Compounds and Molecules

UNIT 7 SECTION 1 NOTES

• Made of individual atoms.• Cannot be broken down into

simpler substances.• Listed on the periodic table.• The building blocks of all

matter.

ELEMENTS: A REVIEW

• Different substances just placed together

• Substances keep their individual properties • Example: Mixing yellow and blue paint

to make green paint: color has changed but not the properties

• Can be separated (Example: sand and water)

MIXTURES: A REVIEW

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• Compound: 2 or more elements chemically joined together in definite ratios

• The characteristics of each element are lost when a compound is formed

• Think of Table salt: Sodium, a metal, combines with chlorine, a gas, to make table salt, a small white crystal.

COMPOUNDS

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• Molecules are the smallest units of a compound that

retains the characteristics of the compound.

MOLECULES

This is one molecule of caffeine:

• Formed through CHEMICAL BONDING

• Compounds have a chemical formula

• Compounds are not easily separated

• New properties: different than the elements that it is made from

COMPOUND CHARACTERISTIC

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• A compound ALWAYS has the same chemical formula.

• A chemical formula shows the types and numbers of atoms or ions making up the simplest unit of the compound.

CHEMICAL FORMULAS

• Note: When there is no subscript, it is understood to be “1”.

• The larger number in front is called a coefficient • H2O: Water: 2 Hydrogen atoms; 1

Oxygen atom• C12H22O11: Sugar: 12 Carbon atoms;

22 Hydrogen atoms; 11 Oxygen atoms• NaCl: Table Salt: 1 Sodium atom; 1

Chlorine atom

EXAMPLES OF CHEMICAL FORMULAS

Use the chemical formula to list each element by symbol and tell how many atoms there are in the compound.

• CO2

• 2H2O

• Mg(OH)2

• 3NaHCO3

• 2H2SO4

• 2CaCO3

• 3C6H8O7

• 4Be(OH)2

EXAMPLES OF CHEMICAL FORMULAS

Use the chemical formula to list each element by symbol and tell how many atoms there are in the compound.

• CO2 C = O =

• 2H2O H = O =

• Mg(OH)2 Mg = O = H =

• 3NaHCO3 Na = H = C = O =

• 2H2SO4 H = S = O =

• 2CaCO3 Ca = C = O =

• 3C6H8O7 C = H = O =

• 4Be(OH)2 Be = O = H =

EXAMPLES OF CHEMICAL FORMULAS

Use the chemical formula to list each element by symbol and tell how many atoms there are in the compound.

• CO2 C = 1 O = 2

• 2H2O H = 4 O = 4

• Mg(OH)2 Mg = 1 O = 2 H = 2

• 3NaHCO3 Na = 3 H = 3 C = 3 O = 9

• 2H2SO4 H = 4 S = 2 O = 8

• 2CaCO3 Ca = 2 C = 2 O = 6

• 3C6H8O7 C = 18 H = 24 O = 21

• 4Be(OH)2 Be = 4 O = 8 H = 8

EXAMPLES OF CHEMICAL FORMULAS

• Law of Definite Proportions:

Compounds are ALWAYS made

of the same elements in the same proportion

by mass.

LAW OF DEFINITE PROPORTIONS

• Chemical Structure is the way the compound’s atoms are bonded to make the compound.

• Just as the structure of buildings can be represented by blueprints, the structure of chemical compounds can be shown by various models. Different models show different aspects of compounds.

CHEMICAL STRUCTURE

• Ball and Stick Model • Space Filling Model• Structural Formula

MODELS OF COMPOUNDS

What determines many of a compound’s properties?

• The atoms present in a compound

• The way the atoms are arranged (chemical structure)

PROPERTIES OF COMPOUNDS

This shows how a crystal lattice is formed from sodium and chlorine atoms to form table salt.

• Network Crystals: typically based on nonmetals like carbon, silicon, and boron

• Held together by COVALENT bonds • VERY strong network or lattice • VERY high melting point and great

physical strength; takes a lot of energy to weaken the bonds.

• Poor conductors of electricity• Often very hard and strong; typically

will not dissolve in water.

STRUCTURE AND PROPERTIES

• Examples of network crystals:

• Quartz: made of silicon dioxide, SiO2 Every Si atom is bonded to 4 oxygen atoms; all bond angles are the same at 109.5˚, which holds the atoms together in a strong, rigid structure

• Diamond

STRUCTURE AND PROPERTIES

• Molecular Crystals: Some compounds are made of molecules

• Compounds made of molecules DO NOT have a strong attraction holding atoms together, so they have a lower melting and boiling point than compounds with ionic bonds. • Example: A molecule of sugar is made

between bonds of carbon, hydrogen, and oxygen and the attraction between the molecules is much weaker than an ionic bond.

STRUCTURE AND PROPERTIES

• Ionic Crystals: Some networks are made of bonded ions, which have very strong attractions between the positively and negatively charged ions

• The strong attraction requires a lot of energy to break the bonds, which is why these network structures have high melting and boiling points.

• Examples: table salt, NaCl; magnesium oxide, MgO

STRUCTURE AND PROPERTIES

• The weaker the force of attraction between molecules, the easier the substance will be

to break apart• Molecules of gases have weak

attractions to one another, so they spread out and take up a

lot of space.

STRENGTH OF ATTRACTION BETWEEN MOLECULES

• Diatomic Molecule: 2 atoms of the same element that have covalently

bonded together.• 7 Diatomic molecules: Oxygen, Iodine,

Hydrogen, Nitrogen, Chlorine, Fluorine, and Bromine• Pneumonic device:

Oh, I Have Nice Closets For Brooms

DIATOMIC MOLECULES

https://www.youtube.com/watch?v=b_SXwfHQ774&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=34

CRASH COURSE