CHM101 - Chapter Five

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Compound

Two or more elements chemical combined in fixed proportions

Ionic Compounds

Form from transfer of electrons, often metal + nonmetal.

Nonmetals form negative (Anion), metals form positive (Cation)

• Contain specific ratios of Ions but no specific number of ions

• Elements that are very “different” (Different sides of the Periodic Table)

Covalent

Form by sharing electrons, contain atoms not ions.

Often nonmetal + nonmetal, elements that are very “similar” (Same side of the periodic table)

• Molecules contain specific numbers of atoms

Law of Definite Proportions

A compound will always have the same chemical composition

• Each product is formed from definite proportions of reactants

• Same mass proportions and atomic ratios of elements present

Law of Multiple Proportions

If the same two elements can combine to form more than one compound

• Each compound will still have a fixed mass ratio of elements

• The mass ratios of the different compounds will be different

  • The combination of elements is in a ratio of small whole numbers of atoms

Chemical Formulas

Represent chemical composition (atomic ratios)

• Symbols tell you what’s present

• Subscripts tell you how many atoms / ions of each element are present

  • N₂H

• Parentheses show that a subscript belongs to a group of elements, not a single element (distribute)

  • N₂(HCl₂)₂

Empirical

• Smallest ratio of Atoms (NH2 instead of N2H4)

  • Can be used for ionic or covalent compounds

  • Basically only used for ions

Molecular

• Actual # of atoms (N2H2)

  • Only use for covalent compounds

    • Molecule = covalent

Structural

Shows how atoms are connected in molecules

Lewis Dot Symbols

Consists of atomic symbol surrounded by 1 dot for each valence electron in the atom

• Only used for main group elements

  • Number of valence electrons = group number

Ions

Electrons are transferred from one atom to another forming charged atoms

Metals

Lose electrons to form positively charged Cations

• Cats are Paw-sitive

Nonmetal atoms

Gain electrons to form negative anions

Electrostatic Force

(+ & - attractions) bonds ions into an ionic compound (Ionic Bond)

• Forms an ion salt with repeating structure: NaCl, LiF

Octet Rule

Rule Ionic bonds follow where atoms lse or gain a valence electron to make 8 (8e^-)

• Atoms with low valence lose electrons while one with high valence lose

Salts

Cations and Anions bind together to form crystals

The net charge on the compound is zero

• Positive and negative charges are balanced

  • Number of positive charges = number of negative charges

  • Not always a 1:1 ratio of ions

Valence electrons

Electrons in the “outermost” energy level

• Column number (Up and down) tells number of valence electrons

• Electrons are negative → gain electrons = negative charge

Noble Gases

Column 8A/18, already have 8 and general have no charge, and thusly are very stable

Transition and Multi-charge metals

Become cations most of the time but their charge cannot always be predicted by column #

• Often have more than one charge which are represented by roman numeral

  • Iron (III) = Fe³

  • Zinc is not commonly charged

Polyatomic lons

“Multiple atoms”

• Charged molecules

• Lose or gain electrons as a group

• Charge is spread over 2 or more atoms

Names of Ions and Compounds

Cations: Add the word ION after element name

Anions: Change the element name to ending in -ide then add ion

Naming Ionic Compounds

Write the name of the cations followed by the name of the anion

• IF the cation can have more than one charge, include a roman number representing the charge after the name of the cation

Names of Covalent Compounds

• Atoms remain uncharged, but share additional electrons to make an octet

  • Number of shared electrons can vary depending on the number needed for each atom to gain an octet

Molecular Compounds

Molecules contain specific numbers of atoms

• The number and type of each atom is show in the molecular formula

Diatomic molecules

Two atoms

• Homonuclear - Same element

  • Not a compound

• Heteronuclear - Different elements

  • A compound

Molecular Compound Formula

Subscripts = # of atoms

Naming Molecular Compounds

Name prefix = # of atoms

• Do not include a prefix for the first element if there is only one atom

  • The o or a at the end of the prefix is often dropped when the element begins with a vowel

    • Monoxide, not monooxide

Molecular Compound Naming Prefixes

• 1: mono-

• 2: di-

• 3: tri-

• 4: tetra-

• 5: penta-

• 6: hexa-

• 7: hepta-

• 8: octa-

• 9: nona-

• 10: deca-

Arrhenius

a formula for the temperature dependence of reaction rates

Acid

• Arrhenius: Compound ionizes in H₂O to form H+ & anions

  • Name by changing anion -ide ending to -ic

  • Add hydro to acids in column 17

Bronsted Acids

H+ grabs H₂O to form H₃O in water

Base

• Arrehenius: Compounds ionizes in H₂O to form OH- & cations

  • Name as salts: Hydroxide salts are considered bases

• Bronsted Base: Pulls H+ from H₂O so NH₃ is a base

Neutralization

Reaction between acids and bases to form water and salt

Molar Mass and Mass Percent Calculations

• Find atomic mass of each element

• Multiply atomic mass of element by subscript, then add all elements together

• Molar mass: Mass of molecule

  • Include every atom

• Formula mass: mass of ions in a salt

  • Use smallest ratio

Mole Based Calculations

Same as single element calculations just using the molar mass of the compound instead of the element

Finding Mass % of a Compound

• Assume 1 mole of compound

  • This will make subscripts = # moles of each element

  • Calculate mass of each element based on subscripts

  • For each element, divide mass by molar mass of compound

Percent Composition of Compounds by Mass

General idea: Part/Total

• Mass %: Mass of each element in the compound divided by the total mass of the compound

• Units should be the same for both values (usually g)