Download A chemical bond forms between atoms when valence electrons

! A chemical bond forms
between atoms when valence
electrons move between them.
They can be transferred or
shared.
What is a chemical formula?
! A chemical formula is a
shorthand way of showing the
number and type of atoms in
a compound or molecule.
Ionic Bond
MgCl2
Magnesium Chloride is used for ice and dust
prevention.
Rule 1
Write the symbol for the more metallic
element first. Then, write the symbol for the
non-metallic element.
Rule 2
Write the oxidation number for each element.
(The numbers can be found on the periodic
table)
Rule 3
Then, criss-cross the oxidation numbers to
use as subscripts to balance the formula.
Subscripts are used to indicate the number of
atoms each element has in that compound.
Ionic Bonding
! The giving up of electrons.
! Often between metals & non-
metals
Metals
! Most elements are classified
as metals (80%)
! Hard, shiny, and malleable
! Conduct heat and electricity
well
! 3 or fewer electrons in the
outer ring
NonMetals
! Gases or brittle
! Dull and insulators
! 5 or more electrons in the
outer ring
Covalent Bonding
Two methane molecules
Covalent Bonding
! The sharing of electrons
! In a covalent bond, both
atoms, attract the shared
electrons at the same time.
! Often form between 2 or more
non-metals
How many valence
electrons does H
have?
How many does H
need to be full?
How many valence
electrons does C
have?
How many does C
need to be full?
What are the formulas for these three
covalently bonded molecules?
What is
the
formula
for this
molecule?
Haha…Water You Talking About?
Hopefully you have known the chemical
formula for water is H2O.
Each H ion carries a +1 charge: H+1
The O ion carries a -2 charge: O-2
Therefore, it takes 2 H+1 ions to balance
1 O-2 ion so the formula for water is H2O.
This is a subscript indicating the number of H ions
Writing Chemical Formulas (Compounds)
Key Point: Compounds do not carry a
charge. The positive (+) charges carried
by the cation must be balanced by the
negative (-) charges carried by the anion.
The pluses must equal the negatives.
Write the + ion first and – ion second.
Chemical
Bonding
Ionic
Chemical Bonding
(Metal and Nonmetal))
Transfer
of Electrons
Positive ions Negative ions
(anions)
(cations)
gain electrons
lose electronns
Metals
Nonmetals
Na+1
Cl-1
Mg+2
O-2
Al+3
P-3
Covalent
(Nonmetal and Nonmetal)
Sharing
of Electrons
Molecules
Polar:
Larger Nonpolar:
atom
Share
holds electrons
most of equally
the electrons
N2
O-2
H 2O
H+1 H+1
N:N
Balancing Chemical
Equations
Terms to know:
Reactants
Yields or Produces
Products
Coefficient
Subscript
Zn + 2HCl
! Zn + 2HCl
Reactants
ZnCl2 = H2
ZnCl2 = H2
Products
Yields/Produces/Equals
! 2HCl The 2 is a coefficient
! ZnCl2 The 2 here is a subscript
Step 1:
Write the formulas of the reactants
on the left side and products on the
right side.
! Example formula: Al + PbO
! Draw an
to indicate
that a reaction takes place.
! What is the formula Al + PbO?
Aluminum plus Lead Oxide
! Write the products on the right side
as single ions (no subscripts).
Al + PbO
AlO + Pb
(Single Replacement Reaction)
Key Point:
The number of atoms on the
reactants (left) side must equal the
number of atoms on the product
(right) side.
Step 2:
Balance the charges (valences) in
the new compound(s) with
subscripts.
•  Al + PbO
Al2O3 + 3Pb
Al+3O-2 + Pb+2
Step 3:
Balance the number of ions on both
sides of the equation (use coefficients).
! 2Al + 3PbO
Al2O3 + 3Pb
! 2Al + 3Pb + 3O = Al2O3 + 3Pb