A-level Chemistry AQA [New Spec] - Relative Atomic & Molecular Mass | A-level Chemistry | OCR, AQA, Edexcel

Relative Atomic & Molecular Mass in a Snap! Unlock the full A-level Chemistry course at http://bit.ly/2KnH0d7 created by Ella Buluwela, Chemistry expert at SnapRevise. SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks. Sign up today and together, let’s make A-level Chemistry a walk in the park! The key points covered in this video include: 1. What is Relativity? 2. Why do we compare to Carbon-12? 3. Relative Isotopic Mass 4. Relative Atomic Mass 5. Relative Molecular Mass 6. Relative Formula Mass What is relativity? Atoms are very small! 10-8cm. Mass is given in relative terms: Relative to the C12 isotope, International Standard. Why 12C? Comparing to C 12 is the international standard. Atomic mass is measured in Unified Atomic Mass Unit (u). C12: 12 u, 1/12th of C12 : 1u, 1u : 1.660540210 x 10-27kg. Relative Isotopic Mass The mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12. For an isotope it is the same as the mass number. Example: Chlorine has 2 stable isotopes. Relative Atomic Mass The weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon-12. Many elements are a mixture of isotopes. Atomic mass takes this into consideration. Example: Chlorine has 2 stable isotopes. ((75.77 x 35) + (24.23 x 37))/100, (2651.95 + 896.51)/100, 3548.46/100, 35.49 Relative Molecular Mass Some compounds and elements are composed of simple molecules. Example: Cl2 is composed of 2 chlorine atoms. Mass number of Chlorine = 35.45. 35.45 x = 70.9. Relative Formula Mass Similar to Mr. Applied to ionic compounds. Relative Atomic mass of each formula unit is calculated. Example: A formula unit of NaCl composed of Na and Cl, Na: 23, Cl: 35.45, NaCl: 35.5 + 23 = 58.45. Summary Atomic Mass is given relative to 1/12th the mass of an atom of carbon-12 Relative Isotopic Mass: Mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12 Relative Atomic Mass: Weighted mean mass of an atom of an element compared with 1/12th the mass of an atom of carbon 12 Relative Molecular Mass can be applied to simple molecules Relative Formula Mass is applied to ionic compounds