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General Chemistry

Faculty of Allied Medical Sciences. General Chemistry. (MGGC-101). Atoms, molecules and ions. Supervision: Prof.Dr.Shehata El-Sewedy Dr.Fatma Ahmed. Outcomes. By the end of this lecture, the students will be able to. 1-Recognize the significant figures in measurements

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General Chemistry

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  1. Faculty of Allied Medical Sciences General Chemistry (MGGC-101)

  2. Atoms, molecules and ions Supervision: Prof.Dr.Shehata El-Sewedy Dr.Fatma Ahmed

  3. Outcomes By the end of this lecture, the students will be able to 1-Recognize thesignificant figures in measurements 2-To differentiate betweenInternational System of Units 3-To know Dalton’s atomic theory 4-Understand Atomic number, Mass number and Isotopes 5-Know the meaning of molecule and its types 6-learn to the meaning of ion and its types

  4. 3. Significant figures in measurements In any measurement, there is always a degree on uncertainty • Rules to determine the number of significant figures • ►The numbers recorded in a measurement are called significant digits or significant numbers. • 1. Digits other than a zero are always significant. • 854 ► 3 sig figures and 3.6 ► 2 sig figures • 2- Zeros between non-zero digits  are Significant. • ► 4 sig figures and 30.76 ► 4 sig figures • 3- Zeros at the beginning of number  are not significant. • 012 ► 2 sig.fig. and 0.012 ► 2 sig.fig • 4- Zeros at the end of number and after the decimal point  are Significant. • 19.60 ► 4 sig figures • 5- Zeros at the end without decimal point  May or may not be significant. (Use exponential notation). • Example: 500 could have 3 sig figures ► 5.00 X 102 • or have 2 sig figures ► 5.0 X 102 • or have 1sig figure ► 5 X 102

  5. Example

  6. Significant figures in calculations 1- In multiplication and division The result must have the same number of S.F. as the number having the least S. F. in the calculation. e.g. 7.5023  2.00 = 15.0046 wrong 5 S.F. 3 S.F  15.0 (only 3 S.F. Correct 34.103  0.0310 = 10.57193 wrong  10.6 (only 3 S.F.) correct

  7. 2- In addition and subtraction The result must have the same number of decimal digits as the number with the least decimal digits in calculation. e.g. 25.23 + 21.3207 = 46.5507 2 d.d. 4 d.d 46.55 (only 2 decimals) 10.31 + 0.002438 = 10.307562  10.31 (only 2 decimals)

  8. Rounding • Look at the leftmost digit to be dropped, then • 1-If this digit is greater than 5, add 1 to the last digit to be retained. Thus, rounding 1.2161 to 3 significant figures gives 1.22. • 2-If digit is less than five, drop it, Thus, rounding 1.2141 to 3 significant figures gives 1.21. • 3-If this digit is 5 : 15.55 = 15.6 odd15.45 = 15.4 even

  9. Example: Perform the following calculations and round the answers to the correct number of significant figures: a. b. c. d. 37.76 + 3.907 + 226.4

  10. Solution: • The factor 5.8 has the fewest significant figures; therefore the answer should be reported to two significant figures. Round the answer to 3.6 • The number with the least number of decimal places is 5.41. Therefore, round the answer to two decimal places, to 5.01 • The answer is 0.37. Note how you have lost one significant figure in the subtraction. • The answer is 268.1

  11. Units of measurement Measurement always consists of two parts, a number and a unit. • 1-Metric system

  12. 2-International System of Units (SI system)This system is commonly used in all countries.Fundamental SI units

  13. Some unit conversations: 1 kilogram = 1  103 gram 1 megagram = 1  106 gram 60 second = 60  1015femto second Femto second = 1  10–15 second Pico meter = 1  10–12 meter 1 meter = 1  1012 pico meter Derived SI units Units which are not fundamental SI units called derived.  Area = (Length)2  Volume = (Length)3  Liter = 103 cm3 = 103 mL  Velocity = m/s (length/time)  Density = g/cm3 (mass/volume)

  14. Dalton’s Atomic Theory (1808) Atoms, molecules and ions 1-Elementsare composed of extremely small particles called atoms. 2-All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements.

  15. 3- Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction. 4- A chemical reactioninvolves only the separation, combination, or rearrangement of atoms

  16. 16 X + 8 Y 8 X2Y

  17. Subatomic Particles Particle Symbol Charge Mass Electron e- - 9.11X10-28 g Proton p+ + 1.67X10-24 g Neutron n 0 1.67X10-24 g

  18. A X Mass Number Element Symbol Z Atomic Number Atomic number and Mass number An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons

  19. Subatomic Particles in Some Atoms 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e- 15e- 30 e-

  20. Isotopes: The isotopes of an element have the same atomic no. (same chemical properties) but differ in their mass no. (different physical properties) i.e they have same no. of protons but different no. of neutrons. Example: the isotopes of hydrogen

  21. Eg. 12C, 13C The 2 atoms have the same at.no. (equal no. of protons) But they differ in their mass no. (different no. of neutrons) 12C: at.no.= 6,mass no.=12, no. of neutrons=6 13C: at. no. =6, mass no.=13, no. of neutrons=7 Eg. O atom 16O, 17O, 18O 8p, 8p, 8p 8n, 9n, 10n 8e, 8e, 8e

  22. H2 H2O NH3 CH4 Molecules and Ions A molecule is an aggregate of two or more atoms held together by chemical forces The forces that hold atoms together in molecules are called chemical bonds. A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4

  23. Molecules can be represented in several different ways: • Chemical formula • Represent the type and actual number of atoms in a molecule, • for example, carbon dioxide CO2(it has 1 carbon atom and 2 oxygen atoms). • Structralformula • Formula by which the individual bonds are shown (may or may not show the actual shape of molecule). • Example

  24. Ions An ion is an atom, or group of atoms, that has a net positive or negative charge. An ion may be a cation or an anion. Cation: ion with a positive charge. If a neutral atom loses one or more electrons it becomes a cation. Anion: ion with a negative charge. If a neutral atom gains one or more electrons it becomes an anion.

  25. Quiz time

  26. What is the number of protons and electrons in S2 – What is the number of protons and electrons in aluminum ion, Al3+ What is the number of protons, neutronand electrons in 16O, 17O, 18O How manySignificant figures and decimal pointsin

  27. Student Question

  28. What the SI units of 1-time 2-length 3-temperature 4-amount of substance 5-mass • Answer the following operation • 18.5+31.3= • 3.2+5.09+3.007= • 36.36÷4.04= • 4.053÷4.00= • 27.00x2.00= • 0.0040x3001.37=

  29. How manySignificant figures in 1)32.01 2)5.010 3)32.00 4)200 5)8.1 Calculate the no. of proton, neutron and electrons for Define and give example: Cation Anion Isotope Structural formula

  30. Assignments

  31. 1-Raymond Chang. Chemistry. 10th ed. 2009 2-Zumdehl. International edition. 2009 Recommended textbooks:

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