ATOMS
TEKS 8.5 A-D
What is an ATOM?
Atoms are the building blocks of all
matter.
Matter is everything around us that
takes up space and has volume. It is
made up of very small atoms.
What are atoms
made of?
• Atoms are made of protons,
electrons and neutrons.
• Protons and Neutrons are located in
the nucleus. Protons have a positive
charge and neutrons have no
charge.
• Electrons are located outside the
nucleus in what is called the electron
cloud. Electrons have a negative
charge.
• The number of protons equal the
number of electrons.
ATOMIC STRUCTURE (BOHR MODEL)
Language of Atoms
• Atomic Number is the number of protons (P) in an atom. The
number of protons determines the identity of the atom.
• Atomic Mass is the number of protons (P) plus neutrons (N) in
the nucleus.
• Valence Electrons are the number of electrons in the outermost
energy level of the electron cloud.
• Valence Electrons determine the chemical properties of atoms,
including the reactivity of the atom.
• Chemical Properties: Atoms with the same number of valence
electrons will have similar chemical properties.
• Reactivity: the reactivity of an atom is its capacity to undergo a
chemical reaction with another atom. The capacity to react is
determined by its valence electrons.
Reactivity
• The atoms that react most easily with other atoms have either
the lowest number of valence electrons or the highest number
of valence electrons.
• Atoms with the lowest number of valence electrons are highly
reactive because they seek stability by releasing valence
electron(s) to other atoms.
• Atoms with the highest number of valence electrons are highly
reactive because they seek stability by gaining electrons to fill
their outermost shell.
Periodic
Table
• Groups of atoms have the same
number of valence of electrons.
• Elements in a group have similar
properties because they have the same
number of valence electrons. They are
organized on the periodic table by
columns. They are also called families.
• Rows on the periodic table are called
periods. Elements in a row or period
have gradual changes in chemical
properties going from left to right.
Classifying Elements
• Three physical properties that are useful for classifying
elements: Luster, Conductivity, and Malleability.
• Groups of elements with the greatest luster, greatest
conductivity and greatest malleability are called METALS.
• Groups of elements that are shiny but not lustrous, have a
semi-conductive property and are brittle are classified as
METALLOIDS.
• Groups of elements that are mostly gases but include dull,
brittle solids and display insulating properties are classified as
NONMETALS.
PERIODIC
TABLE OF
ELEMENTS
• Elements with the properties of
METALS are all left of the staircase.
Most elements are metals. They are
found on the left side of the periodic
table.
• Elements with METALLIOD properties
fall along a staircase line.
• Elements with properties of
NONMETALS are all to the right of the
staircase and hydrogen in the top left.
Chemical Formulas
• Molecules are formed when two or more atoms join (bond)
together.
• If a molecule is the same of the element, it is the molecule of an
element.
• Scientist use formulas to identify substances and determine the
number of atoms of each element in each element containing
subscripts. Formulas provide the following information: a
Symbol determines the identity of the atom and a Subscript or
number of each type of atom of the molecule.