Atomic Structure, Electron Configuration, and Chemical Properties
Bohr’s Atomic Model
Bohr’s model for the hydrogen atom aimed to explain its electronic structure and justify its atomic spectrum. It was based on three main postulates:
- The electron revolves around the nucleus in specific circular orbits of fixed energy.
- Only orbits where electrons possess specific, quantized energy values are allowed. These orbits are called energy levels.
- When an electron transitions from a higher energy level to a lower one, the energy difference is emitted as light (a photon).
Electron
Read MorePeriodic Table: Element Classification, Trends, and Group Properties
Periodic Table Structure and Properties
The Periodic Table is a method of classifying elements. They are arranged in order of increasing atomic number. The columns are called groups. The rows are called periods. Metals are generally found to the left and non-metals to the right. Elements in the same group typically have similar chemical properties. For a specific main group, the group number indicates the number of valence electrons, and the period number indicates the number of electron shells occupied
Read MoreEssential Dental Materials: Properties and Clinical Uses
Dental Materials for Tooth Reconstruction
Materials for rebuilding teeth must be durable (not prone to breaking quickly), resistant to mastication, and aesthetically pleasing, resembling natural teeth.
Pulp Protection and Fillings
Pulp Protective Materials:
- Fluid composites
- Glass ionomer cements
- Calcium hydroxide liners
Types of Fillings:
- Composite Fillings: Made from resin-based materials.
- Amalgam Fillings: Historically used, containing mercury and silver. Often supplied in pre-dosed capsules for mixing.
Types of Chemical Bonds Explained
In chemistry, atoms are held together by chemical bonds. The type of bond formed dictates many of the substance’s properties. Three primary types of chemical bonds are covalent, metallic, and ionic.
Covalent Bonds
In a covalent bond, two bonded atoms share electrons. When the atoms joined by a covalent bond are the same (e.g., N₂, O₂), neither atom attracts the shared electrons more strongly than the other. This is called a nonpolar covalent bond or simply nonpolar.
If the atoms of the covalent
Read MoreKey Metallurgy Definitions
Some significant transformations are induced in steels, such as annealing, generally performed to achieve a smaller grain size and, consequently, improve metal properties.
Anisotropy
Anisotropy is the property of a material according to which certain physical properties, such as elasticity, thermal conductivity, velocity of propagation, and light, vary depending on the direction in which they are examined.
Alloy
An alloy is a system consisting of several elements, of which at least one is a metal, retaining
Read MoreCore Chemistry Concepts: Matter, Atoms, and Reactions
States of Aggregation
Matter exists in different states based on the intensity of forces between particles:
- Solid: Forces of attraction are very intense. Solids are rigid, cannot flow, maintain their own shape and volume, and are incompressible.
- Liquid: Forces are less intense than in the solid state. Liquids can flow, do not have their own shape (taking the shape of the container), maintain their own volume, and are nearly incompressible (often treated as incompressible, though slight compressibility