Compounds & Molecules

ObjectivesBe able to relate the chemical formula

of a compound to the relative numbers of atoms or ions present in the compound

Be able to use models to visualize a compound’s chemical structure

Be able to describe how the chemical structure of a compound affects its properties

Important VocabularyCompoundChemical bondChemical formulaChemical structureBond lengthBond angleStructural formulaBall-and-stick modelSpace-filling model

What are Compounds?Chemically combined elements in

specific amountsExample: NaCl = table salt

Violent Reaction

Compound CharacteristicsChemical bonds distinguish compounds

from mixturesChemical bonds are attractive forces that

hold different atoms or ions togetherThey always have the same chemical

formula, which tells how many atoms or ions of each element are in it

Examples: H20 = ___________________

C12H22O11 = _________________

2 hydrogen & 1 oxygen

12 carbon, 22 hydrogen & 11

oxygen

Compound CharacteristicsThey have chemical structures that show

the bonding within a compoundA chemical structure is the arrangement

of atoms in a substanceBond length is the average distance

between the nuclei of the 2 bonded atomsBond angle is the angle formed by two

bonds to the same atom

Models of Compounds

Three types of models:

Structural Formulas

Ball-and-Stick Models

Space-filling Models

Structural FormulasShow the structures of compounds

using lines and chemical symbols

Ball-and-Stick ModelsShow chemical structure by using

balls for atoms and sticks for bonds

Space-Filling ModelsShow the space occupied by atoms in

a compoundDoesn’t really show bond angles or

lengths

How Does Structure Affect Properties?

Strength of attractions

Melting points

Boiling points

Ability to flow--viscosity

Network Structure Compounds

Compounds with network structures are strong solids

Example: quartz SiO2

All the bond angles are the same

Have a high melting point & boiling point

Networks of Bonded IonsCompounds with this type

of structures: Are ions of opposite

charges tightly bonded together

Form regular shaped crystals

Have high melting and boiling points

Example: NaCl

Compounds Made of MoleculesFor example: Sugar

Is made of carbon, hydrogen, & oxygen The bonds between them are not strongly

attractedGases especially have very “loose” bonds

because the molecules are not attracted to each other

The strength of attractions between molecules varies: Solids are stronger than liquids and

liquids are stronger than gases

Hydrogen BondsAre the attractive forces between water

molecules