Chapter 4 CDS: Coulomb's Law, Ionization Energies, and Valence Shells

The chapter explains how the structure of atoms can be understood using Coulomb's Law, ionization energies, and the concept of electron shells. Scientists observed that elements with similar chemical properties appear at regular intervals on the Periodic Table, a pattern called the Periodic Law. Coulomb's Law states that the attraction between charged particles increases when: The charges are larger. The particles are closer together. Because electrons are negatively charged and nuclei are positively charged, electrons are attracted to nuclei. The strength of this attraction determines how much energy is required to remove an electron from an atom. This energy is called the ionization energy. When ionization energies are graphed by atomic number, a repeating pattern appears. Ionization energies generally increase across a period and then drop sharply when moving to the next period. This led to the shell model of the atom. Electrons occupy shells around the nucleus, and when one shell fills, electrons begin filling a new shell farther away. The outermost shell is called the valence shell, and the electrons in it are called valence electrons. These electrons largely determine an atom's chemical behavior. Elements in the same group have similar numbers of valence electrons and therefore have similar chemical properties. Successive ionization energies provide direct evidence for valence shells. When a large jump appears between two ionization energies, it indicates that all valence electrons have been removed and the next electron would come from an inner shell.

Coulomb’s Law

Relationship describing how the attraction between charged particles depends on charge size and distance.

Potential Energy (V)

Energy associated with the interaction of charged particles. More negatives values indicate stronger attraction.

Nuclear Charge

Positive charge of the nucleus equal to the number of protons (Z)

Atomic Number

Number of protons in an atom’s nucleus. Unique for every element.

Ionization Energy

Energy required to remove an electron from the gaseous atom.

First Ionization Energy

Energy required to remove the first electron from a neutral atom.

Successive Ionization Energies

Energies required to remove additional electrons after the first.

Valence Shell

Outermost occupied electron shell of an atom.

Valence Electrons

Electrons in the outermost shell that determine chemical behavior.

Periodic Law

Chemical and physical properties repeat periodically with atomic number.

Alkali Metals

Group 1 metals with one valence electron (Li, Na, K)

Alkaline Earth Metals

Group 2 metals with two valence electrons (Be, Mg, Ca)

halogens

Highly reactive elements with seven valence electrons (F, Cl, Br)

Noble Gases

Very unreactive elements with full valence electrons.

What two factors determine the strength of attraction in Coulomb’s Law?

The size of the charges and the distance between them.

What happens to attraction when opposite charges get close together?

the attraction becomes stronger.

Why does a larger atomic number generally increase ionization energy?

More protons create a larger nuclear charge, increasing attraction between the nucleus and electrons.

Why does ionization energy (IE) increase across a period?

Nuclear charge increases while electrons remain in roughly the same shell.

Why does ionization energy drop sharply after a noble gas?

The next electron is placed in a new shell farther from the nucleus.

What evidence suggests electrons are arranged in shells?

The repeating pattern of ionization energies across the periodic table.

What are valence electrons?

Electrons in the outermost shell that control chemical properties.

Why do Li, Na, and K have similar chemical properties?

Each has one valence electron.

Why do F and Cl have similar chemical properties?

Each has seven valence electrons.

Why is IE2 always larger than IE1

After one electron is removed, the remaining electrons are more strongly attracted to the nucleus.

What does a large jump in successive ionization energies indicate?

All valence electrons have been removed, and the next electron comes from an inner shell.

How many valence electrons does Na have?

One, the huge jump occurs between IE1 and IE2.

How many valence electrons does Mg have?

two, the huge jump occurs between IE2 and IE3.

Why is the jump from IE4 to IE5 in Si so large?

Si has four valence electrons. After removing four electrons, the fifth electron comes from an inner shell much closer to the nucleus.