Unit 3: Atomic Structure, Elements, and the Periodic Table

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Atom

the smallest unit of an element that maintains the properties of that element

Democritus's Atomic Theory

believed that movements of atoms caused the changes in matter

John Dalton's Atomic Theory

All Atoms of a given element were exactly alike. Atoms of different elements could join to form compounds.

J J Thomson's Plum Pudding Model of the Atom

each atom was a sphere filled with a positively charged fluid. The fluid was called the "pudding." Scattered in this fluid were electrons known as the "plums."

Ernest Rutherford's Nuclear Model of the Atom

the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.

Bohr's Model of the Atom

Placed electrons in planet-like orbits around the nucleus of the atom.

Quantum Model of the Atom

an atomic model in which electrons are treated as waves; also called the wave mechanical model of the atom

Nucleus

an atom's central region, which is made up of protons and neutrons

Proton

subatomic particle that has a positive charge and that is found in the nucleus of an atom

Neutron

a subatomic particle that has no charge and that is found in the nucleus of an atom

Electron

a subatomic particle that has a negative electric charge

Energy level

the energy state of an atom

Orbital

a region in an atom where there is a high probability of finding electrons

Valence electron

an electron that is found in the outermost shell of an atom and that determines the atom's chemical properties

Ion

an atom, radical, or molecule that has gained or lot one or more electrons and has a negative or positive charge

Cation

an ion that has a positive charge

Anion

an ion that has a negative charge

Periodic Table of the Elements

A chart of the chemical elements, arranged in three rows, corresponding to the number of electron shells in their atoms

Periodic law

the law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements

Dmitri Mendeleev

Russian chemist who developed a periodic table of the chemical elements and predicted the discovery of several new elements (1834-1907)

Octet

group of eight

Periods or series

a horizontal row of elements in the periodic table

Groups or families

the vertical columns of the periodic table

Atomic number (Z)

the number of protons in the nucleus of an atom

Mass number (A)

the sum of the numbers of protons and neutrons in the nucleus

Isotope

an atom that has the same number of protons as other atoms of the same element do but that has a different number of neutrons

Atomic mass unit (amu)

a unit of mass that describes the mass of an atom or molecule

Avg. atomic mass

the weighted average of the masses of all naturally occurring isotopes of an element

Metal

an element that is shiny and that conducts heat and electricity well

Metalloid

an element that has some characteristics of metals and some characteristics of nonmetals

Nonmetal

an element that conducts heat and electricity poorly and that does not form positive ions in an electrolytic soloution

Semiconductor

an element or compound that conducts electric current better than an insulator but not as well as a conductor

Alkali metals

one of the elements of Group 1 of the periodic table (lithium, sodium, potassium, rubidium, cesium, and francium)

Alkaline Earth metals

one of the elements of Group 2 of the periodic table (beryllium, magnesium, calcium, strontium, barium, and radium)

Transition metals

one of the metals that can use the inner shell before using the outer shell to bond

Halogens

one of the elements of Group 17 of the periodic table (fluorine, chlorine, bromine, iodine, and astatine); halogens combine with most metals to form salts

Noble gases

an non-reactive element of Group 18 of the periodic table (helium, neon, argon, krypton, xenon, or radon) that has eight electrons in its outer level (except for helium, which has two electrons)

Lanthanides

Shiny, reactive metals found in Period 6 from #57-71. Some of these elements are used to make steel and one is found in computer screens to show color.

Actinides

in the 2nd row of transition metals, radioactive, unstable, do not occur in nature

synthetic elements

Elements which do not occur naturally and are made in laboratories.

mole

the 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 12g of carbon-12

Avogadro's constant

equals 6.02 x 10(twenty-third power); the number of particles in 1 mol

Molar mass

the mass in grams of 1 mol of a substance

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