Unit 3 – Atomic Structure and The Periodic Table

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Law of Conservation of MassMatter is neither created nor destroyed
Law of Definite Proportionsa given compound always contains exactly the same proportion of elements by mass
Law of Multiple ProportionsIf two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers. (divide ratios of each compound and then divide their quotient: if its a whole number answer, its demonstrates the law)

Atomic Mass UnitA unit of mass that describes the mass of an atom or molecule. (amu)
Atomic NumberNumber of protons in an atom
average atomic massweighted average of the atomic masses for the isotopes of an element
isotopesAtoms of the same element that have different numbers of neutrons.
mass numberSum of protons and neutrons
Avogadros numbernumber of representative particles in a mole, 6.02 X 10^23
molethe SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in exactly 12 g of carbon-12
electromagnetic energyA form of energy that travels through space as waves
frequencyHow many wave peaks pass a certain point per given time
wavelengthHorizontal distance between the crests or between the troughs of two adjacent waves
quantumthe amount of energy needed to move an electron from one energy level to another
photonA particle of electromagnetic radiation with no mass that carries a quantum of energy

line emission spectrum
A series of specific wavelengths of emitted light created when the visible portion of light from excited atoms is shined through a prism
orbitalA region of space around the nucleus where an electron is likely to be found.
atomBasic unit of matter
nucleusthe positively charged dense center of an atom
protonA subatomic particle that has a positive charge and that is found in the nucleus of an atom
neutronA subatomic particle that has no charge and that is found in the nucleus of an atom
electronA subatomic particle that has a negative charge
excited stateA state in which an atom has a higher potential energy than it has in its ground state
electron configurationthe arrangement of electrons in an atom
Periodic Lawthe law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements

Periodic Table
A chart of the elements showing the repeating pattern of their properties
anionA negatively charged ion
atomic radiusone-half the distance between the nuclei of identical atoms that are bonded together
ionization energyThe amount of energy required to remove an electron from an atom
valence electronsThe electrons in the outermost shell (main energy level) of an atom; these are the electrons involved in forming bonds.
cationA positively charged ion
electron affinitythe energy change that occurs when an electron is acquired by a neutral atom
electronegativityAtoms ability to attract and hold electrons.
ionA charged atom
Daltons Atomic Theory1) elements are made up of atoms 2) all atoms of a given element are identical 3) the atoms of an element are different from every other element 4) atoms of an element can combine to form a compound. A compound always has the same relative number of atoms 5) atoms are invisible in the chemical process and they are not created or destroyed
thomson atomic modelplum pudding – atom was a positively charged solid mass (pudding) which has negatively charged electrons stuck to it. (plums)
Rutherford atomic modelRutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus
Bohr atomic modelAtoms described as electrons orbiting the nucleus in well defined paths.
modern atomic modelatom consists of a nucleus that contains protons and neutrons surrounded by an electron cloud
Democritus(460-370 BCE) A Greek philosopher who theorized that all matter could be reduced to particles that could not be divided, which he described as “atomos.”
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