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Composition & Mass of Molecules and Compounds

Composition & Mass of Molecules and Compounds. Composition & Mass of Molecules and Compounds. Determining the Number of Atoms in a Formula:.

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Composition & Mass of Molecules and Compounds

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  1. Composition & Mass of Molecules and Compounds

  2. Composition & Mass of Molecules and Compounds Determining the Number of Atoms in a Formula: • The number of atoms in a formula is determined by the subscript to the right of the element and/or the coefficient to the left of the compound (in a balanced chemical equation) • If there is no subscript, this means that there is only one of a particular atom • i.e.: NaCl • 1 Sodium atom • 1 Chlorine atom • When you are dealing with polyatomic ions, remember that the subscript found outside of the brackets is applied to every atom inside the brackets by using the distributive property of multiplication • i.e.: Mg(NO3)2 • 1 magnesium atom • 2 nitrogen atoms • 6 oxygen atoms

  3. Number of Atoms in a Formula • Examples: • B2H6 • 2 boron atoms • 6 hydrogen atoms • 8 atoms in total • Li3PO4 • 3 lithium atoms • 1 phosphorus atom • 4 oxygen atoms • 8 atoms in total • Fe(NO3)2 • 1 iron atom • 2 nitrogen atoms • 6 oxygen atoms • 9 atoms in total

  4. Molar Mass of Atoms • The mass of individual atoms is given to you on the periodic table • It is the value that is listed underneath the name • We have referred to the units of this value as atomic mass unit (amu) • Another unit that we will use from now on is grams per mole (g/mol) • A mole is just a certain amount of molecules • We will learn about this next unit

  5. Molar Mass of Atoms • Examples: • Be • _________________ • Sn • _________________ • Cl • _________________ • Cu • _________________

  6. Molar Mass of Molecules & Compounds • To find the mass of a molecule/compound, simply add up all of the masses of the individual atoms in the compound • Value is known as the molar mass of a molecule/compound • i.e.: NaCl • i.e.: Mg(NO3)2

  7. Molar mass of compounds • This may seem easy but VERY OFTEN, getting the wrong molar mass of a compound means you get an ENTIRE question wrong later in the unit. • THIS IS ANOTHER ESSENTIAL SKILL YOU NEED ON A DAILY BASIS LATER IN THE YEAR!!!

  8. Percent Composition by Mass • The percent composition by mass of a molecule/compound is simply the percentage of one particular element in the molecule/compound • To calculate the percent composition: • Examples: • NaCl • Mg(NO3)2

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