An Element is…A substance that cannot be separated or broken down into simpler substances by a physical or chemical change
• 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.
»The solid cobalt is already broken down as far as it can be. It is an element, which means no physical or chemical change will change what it is.
Cobalt
Atoms• All elements are
made of atoms.• Atoms of the same
element are alike.– Ex: All carbon atoms
look the same
• Atoms of different elements are different.– Ex: Carbon atoms and
helium atoms look different.
A meteorite might travel more than 400 million kilometers to reach Earth. But the particles of iron in a meteorite , a steel spoon, and steel braces are alike.
They are all the same pure substance.
History of 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.
What is a pure substance?
A pure substance is a substance in which there is only one type of
particle that makes it up.
All of the elements on the periodic table are pure
substances!
•Each element has its own unique set of characteristic properties such as: •boiling point,•melting point,•reactivity with an acid •density
•An element may share a property with another element, however other properties can be used to tell the elements apart.
Examples: Helium and Krypton are both unreactive gases. However, their densities differ. So, you could use the property of density to tell the two apart.
Krypton is more dense than air, so if put in a balloon, it would sink.
Open your books to pg. 57 and read
Figure 2This figure shows how each element has its own unique properties. You use these properties to tell the elements apart and to classify them.
Metal-an element that is shiny and that conducts heat and electricity well.
-They are malleable (can be hammered into thin sheets)
-They are ductile (they can be drawn into thin wires)
Nonmetal-an element that conducts heat and electricity poorly
- solid non-metals are dull in appearance, brittle, and unmalleable
-Few familiar objects are made with them
Metalloid-an element that has properties of both metals and nonmetals.
-Called semi-conductors-Some are shiny-Some are dull-Somewhat malleable and ductile
-They conduct heat and electric current well
Compounds• Compounds
are pure substances.
• Compounds are made from more than one element that are chemically combined.
Familiar Compounds
Compound Elements Combined
Table Salt sodium and chlorine
Water hydrogen and oxygen
Vinegar hydrogen, carbon, and oxygen
Carbon Dioxide carbon and oxygen
Baking Soda sodium, hydrogen, carbon, and oxygen
Compounds• Just as each element has its own
physical properties, so does each compound.
• They also can be recognized by their chemical properties
• Compounds join together in a specific mass ratio each time they form. – Ex: Water forms at a 1:8 ratio of hydrogen
and oxygen. For every 1g of hydrogen there is, there must be 8g of oxygen. Without this, water would not be formed.
Compounds Continued…
• the properties of a compound are very different from the properties of the elements that form itexample:
• sodium is a metal that burns easily
• chlorine is a poisonous gas• they combine to form sodium chloride or table salt
Why do compounds form?
• compounds are formed as the result of a chemical change
• the elements combine to form a new substance with new properties
• a chemical change is also required to break a compound down
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