Bond. Chemical Bond.
Get a packet on the back
table
Important Stuff...
• Extra Credit – Alternate Periodic Table – due
tomorrow at the latest.
• First 36 elements change – names and
symbols and basic information. Quiz window
is NEXT week.
Unit 3:
Chemical Bonding
Ionic, Covalent, and Metallic
Review
• The periodic table is divided into
sections called PERIODS (rows) and
GROUPS (columns)
• Those elements in the same group
have SIMILAR chemical properties.
• They also have the same number of
electrons in their outer shell (valence
electrons).
Review: the structure of an atom
• Remember that atoms are made of
protons, neutrons and electrons
• The electrons surround the nucleus
which is made up of protons and
neutrons
How many electrons can be held in
each orbit or shell?
What do these rings indicate?
Although the outer shells can hold 18 and 32, they are
considered stable when the have 8 ELECTRONS in the
outer level.
Valence electrons The outermost s and p electrons of an atom that
take part in forming bonds with other atoms.
Everyone wants to have or feel like they have
how many?
What about Helium, hydrogen, lithium and
beryllium?
What do you notice as you go down a
group?
What about as you go across a period?
What about the groups?
• All atoms in Group 1 (alkali metals)
have 1 electron in the outermost
shell or orbit .
Alkaline Earth metals
• They each have 2 electrons in the
outer shell.
The transition elements
• These elements may have different
numbers of electrons in the outer
shell.
Boron Group
• This group contains elements with 3
electrons in the outer shell
Carbon Group
• This group has 4 electrons in the
outer shell
Nitrogen and Oxygen groups
• Nitrogen group has
5
• Oxygen group has
6
Halogens and Noble Gases
• Halogens have 7
• Noble gases have a
complete outer shell
( 8 electrons)
• The dots…
• Start with a pair on the right, then singles,
and then pair them.
Fill in the top table…
• First three columns, only.
Oxidation Number
• Indicates how many electrons an
atom will gain or lose in a
chemical reaction.
+n (cation) = loses electrons, n=# of
electrons
-n (anion) = gains electrons, n=# of
electrons
What does the oxidation number tell
you?
Group 1 is +1 because all the members
of this groups lose 1 electron to become
stable
Metals will lose valence electrons and
become POSITIVE
What happens to the halogens…how
do they get a negative charge?
• The halogens are -1 because
they need to pick up 1 electron
to complete their shell.
• Nonmetals will gain valence electrons
and become NEGATIVE
Oxidation Numbers: Write on your Periodic Table,
fill in earlier table, too…
Special Oxidation numbers
• The transition elements can have
more than one oxidation number
• See handout – inside front cover
• You must look at the name of the
compound to figure out what the
oxidation number should be.
Putting things together…literally
Forming chemical compounds
Chemical compounds: two or more
elements bonded together
(2 elements = binary compound, 3 =
ternary compound)
The goal of reactions: stability
• What does “stable” mean?
• Every atom wants to have or feel like
they have a full valence shell.
What happens when there are not
eight electrons?
An atom loses, gains or shares electrons
in order to have a complete outer shell.
This is done in a chemical reaction.
To get stable:
Atoms are joined and held together by
chemical bonds.
Three kinds:
• Ionic
• Covalent
• Metallic
Stability
Transferring e-
IONIC
 Sharing
COVALENT
e-
How many electrons will an atom lose?
• No more than 4 electrons…after that
it prefers to pick up the extras rather
than give them away. Think of
ionization energy and
electronegativity…
Types of Chemical Bonds:
Form between a metal and a nonmetal.
Ionic bonds form when electrons are gained
or lost and the two charged atoms (ions) are
attracted to each other
The charge of the compound formed is equal
to zero. If a compound has a charge it
considered a POLYATOMIC ION.
Occurs between ions
Remember:
Atom loses e-  becomes (+) cation
Atom gains e-  becomes (-) anion
Ionic Bonding occurs between positive and
negative ions
When an ionic bond occurs, one element donates
an e- [becoming (+)] and the other element
receives the donated e- [becoming (-)]
Example:
Na & Cl
1s22s22p63s1
donates e-
1s22s22p63s23p5
receives donated e-
Sodium (on the left) loses its one valence electrons
to Chlorine (on the right),
Ionic bond:
In an ionic bond, the metal gives up electrons,
while the nonmetal gains them. The metal and
nonmetal hold together STRONGLY.
NaCl – why a crystal?
• Positive and negative ions line up in an
evenly-spaced lattice in 3 dimensions.
Na+
Cl-
Signs of an ionic compounds:
always look for at least two.
• At room temperature, most are crystals.
• Dissolve well in water, but NOT in a nonpolar liquid
• High melting/boiling points
• The crystals DO NOT conduct electricity –
the ions are NOT free to move.
• Melt ‘em, or dissolve ‘em, the ions can
move and can conduct electricity.
I say “ionic,” you say:
salt
• Polyatomic ions
Cluster of atoms that form a charged
particle. Stay together, even in
compounds.
• Positively charged polyatomic ions act like
metals and combine with non-metals or
negative polyatomic ions.
• Negatively charged polyatomic ions act
like nonmetals and combine with metals
or positive polyatomic ions.
Examples: NH4+ – ammonium; OH- hydroxide
Naming these things
• Metal/cation’s name first, then the
nonmetal/anion
• Replace the nonmetals end letters with –ide (ine, -gen, -ur, -orous change to ‘ide)
• Never ever change the name of a polyatomic
ion, whether it’s first or last. Never, ever.
Writing formulas: Ionic
• To write a chemical formula you must
know the oxidation numbers
• Simply swap the oxidation number
and write as a subscript of the other
element
Every atom in
an ionic
compound be
like…
Get your
Straight Up
Bonding Stuff
packet out.
Important Stuff...
• First 36 elements change – names and
symbols and basic information. Quiz window
is NEXT week.
• Quiz Friday
Let’s practice…
• Bonding Basics: Ionic Bonds – finish up…
• Polyatomic ions –
A bound group of atoms that form a charged
particle.
They are found in ionic compounds.
The atoms in the polyatomic ion almost always
stay together, even in compounds.
Positively charged polyatomic ions act like metals
and combine with non-metals or negative
polyatomic ions.
Negatively charged polyatomic ions act like
nonmetals and combine with metals or positive
polyatomic ions.
Practice…
• Formulas and Names…
Arts and Crafts…
• Ions in Your Hands
– Yes, you need to cut the pieces of paper out. At
least one set of ions per group of two.
– Yes, I said groups of two.
– No – I don’t care. Groups of two.
– Two is not three.
– One is not two.
– The sheet is due tomorrow.
– It’s a lot of work.
– Stop reading this and start working.
Important Stuff...
• First 36 elements change – names and
symbols and basic information. Quiz window
is NEXT week (but not Monday morning – I
have a meeting)
• Quiz tomorrow.
Today:
• Finish up Ions in Your Hands: 20 minutes and
turn it in.
• Covalent Bonds (in Straight Up Bonding Stuff)
Important formula thought…
All the subscripts in
formulas MUST be in
the smallest possible
ratio
Mg3(PO4)2 – yes
Na2O - yes
Mg6(PO4)4 – no
Na6O3 – no
Mg2O2 - no
Types of Chemical Bonds:
• Covalent Bond: forms when atoms
are shared.
• Forms between 2 or more nonmetals
SINGLE BOND
DOUBLE BOND
Forming covalent bonds: electrons
• When forming a covalent compound
between nonmetals, the number of
electrons needed it equal to the
number of electrons shared.
• Example: carbon and chlorine.
Carbon needs four electrons, it
shares four. Chlorine needs one,
each chlorine shares one.
Bond formed between uncharged
atoms.
Since there is no electrostatic
attraction, bond forms by the sharing
of e-  (valence e-)
A covalently-bonded compound is
called a molecule
By sharing electrons, each Hydrogen
atom has two valence electrons, thus
filling their outer orbits. Likewise,
Oxygen now has 8 outer orbit electrons.
This makes a stable molecule.
Can also look like this:
(the “sticks” represent a shared pair of
electrons)
Covalent bonds:
• Not as strong as ionic bonds.
• Not “weaker” just not as strong.
Covalent bonds/compounds:
• Sometimes crystals, sometimes gases,
sometimes liquids. Wider range of forms.
• Have lower melting and boiling points
than ionic compounds
• Many don’t dissolve well in water – but
there are exceptions; dissolve well in
nonpolar liquids
• Don’t conduct electricity in water
I say “covalent,” you say:
sugar
By the way, I say “ionic,” you say:
salt
Signs of an ionic compounds:
always look for at least two.
• At room temperature, most are crystals.
• Dissolve well in water, but NOT in a nonpolar liquid
• High melting/boiling points
• The crystals DO NOT conduct electricity –
the ions are NOT free to move.
• Melt them, or dissolve them in water, the
ions can move and can conduct electricity.
Polyatomic Ions
• NO3-1 – tell me about it.
Polyatomic Ions
• NO3-1 – is covalently molecule, but act like an
ion in a compound (because it has a charge).
Naming compounds: covalent
• Element furthest on the left of the Periodic
Table is named first
• 2nd element’s last letters replaced with –ide
(example: chlorine -> chloride)
• Use Greek prefixes for the number of atoms
(mono, di, tri, tetra, penta, hexa, hepta, octa,
nona, deca) Don’t use mono if there is only
one atom of first element.
Practice:
• Bonding Basics: Covalent
• Btw - sometimes you’ll have more than 2
elements in a covalent compound…
General practice…
Grid sheet & naming sheets – due on Monday,
March 7th
Get your notebook set up for the quiz
I’m
meeeelting!
Today:
•
•
•
•
•
Final I/C thoughts
Ionic & Covalent Quiz
Polarity
Electronegativity & Bonds
Naming/Formula Packet due Monday.
Polar Covalent Molecules
• Sometimes the electrons in covalent
bond are not shared equally.
• In this case one atom pulls the
electrons towards it …why?
Polar Covalent Molecules
• This causes the compound to have
slight positive or negative charges
• As a result a weak bond called a
Hydrogen bond is able to form
Back the bus up – Polar? Nonpolar?
• What’s this?
Yeah….no. Not this time..
Wrong – it’s a water molecule
Hydrogen +
Oxygen -
Hydrogen +
Don’t believe me?
• Believe your eyes…
Other examples of polar and nonpolar
molecules:
Polar
Water
Nonpolar
Fats
Diatomic molecules
Polar Molecules:
Only happens in covalently bonded
molecules.
•“Polar” means that the molecule has “poles”
or a (+) area and a (-) area.
•A molecule’s polarity is due to the unequal
distribution of electrons.
I say “polar,” you say:
water
Water is a polar molecule
• Can “rip” ionic compounds like NaCl apart.
• Positive part of H2O pulls at negative Cl-,
negative part of H2O pulls at positive Na+.
Also • Like dissolves like….
• Polar dissolves polar
• Non-polar dissolves non-polar
Which makes this kind of funny…
I’m
meeeelting!
Metallic Bonding –
between metal atoms
Pieces of metal such as Cu & Fe consist of
closely packed cations
The cations are surrounded by mobile valence
e- that are free to drift from one part of the
metal to another
Metallic Bond  consist of the (+) charged
metal ions plus an “electron sea” of valence
electrons.
These forces are what hold metals together
and give them “metallic” properties.
Metallic Properties due to Bonding
Conduction of electricity (free flowing e-)
High MP & High BP
Malleable  hammered into sheets
Ductile  drawn into wires
Luster  shiny
ALLOYS
• Metal solution made by bonding one metal
into another metal
• Since alloys are mixtures, the different
metals can be separated according to their
different melting points
• Properties of alloys are different from
their parent metals
– Either stronger or weaker
– Either harder or softer
Example of Alloys
• Amalgams (always contain Hg, also
sometimes contain Zn and Ag) used in fillings
• Sterling silver
• Stainless steel
• Gold - less than 24K
• Aircraft aluminum
Electronegativities & Bonds
• Ionic bonds happen between atoms with
large differences between the absolute
differences (ΔEN) of their
electronegativities.
• Covalent bonds happen between atoms
with small differences between the
absolute differences (ΔEN) of their
electronegativities.
Electronegativities:
• The closer the ΔEN is to 4.0, the more
likely the bond between atoms will be
ionic, while a ΔEN value between 1.7 and
0.3 indicates a polar covalent bond will
form, and an ΔEN between 0.3 and 0.0
indicates a non-polar covalent bond will
form.
Hydrate vs. Anhydrous
If a compound has water added it is called a
HYDRATE
When the water is removed it is ANHYDROUS
Na2CO3*10H2O
Naming Acids & Bases
Acids
• Binary Acid
– An acid that contains 2 elements, one of which is
H. Example: HCl.
– Naming – hydro + element stem + ic
– Hydrochloric acid
– What about HBr? HF?
Ternary Acid
• An acid that contains 3 elements, one of
which is H.
• Take the polyatomic ion name:
– If it ends in –ate , change to –ic + acid.
Example - HNO3
– If it ends in –ite , change to –ous + acid.
Example - HClO2
Naming Bases
• Most bases end in OH, except for ammonia,
which is NH3.
– Write name of the first element.
– Make sure it doesn’t need a Roman Numeral
– Add word hydroxide.
Examples:
• NaOH  sodium hydroxide
• Ca(OH)2  calcium hydroxide