DH essays

DH essays The Debate Between Bilingual Education and English Immersion Programs Bilingual Education is defined as any school program that uses two languages. In a more theoretical sense it is any educational program whose ultimate goal is for the participants to be fully versed in all facets of both languages (i.e., able to listen, speak , read, and write in both languages). The definition of a coordinated, developmental bilingual approach has emphasized the goal of being equally fluid in both languages. Realistically, this has not been the goal for most K-12 bilingual schools in the United States. More commonly in the United States we are using the words bilingual program to describe a program that will provide literacy and content in the primary language, while building English fluency, to the point where all instruction will occur in English. These programs are label transitional bilingual programs as their ultimate goal is to transition all students into an English only learning arena. One of the down sides of these programs is that they are not maintenance (development)bilingual programs which are designed to preserve and develop students primary language while they acquire English as a second language. Bilingual Program Models All bilingual program models use the students' home language, in addition to English, for instruction. These programs are most easily implemented in districts with a large number of students from the same language background. Students in bilingual programs are grouped according to their first language, and teachers must be proficient in both English and the students' home language. Early-exit bilingual programs are designed to help children acquire the English skills required to succeed in an English-only mainstream classroom. These programs provide some initial instruction in the students' first language, primarily for the introduction of reading, but also for clarification. Instruction in the f...

Molecular Geometry Definition in Chemistry

Molecular Geometry Definition in Chemistry In chemistry, molecular geometry describes the three-dimensional shape of a molecule and the relative position of the atomic nuclei of a molecule. Understanding the molecular geometry of a molecule is important because the spatial relationship between atom determines its reactivity, color, biological activity, state of matter, polarity, and other properties. Key Takeaways: Molecular Geometry Molecular geometry is the three-dimensional arrangement of the atoms and chemical bonds in a molecule.The shape of a molecule affects its chemical and physical properties, including its color, reactivity, and biological activity.The bond angles between adjacent bonds may be used to describe a molecules overall shape. Molecule Shapes Molecular geometry may be described according to the bond angles formed between two adjacent bonds. Common shapes of simple molecules include: Linear: Linear molecules have the shape of a straight line. The bond angles in the molecule are 180Â °. Carbon dioxide (CO2) and nitric oxide (NO) are linear. Angular: Angular, bent, or v-shaped molecules contain bond angles less than 180Â °. A good example is water (H2O). Trigonal Planar: Trigonal planar molecules form a roughly triangular shape in one plane. The bond angles are 120Â °. An example is boron trifluoride (BF3). Tetrahedral: A tetrahedral shape is a four-faced solid shape. This shape occurs when one central atoms has four bonds. The bond angles are 109.47Â °. An example of a molecule with a tetrahedral shape is methane (CH4). Octahedral: An octahedral shape has eight faces and bond angles of 90Â °. An example of an octahedral molecule is sulfur hexafluoride (SF6). Trigonal Pyramidal: This molecule shape resembles a pyramid with a triangular base. While linear and trigonal shapes are planar, the trigonal pyramidal shape is three-dimensional. An example molecule is ammonia (NH3). Methods of Representing Molecular Geometry Its usually not practical to form three-dimensional models of molecules, particularly if they are large and complex. Most of the time, the geometry of molecules is represented in two dimensions, as on a drawing on a sheet of paper or a rotating model on a computer screen. Some common representations include: Line or stick model: In this type of model, only sticks or lines to represent chemical bonds are depicted. The colors of the ends of the sticks indicate the identity of the atoms, but individual atomic nuclei are not shown. Ball and stick model: This is common type of model in which atoms are shown as balls or spheres and chemical bonds are sticks or lines that connect the atoms. Often, the atoms are colored to indicate their identity. Electron density plot: Here, neither the atoms nor the bonds are indicated directly. The plot is a map of the probability of finding an electron. This type of representation outlines the shape of a molecule. Cartoon: Cartoons are used for large, complex molecules that may have multiple subunits, like proteins. These drawings show the location of alpha helices, beta sheets, and loops. Individual atoms and chemical bonds are not indicated. The backbone of the molecule is depicted as a ribbon. Isomers Two molecules may have the same chemical formula, but display different geometries. These molecules are isomers. Isomers may share common properties, but its common for them to have different melting and boiling points, different biological activities, and even different colors or odors. How Is Molecular Geometry Determined? The three-dimensional shape of a molecule may be predicted based on the types of chemical bonds it forms with neighboring atoms. Predictions are largely based on electronegativity differences between atoms and their oxidation states. Empirical verification of predictions comes from diffraction and spectroscopy. X-ray crystallography, electron diffraction, and neutron diffraction may be used to assess the electron density within a molecule and the distances between atomic nuclei. Raman, IR, and microwave spectroscopy offer data about the vibrational and rotational absorbance of chemical bonds. The molecular geometry of a molecule may change depending on its phase of matter because this affects the relationship between atoms in molecules and their relationship to other molecules. Similarly, the molecular geometry of a molecule in solution may be different from its shape as a gas or solid. Ideally, molecular geometry is assessed when a molecule is at a low temperature. Sources Chremos, Alexandros; Douglas, Jack F. (2015). When does a branched polymer become a particle?. J. Chem. Phys. 143: 111104. doi:10.1063/1.4931483Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th ed.). New York: Wiley-Interscience. ISBN 0-471-19957-5.McMurry, John E. (1992). Organic Chemistry (3rd ed.). Belmont: Wadsworth. ISBN 0-534-16218-5.