View
20
Download
1
Category
Tags:
Preview:
DESCRIPTION
Chapter 11. Chemical Bonding. Bond – a force that holds groups of atoms of two or more atoms together and makes them function as a unit Bond Energy – the amount of energy required to break the bond. Types of Chemical Bonds 11.1. Types of Bonds: 4 TYPES. Metallic. - PowerPoint PPT Presentation
Citation preview
TYPES OF CHEMICAL BONDS 11.1
Bond – a force that holds groups of atoms of two or more atoms together and makes them function as a unit
Bond Energy – the amount of energy required to break the bond
Types of Bonds: 4 TYPES
Cations packed in “a sea of electrons”Metals
Metals consist of closely packed cations floating in a “sea of electrons”.
All of the atoms are able to share the electrons.
The electrons are not bound to individual atoms.
Metallic
Type 1: Metallic
Properties of Meatals Good conductors Ductile Malleable
Electrons act as a lubricant, allowing cations to move past each other
Metals have a Crystalline Structure
Packed spheres of the same size and shape: Body Centered
Cubic Face Centered
Cubic Hexagonal Close
Packed
Example: Body Centered Cubic (Chromium)
Type 2: IONIC
Bond between closely packed, oppositely charged ions
Bond between a metal and a nonmetal
hard solid @ 22oC high mp temperatures nonconductors of
electricity in solid phase good conductors in liquid
phase or dissolved in
water (aq)
IONIC picture
Covalent Bonding (2 types)
Instead of gaining or losing electrons atoms can get stable by sharing electrons
This is always between two non-metals.
Two fluorine atoms, for example, can form a stable F2 molecule in which each atom has 8 valence electrons by sharing a pair of electrons.
In covalent bonds they can share
more than two electrons
Type 3&4: COVALENT
Electrons are shared
Have low melting, boiling points
Do not conduct electricity when melted or dissolved in water
relatively soft solids as compared to ionic compounds at room temp
COVALENT picture
Covalent bond –subtype #1
When two of the same elements bond they are called diatomic molecules, some examples of this are Hydrogen H2, Oxygen O2 and Nitrogen N2.
The atoms in these bonds would have the same electronegativities. This means that both atoms attract the shared electrons to that same extent.
Non-polar Covalent picture
Dipole Moment 11.3
A molecule that has a center of positive charge and a center of negative charge
Dipole often represented by an arrow Points towards
negative charge center and its tail indicates the positive charge center
Cation & Anion Sizes
Cations (positively charges ions) are SMALLER then their parent atom while Anions (negatively charged ions) are LARGER then their parent atom
****Original atom is in GRAY, ion is in color
The Octet Rule The octet rule says that atoms tend to gain, lose or share electrons so they have eight electrons in their outer shell.There are some exceptions to the octet rule (imagine that)
BF3
BCl3PF5
SF6
Ionic Bonding: (this should be review)
http://www.youtube.com/watch?v=T40sM8-SXso
Covalent Bonding:
http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH6404
Follow the interactive website!
Drawing Lewis Structures
Arrange the element symbols. Central atoms are generally those with the highest bonding
capacity. Carbon atoms are always central atomsHydrogen atoms are always peripheral atoms
Add up the number of valence electrons from all atoms. For polyatomic ions, add one electron for each negative charge
and subtract one for each positive charge.
Draw a skeleton structure with atoms attached by single bonds.
Complete the octets of peripheral atoms.Place extra electrons on the central atom.If the central atom doesn’t have an octet, try forming
multiple bonds by moving lone pairs.
Single, Double and Triple Bonds
With Covalent bonds the elements can share two or more electronsA Single Bond is when 2 electrons are shared they are represented by a single line in bond diagramsA Double bond is when 4 electrons are shared they are represented by two lines in bond diagramsA Triple bond is when 6 electrons are shared they are represented by three lines in bond diagrams
Electronegativity Values The electronegativity values can be
found in the periodic table The higher the value the higher the
electronegativity The Pauling scale is used to measure
electronegativity. It is a relative scale running from 0.7 to 4.0 (hydrogen = 2.2).
The units for electronegativity are Pauling units.
Electronegativity
The ability of an atom to attract electrons when bonded
1. Nonmetals have high electronegativity2. Metals have low electronegativity3. Electronegativity increases across a period and
decreases down a group. WHY???
Electronegativity Chart
Why would the metals have low electronegativity numbers?Why don’t the noble gases have electronegativity numbers?
Nonpolar Covalent Bond
When electrons are shared between 2 atoms, a covalent bond is formed.
If the atoms are identical, e.g. Cl2, the electrons are shared equally (nonpolar)
Cl = 3.0 therefore 3.0-3.0 = 0 0 = nonpolar
Polar Covalent Bond
If the electrons are shared between 2 different atoms, e.g. HBr, the sharing is unequal
The bonding electrons spend more time near the more electronegative atom
H = 2.1 and Br = 2.8 THEREFORE 2.8-2.1 = 0.7
0.7 = a polar covalent bond
H Br
Bond Type by Electronegativity Value Remember the higher
the atom’s electronegativity value, the closer the shared electrons tend to be to that atom when it forms a bond
Therefore, the polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond
The greater the difference, the more polar the bond.
Electronegativity Difference
Type of Bond Formed
0.0 to 0.5 nonpolar covalent
0.51 to 1.6 polar covalent
> 2.0 ionic
Electronegativity Differences Why is therea gap between 1.6 and 2.0????
If the two atoms are metals = ionic bond If nonmetal & metal = polar covalent bond
Electronegativity Difference
0 to 0.5
Nonpolar covalent
0.51 to 1.6
Polar covalent
> 2.0
Ionic
Sample Problems
Choose the bond that will be more polar H-P or H-C O – F or O – I N – O or S – O N – H or Si - H
Sample Problems
Choose the bond that will be more polar H-P or H-C O – F or O – I N – O or S – O N – H or Si - H
Polar Molecules (overall polarity of the molecule)
Note: Not all molecules with polar bonds are polar molecules
The dipoles in symmetrical molecules cancels out The bond is polar but the molecule is nonpolar
How to determine polar moleculesThere are two important factors1. The polarity of the individual bonds in the
molecule; 2. The shape or geometry of the molecule. Steps to takea) Determine if a given individual bond is
polar, Look at the difference between electronegativity of the atoms in the perioidc table. If the difference is:
0.3 < non polar 0.3 - greater = polar
b) Determine the shape of molecule. For now I will give them to you. Later you will figure out the shape yourself.
i) if all bonds are non-polar, then the whole molecule is non-polar regardless of its shape.
ii) If there is symmetry in the molecule so that the polarity of the bonds cancels out, then the molecule is non-polar. (symmetry arround the central atom)
iii) If there are polar bonds but there is no symmetry the overall molecule is polar.
Recommended