Chemistry Semester Review

Chemistry Review for Final 2: Atoms, Ions, and Isotopes

By William Lovering

There have been many atomic models over the ages

• Billiard Ball - Dalton

• Tiny Real-Life - Democrats

• Plumb Pudding - Thomson

• Planetary - Rutherford

• Energy Level - Bohr

• Quantum - Schrodinger

Atomic Models

• A visual representation of the structure of an atom, (how an atom looks and made-up of)

• Nucleus

• Inside Nucleus: Protons (positive charge) and Neutrons (no charge)

• Outside Nucleus: Electrons (negative charge)

Dalton

• Was the first modern scientist to propose the atomic theory.

• He thought that atoms were made of microscopic hard balls where every atom of an element had the same properties (for example: radius and mass)

Problems with Dalton's Model

• In experimentation with different gases scientists, most notably J.J. Thomson, discovered positive and negative charged particles in the gas.

• Dalton's Model didn't account for this

Atomic Number, Average Atomic Mass, Mass Number, Isotopes

Isotope Symbols

As you can see to the right there are certain ways elements and isotopes are represented as symbols. There is the element symbol (the biggest part). Then the upper number will the the mass number (number of protons + number of neutrons) and the lower number is just the atomic number (number of protons).

Isotope Symbol Examples

ISOTOPES:

• Same Element

• Different Mass Number

• WHICH MEANS DIFFERENT # of NEUTRONS

What does changing # of Neutrons do?

• Neutrons make atoms stable

• Unstable = Wants to fall apart

• Fall Apart = Split into smaller atoms

• Split Apart = RADIOACTIVE

Average Atomic Mass

• DIFFERENT than Mass Number

• Average of all of the isotopes of an atom found in nature.

How they get that number

• % abundance of that isotope x actual mass of that isotope

• add together

• divide by 100 (if you didn't put into percentage first)

How to tell which isotope is more abundant?

• CLOSEST TO ROUNDED AVERAGE ATOMIC MASS

• So the most abundant isotope of Gold would be?

• Gold - 197

Orbitals

a region of probability where an electron can be found.

s

d

p

f

Remember these are NOT electrons, they're just regions of space where an electron can be found.(Each can hold up to 2 electrons)

The 4 Quantum Numbers

Principle Quantum Number

n=1

n=2

n=3

n=4

Pauli Exclusion Principle

No two electrons in the same atom can have identical values for all four of their quantum numbers.

In other words:

(1) no more than two electrons can occupy the same orbital

(2) two electrons in the same orbital must have opposite spins 

Aufbau Principle

states that electrons fill lower-energy atomic orbitals before filling higher-energy ones (Aufbau is German for "building-up")

Hunds Rule

every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.

Orbital Configuration

the more visual way to represent the arrangement of all the electrons in a particular atom

Each sublevel is labeled by its principal energy level and sublevel

Electrons are indicated by arrows inside the circles. An arrow pointing upwards indicates one spin direction, while a downward pointing arrow indicates the other direction.

Electron Configuration

Electron configuration notation eliminates the boxes and arrows of orbital filling diagrams.

How to Write an Electron Configuration:

1. Start with the shell/period number

2. Followed by the type of orbital

3. Finally the superscript indicates the number of electrons in the orbital

Example: B = 1s² 2s² 2p¹

Multiple Choice

This model was developed after J.J. Thompson discovered electrons, a particle smaller than an atom. It shows electrons floating freely in a positive region.

• The "Plum Pudding Model" of the atom

• The "Rutherford Model" of the atom

• Democritus's model of the atom

• The "Quantum Mechanical Model" of the atom

Multiple Choice

Which has more electrons?

• neither

• carbon - 12

• carbon - 13

Multiple Choice

Choose the correct electron configuration for Nickel (Ni).

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d²

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹⁰

Multiple Choice

Choose the correct electron configuration for Krypton (Kr).

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁸ 3d⁸

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸ 4p3

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸ 4p⁶

Fill in the Blanks

Calculate the Average Atomic Mass (sig figs apply)

Multiple Choice

How many neutrons does this bromine atom have?

• 35

• 45

• 80

Multiple Choice

Which atom has  4 neutrons?

• Li-6
• Li-7
• Li-8
• they have the same # of neutrons

Multiple Choice

Which has more neutrons?

• neither

• carbon - 12

• carbon - 13

Multiple Choice

In the gold foil experiment, most of the positively charged alpha particles passed through the gold foil, but some were deflected or bounced back.  What did we conclude because of this?  

• Atoms are small indivisible spheres

• Atoms are mostly empty space with a small, dense, positive center

• Atoms have negatively charged particles which orbit the nucleus

• Light is a wave, not a particle

Fill in the Blanks

What is the most abundant isotope? (answer in hyphen notation)

Multiple Choice

Who is credited with developing model D?

• Thomson

• Dalton

• Bohr

• Rutherford

Multiple Choice

Which scientist is responsible for first stating that all the atoms of a particular element are identical but are different from the atoms of all other elements?

• Dalton

• Thomson

• Aristotle

• Democritus

• Proust

Multiple Choice

Choose the correct electron configuration for Chlorine (Cl).

• 1s² 2s² 2p¹

• 1s² 2s² 2p⁶ 3s²

• 1s² 2s² 2p⁶ 3s² 3p⁵

Multiple Choice

Chadwick is credited with discovering which part of the atom?

• nucleus

• protons

• electrons

• neutrons