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Significant Figures

Significant Figures. Any digit that is not zero is significant 1.234 kg 4 significant figures Zeros between nonzero digits are significant 606 m 3 significant figures Zeros to the left of the first nonzero digit are not significant 0.08 L 1 significant figure

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Significant Figures

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  1. Significant Figures • Any digit that is not zero is significant • 1.234 kg 4 significant figures • Zeros between nonzero digits are significant • 606 m 3 significant figures • Zeros to the left of the first nonzero digit are not significant • 0.08 L 1 significant figure • If a number is greater than 1, then all zeros to the right of the decimal point are significant • 2.0 mg 2 significant figures • If a number is less than 1, then only the zeros that are at the end and in the middle of the number are significant • 0.00420 g 3 significant figures

  2. How many significant figures are in each of the following measurements? 24 mL 2 significant figures 4 significant figures 3001 g 0.0320 m3 3 significant figures 6.4 x 104 molecules 2 significant figures 560 kg 2 significant figures

  3. 89.332 + 1.1 one significant figure after decimal point two significant figures after decimal point 90.432 round off to 90.4 round off to 0.79 3.70 -2.9133 0.7867 Significant Figures Addition or Subtraction The answer cannot have more digits to the right of the decimal point than any of the original numbers.

  4. 3 sig figs round to 3 sig figs 2 sig figs round to 2 sig figs Significant Figures Multiplication or Division The number of significant figures in the result is set by the original number that has the smallest number of significant figures 4.51 x 3.6666 = 16.536366 = 16.5 6.8 ÷ 112.04 = 0.0606926 = 0.061

  5. 6.64 + 6.68 + 6.70 = 6.67333 = 6.67 = 7 3 Significant Figures Exact Numbers Numbers from definitions or numbers of objects are considered to have an infinite number of significant figures The average of three measured lengths; 6.64, 6.68 and 6.70? Because 3 is an exact number

  6. 1000 mL 1L L2 1.63 L x = 1630 mL mL 1L 1.63 L x = 0.001630 1000 mL Dimensional Analysis Method of Solving Problems • Determine which unit conversion factor(s) are needed • Carry units through calculation • If all units cancel except for the desired unit(s), then the problem was solved correctly. How many mL are in 1.63 L? 1 L = 1000 mL

  7. 60 min m x x x 343 60 s 1 mi s 1 hour = 767 1 min 1609 m mi hour The speed of sound in air is about 343 m/s. What is this speed in miles per hour? meters to miles seconds to hours 1 mi = 1609 m 1 min = 60 s 1 hour = 60 min

  8. Chapter 2 • Development of atomic theory • Atomic structure • Periodic table • Chemical formulas • Naming compounds

  9. Dalton’s Atomic Theory (1808) • Elements are composed of extremely small particles called atoms. • All atoms of a given element are identical. The atoms of one element are different from the atoms of all other elements. • Compounds are composed of atoms of more than one element, in specific ratios. • Chemical reactions only involve separation, combination, or rearrangement of atoms. Atoms are not created or destroyed in chemical reactions

  10. 16 X + 8 Y 8 X2Y Law of conservation of mass Law of definite proportions

  11. Subatomic particles • Electron • Proton • Neutron

  12. Magnetic field ON Electric and magnetic field off Electric field ON J.J. Thomson, measured mass/charge of electron (1906 Nobel Prize in Physics)

  13. (Uranium compound)

  14. Particles emitted in radioactive decay • a-rays (positively charged) • b-rays (negatively charged; electrons) • g-rays (high energy, uncharged)

  15. (1908 Nobel Prize in Chemistry) Protons! Atoms’ positive charge is concentrated in the nucleus

  16. Chadwick’s Experiment (1932) H atoms - 1 proton He atoms - 2 protons mass He/mass H should = 2 measured mass He/mass H = 4 Neutrons! Also shown to reside in the nucleus

  17. Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10-10 m nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

  18. 1 2 3 H (T) H (D) H 1 1 1 235 238 U U 92 92 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei Mass Number A X Element Symbol Z Atomic Number

  19. The periodic table Group 1A: alkali metals Group 2A: alkaline earth metals Group 7A: halogens Group 8A: noble gases (rare gases)

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