CHAPTER 5- ATOMIC STRUCTURE AND THE PERIODIC TABLE

KEY TERMS

Alkali metal- Any metal in group 1 a of the periodic table

Alkaline earth metal- Any metal in group 2 a of the periodic table

Atom-The smallest particle of an element that retains the properties of that element

Atomic mass- The weighted average mass of the atoms in a naturally occurring sample ofelement

Atomic mass unit (amu)- A unit of mass equal to one-twelfth the mass of a carbon-12 atom.

Atomic number- The number of protons in the nucleus of an atom of an element.

Cathode Ray- A stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure.

Dalton’s Atomic Theory- The first theory to relate chemical events at the atomic level.

Electron- A negatively charaged subatomic particle.

Halogen- Any member of the nonmetallic elements in group 7A of the periodic table.

Inner Transition Metal- An element in the lanthanide and actinide series; characterized by addition of electrons to f orbitals.

Isotope- Atoms of the same elment that have the same atomic number but different atomic masses due to a different number of neutrons.

Mass number- The total number of protons and neutrons in the nucleus.

Metal- One of a class of elements that includes a majority of the known elements; metals are characteristicly lustrious, malleable, ductile, and good conductors of heat and electricity.

Metalloid- One of a class of elements having properties intermediate to metals and not metals.

Neutron- A subatomic particle with no charge and a mass of 1 amu; found in the nucleus of the atom.

Noble Gas- Any member of a group of gaseous elements in group zero of the periodic table; the s and p sublevels of their outermost energy level are filled.

Nonmetal- One of a class of elements that are not lustrous and are generally core conductors of heat and electricity; nonmetals are grouped on the right side of the periodic table.

Nucleus- The dense central portion of an atom, composed of protons and neutrons.

Period- A horizontal row of elements in the periodic table.

Periodic law- When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Periodic Table- An arrangement of elements into rows and columns according to similarities in their properties.

Proton- A positively charged subatomic particle found in the nucleus of an atom.

Representative Element- Group A element on the periodic table, these elements, which have only partially filled outermost s and p sublevels, illustrate the entire range of chemical properties.

Transition Metal- Group B element characterized by addition of electrons to d suborbitals.

SUMMARY

Elements are composed of atoms, small particles which are the basic building blocks of matter.

Atoms consist of positively charged protons, negatively charged electrons, and electrically charged neutral neutrons.

Protons and neutrons are located in the nucleus and have account for most of an atom’s mass, but electrons have neglible mass and surround the nucleus.

Because atoms are electrically neutral, every atom has the same number of protons and electrons so that the negative and positive charges cancel each other out. The atomic mass of an element is a weighted average of all the naturally occurring isotopes of that element.

For more practice, try the Chapter Test