Mass of an atom Atomic mass of a substance is found by comparing its mass to an atom that is taken as standard The standard atom has changed over time. At first it was hydrogen, then oxygen and now it is carbon The changes were made in order to make the measurements more precise Atomic Mass Unit (u): a unit of relative measurement assigned to the masses of individual atoms 1/12 the mass of a carbon-12 atom The atomic mass on the periodic table is based on the carbon standard
The amount of a substance that contains 6.02 x 10²³ particles Used to talk about a number of atoms, molecules, ions, and electrons 1 mole of a substances atom has a mass that is equal to the atomic mass of a single atom of the substance
This diagram is a creative way to describe mole relationships.
In the case of atoms, the number of grams necessary to have one mole is the same as the atomic mass of that particular atom The mole concept is a method that determines the mass or weight used when dealing with large quantities of atoms The number of atoms in each mole is the same, but the mass differs
3.01 x 10 23 CO 2 molecules x 2 oxygen atoms x 1 mol oxygen atoms 1 CO 2 molecule 6.02 x 10 23 oxygen atoms = 1.00 mol oxygen atoms If a steel cylinder contains 3.01 x 10 23 carbon dioxide molecules, how many moles of oxygen atoms are in the steel cylinder? 2 oxygen atoms in each CO 2 molecule
.75 mol CO 2 x 6.02 x 10 23 CO 2 molecules mol = 4.5 x 10 23 CO 2 molecules How many carbon dioxide molecules are in.75 mol of CO 2 ? Unitary rate in molecules per mole of CO 2 is 6.02 x 10 23 molecules mol
26g Carbon x 1 mol Carbon 12.0g Carbon = 2.2 mol Carbon How many moles of carbon are in 26g of carbon? The mass of a mole of carbon atoms is the atomic mass in grams on the periodic table: 1 mol of carbon corresponds to 12.0 g of carbon
0.75 mol CO 2 x 6.02 x 10 23 CO 2 molecules x 2 oxygen atoms mol CO 2 CO 2 molecule =9.0 x 10 23 oxygen atoms How many oxygen atoms are in 0.75 mol CO 2 ? 1 CO 2 molecule has 2 oxygen atoms 1 mol oxygen atoms corresponds to 6.02 x 10 23 oxygen atoms
26.98 g 6.02 x 10 23 atoms = 4.48 x 10 -23 g/atom What is the mass of one atom of aluminum? The mass of a mole of aluminum atoms is the atomic mass listed on periodic table: 26.98g corresponds to 6.02 x 10 23 atoms
Atomic MassNumber of AtomsMass Carbon 12.0x 12 =144 Hydrogen 1.01x 22 =22.2 Oxygen 16.0x11 =176 Add the masses 144+22.2+176=342 g What is the molar mass of sucrose, C 12 H 22 O 11 ?
2(27.0g) + 3(32.1g) + 12(16.0g)= 342.3 g What is the molar mass of aluminum sulphate, Al 2 (SO 4 ) 3 ? 2 mol of Al atoms each with molar mass = 27.0 g 3 mol of S atoms each with molar mass = 32.1 g 12 mol of O atoms each with molar mass = 16.0 g
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