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The Atoms Family
Chapter 1
What is an Element?
• A substance that cannot be broken down into simpler
substances by physical or chemical means
• 92 occur naturally on the Earth and in stars
• Each is identified by a one- , two-, or three-letter abbreviation
• Some elements known in ancient times like gold and mercury,
have symbols that reflect their Latin origins (gold-Au, Latin for
Aurum)
The Smallest of All
• The smallest particle of
an element that has all
of the characteristics of
that element is an atom
• Atoms are made of 3
things: protons,
electrons, and neutrons
• Protons (positive) and
neutrons (neutral) are in
the nucleus
• Electrons (negative) are
in energy levels
surrounding the nucleus
Atoms Continued…
• The number of protons in
the nucleus corresponds
to the element’s atomic
number
• The combined number of
protons and neutrons in
the nucleus is its atomic
mass
• The number of protons
and electrons is the same,
resulting in an atom with
no overall charge
(charges cancel each
other out)
Electron Energy Levels
•
•
•
The number and arrangement of electrons determines the size
of the atom
Electrons move around the nucleus in energy levels and each
can only hold so many electrons
1. 1st: 2 electrons
2. 2nd: 8 electrons
3. 3rd: 18 electrons
4. 4th: 32 electrons
The number of electrons in the outermost energy level, called
valence electrons, determines the chemical behavior of the
element
Radioactivity
• When the number of neutrons in nuclei vary, you
have an isotope
• For example, chlorine always has 17 protons, but
the number of neutrons could be either 18 or 20.
This in turn, changes the atomic mass
• The nuclei of some isotopes are unstable and
release radiation
• During the radioactive decay process, the nuclei
of these isotopes loses protons and neutrons
• The decay process changes the identity of an
element, as in the case of Uranium-238 decaying
into Lead-206
So, What Does This Mean
to Earth Science?
• The 2 most abundant elements in the
UNIVERSE are hydrogen (H) and helium (He)
• The 2 most abundant elements in the EARTH’S
CRUST are silicon (Si) and oxygen (O)
• 98.5% of the Earth’s crust is made up of only 8
elements, where Si and O are in greatest
abundance
• Most rocks and minerals that we see at the
Earth’s surface are made of these 8 elements