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chem definitions

Dalton's Atomic Theory 1. All matter is made up of very small particles called atoms. 2. All atoms are indivisible. They cannot be broken down into simpler particles. 3. Atoms cannot be created or destroyed.
Cathode Rays Streams of negatively charged particles called electrons.
Energy level the fixed energy value that an electron in an atom may have.
E=hf E - definite amount of energy emitted from atom. f - light of definite frequency or wavelength in emission spectrum.
Orbital A region in space within which there is a high probability of finding an electron.
Element A substance that cannot be split up into simpler substances by chemical means.
Triad A group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.
Newland's Octaves groups of elements arranged in order of increasing atomic weight, in which the first and eighth element of each group have similar properties.
Mendeleev's Periodic Law when elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically.
Atomic number the number of protons in the nucleus of that atom
Modern Periodic Table an arrangement of elements in order of increasing atomic number
Modern Periodic Law When elements are arranged in order of increasing atomic number, the properties of the elements vary periodically.
Mass Number The sum of the number of protons and neutrons in the nucleus of an atom of that element.
Isotopes atoms of the same element (ie. they have the same atomic number) that have different mass numbers due to the different number of neutrons in the nucleus.
Relative Atomic Mass 1. The average of the mass numbers of the isotopes of the element, 2. Ass they occur naturally, 3. Taking their abundances into account, 4. Expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units.
Hund's Rule of Maximum Multiplicity when two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs.
Pauli Exclusion Principle no more than two electrons may occupy an orbital and they must have opposite spin.
Compound A substance that is made up of two or more different elements chemically combined
The Octet Rule when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.
Ion a charged atom or group of atoms
Ionic Bond the force of attraction between oppositely charged ions in a compound.
Transition Metal One that forms at least one ion with a partially filled d sublevel.
Molecule a group of atoms joined together. It is the smallest particle of an element or compound that can exist independantly.
Valency the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines.
Electronegativity the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.
Electronegativity Difference >1.7 = ionic bonding <0.4 = non-polar covalent
Van der waals Forces weak attractive forces between molecules resulting from the formation of temporary dipoles
Dipole-Dipole forces forces of attraction between the negative pole of one molecule and the positive pole of another.
Hydrogen Bonds particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or flourine. The hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule.
hydrogen bonds contd.. Thus, it acts as a bridge between two electronegative atoms.
Homologous series 1. A series of compounds of uniform chemical type 2. showing gradation of physical properties. 3. having a general formula for its members. 4. each member having a similar method of preparation. 5. each member differing from the previous member by CH2
Structural isomers Compounds with the same molecular formula but different structural formulas.
Aliphatic compound organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) that resemble them in chemical properties.
Aromatic Compounds compounds that contain a benzene ring structure in their molecules.
octane number a measure of the tendency of the fuel to resist knocking
Catalytic cracking the breaking down of long-chain hydrocarbon molecules into short-chain molecules for which there is greater demand.
Whos Gay Sophie
Created by: sophielil



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