A matter of Fact Mixtures, Elements and Compounds Mixtures, elements, compounds



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A Matter of Fact

  • Mixtures, Elements and Compounds

Mixtures, elements, compounds

  • Scientists like to classify things.
  • One way that scientists classify matter is by its composition.
  • Ultimately, all matter can be classified as mixtures, elements and compounds.

Why isn’t it a good idea to classify matter by its phases?

  • Because one kind of substance can exist in more than one phase – such as H20. And matter changes phases rather easily.

Why isn’t matter classified according to its physical characteristics, such as color?

  • Scientists ask themselves these questions?
    • Is the matter uniform throughout?
    • Can it be separated by physical means?
    • Can it be separated by chemical means?

By asking these questions scientists can classify matter into:

  • By asking these questions scientists can classify matter into:
  • Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties.
    • Solutions – a special kind of mixture where one substance dissolves in another.
  • Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means.
  • Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.

Is it uniform throughout?

  • If the answer is no, the matter is a heterogeneous mixture.
    • Considered the “least mixed.”
    • Does not appear to be the same throughout.
    • Particles are large enough to be seen and to be separated from the mixture.

Examples of heterogeneous mixtures

  • Granite is a heterogeneous mixture.

Is it uniform throughout?

  • If the answer is yes, the matter is homogeneous (looks the same throughout).
  • That leads us to another question.

Can it be separated by physical means?

  • If the answer is yes, the matter is a homogeneous mixture or solution.

Homogeneous Mixtures

  • A mixture that appears to be the same throughout.
  • It is “well mixed.”
  • The particles that make up the mixture are very small and not easily recognizable.

Examples of homogeneous mixtures

Colloids

  • In a colloid the particles are mixed together but not dissolved.
  • The particles are relatively large and are kept permanently suspended.

Colloids

  • A colloid will not separate upon standing.
  • The particles are constantly colliding, and this allows a colloid to scatter light – thus colloids often seem cloudy.

Solutions

  • A solution is a type of homogeneous mixture formed when one substance dissolves in another.
  • It is the best mixed of all mixtures.
  • A solution always has a substance that is dissolved and a substance that does the dissolving.
  • The substance that is dissolved is the solute and the substance that does the dissolving is the solvent.

Ocean water is a solution

The universal solvent: Water

Water as a solvent

  • Many liquid solutions contain water as the solvent.
  • Ocean water is basically a water solution that contains many salts.
  • Body fluids are also water solutions.

Types of solutions

  • Gas
  • Gas
  • Air (oxygen in nitrogen)
  • Gas
  • Liquid
  • Soda water (carbon dioxide in water)
  • Solid
  • Liquid
  • Ocean water (salt in water)
  • Solute
  • Solvent
  • Example
  • Solid
  • Solid
  • Gold jewelry (copper in gold)
  • Metals dissolved in metals are called alloys.

Air is a solution of oxygen and other gases dissolved in nitrogen

Alloys

  • Stainless steel is a mixture
  • of iron and chromium.

Can it be separated by physical means?

  • If the answer is no, the matter is a pure substance.

Elements

  • Elements are the simplest pure substance.
    • An element can not be changed into a simpler substance by heating or any chemical process.
  • The smallest particle of an element that has the properties of that element is called an atom.
    • An atom is the basic building block of matter.
  • There are more than one hundred known elements in the universe listed on the periodic table of elements.
    • These elements combine in such a way to create millions of compounds.

Elements

  • All elements are made of atoms.
  • Atoms of the same element are alike.
  • Atoms of different elements are different.

Elements

  • In 1813, a system of representing elements with symbols was introduced.
    • Each symbol consists of one or two letters.
    • Two letters are needed for a chemical symbol when the first letter of that element’s name has already been used.

Common Elements

  • Aluminum
  • Al
  • Bromine
  • Br
  • Calcium
  • Ca
  • Carbon
  • C
  • Gold
  • Au
  • Helium
  • He
  • Hydrogen
  • H
  • Nitrogen
  • N

Compounds

  • Compounds are also pure substances.
  • But compounds are made from more than one element.
  • Water is a compound.
  • Water can be broken down into simpler substances – hydrogen and oxygen.


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