Electron
Configurations
– a Review and
More…
Electron Configurations
e- configuration notation:
• Reminder – this notation uses # of
e- in a sublevel as a superscript
over the sublevel (block) designation
• Write complete e- configuration
notation for elements 2, 6, & 16
• He:
• C:
• S:
Electron Configurations
e- configuration notation
(noble gas shortcut):
•
•
Reminder – this version uses a noble
gas (group 18) “core” instead of
beginning at 1s
Write noble gas shortcut for elements 12,
21, & 35.
• Mg:
• Sc:
• Br:
Electron Configurations
e- dot notation:
• simplest notation, only shows
valence e- (e- that may be lost,
gained, or shared when
chemical compounds are formed
- they are from s & p blocks)
• Draw dot diagrams for elements
1-10
Ion
Formation…
Ion Formation…
Valence electrons:
• outer shell electrons that may
be lost, gained, or shared
when chemical compounds
are formed
Ion Formation…
Octet rule:
• atoms are most stable when
they have a filled outer shell
of valence e- (usually 8 e-)
• noble gases have this
configuration without any help
– other atoms lose, gain, or
share e- to fill their outer shell
Ion Formation…
Ions:
• Atoms that have either gained
or lost e .
–Gain of e gives a negative
ion called an anion.
–Loss of e- gives a positive
ion called a cation.
Ion Formation…
Ion examples:
• The magnesium ion is Mg 2+. How
many p+ and e- does it have?
• The oxide ion is O 2-. How many p+
and e- does it have?
• An ion has 7 p+ and 10 e-. What ion
is it?
• An ion has 4 p+ and 2 e-. What ion is
it?
Bonding
Chemical Bonds
• link between atoms due to
mutual attraction of nuclei for
e-
Chemical Bonds
Why bond???
• Bonding can result in lower
potential energy (this is usually
associated with a release of
energy)
•Lower energy gives greater
stability (greatest stability
@ completed energy level)
Chemical Bonds
Bonds are classified by how the
valence e- are distributed
around nuclei of combined
atoms
Types of Chemical
Bonds
Ionic bond – results from
electrostatic attraction
between positive and negative
ions (usually done when metal
bonds w/ nonmetal)
Types of Chemical
Bonds
Ionic bond
• Created by transfer of e- from one atom to
another
• Active metals readily give up their e-,
usually to a nonmetal atom
• Oppositely charged ions are formed by
this process of transferring e• Cation: + charged ion
• Anion: - charged ion
Types of Chemical
Bonds
Ionic bond
Forming ionic bonds: e- are
transferred from atom with
lower EN value to one with
higher value
Types of Chemical
Bonds
Ionic bond
Forming ionic bonds:
• How can you determine if
bond is ionic? See if atoms
are active metal & non-metal
or look up EN values to get
difference. (if EN difference is
1.7 to 4.0, ionic bond)
Types of Chemical
Bonds
Ionic bond
Types of ions
• Monoatomic – single element
with charge
• Polyatomic – 2 or more
elements with charge
Types of Chemical
Bonds
Ionic bond
Ionic compound – composed of
positive & negative ions
combined so that the positive
& negative charges are equal
in number (Ex. NaCl instead of
Na2Cl or NaCl2)
Types of Chemical
Bonds
Covalent (molecular) bond –
results from the sharing of ebetween two atoms (usually
done w/ nonmetal atoms)
• The e- are not always equally
shared (like tug of war)
Covalent Bonds
• Bonds between 2 unlike atoms
are never completely covalent
• Non-polar covalent – e- are
shared equally ( which only
happens between two identical
atoms)
• Polar covalent – e- are not
equally shared (due to differences
in electronegativity)
Covalent Bonds
• May share 1 or more pairs of
e• Single bond – single pair of
shared e- between two atoms
• Double bond – two pairs of
shared e- between two atoms
• Triple bond – three pairs of
shared e- between two atoms
Covalent Bonds
• Atoms that are bonded
covalently form stable
particles called molecules
•Ex. CO2, P2O5, NH3, etc.
•7 diatomic molecules to
know - H2, N2, O2, F2, Cl2,
I2, Br2
Covalent Bonds
• Molecular compound –
chemical compound whose
simplest formulas are
molecules
Comparing Properties…
Ionic Compounds
• Held together tightly (due to
attraction of charges)
–High melting point
–High boiling point
–Hard & brittle crystalline solids
–Dissolve in water
–Carry a current (very well) in
water
Comparing Properties…
Molecular Compounds
• Most are not tightly held
–Most have low melting point (due
to weak attractions between
molecules)
–Most have low boiling point
–Usually soft, amorphous solids
–Some dissolve in water
–Do not carry current well in water
Determining Bond Type…
Using Periodic Table
• Metal Element (left of staircase) + Nonmetal
Element (right of staircase)
– Ionic Bond
• Two Nonmetal Elements (right of staircase)
– Covalent Bond
Determining Bond Type…
Using Electronegativity Values
1. Page 161 has a EN chart
– Determine the EN difference between the
two elements in the bond
2. Go to page 176 and find the chart of bond
types. Use the EN difference to determine
type of bond (greater difference = more
ionic character).
– Nonpolar covalent: difference of 0 to 0.3
– Polar covalent: difference of 0.3 to 1.7
– Ionic: difference of 1.7 to 4.0
Determining Bond Type…
Using Observed Properties from Lab
Activity
1.
2.
3.
Representing Compounds Ionic
Empirical formula or
Formula unit – indicates
lowest whole number ratio
of cations to anions in any
sample of an ionic
compound
(ex. NaF = 1 Na+ ion + 1 F- ion)
Representing Compounds Ionic
Empirical formula or Formula
unit – simplest unit indicated by the formula
of any compound (ex. NaF = 1 Na+ ion + 1 Fion)
• This “unit” doesn’t represent something that can
be isolated, it is only the smallest possible ratio
to make a neutral electrical charge
• # of ions in one formula unit depends on the
charges of the ions to be combined (ex. B + F,
Na + Cl, K + O, etc)
Representing Compounds Ionic
Just a thought…
Can you use the periodic table
to determine the charge of an
ion?
Representing Compounds Ionic
Determining formula units by
the crisscross method
• Ca + Br
•K + P
• Al + O
• Ca + O
• Al3+ + OH1• Mg2+ + PO43-
Representing Compounds Molecular
• Molecular formula – shows
the types and numbers of
atoms combined in a single
molecule of a compound
•Ex. CO, H2O2, SO3, O2
Representing Compounds Molecular
• Structural formula – shows
kind, number, arrangement,
and bonds (single, double, or
triple) of the atoms in a
molecule (or polyatomic ion)
•Ex.
Representing Compounds Molecular
• Lewis structures - diagrams
that show valence e- as dots,
the inner e- and nucleus are
included in the letter symbol
for the element being
represented
Representing Compounds Molecular
• Lewis
structures
Reminder…
Group 1
Group 15
Group 2
Group 16
Group 13
Group 17
Group 14
Group 18
Representing Compounds Molecular
• Lewis structures
– Structures of individual elements may
be joined to form compounds
– pairs of dots (or a dash) between
symbols represent bonds (or electron
pairs), dots adjacent only to one symbol
are unshared e– Lone (unshared) pair of e- – pair of ethat is not involved in bonding, but
instead belongs exclusively to one atom
Representing Compounds Molecular
• Lewis structures
Ex. F2, NH3, H2O, CH4, O2, CO2,
N2, CH2O, C2H2, PI3
(must draw structures)
Representing Compounds Molecular
• Lewis structures
Octet exceptions:
Less than full octet
• Ex: Boron compounds such as
BF3
More than full octet – atoms beyond
2nd period, most often S & P (extra ego to 3d level)
• Ex: SF4