CHM 2045C: Key Terms Chapter 2: Atoms and Elements

 

Actinide:  an element with an atomic number anywhere from 90 to 103; the actinides are usually shown (along with the lanthanides) at the bottom of the periodic table separated from the main body of elements

 

Alkali metal family:  group 1A on the periodic table (excluding hydrogen)

 

Alkaline earth metal family:  group 2A on the periodic table

 

Allotropes:  different forms of the same element that exist in the same physical state under the same conditions of temperature and pressure; they have different molecular formulas or crystal structures

 

Alpha rays:  particles produced when certain nuclei decay; they consist of a helium nucleus; they have a relative mass of 2 and have a +2 charge

 

Atomic mass unit: one atomic mass unit is one twelfth the mass of a carbon-12 atom

 

Atomic number (Z):  the number of protons in an atom

 

Atomic weight:  a weighted average of all of the isotopes of a particular element.  The atomic weight is often shown on the periodic table; it is the number that contains the decimal places

 

Avogadro’s number:  the number of particles in a mole of that substance, 6.02214155 x 1023 particles (to nine significant figures).

 

Beta rays: particles produced when certain nuclei decay; they consist of electrons.  A beta particle has a charge of -1 and a very small mass.

 

Canal rays:  positively charged particles that travel toward the negative cathode in a cathode ray tube.  These particles are + ions

 

Cathode ray tube:  a glass tube from which most of the air has been removed and which contains two metal electrodes; when a sufficiently high voltage is applied to the electrode, cathode rays flow from the cathode to the anode

 

Cathode rays: a stream of electrons that flows from the negative cathode of a cathode ray tube to the positive anode

 

Chalcogens:  sulfur, selenium, and tellurium

 

Electron:  one of the major subatomic particles.  Electrons have a mass much smaller than that of protons and neutrons, have a relative charge of -1, and travel around outside the nucleus of the atom.

 

Essential element:  an element required for life; a deficiency or absence of an essential element may result in death, developmental abnormalities, or other ailments.

 

Family:  a vertical column on the periodic table, sometimes called a group

 

Gamma rays:  a type of radiation given off when certain nuclei decay; they consist of electromagnetic radiation.  Gamma rays have neither mass nor charge

 

Group: a vertical column on the periodic table, sometimes called a family

 

Halogen family:  group 7A on the periodic table

 

Isotopes:  atoms of the same element that have different mass numbers and thus different numbers of neutrons in their nuclei

 

Lanthanide:  an element with an atomic number anywhere from 58 to 71; the lanthanides are usually shown (along with the actinides) at the bottom of the periodic table separated from the main body of elements

 

Law of chemical periodicity:  the properties of the elements are periodic functions of atomic number

 

Main group elements:  elements found in the taller columns on the periodic table (the A groups on the periodic table most often used in the United States), sometimes called Representative Elements.

 

Mass defect:  the difference between the sum of the masses of the protons and neutrons that go into forming a nucleus and the actual mass of the nucleus, which will always be less.  This difference is due to matter being converted into energy when the subatomic particles come together to form the nucleus

 

Mass number (A):  the sum of the number of protons and number of neutrons in an atom

 

Mass spectrometry:  a technique that can be used to determine the mass of an isotope

 

Metal:  an element to the left of the line separating the metals and nonmetals on the periodic table; they tend to be solids at room temperature, conduct electricity, and are ductile and malleable

 

Metalloid:  an element with some properties of metals and some properties of nonmetals; they are found along the zigzag line on the periodic table.  The metalloids are B, Si, Ge, Sb, and Te

 

Molar mass: the mass in grams of one mole of a material

 

 

 

 

Mole:  the chemical counting unit on our macroscopic level.  One move of a substance contains as many elementary entities (atoms, molecules, or other particles) as there are in exactly 12g of the carbon-12 isotope.  One mole contains Avogardro’s number of elementary entities

 

Neutron:  one of the major subatomic particles.  Neutrons have a relative mass of 1.  They are electrically neutral and are located the nucleus of an atom

 

Noble gas family:  group 8A on the periodic table (before 1963 they were called the Inert Elements)

 

Nonmetal:  an element to the right of the line separating the metals and nonmetals on the periodic table.  Some are solids, one is a liquid, and some are gases at room temperature.  Almost all nonmetals do not conduct electricity

 

Nucleus:  the minuscule center of an atom containing the protons and neutrons

 

Period:  a horizontal row on the periodic table

 

Periodicity:  the property of repeating at regular intervals

 

Proton:  one of the major subatomic particles.  Protons have a relative mass of 1 and a relative charge of +1.  They are located in the nucleus of an atom

 

Radioactivity:  particles or radiation given off by atoms of certain elements

 

Subatomic particle:  a particle that makes up an atom.  The key subatomic particles to know about for most of chemistry are protons, neutrons, and electrons

 

Transition elements:   elements found in the shorter columns in the main body of the periodic table (the B groups on the periodic table most often used in the United States)