Atoms and Moles – Chapter 3 Substances are made of atoms 3.1.
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Transcript of Atoms and Moles – Chapter 3 Substances are made of atoms 3.1.
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Atoms and Moles – Chapter 3
Substances are made of atoms 3.1
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Atomic Theory
Atomic Theory – Atoms are the building blocks of all matter.
Research into this theory led to three laws that all compounds share…
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What does an atom look like?
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Law of Definite Proportions
A given compound contains the same elements in exactly the same proportions by mass, regardless of the size of the sample or the source of the compound.
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Law of Definite Proportions
Sodium chloride is an example. All samples of pure NaCl will be 39.34% Na by mass and 60.66% Cl by mass no matter where the NaCl comes from.
Sodium Chloride
Chlorine
Sodium
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Law of Conservation of Mass
The mass of the products of a reaction equals the mass of the reactants.
Applies when elements combine to produce a compound, decompose, or when atoms in a compound rearrange.
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Law of Conservation of Mass
+
32.07 +32.00 64.07
amu amu amu
S OOOO
S
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E=mc²When you combine sulfur and
oxygen, 296,800 J of energy are given off as heat.
According to E=mc²…
296,800kg•m²/s² = m(2.998 x 108m/s)²
Rearranging this equation gives the mass to be 3.302 x 10-12 kg
Where does this mass go?
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The Law of Multiple Proportions
States that the mass ratio for one of the elements in a compound that combines with a fixed mass of another element can be expressed in small whole numbers.
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Dalton’s Atomic Theory
Dalton used the three laws.Elements and compounds
differ b/c of the types of atoms.
Properties differ because of atoms.
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His Theory
Dalton proposed 5 principles that make up his theory on the atomic structure of matter.
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Dalton’s Five Principles
1. All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed.
2. Atoms of a given element are identical in their physical and chemical properties.
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Dalton’s Five Principles
3. Atoms of different elements differ in their physical and chemical properties.
4. Atoms of different elements combine in simple whole-number ratios to form compounds.
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Dalton’s Last Principle
5. In chemical reactions atoms are combined, separated, or rearranged, but never created, destroyed, or changed.
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Are they still true?
At the time, this explained the chemical data that they had.
Two invalid principles.Is it still a theory?
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Concept Check
According to Dalton, what is the difference between an element and a compound?
What are the five principles of Dalton’s atomic theory?
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Atomic Mass
Atomic Mass – the mass of an atom in atomic mass units (amu)
AveragesAtoms of an element have
different masses.AKA: the Dalton (Da)The mass of C is 12.011 amu
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The mole!
The mole is the SI unit for amount.
Why the mole?
6.023 x 1023
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THE MOLE!
Based on an isotope of carbon.
A mole is exactly the number of atoms in 12 grams of the carbon-12 atom.
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Mole
1 mole of atoms of any element has a mass in grams that is equal to the atoms mass in amu’s.
18.9984 amu of F = 18.9984 g/mol of F
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Avogadro's Number
6.022 x 1023 is Avogadro’s #.It’s the # of particles in 1 mole.If 6 billion people were to count the
atoms in 1 mole, it would take them over 3 million years to count them all if counting at the rate of 1 atom/second.
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Section Review
Complete the section review on page 81. Do problems 1-7.