Post on 17-Jan-2016
Chemical Bonds
Chapter 5 2
Ions
• Ions have different numbers of electrons and protons
• Cations have lost electrons and have net positive charge
• Anions have gained electrons and have net negative charge
Chapter 5 3
Chemical Bonds
• Force of Attraction between any two atoms in a compound
• Involve VALENCE electrons
• Related to shape of molecule
• Related to chemical and physical properties of materials
Chapter 5 4
Types of Bonds
• Ionic BondElectrostatic attraction between positive and negative ions.
Involves transfer of electrons from one atom to another
• Covalent bond
Two atoms share a pair of electrons.
Chapter 5 5
Definitions
• Valence electrons – outermost level with electrons
• Core electrons – all other electrons in an atom
• Isoelectronic – same number of electrons
Chapter 5 6
Octet Rule
• Most stable situation is full octet of electrons in outermost energy level – Exception: H and He need only 2 electrons
• Atoms gain, lose or share electrons to achieve this octet (noble gas arrangement)
• This changing of electrons involves a reaction
Chapter 5 7
Lewis Symbols
• Also called Lewis Dot or Electron Dot
• Way of depicting Valence Electrons around an atom (s and p electrons in highest energy level)
• Show valence electrons as “dots”
Chapter 5 8
Lewis Single Atom
The number of dots is equal to the number of: – valence electrons– outermost energy level electrons – outermost shell electrons– Group number (main groups only)
Chapter 5 9
Lewis Symbol for single atom
• Show atomic symbol
• Show valence electrons as “dots”
Li• •Mg•
Chapter 5 10
Lewis Symbols
Chapter 5 11
Electron-Dot Structures
Chapter 5 12
Write the Lewis structure for:
Mg
C
Ar
I
Rb
P
Chapter 5 13
.
Chapter 5 14
Lewis Dot Symbol for Ions
Electrons are gained or lost to form full octet
Chapter 5 15
Cations (Positive Ions)
Groups IA, IIA, IIIA form ions by removing the electrons in the outermost shell
This is generally the group number of electrons
Ca group IIA lose 2 e- Ca2+
Na group IA lose 1 e- Na+
Chapter 5 16
Chapter 5 17
Anions (Negative Ions)
Groups VA, VIA, VIIA form ions by adding electrons to the outermost shell to make full octet
This is the number of electrons that when added to the group number give eight
N group VA add 3 e- N3-
Cl group VIIA add 1 e- Cl-
Chapter 5 18
Chapter 5 19
What ion is formed from:
FMgOCsBaPAr
Chapter 5 20
.
Chapter 5 21
• Generally, metals in groups IA, IIA and IIIA react with nonmetals in groups VA, VIA and VIIA to form ionic compounds
Chapter 5 22
1. Form positive ion by removing electrons from a group A metal
2. Form negative ion by adding electrons to form a full octet
3. Write the formula for the ionic compound formed
(smallest ratio of ions to give neutral compound)
Chapter 5 23
Reaction of Sodium with Chlorine
Sodium—Soft grayish metal
Chlorine—pale yellow-green gas (poisonous)
Sodium Chloride—White crystalline solid (Table salt)
Chapter 5 24
Reaction of Sodium with Chlorine
Chlorine gains electron from sodium
Chapter 5 25
Ionic Bonding in NaCl
• Form Na+ and Cl- ions
• Opposite charges attract each other
• Organize themselves in orderly arrangement (crystal)
Chapter 5 26
Chapter 5 27
• Do not have “pairs” of Na+ and Cl- ions paired up with each other
• Each Cl- is “associated” with 6 Na+ ions
• Each Na+ is “associated with 6 Cl- ions
• Formula unit: lowest ratio of ions that form compound
Chapter 5 28
Ionic Compounds
Writing Formula
Naming Compound
(Nomenclature)
Chapter 5 29
Combining Ions to Make Compounds
Compound must be neutral
positive charges = negative charges
net charge = 0
Chapter 5 30
To write formula: Need correct number of each ion to give neutral compound
Na+ and Cl- (+1) + (-1) = 0 NaCl
Na+ and S2- (+1) + (-2) =
2Na+ and S2- 2(+1) + (-2) = 0
Na2S (indicate 2 Na+ with subscript)
Chapter 5 31
The formulas of ionic compounds are determined from the charges on the ions.
atoms ions –Na + F : Na+ : F : NaF
sodium fluorine sodium fluoride
The overall charge of NaF is zero (0).
(1+ ) + (1-) = 0
Ionic Formulas: Sodium Fluoride
Chapter 5 32
Sodium Chloride
Chapter 5 33
MgCl2 Ions with 2+ and -1 charges
Chapter 5 34
More Ionic Compounds
Chapter 5 35
Binary Ionic Compounds• Only two elements in compound
Chapter 5 36
Write formula for compound made from :
Mg2+ and S2-
Al3+ and Cl-
Mg2+ and P3-
Chapter 5 37
Write formula for compound made from :
Mg2+ and S2- MgS
Al3+ and Cl- AlCl3
Mg2+ and P3- Mg3P2
Chapter 5 38
Naming Ionic Compounds
Name of positive ion first
Name of negative ion second
Do not need to indicate how many of each ion is in compound
Need to know how to name ions first
Chapter 5 39
Naming Ions
• For cations, simple positive ions– Add the word ion to element name– Examples: Na+ – sodium ion
Al3+ – aluminum ion
• For anions, simple negative ions– Change the usual element ending to -ide– Examples: Cl– – chloride
S2– – sulfide
Chapter 5 40
Common Ions (from single atoms)
Chapter 5 41
Chapter 5 42
Polyatomic Ions
Groups of atoms that combine and have an overall charge
NH4+ ammonium ion
OH- hydroxide ion
Chapter 5 43
Table 4.3
Chapter 5 44
Naming Ionic Compounds
1. Name positive ion first
2. Name negative ion second
Note: Do not need to show how many ions are in formula
Chapter 5 45
Naming Ionic compounds
MgS
AlCl3
Mg3P2
Chapter 5 46
Naming Ionic compounds
MgS Magnesium Sulfide
AlCl3 Aluminum Chloride
Mg3P2 Magnesium Phosphide
Note: Number of ions not in name
Chapter 5 47
Compounds with Polyatomic Ion
Mg2+ NO3-
Mg(NO3)2 magnesium nitrate
Use parentheses to show that there are two nitrate ions
Chapter 5 48
Octet Rule
Atoms tend to gain or lose electrons to reach more stable octet arrangement
Octet has eight valence electrons
(H has only two)
Full octet same as noble gas valence shell
Chapter 5 49
Ionic vs Covalent Compounds
• Ionic:– held together by charges on ions– Contain a metal and a nonmetal
• Covalent:– held together by shared electrons– Contain two non-metals
Chapter 5 50
Covalent Compounds
Contain only covalent bonds
(share electron pairs to complete octet)
Rules for naming covalent (molecular) compounds DIFFERENT than rules for naming ionic compounds
Chapter 5 51
What kind of compound is it?Ionic or Covalent
For compounds with only TWO elements:
An ionic compound contains one metal and one non-metal
A covalent compound contains two non-metals
Chapter 5 52
Ionic or Covalent?
• CaO N2O
• H2S H2O
• MgCl2 IF3
• CS2 Na2O
Chapter 5 53
Naming covalent compounds
• Name each element in order it appears in compound
• For second element, use stem + “ide”
• Use prefix to indicate number of atoms of each element
(mono if only one atom is present)
• Final vowel in prefix may be dropped if element begins with a vowel
Chapter 5 54
Naming Covalent Compounds
Use prefixes to show number of each type of atom
Chapter 5 55
Example
NO2 ( ) nitrogen ( ) oxide
2 O’s nitrogen dioxide
1 N Mononitrogen dioxide
often omit “mono”
Nitrogen dioxide
Chapter 5 56
Name the following:
CCl4
N2O3
SiS2
Chapter 5 57
Name the following:
CCl4 carbon tetrachloride
N2O3dinitrogen trioxide
SiS2 silicon disulfide
Chapter 5 58
Write the formula for
dihydrogen monoxide
Silicon tetrafluoride
dinitrogentetroxide
Chapter 5 59
Write the formula for
dihydrogen monoxide H2O
Silicon tetrafluoride SiF4
dinitrogentetroxide N2O4
Chapter 5 60
Covalent Compounds
Contain only covalent bonds
(share electron pairs to complete octet)
Rules for naming covalent (molecular) compounds DIFFERENT than rules for naming ionic compounds
Chapter 5 61
Naming covalent compounds
• Name each element in order it appears in compound
• For second element, use stem + “ide”
• Use prefix to indicate number of atoms of each element
(mono if only one atom is present)
• Final vowel in prefix may be dropped if element begins with a vowel
Chapter 5 62
Table 4.4