Chapters 1 and 2 Review I Significant Figures A The instruments techniques and conditions that we use to make measurements always limit us B When taking a measurement include all certain digits plus one estimated digit C All non zero intergers are significant D All zeros to the left of the first non zero digit are NOT significant 1 Example 0 0045 2 sig figs E All zeros between non zero digits are significant F All zeros at the end of a number that has a decimal points are significant 1 Example 56 7800 6 sig figs G Zeros at the end of a whole number may or may not be significant H For exact numbers there is no uncertainly as to its value 1 Examples 20 people 5 apples II Adding and Subtracting Sig Figs A When adding and subtracting sig figs the units must match B Exponents in scientific notation must also match C Sig figs are determined by the number of digits after the decimal point 1 Example 5 62 3 2 8 8 III Multiplying and Dividing Sig Figs A Sig figs are determined by whichever number is the limiting number 1 Example 2 0 5000 4 0 IV Periodic Table of Elements A The table is arranged in order of increasing atomic number 1 Atomic Number number of protons in an atom B The elements are also grouped by properties C Atomic Number whole number at the top of the element s box D Atomic Mass decimal number at the bottom of the element s box 1 Atomic Mass is calculated by averaging the weight of all of the elements naturally occurring isotopes E Atoms have mass and we need to know their mass to weigh out a specific number of atoms F For convieience chemists use the following vocabulary 1 Atomic Mass Unit amu 1 amu is defined as 1 12 of the mass of an atom It is the approximate weight of a proton or neutron 2
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