Atomic Structure

1. Atomic Structure

2. Atomic Structure All matter is composed of atoms. Understanding thestructure of atoms is critical to understanding the properties of matter. properties of solidmaterials depend on thegeometrical atomicarrangements,and the interactions between constituent atoms.

3. history of the atom Democritusdevelopedthe idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible) It took ~2400 years from when it was conceived to the time experimental evidence prove of the atom existence.

4. history of the atom 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

5. history of the atom Joseph John Thompson / Cambridge 1898 found that atoms could sometimes eject a far smaller negative particle which he called ELECTRON 1906 Nobel prize in Physics

6. History of the atom 1910 Ernest Rutherford / Cambridge student of Thompson proposeda more detailed model with a central nucleus: positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction 1908 Nobel prize in Chemistry

7. History of the atom NielsBohr / Danish / a footballfanatic 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons. 1922 Nobel prize in physics

8. Bohr’satom Rutherford’s model predicted a rainbow of colorsratherthandiscretelinesobtainedfrom an atomiclinespectra. Toexplainthelinespectra, Bohrproposedthatelectrons of specificenergymoved in circularorbitsaroundthenucleusandcould not existbetweentheseorbits.

9. Atomic Structure Atomsare composed of protons– positively charged particles neutrons– neutral particles electrons– negatively charged particles in orbitals surrounding the nucleus. nucleus

10. Atomic Structure • Every different atom has a characteristic number ofprotons in the nucleus. • atomic number(Z) = number of protons • For an electrically neutral atom, atomic number = number of electrons. • Atoms with the same atomic number have the samechemical properties and belong to the sameelement.

11. Atomic Structure • Zranges from 1 for hydrogen to 92 for uranium (thehighestforthenaturallyoccuringelements).

12. Atomic Structure The atomic mass (A) of a specific atom: the sum of thenumber of protons and neutrons within the nucleus. massnumber: A = Z + N number of protonsis the same for all atoms of a given element, number of neutrons (N) maybe variable.

13. Atomic Structure The number of protons in the nucleus of the atom is equal to the atomic number (Z). The number of electrons in a neutral atom is equal to the number of protons. The mass number of the atom (M) is equal to the sum of the number of protons and neutrons in the nucleus. The number of neutrons is equal to the difference between the mass number of the atom (M) and the atomic number (Z).

14. Atomic Structure / isotopes atoms of some elements have two or more different atomic masses,called isotopes.

15. Atomic Structure Atomic weight: Weighted average of the atomic masses of the atom’s naturally occurring isotopes. Boronconsists of theisotopes: 19.7% B-10 and 80.3% B-11. atomicmass A, B = (19.7 x 10)+(80.3 x 11)]/100= 10.8 Bromine’ isotopes: 50.5% Br-79 and 49.5% Br-81. atomicmass A, Br=[(50.5 x 79)+(49.5 x 81)]/100= 80.0

16. Atomic Structure Inone mole of a substance there are 6.022 x1023(Avogadro’s number) atoms or molecules. Atomic weight = weight of 6.023 x 1023atoms For example, the atomic weight of iron is 55.85 amu/atom, or 55.85 g/mol. 1 amu/atom = 1g/mol= 1 dalton Atomic mass unit (amu): 1⁄12 of the atomic mass of the carbon C:12.011/ H:1.008 etc.

17. subatomicparticles Proton is 1837 times heavier than an electron. Neutron is 1842 times heavier than an electron. Electron is muchlighterwithrespecttothe protonsandneutrons

18. 4 He 2 Atomic Structure Shell proton HELIUM ATOM nucleus N + - + N - # electrons = # protons neutron electron ATOMIC MASS NUMBER = number of protons + number of neutrons ATOMICNUMBER = number of protons

19. Lithium Electrons Protons 7 Neutrons Li three electrons threeprotons fourneutrons. 3

20. Beryllium Electrons Protons 9 Neutrons Be four electrons four protons five neutrons. 4

21. Boron Electrons Protons 11 B Neutrons five electrons five protons six neutrons. 5

22. Carbon Electrons Protons 12 C Neutrons six electrons six protons six neutrons. 6

23. Nitrogen Electrons Protons 14 N Neutrons seven electrons seven protons seven neutrons. 7

24. Oxygen Electrons Protons 16 O Neutrons eight electrons eight protons eight neutrons 8

25. Fluorine Electrons Protons 19 Neutrons F nine electrons nine protons ten neutrons. 9

26. Neon Electrons Protons 20 Neutrons Ne ten electrons ten protons ten neutrons 10

27. Sodium Electrons Protons 23 Neutrons Na eleven electrons eleven protons twelve neutrons 11

28. Atomicstructure How many protons, neutrons and electrons? 1 27 56 H Al Fe 1 13 26 48 39 238 Ti K U 22 19 92

29. Atomicstructure How many protons, neutrons and electrons? 48 Ti 22

30. Atomicstructure How many protons, neutrons and electrons? 56 Fe 26

31. Atomicstructure How many protons, neutrons and electrons? 27 Al 13

32. Atomicstructure How many protons, neutrons and electrons? 39 K 19

33. Atomicstructure Thechargeandmassnumber of an electronare: • charge = 0, Massnumber = 1 • charge = -1, Massnumber = 0 • charge = +1, Massnumber = 1 • charge = +1, Massnumber = 0 • The charge and mass number of a neutron are? • charge = +1, Mass number = 1 • charge = 0, Mass number = 1 • charge = +1, Mass number = 0 • charge = -1, Mass number = 0

34. Atomicstructure Which of thefollowing has 25 protonsand 31 neutrons? • 56Mn • 56Ga • 25Ga • 31Mn • 56Ba

35. Atomicstructure Whydoeschlorinehave an atomicmass of 35.5, which is not a wholenumber? • Chlorine contains an extra electron which makes it weigh more than 35. • Chlorinecontains 17 protonsand 18.5 neutrons • Chlorine normally exists in an excited state, and so it weighs more than 35. • The chlorine was not pure when its atomic mass was measured. • Chlorine, as found in nature, contains a mixture of the isotopes 35Cl and 37Cl, in such proportions as to give an average atomic mass of 35.5

36. Atomicstructure The two main parts of an atom are? a) nucleus and electron energy levelsb) nucleons and protonsc) oxidation number and valenced) protons and neutronse) protons and electrons

37. Atomicstructure The nucleus of the element having atomic number 25 and atomic weight 55 will contain? 25 protons and 30 neutrons 30 protons and25 neutrons 55 protons 55 neutrons

38. Atomicstructure A beryllium atom has 4 protons, 5 neutrons, and 4 electrons. What is the mass number of this atom? 4 5 8 9 13

39. Atomicstructure Thesmallestparticleintowhich an element can be dividedandstillhavetheproperties of that element a) nucleus b) electron c) atom d) neutron How wouldyoudescribethenucleus? a) dense, positivelycharged b) mostlyemptyspace, positivelycharged c) tiny, negativelycharged d) dense, negativelycharged

40. Atomicstructure Whereareelectronslikelyto be found? a) in thenucleus b) in electronclouds c) mixedthroughout an atom d) in definitepaths Every atom of a given element has thesamenumber of a) protons b) neutrons c) electrons d) isotopes

41. Atomicstructure What is themeaning of thewordatom? a) dividable b) invisible c) hard particles d) not ableto be divided Whichstatement is trueaboutisotopes of thesame element? a) Theyhavethesamenumber of protons b) Theyhavethesamenumber of neutrons c) Theyhave a differentatomicnumber d) Theyhavethesamemass

42. Atomicstructure Whichhas theleastmass in an atom? a) nucleus b) proton c) neutron d) electron If an isotope of uranium, uranium-235, has 92 protons, how manyprotonsdoestheisotope uranium-238 have? a) 92 b) 95 c) 143 d) 146

43. Atomicstructure A carbon atom with 6 protons, 6 electrons, and 6 neutronswouldhave a massnumber of a) 6 b) 12 c) 15 d) 18 Thenumber at the top is the a) atomicnumber b) element name c) atomicmass d) chemicalsymbol

44. Atomicstructure How manyelectronsdoes a neutral Cl atom contain? 16 17 18 19 What is thedifferencebetweenatomicmassandatomicweight? 35 Cl 17

45. Atomic Structure Neutral atoms have the same number of protons and electrons. Ions are charged atoms. • cations– have more protons than electrons and are positively charged • anions– have more electrons than protons and are negatively charged

46. 11 protons 11 electrons 11 protons 10 electrons Na+ Na Cl- 17 protons 18 electrons 17 protons 17 electrons Cl Atomic Structure If a neutral atom looses one or more electrons it becomes a cation. e- + If a neutral atom gains one or more electrons it becomes an anion. + e-

47. BohrAtomic model electrons are assumed to revolve around the atomic nucleus in discreteorbitals, and the position of any particular electron is more or less well definedin terms of its orbital. Electronsarepermittedtohaveonlyspecificvalues of energy.

48. BohrAtomic model

49. excitationvsrelaxation An electron may change energybymaking a quantumjump either to an higher energy (with absorption of energy) or to a lowerenergy (with emission of energy). relaxation excitation

50. Quantum Mechanics Unfortunately, extremely small particles (electrons) do not follow the laws of classical (Newtonian) physics. The new physics that mathematically treats small particles is called Quantum Mechanics.