Notes, summaries, assignments, exams, and problems for Chemistry

Chemical Bonding in Dental Materials

Primary Bonds

Factors Influencing Material Properties:

1. Type of bond between atoms and molecules
2. Inter-atomic distance
3. Atomic packing

Matter: Any substance that has mass and occupies space.

Atom: The fundamental unit of matter, consisting of a central nucleus (protons and neutrons) surrounded by electrons.

Types of Primary Bonds:

• Ionic Bond: Attraction between positive and negative ions. Characteristics: Strong, heat resistant, insulator, insoluble in organic solvents, basic bond in ceramics.
• Covalent Bond: Sharing of electrons between two atoms. Characteristics: Strong, insulator, water insoluble, basic bond in polymers.
• Metallic Bond: Attraction between positive atomic cores and free electrons. Characteristics: High

Electrical Conductivity in Solids

Metal atoms possess outer electrons that are not tied to any single atom. These free electrons can move freely within the metal's structure when an electric current is applied, making metals excellent conductors. In contrast, covalent or ionic solids lack such free electrons, preventing electron flow and making them non-conductors.

Electron Configuration Principles

Filling Electron Shells and Orbitals

To determine electron configuration, first fill all lower electron shells. Then, apply specific rules to place valence electrons into their proper shells. Hund's Rule is crucial: it states that electrons will singly occupy all orbitals within a subshell before any orbital is doubly occupied. The Pauli Exclusion Principle... Continue reading "Atomic Structure, Bonding, and Molecular Shapes Explained" »

Basic Definitions of Matter

• Mass: The amount of matter an object has.
• Volume: The amount of space a substance occupies.
• Density: The relation of the amount of mass in a given volume.
• Matter: Anything that has mass and volume.
• Inertia: The tendency of an object to resist a change in motion.
• Weight: The action of gravitational force on an object.

Units of Measurement

• Newtons (N): A unit of force.
• 1 N = 100 g
• 1 kg = 1000 g

Properties of Matter

Chemical Properties

• A material's property that becomes evident during or after a chemical reaction.
• Examples: Flammability, reaction with O₂ (oxygen).

Physical Properties

• Observed or measured without changing the composition of matter.
• Examples: State, density, solubility, malleability, shape.

Changes in Matter

Chemical

Classification of Crystalline Solids

In crystalline solids, the atoms, ions, or molecules are held together by various types of cohesive forces, which may be chemical bonds or intermolecular forces. Based on the nature of bonding between their constituent particles, crystalline solids are classified into distinct types.

Ionic Crystals

Ionic crystals are formed by the interaction of positive and negative ions. These ions are held together by strong electrostatic forces of attraction, also known as ionic bonds. Examples include NaCl, KNO₃, Na₂CO₃, and K₂Cr₂O₇.

Properties of Ionic Crystals

• They occur in the solid state at room temperature.
• They have a distinct geometrical shape due to the close packing of cations and anions.
• They are very hard.
• They are

Understanding Metallic Bonds

A metallic bond is a type of chemical bond where the electrostatic attraction between positive metal ions (kernels) and delocalized electrons holds the metal ions in their respective positions. In metal atoms, the valence electrons are loosely bound and are free to move from one atom to another within the metallic crystal lattice. These free electrons, also known as conduction electrons or delocalized electrons, are uniformly distributed throughout the metal lattice.

When metal atoms lose these conduction electrons, they become positive ions, or kernels (atoms without their valence electrons). The electrostatic (or coulombic) interaction that develops between these positive kernels and the sea of negative electrons... Continue reading "Metallic Bonds and Molecular Crystals: Properties & Types" »

Essential Laws and Principles in Science

Avogadro's Law

Equal volumes of gases under identical temperature and pressure conditions will contain equal numbers of particles (atoms, ions, molecules, electrons, etc.).

Boyle's Law

At constant temperature, the volume of a confined gas is inversely proportional to the pressure to which it is subjected.

PV = k

Charles' Law

At constant pressure, the volume of a confined gas is directly proportional to the absolute temperature.

V = kT

Combining Volumes

Refer to Gay-Lussac's Law.

Conservation of Energy

Energy can be neither created nor destroyed; the energy of the universe is constant. This is the First Law of Thermodynamics.

Conservation of Mass

Also known as Conservation of Matter. Matter can be neither created nor... Continue reading "Fundamental Laws of Chemistry and Physics Explained" »

Temperature Conversions

• Celsius to Fahrenheit: F = (9/5) * C + 32
• Celsius to Kelvin: K = C + 273

Atomic Structure

• Atomic Mass: Protons + Neutrons (upper left symbol)
• Atomic Number: Protons (bottom left symbol)

Quantum Mechanics

• Planck's Constant (h): 6.6260755 x 10^-34 J*s
• Energy of a Photon: E = hv or E = hc / wavelength

Electronic Transitions

• Absorption: When energy is absorbed by an atom, an electron is excited to a higher energy level or orbital.
• Emission: When an electron relaxes from a higher energy orbital to a lower one, it emits a photon.

Filling Orbitals

s = 2, p = 6, d = 10, f = 14

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f

Periodic Trends

• Atomic Radius: Increases down a group and decreases across a row.
• Ionization Energy: Amount of energy

Galvanic Reaction in the Mouth

Biting on aluminum foil can be painful and is usually noticed if you have metal in your mouth from dental work (e.g., fillings, crowns). Basically, when you bite on foil, you set up a battery in your mouth, and the electrical current stimulates nerve endings in your tooth. Here is what happens:

• Pressure from biting brings two dissimilar metals (aluminum foil, mercury in fillings, or gold in crowns) in contact in a moist, salty environment (saliva).
• The two metals have an **electrochemical potential difference** or voltage across them.
• Electrons flow from the foil into the tooth (i.e., **electrical current**).
• The current gets conducted into the tooth's root, usually by the filling or crown.
• The current sets off a nerve

The pH Scale and Acidity Measurement

The pH scale is a system that measures the acidity of a substance. It is ranked from 1 to 14, with 1 being the most acidic and 14 being the most alkaline; 7 is neutral. The pH represents the concentration of hydrogen ions (H+) in a substance and is measured using the pH scale.

Buffers: Maintaining pH Balance

Buffers are substances that tend to maintain a constant pH by liberating or capturing H+ ions. If blood becomes too acidic, bicarbonate accepts H+ ions, and carbonic acid is formed. If it becomes too basic, carbonic acid liberates H+ ions to interact with OH- ions to form water.

Major Classes of Biomolecules

Biomolecules are any molecules produced by a living organism. The four main groups are:

• Nucleic Acids
• Proteins
• Carbohydrates
• Lipids

Examples