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FCS Physics and Chemistry

The Atom..cont
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Location of Electrons
As we noted earlier, electrons are viewed to be in orbitals surrounding the nucleus of the atom.  When electrons are in the lowest available orbitals (closest to the nucleus), they are said to be in the ground stateIf they are exposed to stimuli, in the form of heat for example, they can be promoted to the next orbital.  They are now considered to be in an excited state.   

As we have noted in the section on the Bohr atom, isolated atoms can absorb and emit packets of electromagnetic radiation having discrete energies dictated by the detailed atomic structure of the atoms. When the corresponding light is passed through a prism or spectrograph it is separated spatially according to wavelength, as illustrated in the following image.


Continuum, Emission, and Absorption Spectra

The corresponding spectrum may exhibit a continuum, or may have superposed on the continuum bright lines (an emission spectrum) or dark lines (an absorption spectrum), as illustrated in the following figure.


Origin of Continuum, Emission, and Absorption Spectra

The origins of these three types of spectra are illustrated in the following figure.


Types of Matter
The world is compoed of millions of different types of materials, and they are all combinations of atoms.  As we look at the world around us, two categories of matter can be distinguished.
Homogeneous Matter is matter that has uniform composition throughout.  It is very well mixed, however, not chemically combined.
  • For example: lemonade, milk, pop, our atmosphere etc..
Heterogeneous Matter is matter that does not have a uniform composition.  YOU CAN SEE THE DIFFERENT SUBSTANCES!
  • For example: chocolate chip cookies, cereal, etc...
A pure substance has a constant, defined composition and cannot be separated into simpler substances by physical means. There are two types of pure substances, elements and compounds.

  • Elements are pure substances that are made of only one type of atom. The periodic table is a table containing all elements.
  • Compounds are pure substances that are made of more than one type of atom, and can be decomposed or broken down into its elements by chemical means.

Separation of Mixtures

The properties of a mixture's components often provide a means by which they can be separated.  Density, molecular polarity, freezing point, and boiling point are a few of the properties that can be used to separate the properties of a mixture. 

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