Formation of Compounds - Wikispacessaxonylutheransciencelove.wikispaces.com/file/view/... · ·...
Transcript of Formation of Compounds - Wikispacessaxonylutheransciencelove.wikispaces.com/file/view/... · ·...
Objectives 4.1
• Distinguish the properties of compounds
from those of the elements which they are
composed of.
• Compare and contrast the properties of an
ionic compound and covalent compound
• Analyze evidence to conclude that
differences exist in the ways compound
form
Salt and its Elements
• Sodium and Chlorine
– What are the physical and chemical
properties of these two elements?
– What are the physical and chemical
properties of salt?
Carbon Dioxide
• Carbon and Oxygen
– What are the physical and chemical
properties of these two elements?
– What are the physical and chemical
properties of carbon dioxide?
Water
• Hydrogen and Oxygen
– What are the physical and chemical
properties of these two elements?
– What are the physical and chemical
properties of Water?
• Why do compounds have different
properties than the elements that make
them up?
• How do we know that the elements have
even bonded?
Self Quiz 4.1
• 3 Compounds
– 1 Physical Property of each element that is
different from the compound
– 1 Chemical Property of each element that is
different from the compound
– Compounds can share elements but must
have different properties listed
Objectives 4.2
• Model two types of compound formation:
Ionic and covalent at the atomic level.
– Metallic as well
• Demonstrate how and why atoms achieve
chemical stability by bonding.
• Compare, using examples, the effect of
covalent and ionic bonding on the physical
and chemical properties
Key Terms 4.2
• Octet Rule
• Noble gas
configuration
• Ion
• Ionic compound
• Ionic bond
• Crystal
• Covalent Bond
• Covalent Compound
• Molecule
• Electrolyte
• Intermolecular Force
• Intramolecular Force
– Interparticle Force
Chemical Properties
– Dictated by valence electrons (outermost
electrons)
• Octet Rule: Outermost shell can hold 8
electrons. • Will discuss expanded outer shells later courses
• A full outer shell is associated with
stability, being unreactive
• Full outer shell = Noble Gas Configuration
Attaining the Octet
• Electron Transfer (Steal or Lose)
• Elements which have not lost or gained
electrons are neutrally charged: 1 Proton
for 1 Electron
• Gaining or losing changes this
Review
• How many valence electrons do the following atoms have?
• Ar
• K
• O
• N
• F with a -1 charge
• Mg with a +2 charge
Terminology
• Ion = Atom that has a positive or negative
charge
• Cation = Atom that has a positive charge
– Has lost an electron
• Anion = Atom that has a negative charge
– Has gained an electron
• Electrolyte = An ion in a water solution
Ionic Bonding
• When we say Ionic Bonding, there really is no “Actual” bond.
• Instead, two atoms are electromagnetically attracted to one another by having different charges
• This “Bond” is actually very strong
– (The electromagnetic repulsion between two electrons is roughly 43 powers of 10 times larger than gravitational attraction)
Formation of Ionic Bonding
• Three processes (Endothermic and
Exothermic)
• The loss of an electron from one atom
(always endothermic)
• The gain of an electron from one atom
(first electron is usually exothermic)
• The “Attractive Bond” formed (always
exothermic)
Cl–Na+ Cl–
Ionic bonding• Ionic bonding involves 3 steps (3 energies)
• 1) loss of an electron(s) by one element, 2)
gain of electron(s) by a second element, 3)
attraction between positive and negative
Na Cl
e–1) 2)
3)
Na+
Formation of the Bond
• Consider Mg and O forming an Ionic
Bonding
– Magnesium needs to lose 2 electrons, taking
the 2nd electron away is very endothermic
– Oxygen needs to gain 2 electrons, adding a
2nd electron is always endothermic
• The only way this could happen is if the
final bond formed is very strong
(Electromagnetic Forces)
Formation of the Bond
• The bond between Mg and O is very
strong, much stronger than the bond
formed between Na and Cl.
• The reason is the larger charges
– The bigger the magnet, the harder to pull
apart, which also means
– The more energy released when forming the
bond
Ionic bonding: Mg + O
Mg + O [Mg]2+[O]2–
12p+
12n02e- 8e- 2e-
1e-
[ O ]2–[Mg]2+
6e- 2e-
8n08p+
1e-
8e- 2e-
8n08p+12p+
12n02e- 8e-
OMg
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1e-
17p+
18n07e- 8e- 2e-
13p+
14n0 2e- 8e-3e-
17p+
18n07e- 8e- 2e-
17p+
18n07e- 8e- 2e-
Ionic bonding: Al + Cl
1e-
1e-17p+
18n08e- 8e- 2e-
17p+
18n08e- 8e- 2e-
17p+
18n08e- 8e- 2e-13p+
14n0 2e- 8e-
Ionic Compound
• Composed of Ions
• Ions organized into crystal patterns
How the atoms arrange themselves
• Crystal structure is dependent upon
– Size of atoms
– Ratio of Charges
• Beyond the scope of this course to go into great
detail about this, but there are many different ways
the atoms rearrange themselves
Melting Points/Boiling Points
• MgF2 1534 K Melting 2512 K BP
• NaCl 1074 K 1686 K
• CaI2 1057 K 1373 K
• Water 273 K 373 K
• Ionic compounds in general have higher
melting and boiling points than covalent
bonds. (Strong EMF)
You don’t need to know this but
may find it interesting
• The larger the charges, the higher the
MP/BP
• The smaller the atoms, the higher the
MP/BP
• LiF will have a higher MP than NaCl
Covalent bonding
• Thus far we have looked at when atoms
bond due to the transfer of electrons
• An ionic bond forms when an atom has a
greater attraction for e–s than a second atom
• However, if two atoms have approximately
the same pull on electrons, they share the
electrons (forming a “covalent” bond)
• Atoms bonded like this are called Molecules
Covalent Compounds
• Formed from atoms covalently bonded to
one another.
• Boiling point/Melting point much lower
than Ionic
Covalent bonding
CCl4 - Covalent
C
Cl
Cl
Cl
Cl
HCl - Covalent
H Cl
MgF2 - Ionic
[ F ]2–[Mg]2+
H2O - Covalent
H O H
NH3 - Covalent
H N H
H
NaCl - Ionic
[ Cl ]–[Na] +
OH– - Covalent
O H
H2 - Covalent
H H
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Multiple bondsHCl - Covalent
H Cl H Cl
CO2 - Covalent
C OO
Na2O - Ionic
[ O ]2–[Na]2+
H N H
H
H N H
H
OO
OO
O2 - Covalent
OO C
II
II
I2 - Covalent
[ O ]32–[Al]2
3+
Al2O3 - Ionic
NH3 - Covalent
OO O
O OO
O3 - Covalent
H C H
H
H
H C H
H
H
How many bonds?
• For non-metals, who form bonds, the
number of bonds is equal to the number of
electrons they still need (their would be
ionic charge)
– F = 1
– O = 2
– N = 3
– C = 4
Comparing Ionic and Covalent
– Ionic
• Solid at room
Temperature
• Charged Particles
• Strong IMF’s
– Intermolecular forces
– Covalent
• Gas or Liquid at room
Temperature
• Neutrally Charged
Molecules
• Weak IMF’s
• Strong Intramolecular
forces
Ionic or Covalent Substance?
• Metal + Nonmetal = Ionic Properties
• Nonmetal + Nonmetal = Covalent Prop’s
• Metal+ Metal = Metallic Properties
• Spectrum: The bigger the electronegative
differences, the larger % of ionic character
– But we will use the three rules above
The quiz
• 25 Questions
– 4 Metallic, Ionic, or Covalent Bond
• Na and Fr, Mg and Cl, F and N
– 3 how many electrons do they need gain/lose
• Na 1, Mg 2, O 2, F 1
– 3 Different properties of ionic v covalent
– 4 Questions ionic charge or amount of bonds
• Na +1, Mg + 2, O -2 or two bonds, F – 1 or 1 bond
– Other questions: General terms/process of
forming the bonds