Chapter 2: Modern Atomic Theory

• Matter consists of atoms

• Atoms consist of three fundamental particles, found in the nucleus and the space around the nucleus

Arrangement of Subatomic Particlesnot to scale!

If an atom has a diameter of about 100 m (a football field), the nucleus would be 1 mm in diameter

Nucleus containsprotons and neutrons.

What holds an atom together?

What holds an atom together?

Coulomb’s Law of electrostatic interactions.

What holds an atom together?

Coulomb’s Law of electrostatic interactions.

General Behavior: Like charges repel.Opposite charges attract.

What holds an atom together?

Coulomb’s Law of electrostatic interactions.

If we double a charge from +1 to +2, the force will:

1. Double2. Halve3. Quadruple4. Quarter

What holds an atom together?

Coulomb’s Law of electrostatic interactions.

If we double the distance, the force will:

1. Double2. Halve3. Quadruple4. Quarter

What’s wrong with this picture?

Electrons are held near the nucleus by the electrostatic attraction between them, but …

The forces of nature:

How could we possibly know that the nucleus

is small compared to the size of the atom?

Why not think the protons, electrons and neutrons are all mixed together?

The Rutherford Experiment

We’re not just making it up!

The Rutherford ExperimentWe’re not just making it up!

The Rutherford ExperimentWe’re not just making it up!

Atom Terminology

• All atoms of an element have the same atomic number = number of protons

• In a neutral atom (no charge), the number of positively and negatively charged particles must be equal. Number protons = number electrons

• The mass number = protons + neutrons

Isotopes

• Isotopes are atoms of an element with the same number of protons but different numbers of neutrons, and different mass

• Atom symbols are written using the following format:

X = symbol of elementA = mass numberZ = atomic number

ZA X

11H 1

2H 510X 30

66X

Isotopes, continued

• Most elements have multiple isotopes– 1H, 2H (deuterium), 3H (tritium, radioactive)– 79Br, 81Br– 64Zn, 66Zn, 67Zn, 68Zn, 70Zn

• While atomic mass is the mass of an atom, average atomic mass takes into account isotopes and natural abundance

• We use atomic mass units (amu)1 amu = 1.661 x 10–24 g(about the mass of a proton)

WHAT TIME IS IT?

PuppyDog

Isotopes

Chiuaua: 4 lbs.

Mastif: 120 lbs.

What is the average weight of a collection of these dogs?

96 % Chiuauas @ 4 lbs.

4 % Mastifs @ 120 lbs.

Isotopes and Average Atomic Masses

all isotopes

Average atomic mass = (fractional abundance) (mass of isotope)

Isotopes and Average Atomic Masses

all isotopes

Average atomic mass = (fractional abundance) (mass of isotope)

B has 2 isotopes: B-10: mass = 10.0129 amu abundance = 19.91%

B-11: mass = 11.0093 abundance = 80.09%

Example: Boron

What is the average atomic mass of Boron?

HOWDOYOU

KNOWTHAT?

Mass Spectrometry

The Periodic Table

Groups and Periods

The Periodic Table

Main and Transition Groups

The Periodic Table

Metals, Nonmetals, Metalloids

The Periodic Table

Groups with names.

Structures of the Elements