Download K-2 Science

Molecules, Atoms and
Compounds
Element
A
substance made up of
only one kind of atom.
Examples: Helium, Copper,
and Gold
Compound
A
substance made up of 2
or more DIFFERENT
elements.
Examples: Copper II oxide,
salt (NaCl) and water (H2O)
Element or Compound?
Ca
Na2O
O2
Can be written with
Chemical Symbols
1 or 2 letters used to represent
an element
st
1
letter is always capitalized
If there is a 2nd letter it is lower
case
Chemical Formulas
Subscripts indicate the number of
atoms of the element.
Example: AlCl3
1 aluminum atom
3 chlorine atoms
Chemical formulas

Practice:
 NH4Cl
 Mg(OH)2
 Pb(NO3)2
Drawing Molecules
represents a molecule made up
of 2 different elements
Another way to draw a molecule:
Drawing Molecules
Draw a pictorial representation of the following:
Oxygen
Calcium
Ca
O2
CaO
Drawing Practice

H2 O

NH3

CCl4