Elements that exist as
Molecules
Elements that exist as
Molecules
Elements that exist as
Molecules
Elements that exist as
Molecules
H2;
F2;
H2;
F2;
C;
C;
N2; O2; O3;
Cl2;
Br2;
I2
N2; O2; O3;
Cl2;
Br2;
I2
S8;
S8;
Diatomic Molecules
C;
N2; O2; O3;
Cl2;
Br2;
I2
Allotropic Molecules
H2;
F2;
C;
C;
N2; O2;
Cl2;
Br2;
O3;
I2
N2; O2; O3;
Cl2;
Br2;
I2
Triatomic Molecule
Elements that exist as
Molecules
H2;
F2;
H2;
F2;
S8;
Molecular Compounds
O
C
O
Carbon Dioxide
S8;
S8;
Molecular Compounds
Molecular Compounds
H
O
C
O
H
Carbon Dioxide
Molecular Compounds
H
H
N
H
Ammonia
Molecular, Empirical, and Structural Formulas
•Molecular formulas refer to the actual number of
the different atoms which comprise a single
molecule of a compound.
•Empirical formulas refer to the smallest whole
number ratios of atoms in a particular compound.
Molecular Formula
Water
Hydrogen Peroxide
Ethylene
Ethane
•Structural formulas
H
Ammonia
Compound
Molecular, Empirical, and Structural Formulas
N
H2O
H2O2
C2H4
C2H6
Empirical Formula
H2O
HO
CH2
CH3
Writing Structural Formulas
Rules:
Carbon has four bonds
Hydrogen has one bond
Oxygen has two bonds
Nitrogen has three bonds
H
H O C C H
O H
Ions
The nucleus of an atom remains unchanged after
ordinary chemical reactions, but atoms can
readily gain or lose electrons.
If electrons are lost or gained by a neutral atom,
then the result is that a charged particle is
formed - called an ion.
Valence Electrons
The outermost electrons in an atom.
These are the electrons most
responsible for bonding
Charges on Ions
Monoatomic ions
Let’s revisit the Periodic Table
Ions
Cations (Positive Charge)
Group
1A, 2A, 3A
Charges 1+, 2+, 3+
Anions (Negative Charge)
Groups
5A, 6A, 7A
Charges 3-, 2-, 1-
In general, metal atoms tend to lose electrons,
and nonmetal atoms tend to gain electrons.
Many atoms gain or lose electrons such that
they end up with the same number of electrons
as the noble gas closest to them in the
periodic table.
Polyatomic Ions:
Complex ions having more than
one atom.
Memorize!
Name
Ion
ammonium
NH4+
Carbon-based Anions
cyanide
CNacetate
CH3CO2carbonate
CO32hydrogen carbonate HCO3(Bicarbonate)
Nitrogen-Family Based
Anions
nitrate
nitrite
NO3NO2-
phosphate
PO43hydrogen phosphate HPO42dihydrogen phosphate H2PO41-
Chlorine Family Anions
hypochlorite
chlorite
chlorate
perchlorate
ClOClO2ClO3ClO4-
Miscellaneous Anions
chromate
dichromate
CrO42Cr2O72-
permanganate
MnO4-
Oxygen-Family Anions
hydroxide
OH-
sulfate
hydrogen sulfate
HSO4sulfite
SO42-
SO32-
Naming Oxyanions
polyatomic anions contain oxygen, and are
referred to as oxyanions
Ionic Compounds
Ions of opposite charge
The attractive force of + and is called a Coulombic Attraction
Predict the ionic bond strength
of the following ionic bonds .
Q1*Q2
Force of attraction = ------d2
Not a true chemical bond
Anions (- charge) are
larger than neutral atoms
Cations (+ charge) are
smaller than neutral atoms
Consider a cation and an anion
How to think about formulas of ionic compounds?
Must consider conservation of charge
Same number of + as Pure ionic compounds typically have their atoms
in an organized three dimensional arrangement
(a crystal)
Use empirical
formula to describe.
How to write formulas for
ionic compounds
m-
n+
NaCl
Na
Cl
1. Identify ions
2. “Cross” charges
n+
What you have
really done is
conserve charge.
m-
MgCl2
Mg
Cl
The + = - !
Cl
3. Write formula
m
n
Naming Ionic Compounds
Cations are named as the metal + “ion”
Na+ = sodium ion
Naming Ionic Compounds
MgBr2
Magnesium bromide
Multicharged ions
Metal (Charge in Roman Numerals)
“ion”
Cu 1+
Cu2+
Copper(I) ion
Copper(II) ion
More Examples
Name:
Mg(NO3)2
FeO
CuBr2
NaHCO3
Fe2O3
Iron(III) oxide
Ca3(PO4)2
Calcium phosphate
Naming Binary Compounds
of the Non-metals
Named in order of increasing group number
N2O4
Dinitrogen tetroxide
SF6
Sulfur hexafluoride
N2O
Dinitrogen oxide