ELEMENTS
DEFINITION
• A chemical element is a substance that cannot be
broken down by chemical means. Although elements
aren't changed by chemical reactions, new elements
may be formed by nuclear reactions.
• Elements are defined by the number of protons they
possess. Atoms of an element all have the same
number of protons, but they can have different
numbers of electrons and neutrons. Changing the ratio
of electrons to protons creates IONS , while changing
the number of neutrons form ISOTOPES.
Cont'd
• There are 118 known elements.
• Examples of Elements:Any of the types of atoms
listed on the periodic table is an example of an
element
CONT'D
• Examples of Substances That Are Not Elements
• If more than one type of atom is present, a substance is
not an element. Compounds and alloys are not elements.
Similarly, groups of electrons and neutrons are not
elements. A particle must contain protons to be an
example of an element. Non-elements include:
• water (composed of hydrogen and oxygen atoms)
• steel
• electrons
• brass (composed of multiple types of metal atoms)