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electron shells
a) Atomic number = number of Electrons
• Electrons are placed in shells according to rules:
1) The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.
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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
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Chemical bonds: an attempt to fill electron shells
1. Ionic bonds
2. Covalent bonds
3. Metallic bonds
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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
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Lewis Structure, Octet Rule GuidelinesLewis Structure, Octet Rule Guidelines
When compounds are formed they tend to follow the Octet Rule.Octet Rule: Atoms will share electrons (eOctet Rule: Atoms will share electrons (e--) until it is surrounded by ) until it is surrounded by eight valence electrons.eight valence electrons.
Rules of the (VSEPR) game-i) O.R. works mostly for second period elements.
Many exceptions especially with 3rd period elements (d-orbitals)
ii) H prefers 2 e- (electron deficient)
iii) :C: N: :O: :F:4 unpaired 3unpaired 2unpaired 1unpaired up = unpaired e-
4 bonds 3 bonds 2 bonds 1 bond O=C=O NN O = O F - F
iv) H & F are terminal in the structural formula (Never central)
.. ...
...
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IONIC BONDbond formed between
two ions by the transfer of electrons
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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+
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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+
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Formation of Magnesium Ion
Magnesium atom Magnesium ion
Mg – 2e Mg2+
12 p+ 12 p+
12 e- 10 e-
0 2+
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Some Typical Ions with Positive Charges (Cations)
Group 1 Group 2 Group 13
H+ Mg2+ Al3+
Li+ Ca2+
Na+ Sr2+
K+ Ba2+
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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+
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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+
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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-
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Ions from Nonmetal Ions
In ionic compounds, nonmetals in 15, 16, and 17
gain electrons from metals
Nonmetal ionic charge:
3-, 2-, or 1-
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Fluoride Ion
unpaired electron octet
1 -
: F + e : F :
9 p+ 9 p+
9 e- 10 e- 0 1 -
ionic charge
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Ionic Bond
• Between atoms of metals and nonmetals
• transfer of electrons
• Conductors and have high melting point.
• Examples; NaCl, CaCl2, K2O
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1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.
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COVALENT BONDbond formed by the sharing of electrons
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Covalent Bond
• Between nonmetallic elements of similar electronegativity.
• Formed by sharing electron pairs
• Examples; O2, CO2, C2H6, H2O, SiC
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Bonds in all the polyatomic ions and
diatomics are all covalent bonds
Ex: NO3- CO32-
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when electrons are shared equally
NONPOLAR COVALENT BONDS
H2 CO2 Cl2
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2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom
Oxygen Molecule (O2)
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when electrons are shared but shared
unequally
POLAR COVALENT BONDS
H2O NH3
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- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
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METALLIC BONDbond found in
metals; holds metal atoms together very strongly
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Metallic Bond
• Formed between atoms of metallic elements
• Electron cloud, or sea of electrons around atoms
• Good conductors at all states, lustrous, very high melting points
• Examples; Na, Fe, Al, Au, Co
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Ionic Bond, A Sea of Electrons
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Water
H
O
Each hydrogen has 1 valence electron
Each hydrogen wants 1 more
The oxygen has 6 valence electrons
The oxygen wants 2 more
They share to make each other happy
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Water
• Put the pieces together• The first hydrogen is happy• The oxygen still wants one more
H O
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Water• The second hydrogen attaches
• Every atom has full energy levels
• Remember, the 1st energy level is 2
H OH
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Carbon dioxide• CO2 - Carbon is central atom
• Carbon has 4 valence electrons
• Wants 4 more
• Oxygen has 6 valence electrons
• Wants 2 moreO
C
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Carbon dioxide
• Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short
OC
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Carbon dioxide Attaching the second oxygen leaves
both oxygen 1 short and the carbon 2 short
OCO
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Carbon dioxide The only solution is to share more
OCO
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Carbon dioxide The only solution is to share more
OCO
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Carbon dioxide The only solution is to share more
OCO
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Carbon dioxide The only solution is to share more
OCO
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Carbon dioxide The only solution is to share more
OCO
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Carbon dioxide The only solution is to share more
OCO
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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO
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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO8 valence electrons
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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO8 valence electrons
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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO
8 valence electrons
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How to draw them
• Add up all the valence electrons.• Count up the total number of electrons that
are being shared.• For every pair draw a line.• Fill in the rest of the valence electrons to fill
atoms up.
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HCN
• Put in single bonds• Need 2 more bonds• Must go between C and N
NH C
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HCN Put in single bonds Need 2 more bonds Must go between C and N Uses 8 electrons - 2 more to add
NH C
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HCN Put in single bonds Need 2 more bonds Must go between C and N Uses 8 electrons - 2 more to add Must go on N to fill octet
NH C……
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HCN
NH C