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Chemistry Defs

TermDefinition
Compound is a substance that is made up of 2 or more elements chemically combined
Molecule a group of atoms joined together and is the smallest part of an element that can exist independently
Electronegativity The relative force of attraction an atom has over a shared pair of electrons in a covalent bond
Ionic bond The force of attraction between oppositely charged ions in a compound
Ion a charged atom or group of atoms
Electronegativity difference <.4 non polar POLAR >1.7 ionic
Valency the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
Aliphatic Compound is an organic compound that consists of open chains of carbon atoms and closed chain compounds that resemble them in chemical properties
Octet Rule states that when bonding occurs, atoms will try to reach an electron arrangement with 8 in its outer shell
Octane Number measure of the tendency of a fuel to resist knocking
Catalytic Cracking taking a long chain hydro-carbon molecule and breaking it into short chain compounds for which there is a greater demand
Homogulous Series a series of compounds with uniform chemical type, showing gradation in physical properties, differing from the last by a CH2 unit, having a similar method of preparation having a general formula.
An aromatic compound compounds that contain a benzene ring
Mass number the sum of the number of protons and neutrons in he nucleus of an atom.
Isotopes atoms of the same element that have different mass numbers due to different numbers of nuetrons in the nucleus.
Relative atomic mass average of the mass numbers of all the isotopes of an element, as they occur naturally, taking their abundancies into account, and expressed on a scale in which the carbon-12 isotope has a mass of exactly 12 units.
The Afbau Principle When building up the electronic configuration of an atom in its ground state, the electrons must occupy the lowest possible available energy level.
Hunds Rule of Maximum Muplicity states that when 2 or more orbitals of equal energy are available, the electrons will occupy them singly before filling them in pairs.
The Pauli Exclusion Principle states that no more than 2 electrons may occupy an orbital and they must have opposite spin.
Newlands Octaves groups of elements arranges in order of increasing atomic weight where the first and eighth element of each group have similar properties
Mendeleevs Periodic Law when elements are arranges in order of increasing atomic weight, the properties vary periodically
The atomic number the number of protons in the nucleus of the atom
The modern periodic table arrangement of elements in order of increasing atomic number
An energy level fixed energy value that an electron in an atom may have
E=hf Energy = planks constant x frequency of light
orbital region of space in which there is a high probability of finding an electron
An element a substance that cannot be split into simpler substances by chemical means
A triad a group of 3 elements in which the middle element's atomic weight is approximately equal to the average of the other two.
Bond energy the energy required to break one mole of covalent bonds and to separate the nuetral atoms completley from each other
Heat of neutralisation the heat change when one mole of H+ ions from an acid reacts with 1 mole of OH- ions from a base
A transition metal forms at least one ion with a partially filled d-sublevel
Van der Waals forces weak attractive forces between molecules resulting from the formation of temporary dipoles.
Dipole-dipole forces of attraction between negative pole of one molecule and the positive pole of the other
Hydrogen Bonding type of dipole dipole force that occurs when hydrogen bonds with nitrogen, oxygen and fluorine. The partial positive pole of the hydrogen is attracted to the electronegative atom in another molecule. It acts as a bridge between electro-negative atoms.
Heat of reaction heat change when the numbers of moles of reactants, as indicated in the balanced equation for the reaction react together completely
Heat of combustion heat change when one mole of the substance in completley burned in excess oxygen
The kilogram calorific value the heat energy produced when 1 kg of the substance is completley burned in oxygen.
Radioactivity the spontaneous breaking up of nuclei with the emmission of one or more types of radiation
When an atom loses an alpha particle it changes into an atom of an element two places before it in the periodic table. The mass number decreases by 4.
When an atom loses a beta particle it changes into an atom of an element one place after it on the periodic table. The mass number stays the same
The half life of an element the time taken for half the nuclei in any given sample to decay
The atomic radius covalent radius is defined as half the distance between two nuclei of the same element bonded together by a single covalent bond
The values of atom radius increase down any group...new shell and screening effect of inner electrons
The values of of atomic radius decrease left to right along a period due to increasing nuclear charge and no screening effect.
The first ionisation energy energy required to remove the most loosely bound electron from a nuetral gaseous substance.
The value of electronegativity decrease down the groups: increasing atomic radius and screening effect of inner electrons increase along the periods: increasing nuclear charge and decreasing atomic radius
Chemical Equilibrium a state of dynamic balance whereby the rate of forward reaction is equal to the rate of the backward reaction
If a stress is applied to a system at equilibrium... the system readjusts to relieve the stress applied
Le Chateliers principle predicts that in an all gaseous reaction an increase in pressure will favour the reaction which takes place with a reduction in volume. i.e.. toward the side with the smaller amount of molecules.
An element is a substance that cannot be split up into simpler substances by chemical means.
A triad is a group of 3 elements with similar chemical properties which the atomic weight of the middle element is approx equal to the average of the other two.
Newland's Octaves group of elements arranged in order of increasing atomic weight where the first and eighth element of each group have similar properties
Atomic number number of protons in the nucleus
Mass number sum of the protons and nuetrons in the nucleus
Isotopes atoms o the same element that have different mass numbers due to differing numbers of nuetrons in the nuecleus.
Relative Atomic Mass average of all the mass numbers of the isotopes of that element, as they occur naturally, taking their abundancies into account and expressed on a scale in which the atoms of the carbon 12 isotope has a mass of exactly 12 units.
Created by: Sibeal