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Unraveling the Building Blocks: Dalton's Atomic Theory, Atomic Mass, Molecular Mass and Formula Mass Explained in Detail

1. Dalton's Atomic Theory 


JOHN DALTON


John Dalton proposed the modern atomic theory in 1803. Key points:


1. Atoms are indivisible: Atoms cannot be divided into smaller particles.

2. Atoms are identical: Atoms of the same element have identical properties.

3. Atoms have mass: Atoms have a specific mass.

4. Atoms combine in whole numbers: Atoms combine in simple whole-number ratios to form compounds.

5. Chemical reactions involve atom rearrangement: Atoms are rearranged during chemical reactions, not created or destroyed.


Example


Hydrogen gas (H2) consists of two identical hydrogen atoms.


2. Atomic Mass

Atomic mass is the mass of a single atom of an element, measured in atomic mass units (amu).


1. Protons, neutrons and electrons: Atomic mass includes protons, neutrons and electrons.

2. Isotopes: Atoms with the same number of protons (atomic number) but different numbers of neutrons.

3. Average atomic mass: Weighted average of isotopic masses.


Example


Hydrogen atomic mass = 1.00794 amu (proton + electron + neutron)


3. Average Atomic Mass


Average atomic mass accounts for naturally occurring isotopes.


1. Weighted average: Calculates the average mass based on isotope abundance.

2. Isotopic variation: Reflects the mixture of isotopes in natural elements.


Example


Chlorine average atomic mass = 35.453 amu (75.78% Cl-35, 24.22% Cl-37)


4. Molecular Mass


Molecular mass is the sum of atomic masses in a molecule.


1. Molecular weight: Synonymous with molecular mass.

2. Sum of atomic masses: Calculates the total mass of atoms in a molecule.


Example


Water (H2O) molecular mass = 2(1.00794) + 15.9994 = 18.0153 amu


5. Formula Mass

Formula mass applies to ionic compounds and molecular formulas.


1. Sum of atomic masses: Calculates the total mass of atoms in a formula.

2. Ionic compounds: Includes ions and their charges.


Example


Sodium chloride (NaCl) formula mass = 22.9898 + 35.453 = 58.4428 amu


Key Differences


1. Atomic mass: Single atom mass.

2. Average atomic mass: Weighted average of isotopes.

3. Molecular mass: Sum of atomic masses in a molecule.

4. Formula mass: Sum of atomic masses in a compound's formula.


Importance of Understanding atomic and molecular mass concepts is crucial for:


1. Chemical calculations

2. Stoichiometry

3. Molecular structure

4. Chemical reactions

5. Materials science


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