Download What is an atom?

Atomic Structure
Spectra of Science
Miss Amole
By PresenterMedia.com
What is an atom?
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Simplest unit in an element
Determines the properties of
that element
“atom” is derived from a
Greek word meaning “unable
to be divided”
Contains 3 subatomic
particles: protons, neutrons,
and electrons
Subatomic Particles
• PROTON:
• Positively
charges
• Located in nucleus
• Have mass
Subatomic Particles
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NEUTRON:
• Neutral = no charge
• Located in the nucleus
• Have mass
Subatomic Particles
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ELECTRON:
• Negatively charged
• No mass (negligible)
• Very fast; impossible to
pin point exact location,
speed, and direction
• Located outside nucleus
in electron cloud
• Electron cloud contains
energy levels
• Energy levels contain
orbitals
More About Electrons
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The valence electrons an atom has determines reactivity
• Valence electrons are those located in the outermost
shell or energy level
Each energy level can only hold a certain number of
electrons
More About Atoms
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The number of protons and electrons an atom has is unique
to each element
• That is to say, every element has a different number of
protons in its atom
• Coincides with the atomic number
Even though atoms contain charged particles, they are
electrically neutral
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That is to say an atom has an equal amount of protons and
electrons
Atoms contain mostly empty space
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If the nucleus of an atom was the size of a marble, the entire
element would be the size of a football field
Development of Atomic Theory
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Democritus
• Fourth century BC Greek
philosopher
• First to suggest the existence of
atoms
• Believed universe contained
these invisible units that caused
changes in matter
• Believed atoms were indivisible
Development of Atomic Theory
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John Dalton
• 1808 English schoolteacher
• Suggested all atoms of a
given element were alike
• Believed different atoms
could join together to form
compounds
• His theories are considered
the foundation for modern
atomic theory
Development of Atomic Theory
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Niels Bohr
• 1913 Danish scientist
• Suggested electrons move in
set paths around nucleus that
determine their energy level
• Believed electrons would have
to gain energy to move to a
higher energy level or lose
enregy to move down
Development of Atomic Theory
By 1925, Bohr’s model no
longer explained electron
behavior
• Current thought suggested
electrons are act more like
waves on a vibrating
string than particles
• Impossible to detect an
electrons exact location,
speed, or direction
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Other Forms of Atoms
• Ions
Cations
• Created when an atom loses one or more
electrons and becomes positively charged
• Anions
• Created when an atom gains one or more
electrons and becomes negatively charged
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• Isotopes
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Atoms of the same element with a different
number of neutrons
-Atomic Structure Video
-Atom Builder