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• OBJECTIVES:
–Determine the number of valence electrons in an atom of a representative element.
–Explain how the octet rule applies to atoms of metallic and nonmetallic elements.
• OBJECTIVES:
–Describe how cations form.
–Explain how anions form.
–Explain the electrical charge of an ionic compound.
• OBJECTIVES:
–Describe how cations form.
–Explain how anions form.
–Explain the electrical charge of an ionic compound.
• OBJECTIVES:
–Explain the electrical charge of an ionic compound.
–Describe three properties of ionic compounds.
• OBJECTIVES:
–Describe the arrangement of atoms in a metal.
–Explain the importance of alloys.
The Octet Rule We learned that noble gases are unreactive in
chemical reactions In 1916, Gilbert Lewis used this fact to
explain why atoms form certain kinds of ions and molecules
The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stable Each noble gas (except He, which has 2)
has 8 electrons in the outer level
Formation of Cations• Metals lose electrons to attain a noble gas
configuration.
• They make positive ions (cations)
Electron Dots For Cations• Metals will have few valence electrons
(usually 3 or less); calcium has only 2 valence electrons
Ca
Electron Dots For Cations• Metals will have few valence electrons
• Metals will lose the valence electrons
Ca
Electron Dots For Cations• Metals will have few valence electrons
• Metals will lose the valence electrons
• Forming positive ions
Ca2+NO DOTS are now shown for the cation.
This is named the “calcium ion”.
Electron Configurations: Anions• Nonmetals gain electrons to attain noble
gas configuration.• They make negative ions (anions)
Electron Dots For Anions• Nonmetals will have many valence electrons
(usually 5 or more)
• They will gain electrons to fill outer shell.
P 3-(This is called the “phosphide ion”, and should show dots)
Stable Electron Configurations• All atoms react to try and achieve a noble
gas configuration.• 8 valence electrons = already stable!• This is the octet rule (8 in the outer level is
particularly stable).
Ar
Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to N would like toO would like to
Gain 4 electronsGain 3 electronsGain 2 electrons
Learning Check
A. X would be the electron dot formula for
1) Na 2) K 3) Al
B. X would be the electron dot formula
1) B 2) N 3) P
Chemical bonds: an attempt to fill electron shells
1. Ionic bonds –
2. Covalent bonds –
3. Metallic bonds
IONIC BONDbond formed between
two ions by the transfer of electrons
Ionic Bonding —Ionic Compounds
• Anions and cations are held together by opposite charges (+ and -)
• Ionic compounds are called salts.• The bond is formed through the transfer
of electrons (lose and gain)• Electrons are transferred to achieve noble
gas configuration.
Ionic Bonding
Na ClThe metal (sodium) tends to lose its one electron from the outer level.
The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.
Ionic Bonding
Na+ Cl -
Note: Remember that NO DOTS are now shown for the cation!
Ionic Bonding
• All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).
Ca P
Lets do an example by combining calcium and phosphorus:
Ionic Bonding
Ca P
Ionic Bonding
Ca2+ P
Ionic Bonding
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca
Ionic Bonding
Ca2+ P 3-
Ca P
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+P
3-
Ca2+
Ionic Bonding
= Ca3P2Formula Unit
This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.
For an ionic compound, the smallest representative particle is called a: Formula Unit
Properties of Ionic Compounds1. Crystalline solids - a regular repeating
arrangement of ions in the solid: Fig. 5, page 162
– Ions are strongly bonded together.
– Structure is rigid.
2. High melting points
• Coordination number- number of ions of opposite charge surrounding it
- Page 162
Coordination Numbers:
Both the sodium and chlorine have 6
Both the cesium and chlorine have 8
Each titanium has 6, and each oxygen has 3
NaCl
CsCl
TiO2
Do they Conduct?• Conducting electricity means allowing
charges to move.• In a solid, the ions are locked in place.• Ionic solids are insulators.• When melted, the ions can move around.3. Melted ionic compounds conduct.
– NaCl: must get to about 800 ºC.– Dissolved in water, they also conduct (free to
move in aqueous solutions)
Formation of Ions from Metals
Ionic compounds result when metals react with nonmetals
Metals lose electrons to match the number of valence
electrons of their nearest noble gas
Positive ions form when the number of electrons are
less than the number of protons
Group 1 metals ion 1+
Group 2 metals ion 2+
• Group 13 metals ion 3+
Formation of Sodium Ion
Sodium atom Sodium ion
Na – e Na +
2-8-1 2-8 ( = Ne)
11 p+ 11 p+
11 e- 10 e-
0 1+
Formation of Magnesium Ion
Magnesium atom Magnesium ion
Mg – 2e Mg2+
2-8-2 2-8 (=Ne)
12 p+ 12 p+
12 e- 10 e-
0 2+
Some Typical Ions with Positive Charges (Cations)
Group 1 Group 2 Group 13
H+ Mg2+ Al3+
Li+ Ca2+
Na+ Sr2+
K+ Ba2+
Learning Check
A. Number of valence electrons in aluminum1) 1 e- 2) 2 e- 3) 3 e-
B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5 e-
C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+
Solution
A. Number of valence electrons in aluminum3) 3 e-
B. Change in electrons for octet1) lose 3e-
C. Ionic charge of aluminum 3) 3+
Learning Check
Give the ionic charge for each of the following:A. 12 p+ and 10 e-
1) 0 2) 2+ 3) 2-
B. 50p+ and 46 e-
1) 2+ 2) 4+ 3) 4-
C. 15 p+ and 18e-
2) 3+ 2) 3- 3) 5-
Ions from Nonmetal Ions
In ionic compounds, nonmetals in 5A, 6A, and
7A gain electrons from metals
Nonmetals add electrons to achieve the octet
arrangement
Nonmetal ionic charge:
3-, 2-, or 1-
Fluoride Ion
unpaired electron octet
1 -
: F + e : F :
2-7 2-8 (= Ne)
9 p+ 9 p+
9 e- 10 e- 0 1 -
ionic charge
Ionic Bond
• Between atoms of metals and nonmetals with very different electronegativity
• Bond formed by transfer of electrons
• Produce charged ions all states. Conductors and have high melting point.
• Examples; NaCl, CaCl2, K2O
Ionic Bonds: One Big Greedy Thief Dog!
Naming Ionic Compound
• All names have a predictable pattern.• Name of the cation first, then the anion.
• Cation name remains the same• Anion name will end in –ide.• EXAMPLE: Sodium Chloride
• COMMON ANIONS• Fluorine Fluoride• Chlorine Chloride• Bromine Bromide• Iodine Iodide• Oxygen Oxide• Sulfur Sulfide• Nitrogen Nitride• Phosphorus Phosphide
Section A: Complete the chart using a periodic table to help you.
Answer these questions:
An atom that gains one or more electrons will have a ____________________ charge.
An atom that loses one or more electrons will have a ____________________ charge.
An atom that gains or loses one or more electrons is called an ____________.
A positive ion is called a ______________ and a negative ion is called an _______________.
POSITIVE
NEGATIVE
ION
CATIONANION
“An-Eye-On”
“Cat-Eye-On”
What is an ionic bond?
Atoms will transfer one or more ________________ to another to form the bond.
Each atom is left with a ________________ outer shell.
An ionic bond forms between a ___________ ion with a positive charge and a ________________ ion with a negative charge.
Example B1: Sodium + Chlorine Example B2: Magnesium + Iodine
ELECTRONS
COMPLETE
METALNONMETAL
Example B3: Potassium + Iodine Example B4: Sodium + Oxygen
Example B5: Calcium + Chlorine Example B6: Aluminum + Chlorine
COVALENT BONDbond formed by the sharing of electrons
Covalent Bond
• Between nonmetallic elements of similar electronegativity.
• Formed by sharing electron pairs
• Stable non-ionizing particles, they are not conductors at any state
• Examples; O2, CO2, C2H6, H2O, SiC
Bonds in all the polyatomic ions
and diatomics are all covalent bonds
when electrons are shared equally
NONPOLAR COVALENT BONDS
H2 or Cl2
2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom
Oxygen Molecule (O2)
when electrons are shared but shared
unequally
POLAR COVALENT BONDS
H2O
Polar Covalent Bonds: Unevenly matched, but willing to share.
- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
Polyatomic Ions
• Covalently bonded group of atoms that has a positive or negative charge and acts as a unit.
COMMON POLYATOMIC IONS
• Ammonium -- NH4
• Hydroxide -- OH• Nitrate -- NO3
• Sulfate -- SO4
• Carbonate -- CO3
• Phosphate -- PO4
• Chromate -- CrO4
• Silicate -- SiO3
• Acetate -- C2H3O2
• Peroxide -- O2
What is a covalent bond?
Atoms ___________ one or more electrons with each other to form the bond.
Each atom is left with a ________________ outer shell.
A covalent bond forms between two _________________.
Example C1: Hydrogen + Hydrogen Example C2: 2 Hydrogen + Oxygen
SHARE
COMPLETE
NONMETAL
Example C3: Chlorine + Chlorine Example C4: Oxygen + Oxygen
Example C5: Carbon + 2 Oxygen Example C6: Carbon + 4 Hydrogen
METALLIC BONDbond found in
metals; holds metal atoms together very strongly
Metallic Bonds are…• How metal atoms are held together
in the solid.
• Metals hold on to their valence electrons very weakly.
• Think of them as positive ions (cations) floating in a sea of electrons
Sea of Electrons
+ + + ++ + + +
+ + + +
• Electrons are free to move through the solid.
• Metals conduct electricity.
Metals are Malleable• Hammered into shape (bend).
• Also ductile - drawn into wires.
• Both malleability and ductility explained in terms of the mobility of the valence electrons
1) Ductility 2) Malleability
Due to the mobility of the valence electrons, metals have:
and
Notice that the ionic crystal breaks due to ion repulsion!
Malleable
+ + + ++ + + +
+ + + +
Force
Malleable
+ + + +
+ + + ++ + + +
• Mobile electrons allow atoms to slide by, sort of like ball bearings in oil.
Force
Ionic solids are brittle
+ - + -+- +-
+ - + -+- +-
Force
Ionic solids are brittle
+ - + -
+- +-+ - + -
+- +-
• Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.
Force
Metallic Bonds: Mellow dogs with plenty of bones to go around.
Ionic Bond, A Sea of Electrons
Alloys• We use lots of metals every day, but
few are pure metals
• Alloys are mixtures of 2 or more elements, at least 1 is a metal
• made by melting a mixture of the ingredients, then cooling
• Brass: an alloy of Cu and Zn
• Bronze: Cu and Sn
Why use alloys?• Properties are often superior to the pure
element
• Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware
• Steels are very important alloys– corrosion resistant, ductility, hardness, toughness,
cost
Metals Form Alloys
Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.