Atoms are the building blocks of matter. A molecule is a group of atoms .
Atoms: The building blocks of Matter
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Transcript of Atoms: The building blocks of Matter
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Atoms: The building blocks of
Matter
Counting Atoms
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Atomic Number• The number of
protons in the nucleus of each atom
• Identifies element• Periodic table –
elements are arranged in order of increasing atomic #
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Isotopes
• Atoms of the same element, with different numbers of neutrons
• Only the masses are different.• Mass # = # protons plus the # neutrons
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Designating Isotopes• Hyphen notation/Nuclear symbol
C126 C136Carbon-12 Carbon-13
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Sample Problems1. How many protons, electrons, and
neutrons are in an atom of Chlorine-37?
2. Write the nuclear symbol for oxygen-16.
3. Write the hyphen notation for the element whose atoms contain 7 electrons and 9 neutrons.
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Atomic MassOne Oxygen-16 atom = 2.657 x 10-23g
• Masses of atoms are measured in atomic mass units (amu)
By definition: 1 Carbon-12 atom = 12 amu
so…. 1 amu = 1/12 mass of a Carbon-12 atom
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Atomic MassSome examples:
Oxygen-16: 15.994915 amu1 proton: 1.007276 amu1 neutron: 1.008665 amu1 electron: 0.00054896 amu
How can carbon-12 have a mass of 12 amu?
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Average Atomic Mass• Atomic mass of carbon: 12.0111 amu (on p.t.)• The atomic masses on the periodic table are
weighted averages of the isotopes of each element.Isotope Percent
abundanceAtomic mass
(amu)Carbon-12 98.90 % 12
Carbon 13 1.10 % 13.003355
amuamuamu 0111.12)003355.130110.0()129890.0(
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Isotope Percent Abundance
Atomic Mass (amu)
Oxygen 16Oxygen-17Oxygen-18
99.7620.0380.200
15.99491516.99913117.999160
Copper-63Copper-65
69.1730.83
62.92959964.927793
Uranium-234Uranium-235Uranium-238
0.0050.720
99.275
234.040947235.043924238.050784
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The Mole
Mole – SI unit for amount
By definition…One mole equals the number of atoms in
exactly 12 grams of Carbon-12
Avogadro’s Number: 6.02 x 1023
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Molar Mass
Molar Mass – the mass of one mole of a pure substance
• The molar mass of an element is numerically equal to the atomic mass.1 atom Hydrogen: 1.00794 amu1 mole Hydrogen: 1.00794 g
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Sample Problems:1. What is the mass in grams of 3.6 mol of the
element Carbon?
2. What is the mass in grams of 0.733 mol of the element Chlorine?
3. How many moles of copper are in 3.22 g of copper?
4. How many moles of lithium are in 2.72 x 10-4 g of lithium?
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Mole Conversions1. How many moles of carbon are in 2.25x1022 atoms
of carbon?2. How many moles of oxygen are in 2,000,000
atoms of oxygen?3. How many atoms of sodium are in 3.80 mol of
sodium?4. What is the mass in grams of 5.0 x 109 atoms of
neon?5. How many atoms of carbon are in 0.020 g of
carbon?6. What mass of silver contains the same number of
atoms as 10.0g of boron?