Post on 02-Jan-2016
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Chemical Bonding
Molecules Atoms joined together that act as one unit Molecules come in three sizes:
Small Made of two atoms only Medium Made of 3-100,000 atoms Large Made of over 100,000 atoms
Called macromolecules
Even large molecules cannot be seen with the naked eye!
Chemical Bonding
Molecule formation Molecules form when atoms gain, share, or lose
electrons from their valence shell (ring farthest away from nucleus) so their structure resembles a Noble Gas which is very stable
Octet Rule- all atoms want to have 8 valence electrons
Atoms with 1-3 valence electrons will lose them Atoms with 4 valence electrons will share them Atoms with 5-7 valence electrons will gain more
Chemical Bonding
When atoms lose or gain electrons, they form ions, or charged particles.
Cations- positive ions formed from metals
Have more protons than electrons
Anions- negative ions formed from nonmetals
Have more electrons than protons
Trends in Ion Formation
When metals lose electrons, they become positively charged. Group 1 loses 1 e +1 Group 13 loses 3 e
+3 Group 2 loses 2 e +2
When nonmetals gain electrons, they become negatively charged. Group 17 gains 1 e -1 Group 15 gains 3 e -3 Group 16 gains 2 e -2
Chemical Bonding
When atoms rearrange their electrons, they can form forces of attraction with other atoms. These forces of attraction are called chemical bonds.
Chemical Bonding
Chemical Bonds Ionic Bonds
Formed from positive and negative ions joining together
Involves a metal with a nonmetal
Ionic Bonds Ionic bonds are formed in 2 steps:
1. Metal transfers an electron to a nonmetal, forming ions
2. Oppositely-charged ions attract, forming a bond
Chemical Bonding
Covalent bonds Sharing electrons to
form a bond Usually occurs between
nonmetals or metalloids Can also occur between
two atoms of the same element
Chemical Bonding
Polarity How electrons are shared in a chemical bond
Covalent bonds can be separated by polarity into: Polar bonds- unequal sharing of electrons Nonpolar bonds- equal sharing
Chemical Bonding
Nonpolar bonds share the electrons equal amounts of the time
In polar bonds, one element is stronger than the other and controls the electrons for more of the time. This creates
a dipole.
Chemical Bonding
Polarity of a bond can be represented in three ways: Bubble method Partial charge method Polarity arrow method
Arrow always faces element with larger EN
Polarity
Polarity is determined by the EN difference between the 2 elements in the bond. 0.0-0.3 nonpolar (share equally) 0.4-1.6 polar (shared but not equally) 1.7+ ionic (completely transferred)
Lewis Structures
1. Count the # of valence electrons
2. Draw a simple structure to represent the molecule
3. Place 8 e around the central atom
4. Fill the outside atoms 5. Move lone pairs to make
multiple bonds
1. CCl4 C- 4
Cl- 7 x 4 2. Cl
Cl C Cl
Cl 3. Cl
Cl C Cl
Cl 4.
Chemical Bonding
Molecular GeometryShape of a molecule in 3D space
Bonded pair Lone pair
C : Br Br :
Chemical Bonding
Linear
Bent
Trigonal planar
Tetrahedral
Trigonal pyramidal
Trigonal bipyramidal
Octahedral
Chemical Bonding
Chemical Formulas Represent a compound without having to write the
name Show the number of atoms in the compound There are two types:
Ionic- metals with nonmetals Covalent- nonmetals with nonmetals
Chemical Bonding
Ionic Formulas Naming Ionic Compounds
1. Write the name of the first element
2. Write the name of the second element but add –ide to the end of the name.
Examples: MgS magnesium sulfide
ZnCl2 zinc chloride
Chemical Bonding
Ionic Formulas Charge numbers
Each group is assigned a charge number based on how many electrons are gained or lost by the elements in that group.
Group 1 1 Group 14 4 Group 2 2 Group 15 3Group 133 Group 16 2
Group 17 1
Chemical Bonding
Ionic Formulas Charge numbers
Tansition elements have individual charge numbers
Cr 2 Cu 1 Sn 2Mn 2 Zn 2 Au 3Fe 3 Zr 2 Hg 1Co 2 Ag 1 Pb 2Ni 2 Cd 2 Bi 3
U 6
Chemical Bonding Writing Ionic Formulas
1. Write the symbols for the elements in the compound.
2. Look up the charges for each element and write them as superscripts behind the elements.
3. Cross the numbers in an “X” until they are behind the other element.
Chemical Bonding
Covalent Formulas Naming Covalent Compounds
1. Write the name of the first element.
2. Write the name of the second element but add –ide to the end of the name.
3. Find the prefix that matches the subscript in the formula.
4. Write the prefix in front of the element’s name.
Chemical Bonding
Examples: NO3
Nitrogen oxide3 = triNitrogen trioxide
As2S3
Arsenic sulfide2 = di 3 = triDiarsenic trisulfide
Chemical Bonding
Writing Covalent Formulas1. Write the symbols for the elements.
2. Find the number that matches the prefix in the name.
3. Write the number as a subscript behind the appropriate element.
Chemical Bonding
Examples: Carbon monosulfide
C Smono = 1CS
Dinitrogen pentachloride
N Cl Di = 2 penta = 5
N2Cl5
Chemical Bonding
Polyatomic Ions Groups of elements that act as one element in a
compound Polyatomic ions are given special names
Chemical Bonding
Naming compounds with polyatomic ions1. Write the name of the first element.2. Find the polyatomic ion on your sheet. Write
its name as it appears on the sheet. Examples: Na3PO4
Sodium phosphate
KMnO4
Potassium permanganate
Chemical Bonding
Writing Formulas with Polyatomic Ions1. Write the symbols for the element and the
polyatomic ion.
2. Find the charge number for the element and the polyatomic ion. Write them as superscripts.
3. Cross the charge numbers over.
Molar Conversions
The Mole
A quantity that represents the number of atoms in 12 g of C-12
1 mole = 6.02 x 10 ^23 atoms
How big is a mole?Avogadro’s number