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The Name’s BOND…….
Chemical Bond
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 electrons
Gain 3 electrons
Gain 2 electrons
Cations/Anions
What kind of atoms LOSE electrons and become positive?
What kind of atoms GAIN electrons and become negative?
Diatomic Molecules
Always exist in a chemical bond with another atom, even if the atom is of the same element
H2 , N2 , O2 , F2 , Cl2 , Br2 , I2
Chemical Bond
Involves 2 atoms
Mutual, electrical attraction between nuclei and valence electrons of 2 atoms
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.
ELECTRON STEALING !
Ionic Bonds: One Big Greedy Thief Dog!
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+
Ionic Bonds
Between atoms of metals and nonmetals with very different electronegativity Huge difference in electronegativity Electronegativity value > 1.7
Bond formed by transfer of electrons
Produce charged ions
Form between elements located on opposite sides of the periodic table
Ionic Bonds (cont.)
Conductors
High melting point.
Water soluble
Crystallize (form crystals)
Examples; NaCl, CaCl2, K2O
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.
COVALENT BONDbond formed by the sharing of electrons
Electron sharing!
Covalent Bond
Between nonmetallic elements of similar electronegativity. Small electronegativity difference <1.7
Formed by sharing electron pairs,
Formed between elements on the same side of the periodic table.
Covalent Bond (cont.)
Stable non-ionizing particles
Poor electrical conductors
Brittle, nonmetals, low melting point
Examples; O2, CO2, C2H6, H2O,
Partial Charges
Apply ONLY to COVALENT bonds
Results when there is unequal sharing between 2 atoms
Indicates electronegativity difference between bonded atoms
when electrons are shared equally, small electronegativity difference
NONPOLAR COVALENT BONDS
H2 or Cl2
when electrons are shared but shared
unequally
POLAR COVALENT BONDS
H2O
Polar Covalent Bonds--More
One atom “keeps” electrons closer to it
Electrons tend to reside around one atom more than the other atom
Electrons still remain distributed between the 2 atoms--unequal
Polar Covalent Bonds: Unevenly matched, but willing
to share.
Example: Cl2 , H2O
Multiple Covalent Bonds
Single 1 bond between 2 atoms 2 electrons shared Ex. H2
Double 2 bonds between 2 atoms 4 electrons shared Ex. O2
Multiple Covalent Bonds (cont.)
Triple 3 bonds between 2 atoms 6 electrons shared Ex. N2
Example: H2O, KI
Identify Bond type, Draw Lewis Structure
to show bonding
NaCl, CO
METALLIC BOND
bond found in metals; holds
metal atoms together
very strongly
Electrons
Localized: Electrons hang out in a local area Restricted to an atom/ion or shared between
atoms
Delocalized: Electrons not attached to a particular area Electrons are able to travel and move among
atoms
Metallic Bonds
Formed between atoms of metallic elements Between atoms on left side of periodic table Electronegativities are approximately equal
Electron cloud around atoms, delocalized electrons Valence electrons shared among multiple
atoms, “neighbors”
Electrons move through the whole metal, can jump between energy levels to create conduction bands.
Metallic Bonds (cont.)
Delocalized electrons result in good electrical and thermal conductors
3-D network of metal ions and electron sea
Examples; Na, Fe, Al, Au, Co
Metallic Bond, A Sea of Electrons
Metallic Bonds: Mellow dogs with plenty of bones to go
around.
Alloys
Metallic compounds with 2 different elements
Enhances metallic characteristics
Ex. Sterling silver (approx. 92-93%Ag, other metal—Cu) Brass (Cu and Zn) Stainless steel (contains chromium, prevents
corrosion, structural component)
What is the point of chemical bonding?
Physical/chemical properties vary based on Structure Bond type
Ionic Bonds High melting point High boiling point
Covalent Bonds Lower melting point Lower boiling point