mass realal

Mass Relationships in Chemical Reactions

Atomic Mass

• Definition of Atomic Mass:

  • The atomic mass of an atom is defined as the mass of the atom measured in atomic mass units (amu).

• Constituents of an Atom:

  • An atom is composed of three subatomic particles:

  • Protons: Positively charged particles located in the nucleus.

  • Neutrons: Neutral particles also found in the nucleus.

  • Electrons: Negatively charged particles that orbit the nucleus.

• Definition of Atomic Mass Unit (amu):

  • An atomic mass unit is defined as the mass that is equal to 1/12 the mass of a carbon-12 atom.

Reading the Periodic Table

• Structure of the Periodic Table:

  • Each box in the periodic table represents a different element.

  • Important information provided in each box includes:

  • Element Name

  • Element Symbol

  • Atomic Number: The number of protons in the atom.

  • Atomic Mass: The weighted average mass of an element's isotopes.

Isotopes

• Definition of Isotopes:

  • Isotopes are variants of the same element that have the same number of protons but different numbers of neutrons.

• Average Atomic Mass:

  • The value of atomic mass displayed in the periodic table is the weighted average of an element's isotopes based on their natural abundance.

• Calculating Average Atomic Mass Example (Carbon):

  • Carbon-12 and carbon-13 have abundances of 98.90% and 1.10%, respectively.

  • Carbon-14 is considered rare and contributes insignificantly to the average mass.

  • Calculation:

  • Average atomic mass of carbon =

    • $(0.9890)(12.00 ext{ amu}) + (0.0110)(13.00 ext{ amu})$

    • Result = 12.01 amu.

Avogadro’s Number and Molar Mass of Elements

• Definition of Avogadro's Number:

  • Avogadro's number represents the quantity of atoms in 1 mole of an element.

  • Numerical Value: 6.0221367 x 10²³ atoms/mol.

• Magnitude of Avogadro's Number:

  • The largeness of Avogadro's number can be difficult to comprehensively visualize.

The Mole

• Definition of the Mole (mol):

  • A mole is defined as a quantity of substance that contains as many elementary entities (atoms, molecules, etc.) as there are atoms in exactly 12 grams of carbon-12.

• Mass of a Mole:

  • 1 mole of carbon-12 atoms weighs 12 grams and contains approximately 6.022 x 10²³ atoms.

• Definition of Molar Mass:

  • The molar mass of an element is the mass (in grams) of one mole of its units.

  • For instance:

  • The molar mass of carbon-12 is 12 grams.

  • The molar mass of sodium is 22.99 grams (equivalent to 22.99 amu).

Molecular Mass

• Definition of Molecular Mass:

  • The molecular mass is calculated as the sum of the atomic masses (in amu) present in a molecule.

• Example Problem – Molecular Mass of Water (H₂O):

  • Calculation steps:

  • Total Mass of Hydrogen: 2 atoms of H, each with a mass of 1.00 amu:

    • $(2 ext{ atoms of H} imes 1.00 ext{ amu})$

  • Mass of Oxygen: 1 oxygen atom with a mass of 16.000 amu:

    • $16.000 ext{ amu}$

  • Total Molecular Mass of Water:

    • $(2 imes 1.00) + 16.000 ext{ amu} = 18.00 ext{ amu}$

  • Conclusion: The molecular mass of water is 18.02 amu, indicating that there is 1 mole of H₂O for every 18.02 grams of the substance.