Notes, abstracts, papers, exams and problems of Chemistry

What is Surface Engineering?

Definition: It is the sub-discipline of material science which deals with the surface of solid matter.

Objectives: Involves altering the properties of the surface phase to reduce degradation over time, making it robust to the environment.

Applications: Automotive, aerospace, missile, power, electronic, biomedical, textile, petroleum, chemical, steel, power. Used in almost all types of materials.

Describe SEM and TEM

SEM: Scanning Electron Microscopy images the sample surface by scanning it with a high-energy beam of electrons. Advantages include 3D imaging and greater depth of focus. Disadvantages include low resolution and expensive equipment. Applications include gunshot residue analysis and firearms identification.... Continue reading "Surface Engineering and Microscopy Techniques in Material Science" »

Scientific models used to explain why and how atoms form molecules:

• Lewis dot structure
• Valence bond theory

Valence bond theory describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single electron) that yield a pair of electrons shared between the two bonded atoms. According to valence bond theory, a covalent bond results when two conditions are met: (1) an orbital on one atom overlaps an orbital on a second atom and (2) the single electrons in each orbital combine to form an electron pair.

• Molecular orbital theory

model that describes the behavior of electrons delocalized throughout a molecule in terms of the combination of atomic wave functions. It describes the distribution of electrons in molecules in much... Continue reading "Atomic Models, Periodic Trends, and Chemical Bonding" »

IONIC: thet are solids at room temperatures and have medium to high meltin and boiling points. Ionic bond is strong because it is electrostatic. They are very hard. It is not eassy to scratch an ionic compound. They are fragile. Hitting them forces ions with the same signs together, and they repel and break the crystal. Most disolve well in water, water molecules may surround the ions,weakening their bonds and separating them from the crystal lattice. This is called solvation. They do not conduct electricity well in solid state but hey do in solution or liquid state. SODIUM CHLORIDE

Paradigmatic (vertical) axis

The words organizations, groups, and Amnesty International are related to each other because they all belong to the same semantic group, a relationship known as hyponymy. Organizations serve as a hypernym (a more general or superordinate word), while human rights groups and Amnesty International serve as hyponyms (more specific words, in this case types of organizations). The other two kinds of paradigmatic relationships are those of synonymy (prompted = caused) and antonymy (weak/strong).

Syntagmatic (horizontal) axis
 Unlike the paradigmatic relationships, the syntagmatic relationships of a word are not about meaning. They are about the lexical company the word keeps (collocation) and the grammatical patterns