Compounds and Chemical Bonds
Part 2
G8 Science
Chapter 8.1
Our Story So Far…
• What is the difference between a compound
and a mixture?
• How are chemical bonds formed?
• How are covalent bonds formed?
• What kind of atoms and how many of each
are found in 2NH3?
• Can two different molecules have the same
chemical formula? Why or why not?
Ions
• When at atom gains or loses
one or more electrons, it is
called an ion.
• Losing electrons means
more protons (+) than
electrons (-). The charge is
positive. [Cation]
• Gaining electros means
more electrons (-) than
protons (+). The charge is
negative. [Anion]
• For G8, assume they will
lose all the electrons in the
outer shell, or fill the shell.
Writing Ions
• Charge is written as a
superscript with the
amount and
magnitude of the
charge.
•
• Lithium loses 1 electron and
becomes Li+
• Calcium loses 2 electrons
and becomes Ca2+
• Aluminum loses 3 electrons
and becomes Al3+
• Flourine gains 1 electron and
becomes Flouride, F• Sulfur gains 2 electrons and
become Sulfide, S2-
Your Turn
•
•
•
•
Write the symbol for a sodium ion.
Write the symbol for bromide.
Write the symbol for a calcium ion.
Write the symbol for oxide.
Ionic Bonds
• Ionic bonds are formed
when one atom loses
electrons and other
atoms gains them.
• + ions [cation] and
–
ions [anions] attract.
• These are NOT called
molecules!
• They are not limited to
pairs.
• Ionic bonds are formed
between metals and
nonmetals.
Ionic bonds form crystal
• Predictable pattern, +
and – balance out.
• Form a unit cell that is
repeated to form
crystal.
• Even when too small to
see, it is a crystal form.
• Sometimes covalent
bonds form crystals,
too.
Why Chemical Bonds Form
Reason One
• Chemically bonded atoms have less energy
than free atoms.
• Where did the extra energy go? Energy is
released when chemical bonds form.
• Atoms form bonds because they require less
energy when they are chemically bonded.
Why Chemical Bonds form
Reason Two
• Nobel gasses are unreactive (mostly).
• All other elements are more, or less, reactive.
• The edges of Periodic Table are highly
reactive. The closer to a noble gas, the more
reactive it is.
• Put sodium and chlorine together and you get
a violent explosion, and salt.
• Atoms form bonds because they are more
stable that way.
Your Turn
• Of the following three elements, which two
will form an ionic compound? C, F, Ca?
• Of the following three elements, which two
will form an ionic compound? P, K, I?
• Of the following three elements, which two
will form an ionic compound? Na, Cl, Mg
Activity
• You will be given a handout and a shared
molecule building kit.
• Each atom has a hole indicting that it may be
bonded to another atom at that point.
• Build each molecule according to the formula and
then draw it.
• I will show pictures of the completed molecules.
• If you get done early, work on homework – do
not socialize.