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CH 18 Chemistry Of Earth
and The Known Universe
Atomic Structure
Subatomic Particles
 Proton- P+ positive charged - in nucleus
 Number of P+ distinguishes one atom from another
 Made of 2 up quarks (+2/3 charge) and 1 down
quark (-1/3 charge)
 Neutron- No neutral charged - in nucleus
 Made of 2 down quarks and 1 up quark
Electrons
 Electron- enegatively charged
- swarming in
energy levels
around nucleus of
atom (electron
cloud).
Electrons (e-) are attracted to the positively
charged protons (P+) in the nucleus, helping
them remain close to the nucleus in swarming
levels.
Energy Levels
Electrons e- have a specific amount of
energy when in each level.
 K – Shell has least energy
 M – Shell has most energy (as far as we’re
going)
 e- can occupy only 1 level at a time
 No matter how many levels the outer level
(valence) can have no more than 8 e Most stable atoms have 8 e- in valence

18.2 Comparing Atoms


The number of P+ determines
the type of atom.
If you change the number of P+
you change the atom.
18.2 Atomic Number
 The Atomic Number is total number of
protons in the nucleus of an atom.
18.2 Mass Number
• The total number of
protons and neutrons in
the nucleus of an atom
is called the Mass
Number or Atomic Mass.
18.2 Isotopes
Isotopes are atoms of the same
element that have different
numbers of neutrons.
 Each of the below atoms are
hydrogen, but they are all isotopes
of hydrogen.

Isotopes
• An atom can have 2 or more isotopes
• Isotopes have different numbers of
neutrons
– Thus different mass numbers
– More N add mass to atom
– Heavier elements are radioactive (give off N)
18.3 The Periodic Table of Elements
Elements are made up of only one
kind of atom.
 Compounds are made up of
combinations of atoms.
 Elements that are part of the
same group act alike.

18.3 The Periodic Table of
Elements
 Dimitri Mendeleev (18341907) organized information
about all the known
elements in a table that
visually organized the
similarities between them.
 Mendeleev placed each
element on the table in a
certain row and column
based on its properties.
 The chemical symbol is an abbreviation of
the element’s scientific name.