Atoms: The building blocks of Matter Counting Atoms.
-
Upload
augustus-fields -
Category
Documents
-
view
222 -
download
0
Transcript of Atoms: The building blocks of Matter Counting Atoms.
Atoms: The building blocks of
Matter
Counting Atoms
Atomic Number• The number of
protons in the nucleus of each atom
• Identifies element• Periodic table –
elements are arranged in order of increasing atomic #
Isotopes
• Atoms of the same element, with different numbers of neutrons
• Only the masses are different.• Mass # = # protons plus the # neutrons
Designating Isotopes• Hyphen notation/Nuclear symbol
C126 C136Carbon-12 Carbon-13
Sample Problems
1. 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.
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
Atomic MassSome examples:
Oxygen-16: 15.994915 amu
1 proton: 1.007276 amu
1 neutron: 1.008665 amu
1 electron: 0.00054896 amu
How can carbon-12 have a mass of 12 amu?
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 abundance
Atomic mass(amu)
Carbon-12 98.90 % 12
Carbon 13 1.10 % 13.003355
amuamuamu 0111.12)003355.130110.0()129890.0(
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
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
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 amu
1 mole Hydrogen: 1.00794 g
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?
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?