chem test 1

What is Dalton's atomic theory (basic claim)?

Matter is made of indivisible atoms; atoms of a given element are identical; compounds form from fixed ratios of different atoms.

What did Thomson's cathode ray experiment show?

Electrons exist, are negatively charged, and are part of the atom (led to the "plum pudding" model).

What did Rutherford's gold foil experiment show?

Atoms have a small, dense, positively charged nucleus with mostly empty space around it.

What are the three main characteristics of a wave?

Wavelength (λ, m), frequency (ν, s⁻¹), and speed (c, m/s).

What is wavelength?

The distance between two consecutive peaks of a wave.

What is frequency?

The number of waves per second that pass a given point in space.

What is the speed of light?

2.99 × 10⁸ m/s.

What is the relationship between wavelength and frequency?

λν = c (they are inversely proportional).

Who introduced the concept of quantization, and how?

Max Planck, by studying blackbody radiation; he proposed that vibrational (and thus radiated) energy is quantized.

What is Planck's equation for energy?

E = hν, where h = 6.626 × 10⁻³⁴ J·s (Planck's constant).

What did Einstein's photoelectric effect experiment show?

Light behaves as particles (photons); only light above a threshold frequency ejects electrons, regardless of intensity.

What is the photoelectric effect key equation?

K.E. = hν − hν₀ (or K.E. = Eᵢ − Φ, where Φ is the work function).

What does light intensity control in the photoelectric effect?

The number of photons absorbed per second, and thus the number of electrons ejected — not their kinetic energy.

What is momentum of a photon?

p = hν/c = h/λ.

What did de Broglie's hypothesis say?

Matter can behave as a wave: λ = h/(m·v).

What does the Schrödinger equation describe?

The motion of particles (like electrons) accounting for their wave-like properties: ĤΨ = EΨ.

What does Ψ (the wavefunction) represent?

A function of the electron's position coordinates in 3D space; a specific wavefunction is called an orbital.

What quantum number describes the energy level/shell?

n, the principal quantum number (values 1, 2, 3…∞).

What quantum number describes the subshell/orbital shape?

l, the angular momentum quantum number (values 0 to n−1).

What quantum number describes orbital orientation?

mₗ, the magnetic quantum number (values −l…0…+l).

What quantum number describes electron spin?

mₛ, the spin magnetic quantum number (values +1/2 or −1/2).

How many quantum numbers fully describe an orbital? An electron?

3 for an orbital (n, l, mₗ); 4 for an electron (n, l, mₗ, mₛ).

Match l values to orbital letters.

l=0 → s, l=1 → p, l=2 → d, l=3 → f.

What is the ground state wavefunction of hydrogen?

Ψ₁₀₀ (n=1, l=0, mₗ=0) — the 1s orbital.

What is Pauli's Exclusion Principle?

No two electrons in the same atom can have the same set of four quantum numbers (i.e., no two electrons in an orbital can have the same spin).

How many electrons can one orbital hold?

A maximum of 2, and they must be paired with opposite spins.

For a given n, how many degenerate orbitals exist?

n² degenerate orbitals.

What is Hund's Rule?

When filling orbitals of equal energy, one electron enters each orbital before any orbital gets a second electron, and spins remain parallel.

What is the Aufbau Principle?

Fill energy states one electron at a time, starting from the lowest possible energy, following Pauli's Exclusion Principle and Hund's Rule.

In a multi-electron atom, how does orbital energy ordering compare across l for the same n?

s < p < d < f (energy increases with l for the same n).

Why is E(2s) < E(2p) in a multi-electron atom?

Electrons in orbitals with lower l penetrate closer to the nucleus, so they are less shielded and lower in energy.

What is Zeff and why does it differ from Z?

The effective nuclear charge; it differs from the actual charge Z because of shielding by other electrons.

What are valence electrons?

The electrons that can be gained or lost — those outside the noble gas core.

What are core electrons?

The electrons corresponding to the previous noble gas configuration.

What is ionization energy (IE)?

The minimum energy required to remove an electron from an atom; IE = −Eₙₗ.

Why does successive ionization energy (IE1, IE2, IE3…) increase each time?

It gets progressively harder to remove an electron as the remaining electrons are held more tightly by the same (or higher, if a core electron) nuclear charge.

What happens to orbital energy once a d orbital is filled?

It drops below the corresponding s orbital in energy — this explains some transition metal ion configurations.