1. Atomic Structure and Elementary Particles Flashcards
What is a substance?
A substance is a material with a constant composition and distinct properties. It can be an element or a compound.
What is a mixture?
A mixture consists of two or more substances physically combined, which can be separated by physical means.
Examples of substances and mixtures
Pure substances: Water, gold, refined sugar
Mixtures: Milk, air, oil
How do pure substances and mixtures differ?
Pure substances have a constant composition and distinct properties.
Mixtures can vary in composition and can be separated physically.
Types of mixtures
Homogeneous mixture: Uniform composition (e.g., sugar dissolved in water).
Heterogeneous mixture: Non-uniform composition (e.g., sand in water).
What are elements and compounds?
Element: A substance that cannot be broken down chemically (e.g., oxygen, gold).
Compound: A substance made of two or more elements in a fixed ratio (e.g., water = H₂O).
What are physical properties?
Properties that can be measured without changing the substance’s identity.
Examples: Volume, boiling point, melting point, mass, density, color.
What are chemical properties?
Properties observed during a chemical reaction.
Examples: Flammability, heat of combustion, acidity.
What are extensive and intensive properties?
Extensive properties: Depend on the amount of matter (e.g., mass, volume, weight).
Intensive properties: Independent of the amount of matter (e.g., density, concentration, temperature).
What is density?
Density is the amount of mass per unit of volume.
Common units: g/cm³, kg/m³, lb/ft³.
Why is unit conversion important?
Unit conversion helps in chemistry and engineering by ensuring consistent measurements across different systems (e.g., SI units).
What is Dalton’s Atomic Theory?
Elements are made of atoms.
Atoms of the same element are identical in size, mass, and properties.
Compounds consist of atoms of two or more elements in a fixed ratio.
Chemical reactions involve rearrangement of atoms, not creation or destruction.
What are subatomic particles?
Electrons (negative charge, small mass).
Protons (positive charge, in nucleus).
Neutrons (neutral charge, in nucleus).
How was the electron discovered?
Early radiation experiments (1890s) applied high voltage to metal plates.
Electrons were found to have a high charge-to-mass ratio.
How was the proton discovered?
Ernest Rutherford’s gold foil experiment (early 1900s).
Found that atoms are mostly empty space with a dense, positively charged nucleus.
How was the neutron discovered?
James Chadwick (1932) bombarded beryllium with alpha particles.
Discovered neutral particles with a mass similar to protons → Neutrons.
What is the atomic number (Z)?
Number of protons in an atom.
Defines an element (e.g., carbon has Z = 6).
What is the mass number (A)?
Sum of protons and neutrons in an atom.
Fluorine: 9 protons + 10 neutrons = Mass number 19.
What are isotopes?
Same atomic number (Z), different mass number (A).
Have the same chemical properties but different mass.
Example: Uranium isotopes used in nuclear energy.
What are nuclides?
General term for isotopes and other nuclear species.
Includes metastable isomers, denoted by “m” in mass number.
What are elementary (fundamental) particles?
Beyond protons, neutrons, and electrons.
Includes muons, pions, and other quantum particles.
Studied in quantum mechanics but not needed for basic chemistry.
What is Planck’s Quantum Theory?
Energy is absorbed/emitted in discrete packets called quanta.
Energy of a quantum is proportional to frequency:
𝐸 = ℎ𝜈
where
h = Planck’s constant (6.626×10^−34𝐽⋅s).
Energy cannot be fractioned—only whole multiples of hν exist.
What was the photoelectric effect?
Electrons are ejected from metals when exposed to light of sufficient frequency.
Threshold frequency: Minimum frequency required for ejection.
Brighter light = More electrons ejected, but energy per electron depends on frequency.
How did Einstein explain the photoelectric effect?
Using Planck’s quantum theory, Einstein showed that:
Ek=ℎ𝜈−𝜙
where:
Ek = kinetic energy of ejected electron
ϕ = work function (energy needed to remove the electron)
If photon energy is less than the work function, no electrons are ejected.
What is the emission spectrum of hydrogen?
Energized gases emit light at specific wavelengths.
Hydrogen’s emission spectrum is explained by quantized electron orbits.
Electrons move between discrete energy levels, releasing energy as light.
What was Bohr’s Atomic Model?
Electrons exist in specific orbits with fixed energy levels.
Energy levels are quantized
Ground state:
𝑛=1 (most stable state).
Excited states:
n>1 (higher energy).
How do electrons transition between energy levels?
When electrons drop to lower energy levels, they emit a photon.
Different spectral series correspond to different transitions (Lyman, Balmer, etc.).
What was de Broglie’s contribution to quantum theory?
In 1924, Louis de Broglie proposed that electrons have wave properties.
Electron motion resembles a standing wave.
Proven by Davisson & Germer (USA) and G.P. Thompson (UK) using electron diffraction experiments.
What limitations did Bohr’s atomic model have?
Could not explain multi-electron atoms.
Could not explain spectral line splitting in a magnetic field.
Could not determine electron positions if they behave like waves.
What is quantum mechanics?
Theory that models the wave behavior of subatomic particles.
Based on two main principles:
1. Heisenberg’s Uncertainty Principle:
Position & velocity of an electron cannot be determined simultaneously.
2. Schrödinger’s Equation:
Solving it gives the wave function ψ, which predicts the probability of finding an electron in a region.
What are quantum numbers?
Describe electron behavior & orbitals.
Four quantum numbers:
Principal quantum number ( 𝑛 ) – Energy level, distance from nucleus.
Angular momentum quantum number ( ℓ ) – Shape of orbital.
Magnetic quantum number ( mℓ ) – Orientation of orbital.
Spin quantum number ( ms ) – Electron spin (+1/2,−1/2).
What is an atomic orbital?
A probability function describing where an electron is likely to be found.
Not a fixed path like Bohr’s model.
Boundary Surface Diagram: Shows 90% probability region of an electron’s location.
How are orbitals classified?
Orbital names depend on quantum numbers:
s orbital ( ℓ=0 ) – Spherical shape.
p orbital ( ℓ=1 ) – Dumbbell shape, three orientations.
d orbital ( ℓ=2 ) – Five orientations.
f orbital ( ℓ=3 ) – More complex shapes.
