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The Properties of a Compound are Different from the Properties of the Elements that make up that
Compound
Calcium Chlorine
Calcium Chloride
Copper Chloride
CopperChlorine
NaHCO3 MgCl2
Al(OH)3 Ca(NO3)2
Chemical Formula: Used to represent the kinds and numbers of atoms in a chemical compound.
HC2H3O2Subscript
Be(ClO2)2 Subscript multiplies to all subscripts in parentheses!
What must happen for elements to react with each other?
• Atoms of the elements must collide.
• The valence electrons are what actually collide in when elements form compounds.– This is because the valence
electrons are the outermost layer.
Valence Electrons
• The electrons in the outermost energy level of an atom
• Responsible for an atom’s chemical properties
LEWIS DOT DIAGRAMS
• A diagram where dots are placed around the chemical symbol of an element to illustrate the valence electrons
Octet Rule
• Octet = 8• States that atoms tend to gain, lose or share
electrons in order to acquire a full set of valence electrons. – For most elements this is 8 valence electrons– Hydrogen & Helium only require 2 valence
electrons• The elements are all trying to be like the Group 18
elements, the noble gases b/c they have 8 valence electrons– Atoms form compounds to become stable!
How do atoms obtain a noble gas configuration?
• By sharing or transferring electrons with other atoms– Example: Show how Na & Cl can become stable.
The bond between Na & Cl is due to:
ANIONS: Have gained electrons and have a negative charge (nonmetals)
CA+IONS: Have lost electrons and have a positive charge (metals)
ION: AN ATOM THAT HAS AQUIRED A CHARGE BY GAINING OR LOSING
ELECTRONS
If atoms transfer electrons to form a bond they become IONS
Ionic Compound: Compound formed from ionic bonds
• Ionic Bond: The strong attractive force between ions of opposite charge. Occurs when one atom transfers electrons to another atom to become stable
EMPIRICAL FORMULA Chemical formula for an ionic compound Lowest whole number ratio of ions in an ionic
compound
Types of elements in an ionic compound An ionic bond is formed between a
______________ and a __________ because: Ionic bonds are formed between ions of
opposite charge Therefore, ionic bonds form between
____________ and _____________ because metals form cations and nonmetals form anions.
metal nonmetal
metal nonmetal
How do Ionic Compounds Form? Electrons are _______________________ in an
ionic bond because: one atom is trying to lose electrons to become stable and the other atom is trying to gain electrons to become stable
transferred
EMPIRICAL FORMULA
Al2O3Subscript: # written to the lower right of a chemical symbol that shows the number of atoms of that element present in the compound
3 WAYS TO DETERMINE AN EMPIRICAL FORMULA
1. Use Lewis Dot Diagrams
2. Use charges
3. Use the Crisscross Method
Draw the Lewis Dot Diagram for each element Use arrows to show the transfer of electrons between atoms Determine the number of each element necessary to make
each atom
1DETERMINING THE EMPIRICAL FORMULA BY USING
LEWIS DOT DIAGRAMS TO ILLUSTRATE THE IONIC BOND
PROPERTIES OF IONIC COMPOUNDS
•Made of ions
•Typically a metal and nonmetal(s)
•Crystalline Solids
•Hard yet Brittle
•Strong Interparticle Forces
•High Melting and Boiling Points
•Will conduct electricity when molten or dissolved in water
INTERPARTICLE FORCES: Forces of attractions between neighboring particles (atoms, ions or molecules)
Ionic compounds have __________________ interparticle forces due to the strong electrostatic attraction between the cation(s) and anion(s)
Because of these ________________ interparticle forces, ionic compounds have _____________ melting points.
Strong
Strong
high
CRYSTAL: A regular, repeating arrangement of ions in an ionic compound
The arrangement of ions in an ionic compound determines the crystal structure (shape) of the crystal itself.
ELECTROLYTE: A compound that conducts an electric current when it is in an aqueous solution or in a molten state http://www.youtube.com/watch?v=EBfGcTAJ
F4o
IONIC COMPOUNDS Ions of opposite charge strongly
___________ each other. Ions of like charge strongly ______________ each other.
As a result of this, how are ions arranged in an ionic compound?
attract
repel
Positive ions tend to be near negative ions and farther from other positive ions.
Metallic Bonding:Metallic Bonding: The attraction of free The attraction of free floating valence electrons for the floating valence electrons for the
positively charged metal ions.positively charged metal ions.
Made of just Made of just metal metal atomsatoms
Pure metals are not simply 1 atom of Pure metals are not simply 1 atom of the metal. They are multiple atoms of the metal. They are multiple atoms of
that metal bonded by a sea of electrons.that metal bonded by a sea of electrons.
Metallic Properties Come From Metallic Properties Come From their “Sea of Electrons”their “Sea of Electrons”
Metallic bonds form from a “Sea of Metallic bonds form from a “Sea of Electrons”: The pool of electrons shared Electrons”: The pool of electrons shared by all the atoms in a metallic substanceby all the atoms in a metallic substance
Malleability:Malleability: The ability to The ability to be hammered be hammered into sheetsinto sheets
Metals are malleable because the metal Metals are malleable because the metal atoms can slide through the electron sea atoms can slide through the electron sea to new positionsto new positions
Ductile:Ductile: Able to be Able to be pulled into wirespulled into wires
Metals are ductile Metals are ductile because electrons because electrons in the sea of in the sea of electrons move to electrons move to allow atoms to align allow atoms to align like a wirelike a wire
ConductivityConductivity
Electricity is Electricity is caused by moving caused by moving electronselectronsMetals conduct Metals conduct because the sea of because the sea of electrons is free to electrons is free to move and, move and, therefore, free to therefore, free to conduct electricityconduct electricity
Interparticle ForcesInterparticle Forces
Metallic bonds have strong interparticle Metallic bonds have strong interparticle forces. For this reason metals:forces. For this reason metals: Are typically solidsAre typically solids Are crystallineAre crystalline
Metals are arranged in very compact and orderly Metals are arranged in very compact and orderly patternspatterns
Have average to high meltingHave average to high melting
ALLOY:ALLOY: A mixture composed of 2 or more A mixture composed of 2 or more elements, at least 1 is a metalelements, at least 1 is a metal
NAME OF ALLOYNAME OF ALLOY % MAKE UP% MAKE UP EXAMPLEEXAMPLE
Stainless SteelStainless Steel 73-79% Fe73-79% Fe14-18% Cr14-18% Cr7-9% Ni7-9% Ni
Sterling SilverSterling Silver 92.5% Ag92.5% Ag7.5% Cu7.5% Cu
18-karat white gold18-karat white gold 75% Au75% Au12.5% Ag12.5% Ag12.5% Cu12.5% Cu
14 karat gold14 karat gold 58% Au58% Au14-28% Ag14-28% Ag14-28% Cu14-28% Cu
Covalent Bonding: Bonding in which electrons are shared Electrons spend most of their time between
the atoms.
The attraction between the nucleus and the shared electrons holds the atoms together.
Covalent Bonds Form molecules instead of crystals.
Molecule: The combination of atoms formed by a covalent bond
Types of Elements in a Covalent Bond Therefore, covalent compounds are formed
between 2 or more ____________________ because _____________ are the type of element that want to gain, not lose, electrons.
In a covalent bond, the atoms share electrons because both atoms want to gain electrons.
nonmetals
nonmetals
Ionic Compound (Metal & Nonmetal) or Covalent Compound (All Nonmetals)
Which type of bond would form between the following elements?MgCl2 NI3 AlN
CO2 F2 SnO2
Covalent Bonds Structural Formula: Shows the arrangement
of atoms in a molecule or polyatomic ion
O
HH
Space Filling Model Ball & Stick Model Structural Formula
LEWIS STRUCTURES
• Uses dashes and dots to show the bonding arrangement of atoms in a covalent compound– Drawn to model the bonding in a covalent compound.– Based on: Lewis Dot Diagrams– Dashes (): Each dash represents a bond (or 2
shared electrons)
LONE PAIR
Triple Covalent Bond 3 shared pairs of electrons between 2 atoms
Represented by: ≡ Example:
Lone Pairs (): Represents an unshared pair of electrons
Using Lewis Dot Diagrams to Determine the Lewis Structure Draw the Lewis Dot Diagrams for each atom
in the Molecular Formula Determine how the atoms will SHARE
electrons so that all atoms are
(N-A)/2 = # of Bonds in Molecule N = # of electrons needed to make an each element
in the compound stable N = 8 electrons for all elements except H and He which
need 2 electrons A = # of valence electrons each element in the
compound has There are 2 electrons per bond so we divide the # of
electrons they need to share by 2 to determine the number of bonds
Some General Guidelines• Carbon is typically in the center of the molecule• If possible, keep the molecule symmetrical• Hydrogen & the halogens can only accept one
electron and, therefore, tend to be on the perimeter of the molecule
• Sometimes, the formula will help you figure out the structure
• Check your work: Do all atoms have 8 electrons? Does H have only 2 electrons?
Exceptions to the Octet Rule
1) Atoms with less than an octet Boron may not acquire a full octet, it may
only obtain 6 electrons--it has only 3 valence electrons to start
2) Atoms with more than an octet Especially phosphorus & sulfur
3) Molecules with Odd Numbers of Electrons Any molecule that has an odd number of
available electrons, especially compounds of Nitrogen
Coordinate Covalent Bond
A covalent bond in which one atom contributes both bonding electrons
C
C OO
Properties of Covalent Compounds Made of molecules All nonmetals Often liquids or gasses Brittle if solid Weak Interparticle Forces Low Melting and Boiling Points Do not conduct electricity when molten or
dissolved in water
More Properties… Covalent compounds have ______________
interparticle forces Because of these _______________ interparticle forces,
covalent compounds have low melting and boiling points
Bond Dissociation Energy: The energy needed to break the bond between two covalently bonded atoms A high bond dissociation energy corresponds to a strong
covalent bond
weak
weak
Ionic Ionic CovalentCovalent MetallicMetallic
Type of Type of ElementsElements
StateState
Electrons Electrons are…are…
Hard or Hard or brittle?brittle?
Melting Melting PointsPoints
Made of…Made of…
MOLECULAR GEOMETRY
• VSEPR THEORY– Valence Shell Electron Pair Repulsion Theory
• In small molecules, the pairs of valence electrons are arranged as far apart from each other as possible
NO!!!
YES!!!
Ball-and-Stick Models
• Drawings that represent molecular compounds. The balls are used to represent atoms and the sticks are used to represent bonds.
Geometry Bonds Lone Pairs Bond Angles
Example
Tetrahedral 4 0 109.5
Trigonal Planar
3 0 120
Trigonal
Pyramidal 3 1 107
Bent 2 2 105
Linear 2 or
Diatomic molecules
0 180
Bond Length • Different pairs of atoms form bonds
with different lengths– Not represented in a ball-and-stick
model
• As you move down a group on the periodic table, the atoms form longer bonds because the atoms become larger
• Multiple bonds are shorter than single bonds– The more electrons there are, the
more attraction there is for the opposite nuclei
– Bonds are “electrical glue”
Electronegativity: The ability of an atom to attract electrons when the atom is in a compound
• Shows how much an atom will attract valence electrons
• The higher the electronegativity the more an atom attracts the electrons towards it
EN
The difference between two atoms electronegativities determines the type of bond formed between those two atoms EN = EN1-EN2
is the Greek Letter delta and means change EN is always positive (always subtract the
smaller number from the larger number) Example: Calculate the EN between
Cesium and Fluorine
You can think of bonding as a tug-of-war for electrons
between atomsThe electronegativity of the atom tells you how hard
that atom is pulling for the electrons
Ionic Bond
When one atom wants the electrons so much more than the other atom that it pulls the electron off the other atom (a tug-of-war where one side wins) EN > 2.0 (greater than 2.0)
Nonpolar Covalent Bond
Like an even tug-of-war—both atoms want the electrons equally so the electrons stay between them EN < 0.4 (less than 0.4)
Polar Covalent
One atom wants the electrons more than the other but not enough to pull it all the way towards itself—like an uneven tug-of-war EN is between 0.4 & 2.0
Polar Covalent Bonds
Polar bonds have partially charged atoms due to the unequal sharing of electrons Dipole: A partial charge on an atom.
If the EN on a bond is between 0.4 and 2.0 then that bond has a dipole (partial charge)
This is because one atom wants the electrons more than the other but not enough to cause a complete transfer
DIPOLE
: Symbol for a dipole or a partial charge Used to label the partial charges on a
polar bond Two ways to label the dipoles
(partial charges) on a polar bond
FEN = 4.0-2.1=0.9 (polar)
H FHor
+ -
2.1 4.0 C-Cl
To determine the polarity of a molecule:
1) Does the molecule have only nonpolar bonds? YES: It is nonpolar
2) Is the molecule completely symmetrical in all dimensions?
YES: It is nonpolar
If the molecule contains at least 1 polar bondand is not completely symmetrical in all
dimensions, then the whole molecule is POLAR
Electronegativity Differences & Bonding
The greater the difference between the electronegativities of the bonding atoms, the more unequally those atoms share electrons
The symbol for electronegativity difference: EN
Ionic Bonds
EN is > 2.0 This is because one atom wants the
electrons much more than the other Because of the high EN you can
assume that the electron on the less electronegative atom is transferred to the other atom
Nonpolar Covalent Bonds
EN is < 0.4 This is because both atoms have almost
an equal attraction for the electrons Because of the low EN the atoms are
shared equally These molecules are gases or low-boiling
point liquids at room temperature These bonds are also known as Nonpolar
Covalent Bonds
Example
Label the dipoles on a CCl bond.
Could also use vectors to label a polar bond.
Example: Use a vector to label the dipoles on a C-Cl bond.
To determine the polarity of a molecule:
• Draw the Lewis Structure of the Molecule with the correct geometry
• Use electronegativity values to determine if any of the individual bonds are polar. If so, label the dipoles.
• Using vector addition, check to make sure the dipoles do not cancel out.– If at least 1 vector/dipole does not cancel out, the
molecule is polar.– If all the vectors/dipoles do cancel out, the molecule is
nonpolar• Vectors will only ALL cancel out if the molecule is linear or
tetrahedral and completely symmetrical!
Properties of Polar Covalent Bonds
• Higher Boiling Points than Nonpolar Covalent Bonds
• Molecules can “stick” together and form puddles
• Hydrophilic: ionic & polar (mix easily with water)– Like dissolves like
ATTRACTIONS BETWEEN MOLECULES
Responsible for determining whether a
molecular compound is a gas, liquid or
solid at a given temperature.
Van der Waals Forces
Consist of Dipole Interactions & Dispersion
Forces
Dipole Interactions: Occur when polar molecules are attracted to one another
Similar to but much weaker than ionic bonds
Dispersion Forces: Caused by the motion of electrons•Weakest of all molecular interactions
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