Understanding Atoms, Crystals, and Chemical Bonds

Atomic Structure Fundamentals

The atom is a structure with a core that is very small relative to the total size of the atom.

• Nucleus: Contains protons and neutrons.
• Electrons: Move at a distance from the nucleus that is very large compared to the size of the core.

Isotopes and Chemical Elements

Isotopes are atoms of the same chemical element that have the same number of protons but a different number of neutrons.

Bohr Model vs. Quantum Mechanical Model

The most important difference between these models is as follows:

• Bohr Model: Assumes electrons are in specific orbits at defined distances from the nucleus.
• Quantum Mechanical Model: Provides that electrons occupy positions with varying probabilities; their exact position cannot be predicted accurately.

Orbitals and Valence Electrons

• Orbital: The region of space where there is a high probability (90%) of finding an electron.
• Valence Electrons: Electrons in the outermost energy level responsible for the chemical behavior of the atom.
• Valence: The number of electrons needed for an element to complete its last energy level.

Chemical Bonding

Chemical bonds are the unions that hold atoms together due to electrical forces of attraction. The nature of these forces varies depending on the atoms involved.

Crystalline Structures

A crystal exists when the particles that make up matter have a perfectly ordered structure extending in all three dimensions.

Types of Crystals

• Ionic Crystals: Formed by ions. They are ordered so that each ion is surrounded by the greatest possible number of ions of the opposite sign. Ionic compounds do not form molecules; their formulas indicate the proportion of atoms. They typically have high melting and boiling points.
• Covalent Crystals: Formed by atoms linked by covalent bonds (e.g., diamond and graphite). These are generally very hard, have high melting and boiling points, and do not conduct electric current.
• Metallic Crystals: Formed by metal cations immersed in a sea of free valence electrons. Metals have a characteristic luster, are good conductors of electricity and heat, and are malleable and ductile.