Chapter 5 ‐ Chemical Bonding · Chapter 5 ‐ Chemical Bonding ... Chemical Bonds: are attractive...
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Chapter 5 Notes.notebook mh.notebook 1 February 20, 2018 Apr 308:46 PM Chapter 5 ‐ Chemical Bonding Apr 308:51 PM Section 5.1 ‐ Elements and Compounds What is the difference between elements and compounds? ‐ Elements are pure substances which cannot be broken down into any simpler substances. ‐ Compounds are pure substances that consist of two or more elements bonded in fixed ratios. ‐Only a few elements are found in a pure form. Most are found as compounds.
Transcript of Chapter 5 ‐ Chemical Bonding · Chapter 5 ‐ Chemical Bonding ... Chemical Bonds: are attractive...
Chapter 5 Notes.notebook mh.notebook
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Chapter 5 ‐ Chemical Bonding
Apr 308:51 PM
Section 5.1 ‐ Elements and Compounds
What is the difference between elements and compounds?
‐ Elements are pure substances which cannot be broken down into any simpler substances.
‐ Compounds are pure substances that consist of two or more elements bonded in fixed ratios.
‐Only a few elements are found in a pure form. Most are found as compounds.
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Near the beginning of the course, we learned about electron configurations.
Eg. Draw the electron configuration for the carbon atom.
Draw the electron configuration for the sodium ion.
May 15:44 PM
The only electrons that are involved in bonding are the valence electrons (electrons in the outer ring).
Lewis Dot Diagrams: Show the arrangement of valence electrons around a nucleus.
‐ any electron that is not paired up is called an unshared pair(single electrons in the outer shell) .They participate in bonding while electron pairs usually do not.
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Lewis Dot Diagrams and the Periodic Table
May 22:26 PM
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May 15:43 PM
Section 5.2 ‐ Bond Formation
Why do you think atoms form bonds?
to form full outer shells!!!!
May 16:07 PM
Bonds form so that atoms can satisfy the octet rule.
Octet Rule: when bonds form, atoms lose or gain electrons so that they can create a full outer ring/energy level and have a noble gas configuration. (Hydrogen and helium are the exceptions because the form a full shell with 2 electrons instead of 8)
Chemical Bonds: are attractive electrostatic forces that hold atoms together.
There are three types of bonds:1. Ionic Bonding2. Covalent Bonding3. Metallic Bonding
NOTE: NOBLE (group 8 )GASES ALREADY HAVE FULL SHELLS AND DO NOT NATURALLY FORM BONDS WITH OTHER ELEMENTS.
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1. Covalent Bonding (Molecular Compounds) ‐ A COVALENT BOND is the electrostatic attraction between the nuclei of 2 atoms and a pair of shared electrons.
‐ Individual units in covalent bonds are called molecules.‐ The atoms share electrons to follow the octet rule.
‐ Electrons that are shared between atoms are called SHARED PAIRS. ‐One pair of shared electrons makes one bond and is called a SINGLE COVALENT BOND. ‐Two pairs of shared electrons make two bonds and is called a DOUBLE COVALENTBOND. ‐Three pairs of shared electrons make three bonds and is called a TRIPLE COVALENT BOND.
May 44:35 PM
Examples: ‐ Hydrogen
‐ Chlorine
‐ Fluorine
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Molecules can be made up of multiple atoms. For example, consider methane, which is made up of carbon and hydrogen atoms:
May 16:23 PM
Multiple Bonds‐ When non‐metal atoms have more than one unpaired electron available
for sharing, they can share more than one electron to form bonds.
Example: ‐ Oxygen molecule:
‐ Nitrogen molecule:
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Types of covalent bonds:
Single Covalent Bond: consists of one pair of shared electrons
Double Covalent Bond: consists of two pairs of shared electrons
Triple Covalent Bond: consists of three pairs of shared electrons
Some covalent compounds bond in a special way to form a continuous 3 dimensional arrays that are extremely strong (diamond). They are called NETWORK SOLIDS. Different shapes of a network solid of the same element are called ALLOTROPES.(diamond and graphite)
May 16:09 PM
Ionic BondingIonic bonds involve an electrostatic attraction between the positive and negative ions caused by the transfer of electrons from one substance to another.
Consider sodium and chloride:
Magnesium and Oxygen:
Calcium and Fluorine:
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What is an ionic bond?‐ An attraction between positive and negative ions that forms a crystal
lattice. ‐The smallest neutral unit of an ionic compound is called the Formula Unit.
When the ratio of positive to negative is not 1:1, the crystal lattice becomes more complex, but is still arranged so the positive and negative are as close as possible.
May 44:18 PM
Metallic Bonding
METALLIC BOND‐ An electrostatic attraction between the positively charged metal ions and the pool of valence electrons that moves freely among them.‐ Cannot be explained by the models for ionic bonding or molecular bonding.
How metallic bonds form:‐ The valence electrons in metals
are loosely held, so they are free to move between atoms.
‐ The free‐moving electrons form a sea of electrons which surround the positive ions.
‐ The attraction between the positive and negative charges is what holds the meal together.
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PROPERTIES OF METALS:
1.conduct electricity/heat2.malleable3.ductile4.lustrous
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Property Ionic Compound
Covalent Compound Metal
State of matter solid Solid, liquid, or
gasSolidexcept Hg
MP/BP High Low to high High
Conducts electricity Yes Not usually Yes
Solubility in water High Low to high No
Derivation Metal and nonmetal Nonmetals Metal
Representative Particle
Formula unit Molecule ___
Bond Formation
Transfer electrons
Share electrons
Cation in sea of e
Brittleness Very brittle
Polar = highmed brittleNonpolar = soft
Malleable and ductile
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Section 5.3 ‐ Bonds as a ContinuumIn this section, we will learn about three topics:
1. Trend in Atomic Size2. Trend in Ionic Size3. Trend in Electronegativity
May 810:14 PM
1. Trend in Atomic Size
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1. Trend in Atomic Size:a) Decreases as you move across the period (left to right)
Why? ‐ Electrons are being added to the same energy levels, and new energy levels are not added. ‐ The increase in the nucleus charge causes a greater pull on the outer electrons toward the nucleus.
b) Increases as you move down the group.Why?‐ As you go down the group, electrons are being added to higher energy levels.‐ Since a large number of rings are added, the inner electrons shield the outer electrons from the pull of the positive nucleus (shielding effect).
May 810:26 PM
Trend in Ionic Size
a) Positive ions are always smaller than the neutral atoms from which they are formed.Why?The loss of the outer ring/energy level results in an increased attraction by the nucleus for the fewer remaining electrons.
Lithium Atom Lithium Ion
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b) Negative ions are always larger than the neutral atoms from which they are formed.
Why?The increased number of electrons results in a lower effective nuclear attraction.
Nitrogen Atom Nitrogen Ion
Feb 164:25 PM
Trends in ionic size
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Trend in Electronegativity
Electronegativity: When involved in a bond, some elements attract the shared electrons more than other atoms. This property is named electronegativity.
Example:
Electronegativity Trend: The smaller the atom or ion the better it attracts electrons.
Feb 164:27 PM
the smaller the atom the greater the electronegativity
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Bond Type and ElectronegativityYou can use electronegativity to predict the type of bonds that atoms will form.For example, if two atoms have the same electronegativity, they will form nonpolar covalent bonds.
How to predict the type of bond that will form:‐ find the electronegativity values for the elements involved‐ find the difference between these values‐ use the table to decide the type of bond.
Difference between Electronegativities Type of Bond
0 ‐ 0.4 non‐polar covalent bond
0.4 1.0 moderately polar covalent bond
1 ‐ 2 very polar covalent bond
> 2 ionic bond
May 109:20 AM
‐ The atom with the larger electronegativity value has the electron more than the other atom, and therefore gains a slightly negative charge (δ‐)
‐ The other atom becomes slightly positive (δ+)
‐ This bond is called a dipole because it has two different poles, one positive and one negative.
Example: For each of the following pairs of atoms, use electronegativies to predict the type of bond that will form.
a) oxygen and hydrogen
b) nitrogen and hydrogen
c) fluorine and lithium
d) sulfur and bromine
