protons as electrons‚ so it is neutral in charge. It is a single particle of a chemical event. When an atom gains or loses an electron it becomes an ion. Ions are charged‚ while atoms are uncharged. An ion has either a positive or negative charge because there are unequal numbers of electrons and protons. A positive ion is called a cation‚ while a negative ion is called an anion. 3. Define electronegativity and explain what it has to do with the behavior of outer-shell electrons.
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Chp. 4 Biology Study Guide Page 1 8/30/2011 BIOLOGY STUDY GUIDE CHAPTER 4– THE CHEMICAL BASIS OF LIFE Matter = anything that takes up space and has mass (major types of matter = solid‚ liquid‚ and gas) Any type of matter is made of one or more elements. o Element = a substance that cannot be broken down into other substances by regular chemical processes. (examples: gold‚ silver‚ mercury‚ etc.) There are approximately 25 elements necessary for life. • Examples: oxygen‚ carbon‚ hydrogen‚
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This molecular orbital model can be used to explain why He2 molecules don’t exist. Combining a pair of helium atoms with 1s2 electron configurations would produce a molecule with a pair of electrons in both the bonding and the * antibonding molecular orbitals. The total energy of an He2 molecule would be essentially the same as the energy of a pair of isolated helium atoms‚ and there would be nothing to hold the helium atoms together to form a molecule. The fact that an He2 molecule is neither
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However in covalent bonds the nuclei are positive and the electrons which are being shared are negative. The intermolecular forces in hydrogen chloride are Dipole-Dipole forces: The slightly negative end of another hydrogen chloride particle will become attracted to the other end of the particle which has a slight positive charge. Therefore the two dipoles will become drawn together because the electrons are not shared between the two particles of hydrogen chloride. Dipole-Dipole
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WITH MATTER 1 SCATTERING of E.M. RADIATION Type of scattering depends on the e.m. energy‚ ~! wrt the electron energy: Ionization energy EI Rest-mass energy me c2 2 CLASSICAL MODEL E.M. wave interacting with an oscillating electron Frequency of oscillation is given by Coulomb energy: !02 = kC /me e.m. field adds a driving force at e.m. frequency !‚ F = Radiated power is related to the electron acceleration‚ a 2 ✓ ◆2 !4 2 cE (!02 ! 2 )2 0 cE02 = P/I0 ‚ I0 = The cross-section is then 8⇡ ✓ 2 ◆2
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Lab 6: Electrophilic Aromatic Substitution(1) Nitration of Methyl Benzoate(2) Synthesis of 1‚4-Di-t-butyl-2‚5-dimethoxybenzene byFriedel-Crafts Alkylation of 1‚4-DimethoxybenzenePurpose1)To carry out the nitration of methyl benzoate‚ and then identify the major product formed (position at which nitro-group substitution takes place) by thin-layer chromatography (TLC)‚ the percent yield and the melting point range. 2)To synthesize 1‚4-Di-t-butyl-2‚5-dimethoxybenzene by Friedel-Crafts Alkylation of
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The VSEPR Model 10.33 Predict the shape or geometry of the following mole- cules‚ using the VSEPR model. a. SiF4 b. SF2 c. COF2 d. PCl3 10.34 Use the electron-pair repulsion model to predict the geometry of the following molecules: a. GeCl2 b. NF3 c. SCl2 d. XeO4 10.35 Predict the geometry of the following ions‚ using the electron-pair repulsion model. a. ClO3? b. PO43? c. SCN? d. H3O? 10.36 Use the VSEPR model to predict the geometry of the fol- lowing ions: a. N3? b. BH4? c. SO32? d. NO2
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Element name-Helium Element Symbol-He Atomic number-2 Group name or number- Part of the noble gases in group 18 Atomic mass (to nearest thousandth)-4.003 Number of protons-2 Number of neutrons-2 Number of electrons-2 Number of valence electrons-2 List of isotopes-He3 and He4 Electron Configuration-1s2 Discovered By-Pierre Janssen Year discovered-1868 Circumstances of discovery- Janssen discovered helium in 1868 when he was looking in a telescope when he found the yellow spectrum lines of helium
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encounter resistance to their flow which means that they collide with atoms in the conductor. More resistance means that more energy is needed to push the same number of electrons through part of the circuit. So by increasing the voltage more electrons will flow through the circuit‚ which means there would be a lot more electrons flowing in the circuit therefore there will be a lot more energy being produced. This means that the more voltage flowing through the circuit the faster the reaction will
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based on total external reflectivity. Using this method we can calculate the thickness of the film electron density profile of the material and roughness of the film surface. After a short introduction of Fresnel’s reflectivity‚ the Parratt formulation is used for the calculation reflectivity for a stratified film. Then after discussing the experimental technique‚ we have calculated the thickness‚ electron density and roughness from the experimental curve. CONTENTS Introduction---------------
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