Chemical bonding

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Bonds: a force that holds groups of two or more atoms together and makes them function as a unit
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Required 2 e- to make a bond
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Bond energy: amount of energy required to form or to break the bond

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Occurs in ionic compound
Results from transferring electron
Created a strong attraction among the closely pack compound

Electron Affinity ( E ea): The energy released when a neutral atom gains an electron to form an anion

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Formation of a covalent Bond
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Two atoms come close together, and electrostatic interactions begin to develop
Two nuclei repel each other; electrons repel each other
Each nucleus attracts to electrons; electrons attract both nuclei
Attractive forces > repulsive forces; then covalent bond is formed

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Electronegativity
(EN): the ability of an atom in a molecule to attract the shared electron in a bond
Metallic elements – low electronegativities
Halogens and other elements in upper righthand corner of periodic table – high electronegativity

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Polar covalent bonds – the bonding electrons are attracted somewhat more strongly by one atom in a bond
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Electrons are not completely transferred
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More electronegative atom: δ- .
(δ represents the partial negative charge formed)
Less electronegative atom: δ+

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Predicting bond polarity
Atoms with similar electronegativity (Δ EN <0.4)
–form nonpolar bond
Atoms whose electronegativity differ by more than two (Δ EN > 2) – form ionic bonds
Atoms whose electronegativity differ by less than two (Δ EN < 2) – form polar covalent bonds

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For each of the following pairs of bonds, choose the bond that will be more polar a. H-P, H-C b.
N-O, S-O

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Dipole moment:
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 a vector quantity from the center of the positive charge to the center of negative charge
Represents with an arrow
E.g Draw the dipole moment for HF, H
2
HCl, OF
O,

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Atoms in stable compounds almost always have a noble gas electron configuration
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Predicting Formulas of Ionic Compound
Electrons lost by a metal come from the highestenergy occupied orbital
Electrons gained by a nonmetal go into lowestenergy unoccupied orbital

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Predicting formulas of Ionic compound by showing how they loses or gains electrons
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Ca and O
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Sr and Cl

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Lattice energy (U) – the sum of the electrostatic interaction energies between ions in a solid
Refer to the breakup of a crystal into individual ions

 represents how an atom’s valence electrons are distributed in a molecule
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Show the bonding involves (the maximum bonds can be made)
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Try to achieve the noble gas configuration

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Duet Rule: sharing of 2 electrons
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E.g H
2
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H : H
Octet Rule: sharing of 8 electrons
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Carbon, oxygen, nitrogen and fluorine always obey this rule in a stable molecule
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E.g F
2
, O
2
Bonding pair: two of which are shared with other atoms
Lone pair or nonbonding pair: those that are not used for bonding

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Recall: Elements typically obey the octet rule; they are surrounded by eight electrons single bond: involves two atoms sharing one electron
Double bond: involves two atoms sharing two pair of electrons
Triple bond: involves two atoms sharing 3 pair of electrons
Use 6N + 2 Rule
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N = number of atoms other than Hydrogen

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If
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Total valence – (6N + 2) = 2
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 1 double bond
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Total valance e- - (6N + 2) = 4
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 two double bonds or 1 triple bond

O
O
O
O
Cl O Cl
O
O O
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Draw a dot Lewis structure of ClO
4
-
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Calculate the total number of valence electrons of all atoms in the molecule
Cl – Valence e- = 7
O – Valence e - = 6 x 4 = 24e-
ClO
32 e-
4
=> total valence e- = 7 + 24 +1 ( -1 charge) =

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Create a skeletal structure using the following rules:
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 a.Hydrogen atoms (if present) are always on the “outside” of the structure. They form only one bond b.The central atom is usually least electronegative . It is also often unique (i.e,. the only one atom of the element in the molecule).
Remember, there might be no “central” atom.
c.Connect bonded atoms by line (2-electron, covalent bonds

O
O
Cl O
O
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Place lone pairs around outer atoms (except hydrogen) so that each atom has an octet

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Calculate the number of electrons you haven’t used.
Subtract the number of electrons used so far, including electrons in lone pair and bonding pairs, from the total in Step 1. Assign any remaining electrons to the central atom as lone pair
Cl-O bonds = 4 x 2e- = 8 e-
O – 4 x 6e- = 24 e-
Total used = 8 + 24 = 32 e-

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If the central atom is B (boron) or Be (beryllium), skip this step
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If the central atom has an octet after step 4, skip this step
If the central atom has only 6 electrons, move a lone pair from an outer atom to form a double bond between outer atom and the central atom
If the central atom has only 4 electrons, do Step 5a to two different outer atoms (i.e, form two double bonds) or twice to one outer atom (i.e., form one triple bond)

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Give the Lewis structure for the following
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Na
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H
2
O
CF
4
,
CO2
O
NH
4
+
BeF
2
NO
3
,