# Ocr B Chemistry F331 Notes Essay

259 WordsJun 13, 20142 Pages
OCR B CHEMISTRY F331 (Unit 1) Revision Guide 2014 Formulae, equations and amount of substance | Key Terms (a). * Atomic Number: Atomic number is the number of protons in the nucleus. * Mass Number: Mass number is defined as the sum of the numbers of protons and neutrons in the atom’s nucleus. * Isotopes: Atoms with the same number of protons but different number of neutrons are called isotopes; they therefore have different masses. * Avogadro’s constant: The number of toms per mole is called the Avogadro’s constant. It has a value of 6.02x10^23. * Relative atomic mass: The relative atomic mass of an element is the average mass of one atom of the element relative to 1/12th the mass of one atom of carbon-1 (Ar), On a scale where carbon-12 = exactly 12. * Relative Isotopic mass: The relative isotopic is the mass of the atom of an isotope relative to carbon-12 = exactly 12. * Relative formula mass: The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of all the atoms present in its formula. * Relative Molecular Mass: is the traditional name used for ‘relative formula mass’. * Molar Mass: Molar mass is the mass per mole of an atom (M). It has the same numerical value as the relative formula mass. * 1 Mole (One Mole) = One mole is the amount of any substances that contains the same number of particles as there atoms in exactly 12g of carbon-12. The particles (atoms, molecules, ions, e.c.t.) need to be specified. | Calculations