Atomic Structure and Subatomic Particles

Electrons

• Small, negatively charged particles
• Orbit the nucleus
• Have no mass
• Number of electrons = number of protons

Protons

• Small, positively charged particles
• Located in the nucleus
• They, along with neutrons, make up most of the mass of the atom
• The number of protons defines the type of atom
• Number of protons = number of electrons

Neutrons

• Small, neutrally charged particles
• Located in the nucleus
• They, along with protons, make up most of the mass of the atom
• A differing number of neutrons defines an "isotope" of an atom

Properties of Subatomic Particles

Atomic Theory of Matter

• The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton.

Dalton's Postulates

• Each element is composed of extremely small particles called atoms.
• All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.
• Atoms are neither created nor destroyed in chemical reactions; they are merely rearranged.
• Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Dalton's Atomic Theory (1808)

• Elements are composed of extremely small particles called atoms.
• All atoms of a given element.
• Compounds are composed of atoms of more than one element.

The Mole Concept

• The mole is a unit of measure for an amount of a chemical substance.
• Avogadro’s Number (symbol N) is the number of atoms in 12.01 grams of carbon.
• A mole is Avogadro’s number of particles, that is 6.02 × 1023 particles.
• We can use the mole relationship to convert between the number of particles and the mass of a substance.

The Mole

• One mole = amount of any substance that contains as many particles of that substance as there are atoms of C in 12 g of pure carbon-12
• 1 mole = 6.022× 1023 particles = Avogadro’s Number
• 1 mole of Fe = 6.022× 1023 atoms of Fe
• 1 mole of H2O = 6.022× 1023 molecules of H2O

Mole Calculations

• To convert from moles to atoms: Multiply by Avogadro's number (6.02 x 10^23)
• To convert from atoms to moles: Divide by Avogadro's number (6.02 x 10^23)

Molar Mass

• The atomic mass of any substance expressed in grams is the molar mass (MM) of that substance.
• The atomic mass of iron is 55.85 amu.
• The molar mass of iron is 55.85 g/mol.

Calculating Molar Mass

• The molar mass of a substance is the sum of the molar masses of each element.

Atomic Mass

• Atomic Mass (Atomic Weight) = number of grams in 1 mole of that element.

Mass-Mole Calculations

• To convert from moles to grams: Multiply by the molar mass.
• To convert from grams to moles: Divide by the molar mass.

Mole-Volume Calculations

• To convert from liters at STP (Standard Temperature and Pressure) to moles: Divide by 22.4 L/mol.
• To convert from moles to liters at STP: Multiply by 22.4 L/mol.
• To convert from liters at STP to molecules: Multiply by Avogadro's number and then by the number of molecules in one mole (6.02 x 10^23).

Chemical Formulas

• A molecule is composed of two or more nonmetal atoms.
• A chemical formula expresses the number and types of atoms in a molecule.

Writing Chemical Formulas

• The number of each type of atom in a molecule is indicated with a subscript in a chemical formula.
• If there is only one atom of a certain type, no ‘1’ is used.

Percent Composition

• The percent composition of a compound lists the mass percent of each element.
• For example, the percent composition of water, H2O is: 11% hydrogen and 89% oxygen

Calculating Percent Composition

• To find the percent composition of a compound, divide the mass of each element by the total mass of the compound and multiply by 100%.

Empirical Formulas

• The empirical formula represents the simplest whole number ratio of ions in a formula unit or atoms of each element in a molecule.

Empirical Formulas from Percent Composition

• Assume a 100 g sample and calculate the moles of each element.
• Divide the moles of each element by the smallest number of moles.
• The resulting numbers represent the subscripts in the empirical formula.

Molecular Formulas

• The actual molecular formula is some multiple of the empirical formula.
• To determine the molecular formula, find the empirical formula mass and divide the molecular mass by it.
• The resulting number represents the multiple of the empirical formula.

This quiz focuses on the fundamental concepts of atomic structure, including the properties of subatomic particles such as electrons, protons, and neutrons. Additionally, it touches on Dalton's atomic theory and the significance of atomic composition in defining elements. Test your understanding of these essential topics in chemistry!