Chapter 112: The Atom

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Chapter 11-2 The Atom

• Physical Science
• Hartner

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What are atoms?

• Atoms are the basic building blocks of
• matter that make up everyday objects.
• A desk, the air, even you are made up of
• atoms!
• There are 90 naturally occurring kinds of
• atoms.
• (Scientists in labs have been able
• to make about 25 more)

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The Atom is made of 3 Basic Particles
Electron tiny, very light particles that have a
negative charge found circling the nucleus in
the electron cloud
Neutron larger heavier than e- but have no
electrical charge (neutral) found in the nucleus
Proton large heavy like Neutrons with a
positive charge found in the nucleus
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• Protons and Neutrons join to form
• the nucleus

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Atomic Mass Unit (a.m.u.) - the SI Unit used to
express the masses of particles in atoms.
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Example

• If the nucleus was the size of a basketball,
• then the closest electron would be 8 miles
• away.

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Atomic Number

• In periodic table, the elements are arranged
• in order of increasing atomic number
• the number of protons in one atom of a
  particular element.
• An undisturbed atom is electrically neutral,
• so the number of electrons in it is the same
• as its atomic number.

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Neutral Atoms (no charge)
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Ions

• Some Atoms can have electrical charges
• b/c they either gain or lose electrons
• the of protons never changes in an atom 
• If an atom gains electrons, the atom
• becomes negatively charged. 
• If the atom loses electrons, the atom
• becomes positively charged  
• An atom that carries an electrical charge
• is called an ion.

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• Normal Hydrogen Atom
• Positively Charged
• Hydrogen Ion (H)
• Negatively Charged
• Hydrogen Ion (H-)

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Isotopes

• Atoms that have the same number of
• protons but have different number of
• Neutrons are called Isotopes.
• Hydrogen - 1 Hydrogen-2 (Deuterium) Atomic
  1 Atomic 1
• Mass 1 Mass 2

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Atomic Mass

• Most elements contain a mixture of two or
• more isotopes.
• Examples
• Hydrogen 1 2 Carbon 12, 13, 14
• Copper 63 65
• Atomic Mass the weighted average of the
• masses of all naturally occuring isotopes of
• that element.

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Forces in Atoms

• Gravitational Forces amount of gravitational
• force b/w objects depends on their masses and
• distances apart.
• Electromagnetic Forces
• Opposite charges attract. Like charges repel.
• Strong Forces hold protons and neutron together
  in the nucleus.
• Weak Forces occur within radioactive atoms