Unit 3 CHEM - Exam Prep.

What are five nuclear models?

What are five nuclear models?

1. Dalton

2. Thomson

3. Rutherford

4. Bohr

5. Quantum model

What is radioactivity? An isotope? A neutral atom? A radioisotope?

RADIOACTIVITY

• The spontaneous decay or disintegration of an atom’s nucleus.

ISOTOPE:

• Atoms with the same number of protons but different number of neutrons.

NEUTRAL ATOM:

• Atoms with the same number of protons and electrons.

RADIOISOTOPES:

• Istope that’s emitting radioactive gamma rays and/or subatomic particles (alpha/beta particles).

What is Dalton’s nuclear model?

Billiard Ball Model

Smallest particles of matter in solid, hard spheres. Holes in the model allow for multiple balls to hook to one another and demonstrate compounds.

What is Thomson’s nuclear model?

Plum Pudding Model

Atoms are diffused clouds of positive charge with negatively charged electrons embedded throughout.

What is Rutherford’s nuclear model?

Atoms are tiny and dense with a positively charged core (nucleus) where all mass is concentrated with electrons circulating around it (similar to how planets orbit the sun).

What is Bohr’s nuclear model?

Electrons move in specific orbits (according to spectroscopy) around the nucleus that possesses specific energy levels. These levels increase as the distance from the nucleus increases. Electrons may move into further orbits by gaining more energy.

What is the quantum mechanical model? (2 points)

1. Electrons can be in different orbitals by absorbing/emitting quanta of energy (Planck; burst or packet of energy).

2. The location of electrons is given by a probability distribution (Schrodinger: region of probability found using Schrodinger’s Wave Equation; orbitals).

What are the limitations of Bohr-Rutherford models?

BOHR:

• Only accurate for hydrogen.

• Doesn’t explain how electrons can stay in orbit without falling into the nucleus.

RUTHERFORD:

• Doesn’t consider the stability of an atom (as electrons lose energy during their acceleration in orbit, they would eventually collapse into the nucleus).

• Doesn’t explain the arrangement of electrons around the nucleus.

What is the photoelectric effect? What experiment demonstrated this theory?

The frequency of light determines the energy of the emitted electrons.

EXPERIMENT: Shining a light on a metal surface had more electrons emitted from the metal when a high-frequency light was shone.

Who suggested wave-particle duality? What is it?

Louis de Broglie: Light has both wave (disturbances spead over space, traveling over time) and particle (localized bundles of energy and momentum with mass) properties.

• wavelengths must be quantized or they would cancel out.

What does wave-particle duality mean for our ability to predict both position and momentum(speed) of an electron?

It is impossible, only identifying a region of probability for an electron is possible.

What are quantum numbers?

Numbers used to describe electrons in their orbitals, similar to addresses.

How many electrons can orbitals hold?

Two

What is the principal quantum number (n)?

Number that specifies the energy level/shell of an atomic orbital.

What is the secondary quantum number (l)? What is the range of possible numbers?

Angular momentum quantum number: describes orbitals shape and sublevel.

• 0 to (n-1)

What letters/shapes are assigned to each sublevel/secondary quantum number?

s (sphere) = 0

p = 1

d (double dumbbell) = 2

f = 3

What is the third quantum number (m subscript l)? What are the integer values for this quantum number?

Magnetic Quantum Number: describes an orbital’s orientation in space around the nucleus.

• -l to +l, including 0

What is the fourth quantum number (m subscript s)? What are the two possible values?

Spin Quantum Number: describes the spin of the electron.

• -1/2 (spin-down/counter clockwise) and +1/2 (spin-up/clockwise)

What is the rule for the spins of two electrons in the same orbital?

They must have opposite spins.

What is the Pauli Exclusion Principle?

No two electrons in an atom can have the same set of 4 quantum numbers.

What is electron configuration?

A shorthand notation that shows electron arrangement within orbitals.

What are three types of electron configuration?

1. Energy Level Diagrams

2. Complete Electron Configuration

3. Shorthand Electron Configuration

What components make up electron configuration notation?

• Principal quantum number (shell)

• Secondary/Angular momentum quantum number (subshell)

• Number of electrons in the orbital (shell) or subshell

What do orbital diagrams use to represent orbitals?

• Boxes or lines holding the spins for the electrons present in that orbital

• Principal quantum number of the orbital

• Secondary/Angular momentum quantum number (subshell)

What is the Aufbau Principle?

• Number of electrons in atom = atomic number

• Start by filling the orbital with the lowest energy when adding electrons

• Each orbital can have a maximum of two electrons.

Arrows move through numbers in a downwards diagonal from right to left

1s

2s2p

3s3p3d

4s4p4d4f

5s5p5d5f…

What is Hund’s Rule?

Single electrons with the same spin must occupy each equal energy orbital before electrons with opposite spins can occupy the same orbitals.

• BUS ANALOGY: when boarding a bus, all empty seats must be filled before people double up.

• Fill orbitals with the upwards spin first, if electrons can be on their own in an orbital they will be.

What do you use when writing shorthand electron configuration?

The last noble gas in the periodic table (at the end of the period above).

• Then continue writing regular notation.

What is an expanded valence shell?

When atoms in period 3 and above have more than eight electrons in their valence shell.

• Expanded octets

What is the VSEPR Theory?

Electron groups around an atom are positioned as far as possible from the others to minimize repulsion.

What are the five basic electron-group arrangements?

1. linear

2. trigonal planar

3. tetrahedral

4. trigonal bipyramidal

5. octahedral

What are bond angles?

Angles between two bonds originate from the same atom that impact the stability of an atom.