Ch 6.1 Chemical Bonding
Chemical Bonds
– the attractive forces that hold different atoms or ions together
(Intramolecular or electrostatic Forces
Why Bond?
Atoms bond to achieve a full outer energy level
OCTET RULE: They want 2/8 VALENCE electrons.
Few exceptions
Ex. BF3 and SF6
Bond Structures
Ionic Crystal or formula Units (strongest Bond)
Network Structures (Strong Covalent solids)
Molecular (most common covalent bond, weakest)
Chemical Bonds: Types
COVALENT METALIC IONIC
ALL NONMETALS atomsHolding a compound or
element togetherALL METALS
holding an elementtogether
METAL and NONMETAL ionsHolding a compound
together
Ch. 6.4 Metallic bond
Formed by the attraction between positively charged metal ions and the “sea of electrons” around them.
Held together by delocalized, free-flowing electrons along the bond
Holds metal elements and alloys together
Metallic bond Properties
Strong Bonds
Malleable
High melting points
Ductile
Good conductors of electricity
Ch 6.1 Electronegativity Difference (END)
the difference in electronegativity between two atoms in a bond.
Bonds are rarely ionic or covalent.
Electronegativity Difference (ED)
EX. NO N=3.0 O=3.4
[3.4-3.0] = 0.4
Electronegativity difference of NO = 0.4
Tells us two things
Bond Properties and Polarity
If ED is > 1.7, then the compound has more polar ionic properties. (strongest)
If ED is < 1.7, then the compound has more polar covalent properties
If the ED is < 0.3, then the compound is nonpolar covalent. (weakest)
Polarity (ch. 6.1, 6.5)
Property of a molecule’s bond caused by an unsymmetrical charge distribution
Polar molecules are unsymmetrical in shape
Nonpolar molecules are symmetrical in shape
It is important to note that nonpolar molecules can have polar bonds
Polar Covalent Molecules
The atom with the higher electronegativity will attract the electrons more strongly.
This will cause partial charges to develop on each side of the molecule (ع +ع-)
Contain Dipole forces
Unequal Sharing
Nonpolar Covalent Molecules
Molecules where the atoms have similar electronegativity's
This will cause partial charges cancel
Equal sharing
Held by weaker London dispersion forces
Using Dot Diagrams
Dot diagrams may be used to show how electrons are shared or how they will be transferred
Ch 6.2 Covalent Bonds
A bond formed by the sharing of valence electrons (co – VALENT)
Also called molecules
Formed between two or more nonmetal atoms
Molecular bond Properties (<1.7)
Weak bonds (molecules)
The longer the bond the less bond energy needed to break bond
Molecular compounds have low melting points and are bad conductors of electricity (no ions)
Can be solids, liquid or gas phase at room temp.
Empirical Formula
The simplest whole-number ratio a
chemical formula can have.
Different covalent compounds can
have the same empirical formula
Ionic formulas are always empirical
Naming Covalent Compounds Prefixes for # of atoms
Mono – 1
Di - 2
Tri - 3
Tetra - 4
Penta - 5
Hexa – 6
Hepta - 7
Octa - 8
Nona - 9
Deca - 10
Naming Covalent Compounds
Step 1
Identify the number of atoms in the first element
Ex. H2O two H atoms
Naming Covalent Compounds
Step 2
Identify the number of atoms in the 2nd element.
Ex. H2O one O atom
Naming Covalent Compounds
Step 3
Name the compound with the appropriate prefixes. Ex. H2Odihydrogen monoxygen
Ionic bond (ch. 6.3)
A bond formed by the attraction between oppositely charge ions.
The transferring of valence electrons
Each ion will have 2/8 valence electrons
Formed between metal ions and nonmetal ions
Na+ + Cl- NaCl
Ionic bond Properties (>1.6)
Very Strong bonds (formula units)
Compounds made up of ionic bonds have high melting points and are good conductors of electricity when dissolved or melted (ions free to move)
solid phase (salts)
Ch. 7.1 Writing Ionic formulas
Step 1 Calcium Fluoride
Write both positive and negative ions (use ion table if you need it)
Ca2+ F-1
Ionic bonds
Ionic bonds may contain polyatomic ions in them.
An ion made from two or more atoms covalently bonded together that act like a single ion.
A molecule with a charge, example sulfate (SO4)-2
EX Na+1 + (SO4)-2 → Na2(SO4)
Covalent Bond Ionic bond between 2 ions
Ch. 7.1
Naming Ionic Compounds
Step one – Name the first ion in the formula
Ex. CaCl2 – calcium
Na2(SO4) - sodium
Naming Ionic Compounds
Step two – Name the second ion
Ex. CaCl2 –Calcium Chloride
Na2(SO4)-sodium sulfate