03a matter and structure of atoms


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03a matter and structure of atoms

  1. 1. 1 CHEM-111CHEM-111 General ChemistryGeneral Chemistry Unit Three (a)Unit Three (a) Matter and the Structure of AtomsMatter and the Structure of Atoms by CHEMISTRY DEPARTMENT
  2. 2. 2 Matter and Structure of AtomsMatter and Structure of Atoms • Subatomic particles • Atomic Number and Mass Number • Isotopes and Atomic Mass • Electronic structure of Atoms • Electron Configurations Contents
  3. 3. 3 AtomAtom The word atom is derived from the Greek word ‘atom’ which means indivisible (inseparable). Atoms are the building blocks of everything we see around us; yet, we cannot see atom or even a billion of atoms with the naked eyes Atom is the smallest unit of an element that retains (keeps) its chemical properties. Surrounding orbiting electrons Positively charged nucleus
  4. 4. 4 Measuring the size of atoms The size of atoms is measured in nanometers (nm). One nanometer is a meter divided by 109 . Name of Object Length in Meter Girl 1 meter Cassette 1/10m (1decimeter) Fingernail 1/100m (1centimeter) A pin head 1/1000m (1millimeter) A diameter of blood capillary 1/10,000 meter Blood cells 1/100,000 meter Bacteria 1/1,000,000m (micrometer) Influenza virus 1/10,000,000 meter A molecule of soap 1/100,000,000 meter
  5. 5. 5 1/1,000,000,000 meter =1 nanometer(1nm) All atoms are less than 1 nm in diameter The size of atoms in nanometer Atoms Size in nm Hydrogen atom 0.074 nm Carbon atom 0.15 nm Copper atom 0.26 nm Magnesium 0.32 nm Hydrogen atoms are so small that about 14,000,000,000 (14 billions ) hydrogen atoms in a line would measure a meter
  6. 6. 6 MoleculesMolecules A smallest unit of two or more atoms held together by covalent bond and behaves as an electrically neutral single particle. H2 Cl2 H2O CO2 CH4 HClCl2 H O H H2O
  7. 7. 7 Types of Molecules 1-Monoatomic Molecules Molecules composed of single atom which can live alone. Elements of group VIII ( noble gases) can live as mono- atomic molecules as: He , Ne , Ar , Kr and Xe . 2-Diatomic molecules Molecules made up of two atoms ( same or different ). Elements, H, N,O, F, Cl, Br, I , exist as diatomic molecules as: H2, N2,O2,F2,Cl2,Br2, I2 & HCl 3-Polyatomic molecules Molecules composed of more than two atoms. H2O, CO2, CH4 , C2H5OH.
  8. 8. 8 Carbon oxygen CO2 NH3 CH4 Poly atomic molecules BCl3
  9. 9. 9 Structure of AtomStructure of Atom  The atom is comprised of a positively charged nucleus composed of protons and neutrons. Small nucleus is surrounded by orbiting electrons.  Protons and neutrons have similar masses and electrons are much lighter (over 1,000 times lighter). Protons (p+) and electrons (e- ) have equal and opposite charges while neutrons (n0 ) have no charge. The light negatively charged electrons move around in an orbit in the space around the nucleus.
  10. 10. 10 Neutron Proton Nucleus Electron Atom
  11. 11. 11 1. Matter is composed of tiny indivisible particles - atoms. 2. All atoms of an element are similar to one another but different from atoms of other elements. 3. Atoms of various elements in a compound are in a fixed numerical ratio. 4. In chemical reactions, atoms are combined, separated, or rearranged but never created or destroyed during a chemical reaction. I- Dalton’s Atomic Theory
  12. 12. 12 II- Earnest Rutherford Gold Foil Experiment Bombardment of α-Particles on thin gold foil
  13. 13. 13 Bombardment of α-Particles on thin gold foil resulted Some α-Particles to pass straight, few deflected and some bounced back. Conclusion: 1. Most part of an atom is empty space , occupied by fast moving electrons. 2. The dense core of atom from where particles deflected is Nucleus. 3. Most of the mass of atom is in nucleus where proton & neutrons reside. Structure of Atom
  14. 14. 14 electron, proton and neutron The chemistry of an element depend on subatomic particles Name Symbol Charge Approximate Mass (amu) Mass in Grams electron e- -1 0.0005 9.11 x 10-28 proton p+ +1 1.0 1.67 x 10-24 neutron n 0 1.0 1.67 x 10-24 Subatomic particles
  15. 15. 15 The space filling, the nature of electron wave is electron cloud. Amount of electron charge per unit volume is electron density In an atom, the protons and neutrons are found in the nucleus; the electrons are located outside the nucleus. Electron cloud Nucleus Proton Neutron Electron Cloud and Electron density
  16. 16. 16 The atomic symbolThe atomic symbol X A Z C A - Atomic mass = Total number of protons & neutrons Z -Atomic number = Number of protons or electrons C - Charge = + or – , or 0 values We use the following symbol to describe the atom: A= Z + n0 where n0 is the number of neutrons. Number of Neutrons = A- Z n0 = A - Z Element symbol
  17. 17. 17 A = Atomic mass Z = Atomic number = number of protons = number of neutrons = number of electrons
  18. 18. 18 Element Symbol Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons Hydrogen H 1 1 1 0 1 Carbon C 6 12 6 6 6 Nitrogen N 7 14 7 7 7 Fluorine F 9 17 9 8 9 Iron Fe 26 56 26 30 26 Composition of Some Atoms
  19. 19. 19 Atomic Number and Mass number Atomic Number (Z): The number of protons present in nucleus of an atom is its atomic number. It also equals the number of electrons moving around the nucleus. Mass number (A): The sum of number of protons & neutrons or total number of nucleons in nucleus of an atom is its mass number. Mass number = number of protons + number of neutrons X A Z X A Z 6C12 , 8O16 , 7N14
  20. 20. 20 ISOTOPESISOTOPES • Most of the elements exist as mixtures of several kinds of atoms called isotopes. • Isotopes are the atoms of the same element but with different number of neutrons but the same number of protons . • Isotopes of carbon Isotopes of chlorine C C C Cl Cl 12 6 176 6 14 35 37 17 13
  21. 21. 21 Atoms can be split into smaller parts. An atom is composed of three types of subatomic particles: proton, neutron, and electron. In a neutral atom, the number of positively charged protons in the nucleus is equal to the number of orbiting electrons. If you add or subtract a proton from the nucleus, you make a new element. If you add or subtract a neutron from the nucleus, you make a new isotope of the same element you started with. How You generate a New Isotope electrons. protons neutron
  22. 22. 22 Identifying Protons and Neutrons in IsotopesIdentifying Protons and Neutrons in Isotopes Question1 :State the number of protons and neutrons in Isotopes of Neon. 20 21 22 10 10 10 NeNe Ne Question 2:What are the number of protons ,neutrons and electrons in the following isotopes ? 30Si Zn 26 14 70 Hint: Atomic mass = Atomic number + number of neutrons
  23. 23. 23 Hydrogen in nature occurs as mixture of its isotopes Mass of H= 1.007amu Isotopes of Hydrogen Atomic number ( Z) ( no. of protons) Number of Neutrons ( n0 ) (no. of neutrons) Mass number (A) ( p + n) Protium H1 1 0 1+ 0 = 1 Deuterium H2 1 1 1 +1 = 2 Tritium H3 1 2 1 +2 = 3
  24. 24. 24 The nuclei of different isotopes of the same element have the different numbers of neutrons. Example: Tritium DeuteriumProtium Isotopes of Hydrogen 1 Proton 1 Proton1 Proton 1 Neutron 2 Neutrons
  25. 25. 25 Isotopes of HydrogenIsotopes of Hydrogen element symbolH 1 1 mass number = A atomic number = z (Deuterium) (Tritium)((Protium)) H 1 1 H 2 1 H 3 1 p p pn n n Nucleus of Tritium Nucleus of Protium Nucleus of Deuterium
  26. 26. 26 Measuring the Mass of An Atom Average Atomic Mass/Weight: Most of the elements exist in nature as a mixture of several kinds of isotopes with slightly different masses so the average of the atomic masses of naturally occurring isotopes of an element is taken. Atomic mass & atomic weight are often used interchangeably. We can measure masses of ions by using an instrument called Mass spectrometer.
  27. 27. 27 MEASUREMENT OF RELATIVE ATOMIC MASSES An oxygen atom is 16/12 or 4/3 of C-12 atom. Magnesium is 24/12 or twice of C- atom Atomic Mass Unit (AMU): Atoms are too small to be seen or weighed in grams. The atomic mass of any nuclide is determined by comparing it with the mass of C-12 atom. 1 amu is exactly 1/12th of mass of a C-12 atom
  28. 28. 28 AVERAGE ATOMIC MASS Atomic masses of naturally occurring isotopes. Isotopes Mass number % Percentage natural abundance Atomic mass (amu) Average atomic mass of elements (amu) Hydrogen-1 Hydrogen-2 1 2 99.985 0.015 1.007825 2.014102 1.00794 Carbon-12 Carbon-13 Carbon-14 12 13 14 98.90 1.10 Trace 12 13.003355 14.003242 12.0111 Oxygen-16 Oxygen-17 Oxygen-18 16 17 18 99.762 0.038 0.200 15.994915 16.999131 17.999160 15.9994 Uranium-234 Uranium-235 Uranium-238 234 235 238 0.005 0.720 99.275 234.040947 235.043924 238.050784 238.029
  29. 29. 29 Mg is more abundant (rich) in nature Isotopes of Mg 24 12
  30. 30. 30 3 Naturally occurring Isotopes of Mg Atomic symbol Mg Mg Mg Number of Protons 12 12 12 Mass number 24 25 26 % abundance 78.9% 10.0% 11.1% Number of neutrons 12 13 14 12 25 2624 1212
  31. 31. 31 1) Number of protons in all isotopes of an element same. Thus the chemical properties are also identical except the rate of the reaction. 2) Number of valence electrons of all the isotopes of same element are similar and have the same valence. 3)The physical properties, such as mass, density, melting point, boiling point of isotopes of same elements are different. 4)Some isotopes are unstable and tend to breakdown or decay, to a more stable isotopes. Such isotopes are called radio isotopes because they produce radiations. These isotopes are useful in medicine. Isotopes & Their Properties
  32. 32. 32 Properties of an element determined by number and distribution of its electrons around nucleus. 1. So Z (atomic number) distinguishes atom of an element from atom of another element, or Z identifies which element it is. 2. If atoms of same element differ in mass (in A) (atomic mass), i.e. they have different number of neutrons. Chemically isotopes are identical except rate of reaction, as in isotopes of H. Isotopes & their Properties
  33. 33. 33 Exercise Name of Elements Symbol Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons - Al - 27 - - - - - 12 - - 12 - Potassium - - - - 20 - - - - - 16 15 - - - - 56 - - 26 Take the help of Periodic Table and complete the following table for neutral atoms
  34. 34. 34 ExerciseExercise M. C. Q:M. C. Q: 1. What is the correct number of Protons and neutrons in Al? a. 13protons; 14 neutrons b. 14 protons; 13 neutrons c. 13protons; 27neutrons d. 27protons; 13 neutrons 2. Total number of elements placed in the periodic Table are: a. 115 b. 109 c. 90 d. 120 3. The substances He and Ne are examples of: a. Mono-atomic molecules b. Di-atomic molecules c. Poly-atomic mole d. None of the above
  35. 35. 35 4.Choose the correct statement a. Protons have negative charge b. Electrons are neutral c. Protons have positive charge d. Neutrons are charged particles 6. “Atom” is a Greek word that means: a. Visible b. Invisible c. Divisible d. Indivisible 5. Total number of Protons and Neutrons in an atom expresses: a. Atomic Number (Z) b. Atomic Mass (A) c. Charge ( C) d. Both a & b. 30 a. Atomic Number (Z) b. Atomic Mass (A) c. Charge d. Both a & b. 7. The element Zinc is represented by symbol Zn. The number 65 stands for:, 65
  36. 36. 36 8.Which particle has a mass less than a proton: a) Electron b) Neutron c) Atom d) Molecules 9.The atomic masses of three isotopes of Hydrogen (Protium, Deuterium and Tritium) are in the order of: a) 3,2,1 b) 3,1,2 c) 2,1,3 d) 1,2,3 10.Amount of electron charge per unit volume is electron density a) True b) False 11.Mono atomic Molecules are : a) Molecules composed of single atom b) Molecules composed of two atoms c) Molecules composed of many atoms