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Unit Chemistry 2 RAM, RFM, Moles, % of an Element in a Compound, Atom Economy. Candidates should use their skills, knowledge and understanding of how science works: Atoms can be represented as shown: Mass number 23 Na Atomic Number 11 The relative masses of protons, neutrons and electrons particle Mass Charge Position Proton 1 + nucleus Neutron 1 0 nucleus Electron Very small shells The total number of protons and neutrons in an atom is called its mass number. Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element. HT The relative atomic mass of an element RAM (Ar) compares the mass of atoms of the element with the 12 C isotope. It is an average value for the isotopes of the element. The relative formula mass RFM (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. The relative formula mass of a substance, in grams, is known as one mole of that substance. The percentage of an element in a compound can be calculated from the relative mass of the element in the formula and the relative formula mass of the compound. HT The masses of reactants and products can be calculated from balanced symbol equations. Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product because: a)the reaction may not go to completion because it is reversible b)some of the product may be lost when it is separated from the reaction mixture c)some of the reactants may react in ways different to the expected reaction. HT The amount of a product obtained is known as the yield. When compared with the maximum theoretical amount as a percentage, it is called the percentage yield. The atom economy (atom utilisation) is a measure of the amount of starting materials that end up as useful products. It is important for sustainable development and for economical reasons to use reactions with high atom economy. Strengths: Weaknesses: GCSE Text Book Revision Guide p.116-117 p.42 p.118-119 p.43 p.44 p.120-121 p.122-123 p.45 p.124-125 p.45-46 To improve I need to: ………………………………………. …………………………………… ………………………………………………………………………………… …………………………………. ……………………………………………………………………………..... ……………………………………