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Atomic Concepts; History of the atom and valence electrons

Learn how the atom has developed throughout the years and how valence electrons affect the chemical properties of an element

Elizabeth Reinhardt

on 17 May 2011

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Transcript of Atomic Concepts; History of the atom and valence electrons

Concepts History of
the atom Dalton- Atoms are tiny
particles, with no
internal structure Billard Ball J.J. Thomson- discovered electrons
exist within an atom
through the use of a
cathode ray and
two magnetic plates Plum Pudding a narrow beam of alpha particles was directed at a gold foil in which some deflected off at odd angles while most passed through Rutherford- Rutherford concluded
that in the middle there
was most of the mass
which was positive
called the nucleus. Bohr- electron is found only
in specific, circular paths,
or orbits a fixed distance
from the nucleus.
Atom has energy levels. Modern Cloud Theory The nucleus contains both protons
and neutrons. Probability of
finding an electron is higher in
the denser regions of the cloud. Electron cloud Scientists constantly use other
scientist’s discoveries to help
create a more modern version.
The challenging of previous
theories through experiment
and evidence allows the human
race to acquire more knowledge
in a certain field. 1913 Bohr changed Rutherford’s
model to include more recent
discoveries about how the energy
of an atom changes when it
absorbs or emits light. Democritus (460 B.C. – 370 B.C.)
was a Greek philosopher who
believed atoms were indestructible
and indivisible. Dalton used
Democritus’s ideas on atoms to
create his scientific theory. Valence Electrons & Chemical Properties
Associated Lewis electron-dot structures help determine:
1) type of covalent bond made
2) type of ion an atom will make Find amount of valence electrons:
F-7 Start with element symbol in middle:

X From the top add a dot (representing one electron) around the element symbol clockwise The outermost electrons in an atom are called the valence electrons. In general, the number of valence electrons affects the chemical properties of an element. A full octet (8 valence electrons) will result in no reaction because that atom does not want to gain/lose electrons. Atoms with one valence electron are highly reactive as they do want to lose one electron in order to gain a full octet. All these atoms are coloum 1 or the alkali metals. Atoms with seven valence electrons are highly reactive as they want to gain one electron in order to gain a full octet. All these atoms are coloum 17 or the halogens. The magnet is at first positive because the ray is attracted to it, but than the person switches it to negative wehere the cathode ray is repeled.
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