Transcript Ch 8 Matter Section..

Chapter 8
Earth Chemistry
Section 2
8.2 – Atomic Number
► An
atom of a specific element is different
from other elements by the number of
protons it has
► Atomic Number is the number of protons
in an atom.
► All atoms of any element have exactly the
same number of protons
8.2 – Atomic Number
► The
number of protons also equals the
number of electrons in a neutral atom
► So, the atomic number tells us how many
protons which equals how many electrons
► Example: Oxygen’s atomic number is 8
► It has 8 protons and 8 electrons
8.2 – Atomic Number
► The
periodic table is a list of all the known
elements in order by their atomic numbers
► It is used to classify the elements into
groups
8.2 – Mass Number
► Each
atom has a mass number.
► Mass number is the number of protons
plus the number of neutrons in the atom
► The mass number is not on the periodic
table
8.2 – Mass Number
► You
can use the atomic number and mass
number to find the total number of protons,
neutrons, and electrons
► Mass # - Atomic # = # Neutrons
8.2 – Combinations of Atoms
► Elements
rarely occur in pure form in the
Earth’s crust
► They are generally found in combination
with other elements
► A compound is a substance made of two or
more elements
8.2 – Combinations of Atoms
►A
compound is a new substance
► It has different properties than the elements
that make it.
► Example: Water is made of when 2 atoms of
hydrogen combine with 1 atom of oxygen.
► Water is a liquid, while hydrogen and
oxygen are colorless gases.
8.2 – Combinations of Atoms
► The
smallest unit of a compound is called a
molecule
► Molecules are made of 2 or more atoms
► Example: There are millions of water
molecules in a bottle of water
8.2 – Combinations of Atoms
► Atoms
join together to become more stable.
► An unstable metal atom will join with an
unstable nonmetal atom to become a stable
compound
► An unstable atom will always combine with
another unstable atom to be more stable
8.2 - Combinations of Atoms
► When
looking at a chemical formula for a
compound, each capital letter represents a
new element
► Subscripts tell us how many atoms of that
element are in the compound
► If there are no subscripts, then there is only
one atom of that element
8.2 - Combinations of Atoms
► Example:
► It
C2H4
has 2 Carbon atoms and 4 Hydrogen
atoms