Unit 3 CHEM - Exam Prep.

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.