Chapter Two: Matter (Applied Health Science Technology - Fall 2024) PDF

Chapter Two Matter For Applied Health Science Technology Students Fall 2024  Biomaterial classification 1. According to nature of materials It can be classified to A- Metals: e.g. amalgam and metallic denture base B- Polymers: e.g. acryl...

Chapter Two Matter For Applied Health Science Technology Students Fall 2024  Biomaterial classification 1. According to nature of materials It can be classified to A- Metals: e.g. amalgam and metallic denture base B- Polymers: e.g. acrylic resin ‫الراتنجات أو املواد الصمغية‬ C- Ceramics: e.g. dental porcelain 2. Properties of materials: can be classified according to A. Microscopic properties I. Atomic structure II. Crystal structure B. Macroscopic properties. I. Physical properties: based on the laws of physics that describe mass, energy, force, heat, electricity, color, density, thermal conductivity. II. Mechanical properties: considered a subgroup of physical properties Which describe the material’s ability to resist forces. III. Chemical properties: describe setting reactions as well as corrosion of materials. IV. Biological properties: describe the effect of the material on living tissues. A chemical bond is an attraction between atoms brought about by a sharing of electrons between atoms or a complete transfer of electrons. Types of Atomic Bonding Primary Secondary bonds bonds Covalent Metallic Hydrogen van der Ionic bond bond bond bond Waal forces I - Primary bonds 1. Ionic Bond In ionic bonding, electrons are completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond. For example, during the reaction of sodium with chlorine: Resulting in A positively charged sodium ion (left) Sodium (on the left) loses its one and a negatively Valence electron to chlorine (on the right) charged chlorine ion (right). Ionic compounds share many features in common: Ionic bonds form between metals and nonmetals. Ionic compounds dissolve easily in water and other polar solvents. In solution, ionic compounds easily conduct electricity. Ionic compounds tend to form crystalline solids at high melting temperatures. In dentistry ionic bond is found in gypsum investment, phosphate cement and ceramic. 2. Covalent bond consists of a pair of electrons shared between two atoms. Hydrogen gas forms the simplest covalent bond in the diatomic hydrogen molecule. It can classified to two types Polar and nonpolar covalent bonding  A polar bond is formed when electrons are unequally shared between two atoms. Polar covalent bonding occurs because one atom has a stronger affinity for electrons than the other. In a polar covalent bond, the bonding electrons will spend a greater amount of time around the atom that has the stronger affinity for electrons. Both atoms in the H2 molecule have an equal attraction (or affinity) for electrons, the bonding electrons are equally shared by the two atoms and a nonpolar covalent bond is formed.  In dentistry: monomer molecules of dental resin are held by covalent bonds within the polymer chain. shared electrons H from carbon atom CH 4 H C H shared electrons H from hydrogen atoms  3. Metallic bond In metals, the metal atoms lose their outer electrons to form metal cations. These electrons are often described as delocalised electrons; delocalised means "not fixed in one place" or "free to move". This is shown in the diagram below. Where (-) are electrons, (+) metal ions. As the metal cations and the electrons are oppositely charged, they will be attracted to each other, and also to other metal cations. These electrostatic forces are called metallic bond, and these are what hold the particles together in metals. +……e-……. + e- : delocalised electrons Electrostatic forces of attraction +: metal cation  A metal may be described as a cloud of free electrons. II. Secondary bonds 1. Hydrogen bond: A hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge. Examples of hydrogen bond donating (donors) and hydrogen bond accepting groups (acceptors) 2. van der Waal bond  The dipoles can be formed as a result of unbalanced distribution of electrons in asymettrical molecules.  Example: attraction of gases by liquid alloys is by van der waal bond.  Properties of Some Representative Elements The periodic table rearranged by Mosley. He arranged the elements by increasing atomic number. 1- Group IA (Alkali Metal Group): The metals in Group IA (Li, Na, K, Rb, Cs, and Fr) are called alkali metals because they all form hydroxides (such as NaOH) that were once known as alkalies. And they have: 1- They are all soft metals, easily cut with a knife. 2- They all contain one valence electron which is given up easily in a chemical compound. 3- They are all soluble in water. 4- They are very reactive with oxygen forming oxides. 5- They are very reactive with water forming hydroxides. 6- They are so reactive to oxygen and water that they do not occur in nature in their pure state and must be stored under some inert liquid to keep them from reacting. 7- Their reactivity increases as you go down the group because their size increases making it easier for an electron to be removed. 2- Group IIA or Alkaline Earth Metals Group The elements in Group IIA (Be, Mg, Ca, Sr, Ba and Ra) are all metals. These elements are often called the alkaline-earth metals. The term alkaline reflects the fact that many compounds of these metals are basic or alkaline. The term earth was historically used to describe the fact that many of these compounds are insoluble in water. The characteristics that alkaline earth metals share are: 1. They are not as soft as the Group IA metals. 2. They all contain two valence electrons. 3. They are too reactive to occur in nature in their pure state, but NOT as reactive as alkali metals. 4. They react more mildly with oxygen to produce oxides of metals and will only react with water at temperatures where the water is steam. 5. Their reactivity increases as you go down the column due to the increase in size and ease that electrons can be removed.  3- Group VIA - the Oxygen Family This group contains two common elements, oxygen and sulfur. Their configuration shown in the table below, Oxygen exists in two forms: O2 the most stable form and O3 ozone. Sulfur exists in many forms at different temperatures. Chalcogens contains 2 non-metals (oxygen and sulfur), 2 semiconductors (selenium and tellurium) and one radioactive metal (polonium). Element Symbol Electronic configuration Usual oxidation state Oxygen O [He]2s22p4 -2 Sulfur S [Ne]3s23p4 +6, +4, -2