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Atoms: The building blocks of Matter

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

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Atoms: The building blocks of Matter

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  1. Atoms: The building blocks of Matter Counting Atoms

  2. Atomic Number • The number of protons in the nucleus of each atom • Identifies element • Periodic table – elements are arranged in order of increasing atomic #

  3. Isotopes • Atoms of the same element, with different numbers of neutrons • Only the masses are different. • Mass # = # protons plus the # neutrons

  4. Designating Isotopes • Hyphen notation/Nuclear symbol Carbon-12 Carbon-13

  5. Sample Problems • How many protons, electrons, and neutrons are in an atom of Chlorine-37? • Write the nuclear symbol for oxygen-16. • Write the hyphen notation for the element whose atoms contain 7 electrons and 9 neutrons.

  6. Atomic Mass One 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

  7. Atomic Mass Some 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?

  8. 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.

  9. 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

  10. 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

  11. Sample Problems: • What is the mass in grams of 3.6 mol of the element Carbon? • What is the mass in grams of 0.733 mol of the element Chlorine? • How many moles of copper are in 3.22 g of copper? • How many moles of lithium are in 2.72 x 10-4 g of lithium?

  12. Mole Conversions • How many moles of carbon are in 2.25x1022 atoms of carbon? • How many moles of oxygen are in 2,000,000 atoms of oxygen? • How many atoms of sodium are in 3.80 mol of sodium? • What is the mass in grams of 5.0 x 109 atoms of neon? • How many atoms of carbon are in 0.020 g of carbon? • What mass of silver contains the same number of atoms as 10.0g of boron?

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