A × 10 When you do calculations with measurements, you must make sure that your answer suggests no greater precision than was present in the original measurements. Here are some guidelines for writing your answers in scientific notation:
For addition and subtraction: Use exponential notation to express both numbers using the same power of 10, and then do the math. Round the sum or difference to the same number of decimal places as held by the measurement with the fewest decimal places. If your answer isn't in scientific notation (the first number in your answer isn't between 1 and 10), convert as needed. For multiplication and division: Express both numbers in scientific notation so you can clearly see how many significant figures each number has. Round the product or quotient to the same number of significant figures as held by the measurement with the fewest significant figures.
Analyzing Atomic Structure for Chemistry
Chemistry deals with atoms, which are composed of subatomic particles that differ in mass and charge. Altering the numbers of these particles can alter the element or the isotope identity of an atom. Here are some subatomic facts:
Proton, p : 1 atomic mass unit (amu), +1 charge
Neutron, n : 1 amu, 0 charge
Electron, e : 1/1,836 amu, –1 charge
Atomic number:= the number of protons and Determines the element
Mass number: = the number of protons plus neutrons and Determines the isotope
How to Name a Chemical Compound
Someone who doesn't know chemistry may think that compounds should already have names, but you know differently. The following steps take you through the process of writing the name of any chemical you're likely to encounter in a general chemistry class:
Does the formula begin with an H?
If so, the compound is most likely an acid. Use the rules for naming an acid.
Does the formula contain a metal (not hydrogen)?
If it doesn't, you need to use prefixes when naming because you're dealing with a molecular (covalent) compound. Be sure to change the ending of the second element to -ide. If there is a metal, you're dealing with an ionic compound — proceed to Step 3.
Is the cation a transition metal (Group B) or a metal with a variable charge?
If the cation is a Group B metal (or other metal of variable charge, like tin), you need to use a Roman numeral to specify its charge. If the cation isn't a transition metal and you know the charge, you don't need to specify the charge.
Is the anion a polyatomic ion?
If so, you write the name of the polyatomic ion. If the anion isn't a polyatomic ion, you use an -ide ending.
Conversion Tips for Chemistry In a general chemistry class, you usually end up having to perform a lot of conversions involving moles (mol). Whether you're converting from moles to grams, moles to volume, or moles to particles (atoms or molecules), use this quick guide to remind you of how to do each type of mole conversion:
Converting from mass (grams) to moles: Divide your initial mass by the molar mass of the compound as determined by the periodic table.
Converting from moles to mass (grams): Multiply your initial mole value by the molar mass of the compound as determined by the periodic table.
Converting from volume (liters) to moles: Divide your initial volume by the molar volume constant, 22.4 L.
Converting from moles to volume (liters): Multiply your mole value by the molar volume constant, 22.4L.
Converting from particles (atoms, molecules, or formula units) to moles: Divide your particle value by Avogadro's number, 6.02×10 . Remember to use parentheses on your calculator!