Chemistry Revision Essay Example

due to an increase in effective nuclear charge. Elements within the same group share similar chemical properties due to having the same number of outer electrons, with elements arranged on the periodic table according to their atomic number. Mendel arranged elements in increasing order of relative atomic mass, placing elements with similar chemical properties in the same group and reversing the order of some elements if they fit better in another group. He left gaps for undiscovered elements, adding noble gases which were not present in his table. The Atomic Spectra exhibits an Atomic absorption spectrum with black lines on a colored background, and an Atomic emission spectrum with colored lines on a black background, which results from heating in a flame or using an electrical discharge tube.When black lines occur on an absorption spectrum, colored lines appear in corresponding locations. Line emission spectra are peculiar to specific elements since electrons become energized by absorbing energy, transit to higher energy levels, and then return to lower energy levels by giving off visible light radiation. The subsequent lines generated from this process have particular frequencies that correspond to delta E = HP. Distinct energy levels are present in different elements, and electrons are in discrete quantized energy levels. Nomination energy is the energy required for one mole of atoms in the gaseous phase to lose one mole of electrons and form one mole of atoms. Group 1 metals naturally lose electrons more readily, resulting in a low nomination energy. This energy decreases down group 1. Noble gases have a high nomination energy since they do not want to lose electrons. A dative bond is a covalent

bond where both electrons participating in bonding originate from the same atom- for example, carbon monoxide. Electronegativity is the tendency of an atom in a molecule to attract electrons towards itself. It increases towards the right of the period due to an increase in effective nuclear charge, and up a group due to smaller atoms with less shielding. Hence, this leads to polarized molecules. Ionic compounds have high melting points, conduct electricity when molten or in solution, as well as being soluble in water. Metallic bonding is on the left of the periodic table, covalent on the right, giant metallic structure on the left, giant covalent network in the middle, and simple molecular on the right side.Metal ions in a lattice lose their outer electrons to form positively charged ions that are evenly spaced. The remaining electrons create a sea of electrons that move randomly throughout the lattice. These negatively charged electrons create electrostatic attractions with the positively charged ions, which form the metallic bonds. Anions with a -1 charge become more soluble as you move down the group, while those with a -2 charge become less soluble. As you move down a group, the thermal stability of reactions with reprobates increases, making it less likely for them to break down into metal oxide and carbon dioxide.

The time it takes for a substance to go cloudy increases as you move down the group, and the number of moles present can be calculated using actual mass and relative formula mass. Mass spectroscopy is used to determine the atomic or molecular mass of particles in a sample and identify the mass and relative abundance of different isotopes.

It also investigates the structure of molecular compounds. Accelerated noise is used to provide particles with the same kinetic energy in the drift region, where heavier ions travel more slowly. Fragmentation occurs when tetrahedral structures with 4 electron density regions experience electron pairs pushing each other away to minimize repulsion.

The structure of water is a bent molecule. Linear and planar molecules have 1800, two regions of electron density, and three regions of electron density, respectively. The empirical formula represents the simplest ratio of atoms, while the molecular formula represents the actual ratio of atoms. Structural formulas display all the atoms and bonds, while skeletal formulas only display the structure as a series of lines and not any symbols. A homologous series refers to a group to which a compound belongs, such as alkaline or acidic. Standard conditions for a solution are at 298 Kelvin, 1 ATM, and 1 mold-3.

Enthalpy of formation is the enthalpy change that occurs when one mole of a compound forms from its elements. Enthalpy of combustion represents the enthalpy change that occurs when one mole of a substance burns completely in oxygen. Enthalpy of reaction is the enthalpy change when bowls of quantities of reactants react together under standard conditions. According to Hess' Law, the enthalpy change is independent of the route by which the reaction takes place provided the conditions remain constant. Bond enthalpies are average values taken in the gaseous state.

The octane number of a fuel refers to its propensity to auto-ignite. Higher octane numbers can be achieved through the use of branched chains, while shorter chains lead to a higher octane number. Additionally, rings,

such as those associated with cleanliness or arenas, can also result in a higher octane number. Higher ratings lead to improved engine efficiency and prevent damage. On the other hand, low octane ratings are appropriate for use in high-compression engines. It is important to carefully blend petrol to ensure the correct octane rating. In winter, it is necessary to be mindful of the low boiling point of front-end components, which easily ignite. Conversely, higher boiling points during the summer months can cause petrol to vaporize and escape on a hot day. Commiseration is the process of producing branch chains, while cracking converts large hydrocarbons into smaller alkaline and alkiness molecules. Reforming involves the formation of rings, including those that promote cleanliness and arenas and sometimes produce hydrogen gas. Knowledge of catalysts used is critical. Oxygenates are added to reduce carbon monoxide emissions and increase octane ratings. Nitrogen monoxide is produced in the engine and results from the reaction of nitrogen from the air with oxygen at high temperatures. High temperatures are required to break the triple nitrogen-nitrogen bond. Nitrogen monoxide dissolves in water and creates an acidic solution leading to acid rain and ozone formation as well as photochemical smog. However, passing NO over the catalytic converter results in conversion into nitrogen gas instead. Carbon monoxide is produced through incomplete combustion and can be toxic, leading to smog and soot formation during burning with yellow flames being more prominent than usual.Unborn hydrocarbons, which can contribute to the production of smog and act as greenhouse gases, pose a problem. Lead is toxic and carbon dioxide is a greenhouse gas, while sulfur dioxide contributes to acid rain.

The catalytic converter is a device that converts carbon monoxide into carbon dioxide and nitrogen monoxide into nitrogen gas. "clean burning fuels" are used in most of California and produce little to no CO. Structural isomers are molecules with the same molecular formula but a different arrangement of atoms. Isolates have holes and act as molecular sieves, separating branch chain isomers from straight-chain isomers by trapping the branched isomers and allowing straight-chain isomers to pass through. Entropy refers to the amount of disorder in a system, with solids having low entropy and gases having high entropy. The entropy change is positive when going from a solid to liquid or producing more molecules. It's favorable for substances to mix if it leads to an increase in entropy.