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TEMA 2.ENLLA QUMIC
2.1 Estructura atmica
2.2 Enlla inic, nombre de coordinaci
2.3 Enlla covalent
2.4 Enlla metllic
2.5 Forces febles tipus Van der Waals
2.6 Materials: classificaci segons tipus denlla
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Atom the smallest unit of matterindivisible
Heliumatom
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a)
Atomic number = number of Electrons
b)
Electrons vary in the amount of energy
they possess, and they occur at certainenergy levels or electron shells.
c) Electron shells determine how an atom
behaves when it encounters other atoms
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Fig. 2.1
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Comparison of the(a)
Bohr and
(b)
(b) wavemechanical
atom models in terms ofelectron distribution.
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Fig. 2.3
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Schematicrepresentationof the relativeenergies of the
electrons for thevarious shellsand subshells.
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Electrons are placed in shells
according to rules:
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Why are electrons important?
1)
Elements have different electronconfigurations!
different electron configurations meandifferent levels of bonding
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The electronegativity values for the elements
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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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IONIC BOND
Bond formed between
two ions by the
transfer of electrons
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Fig. 2.4
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Formation of Ions from Metals
"
Ionic compoundsresult when metalsreact with
nonmetals
"
Metals loseelectrons to match the number of valence
electrons of their nearest noble gas"
Positive ionsformwhen the number of electrons are
lessthan the number of protons
Group 1 metals ion 1+
Group 2 metals ion 2+
Group 3 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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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
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Ionic Bond
Between atoms of metals and nonmetalswith very different electronegativity
Bond formed by transfer of electrons Produce charged ions all states. Conductors
and have high melting point.
Examples; NaCl, CaCl2, K
2O
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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 theCl becomes (Cl-), charged particles or ions.
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Fig. 2.6
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Fig. 2.7
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Fig. 2.8
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Fig. 2.9
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Fig. 2.10
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Schematic representation of ionic bonding insodium chloride (NaCl).
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Fig. 2.11
Coordination number
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Fig. 2.12
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COVALENT BOND
bond formed by the sharing ofelectrons
Between nonmetallic elements of similarelectronegativity.
Formed by sharing electron pairs
Stable non-ionizing particles, they are notconductors at any state
Examples; O2, CO2, C2H6, H2O, SiC
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Covalent bonds- Two atoms share one ormore pairs of outer-shell electrons.
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NONPOLAR
COVALENT BONDS
when electrons are shared equally
H2or Cl2
POLAR COVALENT BONDSwhen electrons are shared but shared unequally
H2O
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- water is apolarmoleculebecause oxygen is more electronegativethan hydrogen, and therefore electrons are pulled closer to oxygen.
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Fig. 2.14
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Fig. 2.15
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Fig. 2.16
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Fig. 2.17
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Fig. 2.18
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Fig. 2.19
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Bond Properties
bond order, bond length, bondenergy, bond polarity
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Bond OrderFractional bond ordersin resonance structures.Consider NO2
-
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Bond OrderBond order is proportional to two important bond
properties:(a) bond strength
(b) bond length
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Bond Length
Bond length is the distance between the nuclei of twobonded atoms.
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Bond Length
Bond length depends on
bond order.
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Using Bond Energies
Estimate the energy of the reaction
HH + ClCl ----> 2 HCl
Net energy = "Hrxn =
= energy required to break bonds
- energy evolved when bonds are made
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Using Bond Energies
Estimate the energy of the reaction
HH + ClCl ----> 2 HCl
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METALLIC BOND
bond found in metals; holds metal
atoms together very strongly Formed between atoms of metallic elements
Electron cloud around atoms
Good conductors at all states, lustrous, veryhigh melting points
Examples; Na, Fe, Al, Au, Co
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Fig. 2.20
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A Sea of Electrons
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Metals Form Alloys
Metals do not combine with metals. They formAlloys which is a solution of a metal in a metal.
Examples are steel, brass, bronze etc.
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Fig. 2.21
Dipole-Dipole interaction
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Fig. 2.22
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Fig. 2.23
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