Nucleus
The central core of an atom containing protons and usually neutrons.
Proton
A small, positively charged particle in the nucleus of the atom.
Neutron
A small particle in the nucleus of the atom, with no electrical charge.
Electron
A tiny negatively charged particle that moves around the nucleus of an atom.
Atomic Number
The number of protons in the nucleus of an atom.
Isotope
An atom with the same number of protons and a different number of neutrons from other atoms of the same element.
Atomic Mass
The average mass of all the isotopes of an element.
Periodic Table
A chart of the elements showing the repeating pattern of their properties.
Chemical Symbol
A one- or two-letter representation of an element.
Period
A horizontal row of elements in the periodic table.
Group
Elements in the same vertical column of the periodic table; also called family.
Metal
A class of elements characterized by physical properties that include shininess, malleability, ductility, and conductivity.
Malleable
A term used to describe material that can be pounded into shapes.
Ductile
A term used to describe a material that can be pulled out into a long wire.
Conductivity
The ability of an object to transfer heat or electricity to another object.
Reactivity
The ease and speed with which an element combines, or reacts, with other elements and compounds.
Corrosion
The gradual wearing away of a metal element due to a chemical reaction.
Alkali
An element in Group 1 of the periodic table.
Alkaline Earth
An element in Group 2 of the periodic table.
Transition
One of the elements in Groups 3 through 12 of the periodic table.
Alloy
A mixture of two or more elements, one of which is a metal.
Particle Accelerator
A machine that moves atomic nuclei at higher and higher speeds until they crash into one another, sometimes forming heavier elements.
Nonmetal
A class of elements characterized by physical properties that include dull, brittle, and are poor conductors.
Diatomic Molecule
A molecule consisting of two atoms.
Halogen
An element found in Group 17 of the periodic table.
Noble Gas
An element in Group 18 of the periodic table.
Metalloid
An element that has some characteristics of both metals and nonmetals.
Semiconductor
A substance that can conduct electricity under some conditions.
An element's properties can be predicted from its
location in the periodic table.
How did chemists change Mendeleev's periodic table in the early 1900s?
They used atomic number instead of atomic mass to organize the elements.
Dmitri Mendeleev created the first
periodic table.
The particles that are lost, gained, or shared in chemical reactions are
electrons
This family is the most reactive group of metals in the periodic table.
Alkali
What groups/families are shown at the bottom of the periodic table in order to keep the table a reasonable size.
Lanthanides and Actinides
True or False--Nonmetals are good conductors of electricity.
False
True or False--The reactivity of the metal elements generally increases as you move from left to right across the periodic table.
False
True or False--Elements in a group on the periodic table have similar properties.
True
Why do scientists use models to study atoms?
Atoms are too small to be seen.
Why would it probably be very difficult to determine the chemical and physical properties of a newly discovered synthetic element?
The element's nuclei would break apart very quickly.
At room temperature, more than half of the nonmetal elements are
gases
In an atom, the number of protons equals the number of
electrons
What information can be found in a square of the periodic table?
Atomic number, chemical symbol, name, atomic mass
What parts of the atom move around the nucleus?
electrons
What prediction did Mendeleev make that came true less than 20 years later?
He said that three new elements would be discovered, and he described their properties.
What group/family does not ordinarily form compounds?
Noble Gases
Why is it difficult to determine the chemical and physical properties of newly discovered synthetic elements?
The element's nuclei breaks apart easily.
Mendeleev was able to predict that new elements would be discovered based on their...
properties