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ChemistrySC:Ch. 2

Atoms, Molecules, and Ions

actinide inner transition metal in the bottom of the bottom two rows of the periodic table
alkali metal element in group 1
alkaline earth metal element in group 2
alpha particle (α particle) positively charged particle consisting of two protons and two neutrons
anion negatively charged atom or molecule (contains more electrons than protons)
atomic mass average mass of atoms of an element, expressed in amu
atomic mass unit (amu) (also, unified atomic unit, u, or Dalton, Da) unit of mass equal to 1/12 of the mass of a C-12 atom
atomic number (Z) number of protons in the nucleus of an atom
binary acid compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)
binary compound compound containing two different elements
cation positively charged atom or molecule (contains fewer electrons than protons)
chalcogen element in group 16
chemical symbol one-, two., or three-letter abbreviation used to represent an element or its atoms
covalent bond attractive force between the nuclei of a molecule´s atoms and pairs of electrons between the atoms
covalent compound (also, molecular compound) composed of molecules formed by atoms of two or more different elements
Dalton (Da) alternative unit equivalent to the atomic mass unit
Dalton´s atomic theory set of postulates that established the fundamental properties of atoms
electron negatively charged, subatomic particle of relatively low mass located outside the nucleus
empirical formula formula showing the composition of a compound given as the simplest whole-number ratio of atoms
fundamental unit of charge (also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 x 10 to the -9 C
group vertical column of the periodic table
halogen element in group 17
inert gas (also, noble gas) element in group 18
inner transition metal (also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide
ion electrically charged atom or molecule (contains unequal numbers of protons and electrons)
ionic bond electrostatic forces of attraction between the oppositely charged ions of an ionic compound
ionic compound compound composed of cations and anions combined in ratios, yielding an electrically neutral substance
isomers compounds with the same chemical formula but different structures
isotopes atoms that contain the same number of protons but different numbers of neutrons
lanthanide inner transition metal in the top of the bottom two rows of the periodic table
law of constant composition (also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
law of definite proportions also, law of constant composition) all samples of a pure substance compound contain the same elements in the same proportions
law of multiple proportions when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers
main-group element (also, representative element) element in columns 1, 2, and 12-18
mass number (A) sum of the numbers of neutrons and protons in the nucleus of an atom
metal element that is shiny, malleable, good conductor of heat and electricity
metalloid element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals
molecular compound (also, covalent compound) composed of molecules formed by atoms of two or more different elements
molecular formula formula indicating the composition of a molecule of a compound and giving the actual number of atoms of each element in a molecule of the compound
monatomic ion ion composed of a single atom
neutron uncharged, subatomic particle located in the nucleus
noble gas (also, inert gas) element in group 18
nomenclature system of rules for naming objects of interest
nonmetal element that appears dull, poor conductor of heat and electricity
nucleus massive, positively charged center of an atom made up of protons and neutrons
oxyacid compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ions when dissolved in water)
oxyanion polyatomic anion composed of a central atom bonded to oxygen atoms
period (also, series) horizontal row of the periodic table
periodic law properties of the elements are periodic function of their atomic numbers
periodic table table of the elements that places elements with similar chemical properties close together
pnictogen element in group 15
polyatomic ion ion composed of more than one atom
proton positively charged, subatomic particle located in the nucleus
representative element (also, main-group element) element in columns 1, 2, and 12–18
series (also, period) horizontal row of the period table
spatial isomers compounds in which the relative orientations of the atoms in space differ
structural formula shows the atoms in a molecule and how they are connected
structural isomer one of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently
transition metal element in columns 3–11
unified atomic mass unit (u) alternative unit equivalent to the atomic mass unit
In the 5th century BC, what did Leucippus and Democritus argue? They argued that all matter was composed of small, finite particles that they called atomos; thought of atoms as moving particles that differed in shape/size, and could join together.
What did Aristotle and other philosophers think about matter? Concluded that matter consisted of various combinations of the four elements: fire, water, air, earth; these were philosophical concepts and were not tested
When was Dalton´s Atomic Theory published? First published in 1807
What was the first postulate of Dalton´s Atomic Theory? Matter is composed of exceedingly small particles called atoms, which are the smallest unit of an element that can participate in a chemical change
What was the second postulate of Dalton´s Atomic Theory? All elements consist of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element
What was the third postulate of Dalton´s Atomic Theory? Atoms of one element differ in properties from atoms of all other elements
What was the fourth postulate of Dalton's Atomic Theory? A compound consists of atoms of two or more elements combined in a small, whole-number ratio; in a compound, the number of each of its elements are always present in the same ratio
What was the fifth postulate of Dalton´s Atomic Theory? Atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from those present before the change
What does Dalton´s atomic theory provide? It provides a microscopic explanation of the many macroscopic properties of matter
Who was responsible for the Law of Definite Proportions? French chemist Joseph Proust
Are different compounds but same ratio the same substance? No, samples that have the same mass ratio are not necessarily the same substance
Who invented the cathode ray tube? English physicist J. J. Thomson
What was J. J. Thomson´s conclusion on his experiments with the cathode ray tube? The particles are attracted by positive charges and repelled by negative charges (like charges repel and unlike charges attract)
What did J. J. Thomson´s cathode ray particle eventually turn into? His cathode ray is what we now call an electron, a negatively charged, subatomic particle w/ a mass more than one thousand-times less that of an atom
Who uncovered more information about the electron in 1909? In 1909, American physicist Robert A. Millikan uncovered more info. about the electron through his "oil drop" experiment
What did Millikan conclude in his "oil drop experiment"?



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