Transcript Physical Science

Physical Science
Ch. 19
Section 1
Stability in Bonding
• Compounds
–Two or more elements
combining to make a
substance
• Compounds have
different properties than
the elements that make
them up
• Chemical Formula
–composed of symbols and
subscripts indicating the
number of atoms of an
element in a compound.
• Subscript
–Means “written below”
• Atoms form compounds when
the compound is more stable
than the separate atoms.
• Noble gases
–Elements in far right column
–Are more chemically stable than
other elements because they
have a complete outer energy
level.
• Stable Compounds
–Elements that do not have full
outer energy levels are more
stable in compounds.
–Atoms can lose, gain, or
share electrons to get a
stable outer energy level.
• Chemical bond
–the force that holds atoms
together in a compound.
Section 2
Types of Bonds
Forming a bond
• Chemical Bonds
–When two elements come
together by either transferring
or sharing electrons
–When elements lose or gain
electrons
• The result of bonding is a
net charge of zero
• Ion
–A charged particle because it has
more or fewer electrons than
protons.
• Cation
–Positively charged ion
–When an atom loses an electron
• Anion
–Negatively charged ion
–When an atom gains an electron
• Molecules
–Neutral particles formed as
a result of sharing
electrons.
• Covalent bond
–the force of attraction
between atoms sharing
electrons.
• Ionic bond
–the force of attraction
between opposite charges
of the ions
• Chemical Bonding
–Result is a neutral
compound.
–Sum of the charges is zero.
• Atoms can form double or
triple bonds depending on
whether they share two or
three pairs of electrons
–Saturated
• all single bonds
–Unsaturated
• Not all single bonds
• Must contain at least one
double or triple bond
•Polar molecule
–Opposite ends have
opposite charges
•Nonpolar molecule
–electrons are shared
equally.
• Ionic Compounds
–With ions (cations and anions)
–Between metal and non-metal
–Transfer of electrons
• Covalent Compounds
–With molecules
–Between two non-metals
–Sharing of electrons
Section 3
Writing Formulas and
Naming Compounds
• Chemists use symbols from the
periodic table to write formulas
for compounds.
• Binary compound
–composed of two elements
• Oxidation number
–how many electrons an atom has
gained, lost, or shared to become
stable
–The apparent charge on an
element
• To write formulas
–Use oxidation numbers
–Least common multiples
• When writing formulas,
remember that the compound is
neutral.
• A formula must have the correct
number of positive and negative
ions so the charges balance
–The formula must have a neutral
charge
Writing Binary Compounds
1. Write down first element & it’s
oxidation number
2. Write down second element &
it’s oxidation number
3. Add multiples of the
appropriate element until total
charge is zero
4. Use subscripts to show ratio
of the atoms of each element
Calcium Oxide
Ca +2
-2
O
+2
-2
So 1 Ca and 1 O
CaO
Lithium Nitride
Li +1
N-3
+1 -3
+1
+1
So 3 Li and 1 N
Li3N
Magnesium Phosphide
Mg +2
P-3
+2
+2
-3
-3
+2
So 3 Mg and 2 P
Mg3P2
Potassium Sulfide
K +1
-2
S
+1
+1
So 2 K and 1 S
K2S
-2
Naming Binary Compounds
1. Write down name of
first element
2. Write down name of
second element
3. Change the ending of
the second element to
–ide
NaCl
• Sodium
Chlorine
-ide
Sodium Chloride
K2O
• Potassium
Oxygen
-ide
Potassium Oxide
•Poly
–Means “many”
•Polyatomic ion
–positively or negatively
charged, covalently
bonded group of atoms
–Many atoms
• Hydrate
–compound with water
chemically attached to it
• Binary covalent
compounds
–Name by using prefixes to
indicate how many atoms of
each element are in the
compound
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
MonoDiTriTetraPentaHexaHeptaOctaNonDec-
Prefixes for
Covalent
Compounds