chemical bonding
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Bonding Atoms
Why do atoms bond?
- each atom wants a full outermost energy level
- gain, lose, and share valence electrons to achieve the duet or octet rule aka: “being happy”
- gives each atom an electron configuration similar to that of a noble gas
ex. Group 18: He, Ne, Ar
Chemical Structure/Models
Chemical Structure/Molecular Models
- arrangement of bonded atoms or ions
- bond length: the average distance between the nuclei of two bonded atoms
- bond angles: the angle formed by two bonds to the same atom
Molecular Models of Compounds
Ball and stick
- atoms are represented by balls
- bonds are represented by sticks
* good for “seeing” angles
Structural
- chemical symbols represents atoms
- lines are used to represent bonds
* good for “seeing” angles H H
O
Molecular Models Cont.
Space filling
- colored circles represent atoms, and the space they take up
- no bonds, no bond angles
Electron Dot/Lewis Structure
- chemical symbol represent atom
- dots represent valence electrons
- 2 center dots represent a bond
- no bond angles, no bond length
Chemical Bonds
Chemical Bonds
- attractive force that holds atoms or ions together
- 3 types
ionic, covalent, metallic
- determines the structure of compound
- structure affects properties
- melting/boiling pts, conductivity etc.
Ionic Bonds / Ionic Compounds
Definition
- bond formed by the attraction between oppositely charged ions
cation: positive: lost e-’s
anion: negative: gained e-’s
- oppositely charged ions attract each other and form an ionic bond
ex. Na+ + Cl- = NaCl
- electrons are transferred from one atom to another
- negative ions attract more positive ions, and soon a network is formed
Properties of Ionic CompoundsStructure affects properties
- strong attractions between ions: strong bonds
- high melting/boiling pt
- shatter when struck (think of it as one unit)
- conductivity
solid: ions are so close together, fixed positions, (can’t move)
NO conductivity
liquid: ions are freely moving due to a broken lattice structure
Good conductivity
Covalent BondsDefinition
- chemical bond in which two atoms share a pair of valence electrons
- can be a single, double, or triple bond
single, 2e-’s (-); double, 4e-’s (=); triple, 6e-’s( )
- always formed between nonmetals
- mostly low melting/boiling points
2 types of bonds
- polar
- non polar
Covalent Bond Cont.
Non Polar
- bonded atoms that share e-’s equally
- same atoms bonded
ex. Cl – Cl: Cl2
Polar
- bonded atoms that do not share e-’s equally
- different atoms bonded
H
ex. H – N – H: NH3
Metallic Bonds
Definition
- a bond formed by the attraction between positively charged metal ion (cation) and the shared electrons that surround it (sea of electrons)
ex. Cu
Properties
- Conductivity: Good: electrons can move freely
- Malleable: lattice structure is flexible
Naming Ions Monoatomic Ions
- cation
-name of element with ion
ex. (Na) Sodium (Na+) Sodium ion
- anion
- name of element with the suffix –ide
ex. (Br) Bromine (Br-) Bromide
Ions with multiple cations
- transition metals
- most form 2+, 3+ and 4+
ex. Cu+, Cu2+
Naming Metals with Multiple Ions
Transition Metals
- form multiple ions
- in order to name the ion use a roman numeral to indicate the charge
ex. Cu2+: Copper (II), Titanium (III): Ti3+
Practice Problems:
Fe3+: Iron (III) Mercury (III): Hg3+
Pb4+: Lead (IV) Chromium (II): Cr2+
Polyatomic Ions
Definition
- an ion made of one or more atoms that are covalently bonded and that act as a unit
(atoms that have lost or gained electrons)
ex. CO3 2-
, NH4+
- behave the same as other ions
- polyatomic ions can combined like
any other ion (as a unit)
ex. NH4NO3 1:1 ratio
(NH4)2SO4 2:1 ratio
Polyatomic Ions
Naming polyatomic ions
- not logical
- rules for some compounds
-ite & -ate endings
- indicates the presence of oxygen
- called oxyanions
- if (-) does not specify how many oxygen atoms are present
ex. Sulfate:4, Nitrate:3, Acetate:2
Polyatomic Ions Cont.- often several oxyanions differ only in
the number of oxygen atoms present
ex. Sulfur
- ion with more oxygen takes the –ate ending
ex. SO4
- ion with less takes the –ite ending
ex. SO3
Common Oxyanions
* Make sure you know these: memorize
Naming Ionic Compounds
Naming ionic compounds (binary)
Formula to Name
- name of cation followed by the name of the anion
ex. NaCl: Sodium Chloride
ZnO: Zinc (II) Oxide
CuCl2: Copper (II) Chloride
- formulas must indicate the relative number of cations and ions if transitional
Naming Ionic Compounds
Practice Problems
MgBr2
Magnesium Bromide
KI
Potassium Iodide
CuCl2
Copper (II) Chloride
Fe2S3
Iron (III) Sulfide
Formulas of Ionic Compounds
Writing formulas for ionic compounds
Name to Formula
- balance the cation charge and anion charge, leaving NO net charge
- use subscripts to denote the number of atoms in the formula
ex. NaCl: Na+ Cl- : NaCl
CaCl: Ca2+ Cl- : CaCl2
**1 to 1 ratios do not designate charge**
**Criss-Cross charges into subscripts**
Practice Problems
Write the formula for the following atoms
a. lithium oxide Li2O
b. beryllium chloride BeCl2
c. titanium (III) nitride
TiN
d. cobalt (III) hydroxide
Co(OH)3
Naming Covalent Compounds Prefix System
# of atoms prefix
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca
Naming Covalent Compounds Cont.
Rules for the prefix system
1. less electronegative element is given first. It is given a prefix only if it contributes more than one atom to a molecule of the compound
2. The second element is named by combining (a) a prefix indicating the number of atoms contributed by the atom (b) the root of the name of the second element, and (c) the ending –ide
3. The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel
ex. Monoxide or pentoxide
Naming Covalent Compounds Cont.
Naming covalent compounds from formula
1. SiO2
Silicon dioxide
2. PBr3
Phosphorus tribromide
3. CI4
Carbon tetraiodide
4. N2O3
Dinitrogen trioxide
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