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20 Cards in this Set

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neutron
A subatomic particle that has a mass approximately equal to that of the hydrogen atom, carries zero electric charge, and is located in the nucleus of an atom.
proton
A subatomic particle that has a mass approximately equal to that of the hydrogen atom, carries an electric charge of +1, and is located in the nucleus of the an atom.
Dalton's atomic theory
The theory of matter fomulated by John Dalton: (1) All matter is made of atoms; (2) atoms can neither be created of destroyed; (3) all atoms of a given element are identical; (4) atoms of different elements are different from one another; (5) all chemical reactions involve the combining or separating of atoms in the reactant compounds.
law of definite proportions
A statement of the fact that the amounts of the elements in a compound are determined by the identity of the compound.
law of Mendeleev
Another name for chemical periodicity. See also law of octaves.
law of octaves
The pattern discovered by Medeleev in which each element in his version of the periodic table has properties similar to those of the elements eight positions to the left and eight positions to the right.
nucleus
The tiny, positively charged core of an atom, made up of protons plus neutrons (except in the case of the hydrogen nucleus, which contains no neutons). The electric charge of the nucleus binds the electrons to the atom, and the number of protons determines which element the atoms is.
alpha (special character "a") emission
A nuclear reaction in which a radioactive nucleus ejects an alpha particle (4/2He) and thereby becomes a daughter isotope containing two fewer protons and two fewer neutrons.
atomic number (Z)
The number of protons in the nucleus of an atom. All atoms of a particular element have the same atomic number, which is indicated by a subscript to the left of the element symbol.
chemical periodicity
The fact that, if you arrange the elements in order of increasing atomic number, elements spaced at periodic (regular) intervals have similar chemical properties. For the first 18 elements, an element's properties are similar to those of the elements 8 ahead of it and 8 behind it. Beyond element 18, the interval (periodicity) increases to 18 or 32 elements. This periodicity is the basis for the periodic table.
law of multiple proportions
A statement of the fact that, for two elements A and B capable of forming more than one compound with each other, a given amount of A yields compounds having the general chemical formula AxBx in which the ration is always a small whole number. This law provides compelling evidence for the existence of atoms.
periodic table
A table of the elements arranged in order of increasing atomic number. The elements are arranged in rows (periods) in such a way that all the elements in a given column (group) have similar chemical properties.
mass number
The number of protons plus neutrons in the nucleus of an atom.
isotopes
Different forms of an element having the same number of protons but different numbers of neutrons (and therefore different atomic weight).
atomic weight (mass)
a unitless number expressing the mass of a particular atom relative to the mass of an atom of carbon -12, which is arbitrarily assigned a mass of exactly 12.
law of conservation of matter
A statement of the fact that no matter is ever created or destroyed in any chemical reaction.
electron
A subatomic particle that has a mass 1/1836 that of a hydrogen atom, carries an electric charge of -1, and moves about at high velocity around the nucleus of an atom.
percent by mass (wt %)
A unit of concentration for solutions, used most frequently for solutions made up of a solid solute dissolved in a liquied solvent and defined as Grams of solute over Grams of solution times 100.
alpha (special character "a") particle
A helium nucleus (4/2He) ejected from some radioactive nuclei during a process known as alpha emission.
law of constant composition
Another name for law of definite proportions.