Chemical Bonding

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

Small Molecules Examples:

NaCl KI CO LiF

Chemical Bonding

Medium molecules Sugar Water Octane Alcohol

Chemical Bonding

Large molecules (macromolecules) Plastics Proteins Medicine Viruses DNA

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

Bell ringer

A magnet has two poles. What does that mean?

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

Metallic Bonding

Intermolecular Forces

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

Examples: Aluminum fluorideAl FAl3 F1

AlF3

Calcium oxideCa OCa2 O2

CaO

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.

Chemical Bonding

Examples: Sodium hydroxideNa OHNa1 OH1

NaOH

Boron nitrate

B NO3

B3 NO31

B(NO3)3

Molar Mass

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

Q: If a mole of moles is digging a mole of holes, what do you see?A: A mole of molasses

Chemical Bonding

Conversion factor