TEKS 6.5A: Know that an element is a pure substance represented by chemical symbols.
TEKS 6.5C: Differentiate between elements and compounds on the most basic level.
What are elements?
• An element is a pure substance that cannot be broken down
into any other substances.
• Each element can be identified by its specific physical and
chemical properties.
• Each element is represented by a one- or two-letter symbol.
• Carbon: C
Oxygen: O
• Hydrogen: H
Aluminum: Al
• Elements are made of particles called atoms. Elements have
different properties because their atoms are different.
1. Apply Concepts Give an example of a common object
made from a single element.
TEKS 6.5A: Know that an element is a pure substance represented by chemical symbols.
TEKS 6.5C: Differentiate between elements and compounds on the most basic level.
What are compounds?
• Atoms can be held together
by a chemical bond. Two or
more atoms combined by
chemical bonds may form a
particle called a molecule.
• A compound is a substance
made of two or more elements
that are chemically combined
in a set ratio. Molecules of a
compound are always made
up of the same ratio of atoms
of each element.
(contd.)
TEKS 6.5A: Know that an element is a pure substance represented by chemical symbols.
TEKS 6.5C: Differentiate between elements and compounds on the most basic level.
• A chemical formula represents a compound. The numbers in
a chemical formula show the ratio of atoms of each element. If
there is no number, the number is assumed to be 1.
• In the formula for carbon dioxide, CO2, the 2 means there
are two atoms of oxygen (O) for each atom of carbon (C).
• In the formula for carbon monoxide, CO, there is one atom
of oxygen for each atom of carbon.
• Compounds have different properties than the elements in
them have.
• Sulfur: yellow, powdery element
• Silver: shiny, metal element
• Silver sulfide (tarnish): black compound
2. Identify The formula for water is H2O. How many atoms of
hydrogen are there for each atom of oxygen?