASS SPECTRUM, as a mass-to-charge ratio. Each ion reaching the mass spectrum detector adds to the SIGNA:L, the greater the abundance, the larger the signal
   • CANT find RAM of an isotope by adding the relative masses of subatomic particles as strong nuclear forces holding p + n together leads to a slight MASS DEFECT - shows need of a standard isotope (carbon-12)
   • ir/Ar = no units! (are ratos)
   • Mass spectrum = records the abundances of each isotope, as a % (x axis = Ir, y axis = % abundance)
   • m/z = relative mass of ion/ relative charge on ion
   • Relative molecular mass/ relative formula mass (Mr) = the sum of the relative masses of all the elements in a compound, in the proportions present

3. Formulae and Equations

   • Binary compounds = contain TWO elements only
   • Compounds = multiple elements bonded together
   • Polyatomic ion = ions that contain multiple elements bonded together
   • Balancing equations - no. of atoms on right side = no. of atoms on left side. CAN use fractions
   • Metals LOSE electrons to form CATIONS, non - metals GAIN electrons, to form ANIONS
   • Ionic compound = contains a cation and an anion, and the charges cancel out
   • MEMORISE: ammonum = NH4+, hydroxide = OH-, nitrate = NO3-, carbonate = CO3-, sulfate - SO42-
   • Covalent compounds DONT contain ions (exist as molecules, covalently bonded together
   • State symbols: (g) = gas, (l) = liquid, (s) = solid, (aq) = aqueous