1. THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are... Relative massRelative charge PROTON NEUTRON ELECTRON

2. THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are... Relative massRelative charge PROTON1+1 NEUTRON10 ELECTRON 1 1833

3. MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z)Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus

4. MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z)Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Na 23 11 Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS

5. MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z)Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Na 23 11 Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS THESE ALWAYS GO TOGETHER – ANYTHING WITH 11 PROTONS MUST BE SODIUM

6. MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z)Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Na 23 11 Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS

7. MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z)Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Na 23 11 Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS THERE WILL BE 12 NEUTRONS IN THE NUCLEUS 23 – 11 = 12

8. MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z)Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Na 23 11 Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS

9. MASS NUMBER AND ATOMIC NUMBER Ions 27 13 Al 35 17 Cl Atomic number, Z Mass number, A Protons Neutrons Electrons

10. MASS NUMBER AND ATOMIC NUMBER Ions 27 13 Al 35 17 Cl Atomic number, Z 13 17 Mass number, A 27 35 Protons 13 17 Neutrons 14 18 Electrons 13 17

11. Formation of ions An ion is a positively or negatively charged atom Atoms form ions by losing or gaining electrons. When an atom loses one electron,it has an electric charge of +1, e.g. Na + Because the number of electrons in the atom becomes one fewer than the number of protons If one electron is gained, an electric charge of -1 is formed, e.g. Cl - Because the atom contains one more electron than it does protons

12. Atomic structures of ions Ions 23 Na +35 17 Cl - Atomic number, Z Mass number, A Protons Neutrons Electrons Overall charge

13. Atomic structures of ions Ions 23 Na + 35 17 Cl - Atomic number, Z 11 17 Mass number, A 23 35 Protons 11 17 Neutrons 12 18 Electrons 10 18 Overall charge 11 – 10 = +1 17 – 18 = -1

14. MASS NUMBER AND ATOMIC NUMBER ProtonsNeutronsElectronsCharge Atomic Number Mass Number Symbol A192119 B20040 C+1123 D660 E613 F162-16 G 27 Al 3+

15. MASS NUMBER AND ATOMIC NUMBER ProtonsNeutronsElectronsCharge Atomic Number Mass Number Symbol A1921190 40 40 K B20 0 40 40 Ca C111210+1123 23 Na + D6660612 12 C E6760613 13 C F16 182-1632 32 S 2- G1314103+1327 27 Al 3+

16. TRY QUESTIONS 1 – 2 PAGE 7

17. RELATIVE MASSES Relative Atomic Mass (A r ) Is the weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12 A r =average mass per atom of an element x 12 mass of one atom of carbon-12 Relative Isotopic Mass Is the mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12 For an isotope, the relative isotope mass is the same as the mass number. e.g. so for oxygen -16, the relative isotopic mass = 16.0

18. Relative Molecular Mass (Mr) Is the weighted mean mass of a molecule compared with on-twelfth of the mass of an atom of carbon-12 commom examples;CO 2, N 2 Relative molecular mass is obtained by adding together the relative atomic masses of each atom making up the molecule Mr(Cl 2 ) = 35.5 x 2 = 71.0 »Relative Formula Mass Used for any formula of a species or ion, e.g. NaCl, OH¯ by adding together the relative atomic mass of each atom making up a formula unit. CaBr 2 : relative formula mass = 40.1 + (79.9x2) = 199.9 RELATIVE MASSES

19. ISOTOPES DefinitionAtoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons.

20. ISOTOPES DefinitionAtoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons. PropertiesChemical properties of isotopes are identical Physical properties (such as density) can differ

21. ISOTOPES DefinitionAtoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons. PropertiesChemical properties of isotopes are identical Physical properties (such as density) can differ TheoryRelative atomic masses measured by chemical methods rarely produce whole numbers but they should do (allowing for the low relative mass of the electron). This was explained when the mass spectrograph revealed that atoms of the same element could have different masses due to the variation in the number of neutrons in the nucleus. The observed mass was a consequence of the abundance of each type of isotope. ProtonsNeutrons 1 H 1 10 2 H 1 11 3 H 1 12 ISOTOPES OF HYDROGEN

22. ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms ProtonsNeutrons% 35 Cl 17 1875 37 Cl 17 2025

23. ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms Method 1 Three out of every four atoms will be chlorine-35 Average = 35 + 35 + 35 + 37= 35.5 4 ProtonsNeutrons% 35 Cl 17 1875 37 Cl 17 2025

24. ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms Method 1 Three out of every four atoms will be chlorine-35 Average = 35 + 35 + 35 + 37= 35.5 4 Method 2 Out of every 100 atoms 75 are 35 Cl and 25 are 37 Cl Average = (75 x 35) + (25 x 37) = 35.5 100 ProtonsNeutrons% 35 Cl 17 1875 37 Cl 17 2025

25. MASS SPECTRA An early application was the demonstration by Aston, (Nobel Prize, 1922), that naturally occurring neon consisted of 3 isotopes... 20 Ne 21 Ne 22 Ne. positions of peaks gives atomic mass peak intensity gives relative abundance highest abundance is scaled up to 100% - other values are adjusted accordingly. Calculate the average relative atomic mass of neon using the above information. Out of every 100 atoms 90.92 are 20 Ne, 0.26 are 21 Ne and 8.82 are 22 Ne Average = (90.92 x 20) + (0.26 x 21) + (8.82 x 22) = 20.179 100 Relative atomic mass = 20.18 19 20 21 22 23 m/z 90.92 0.26 8.82 Abundance / %

26. MASS SPECTRA Naturally occurring potassium consists of potassium-39 and potassium-41. Calculate the percentage of each isotope present if the average is 39.1. Assume there are x nuclei of 39 K in every 100; so there will be (100-x) of 41 K so 39x + 41 (100-x) = 39.1 100 therefore 39 x + 4100 - 41x = 3910 thus - 2x = - 190 and x = 95 ANSWER There will be 95% 39 K and 5% 41 K

27. Now try questions 1 – 3 Page 9