chemical bonds chemical bond mutual electrical attraction between the nuclei and valence electrons...
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Chemical Bond Mutual electrical attraction between the
nuclei and valence electrons of different atoms that binds the atoms together.
Ionic BondBonding that results from the electrical attraction between large numbers of cations and anions
A large difference in electronegativity between two atoms in a bond will result in ionic bonding
Covalent (Molecular) BondSharing electrons pairs between
two atomsA small difference in
electronegativity between two atoms in a bond will result in covalent bonding.
ElectronegativityA measure of the ability of an atom in a chemical compound to attract electrons.
Valence Electrons
Electrons in the highest occupied energy level of an elements’ atom
Determines the chemical properties of an element
Examples:
The Octet Rule
Atoms tend to gain, lose, or share enough electrons to become surrounded by eight valence electrons
Non-metallic elements gain electrons or share them
Metallic elements lose electrons
Electron Dot Notation
An electron configuration notation in which only the valence electrons of an atom of a particular element are shown
Indicated by dots placed around the element’s symbol
○ Example:
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
Dot notation can be used to represent moleculesExample: (H : H) represents a shared
electron pair An unshared pair or lone pair is a
pair of electrons that is not involved in bonding and belongs exclusively to one atomExample: Lone Pair
Lewis Structures
Electron distribution is depicted with Lewis electron dot structures
Electrons are distributed as shared or Bond Pairs or unshared or Lone Pairs
Steps:
•Write electron dot notation for each atom in molecule.
•Determine total number of valence electrons.
•Arrange atoms to form skeleton structure for molecule.
•If Carbon is present it will go in the center. Otherwise least electronegative atoms will be in the center. Hydrogen never is in the center
Steps ContinuedConnect atoms by electron-pair bonds
Add unshared pairs of electrons so each nonmetal is surrounded by 8 electrons
•Count the electrons to see it matches the number of valence electrons
•If too many electrons create double or triple bonds.
Lewis Structure Bond Formula
N A
2 # bonds
•To determine how many bonds exist in a molecule, use the following formula: N-A = # of Bonds 2
•Electrons are shared and represented by a dash
• lone electrons are represented by dots.
N-A = # of Bonds 2 Where: N = # of needed electrons, ( 8 for all elements but H, which
is 2.) A = # of available electrons (the
number of valence electrons.)
Example: Write the Lewis structure of NH3
The total number of valence electrons is:
The number of electrons needed is:
A = 8
1 x 8 = 8
3 x 2 = 6N = 14
Connect the atoms with electron pairs. Remember 8 electrons are needed to obey the octet rule
Finish the structure by using the remaining electrons as lone pairs
Check that the final Lewis structure has the correct number of valence electrons (8) except Hydrogen (2)
Write the Lewis structure of H2CO
2 (H) 2 x 1 = 2
1 (C) 1 x 4 = 4
1 (O) 1 x 6 = 6
A = 12
Needed (N)Available (A)
2 (H) 2 x 2
1 (C)1 x 8
1 (O)1 x 8
= 4
= 8
= 8
N = 20
Cl ClThis is the chlorine molecule,
Cl2
Single Covalent BondCovalent bond produced by the sharing of one pair of electrons between two atoms
or
Multiple Covalent Bonds Double Bond
Covalent bond produced by the sharing of two pairs of electrons between two atoms○Shown by either two side-by-side
pairs of dots or by two parallel dashes
Triple BondCovalent Bond produced by sharing of
three pairs of electrons between two atoms
Carbon forms a number of compounds containing triple bonds
Lewis structures for molecules that contain carbon, oxygen or nitrogen, remember that multiple bonds between pairs are possible
If too many electrons have been used, subtract one or more pairs until the total number of valence electrons is correct. Then move one or more lone electron pairs to existing bonds between non-hydrogen atoms until the outer shells of all atoms are completely filled.
Ionic Bonding & Ionic Compounds
Ionic CompoundComposed of positive
(cations) and negative (anions) ions that are combined so that the numbers of positive and negative charges are equal.
Most ionic compounds exist as crystalline solids.A crystal of any ionic compound is
a 3-D network of positive and negative ions mutually attracted to each other.
Formation of an ionic bond can be viewed as a transfer of electrons
Crystal Lattice
In an ionic compound, the ions minimize their potential energy by combining in an orderly arrangement.
The distance between ions and their arrangement in a crystal represents a balance among all forces.
Properties of Ionic Compounds
High melting points Solids at room temperature Soluble in polar solvents,
insoluble in Nonpolar solvents Molten compounds & aqueous
solutions conduct electricity
Metallic Bonding
Chemical bonding is different in metals than it is in ionic, molecular or covalent network compounds
Metallic Bonding
Chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons
An attraction of the free-floating valence electrons for the positively charged metal ions.
Metallic Properties
Good conductors of electricity and heatMalleability
○ Ability of a substance to be hammered or beaten into thin sheets
Ductility○ Ability of a substance to be drawn,
pulled, or extruded through a small opening to produce a wire.
Intermolecular Forces Reviewing what we know
Low density Highly compressible Fill container
Solids
• High density • Slightly compressible • Rigid (keeps its shape)
Gases
Polar Molecule vs. Nonpolar Molecule
•One very important property of molecule is whether it is polar or nonpolar.
•If the electrons in a molecule are not evenly distributed, the molecule can have a negative and positive side.
•A polar molecule will dissolve in another polar substance (such as water).
•Nonpolar molecule will dissolve in another nonpolar substance (such as carbon tetrachloride).
Polar vs. Nonpolar Rules
1. If the central atom has no lone pairs and has all the same types of atoms attached to it, then the molecule is nonpolar.
2. If the central atom has no lone pairs but different atoms attached to it, the molecule is polar.
3. If the central atom has lone pairs, the molecule is polar.
Dipole – dipole attraction
A dipole is created by an uneven charge distribution (electronegativity)
Dipole-Dipole is an electrostatic attraction between polar molecules.
London Dispersion Forces
Attraction of instantaneous and induced dipoles; exist between all molecules.
Formation of instantaneous dipoles
VValencealenceSShellhellEElectronlectronPPairairRRepulsionepulsion Theory Theory
Planar triangular
OctahedralTrigonal bipyramidal
VSEPR theory
(Valence Shell Electron Pair Repulsion) states that repulsion between valence electrons causes these sets to be oriented as far apart as possible.
Molecular Shape
Atoms bonded to
central atom (B)
Lone pairs (E)
Type of Molecule
Linear 2 0 AB2
Bent or angular
2 1 AB2E
Trigonal-planar
3 0 AB3
Molecular ShapeAtoms
bonded to central atom
Lone pairs Type of Molecule
Tetrahedral 4 0 AB4
Trigonal- pyramidal
3 1 AB3E
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