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• Module 5: Elements to Compounds
• The Study of Chemistry: Macroscopic and Microscopic
• Classification of Matter

  Matter (Separation by physical methods):

  1. Mixtures
  2. Pure substances

  Mixtures:

  1. Homogenous mixtures
  2. Heterogeneous mixtures

  Pure substances (Separation by chemical methods):

  1. Compounds
  2. Elements
• Chemistry is the study of matter and the changes it undergoes
• Matter is anything that occupies space and has mass
• A substance is a form of matter that has a definite composition and distinct properties

  Ex. liquid nitrogen, gold ingots, and silicon crystals
• A mixture is a combination of two or more substances in which the substances retain their distinct identities
• Homogeneous mixture – composition of the mixture is the same throughout.

  Ex. soft drink and solder
• Heterogeneous mixture – composition is not uniform throughout

  Ex. cement, iron filings in sand, and milk
• Physical means can be used to separate a mixture into its pure components

  Ex. distillation and magnet
• An element is a substance that cannot be separated into simpler substances by chemical means

  • 118 elements have been identified
  • 82 elements occur naturally on Earth (gold, aluminum, lead, oxygen, carbon, sulfur)
  • 36 elements have been created by scientists (technetium, americium, seaborgium)
• A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions.

  • Compounds can only be separated into their pure components (elements) by chemical means.
  • Ex. lithium fluoride, quartz, and dry ice – carbon dioxide
• A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces.

  • A diatomic molecule contains only two atoms (H, N, O, F, Cl, Br, I)
  • A polyatomic molecule contains more than two atoms
• An ion is an atom, or group of atoms, that has a net positive or negative charge.

  • cation – ion with a positive charge. If a neutral atom loses one or more electrons it becomes a cation.
  • anion – ion with a negative charge. If a neutral atom gains one or more electrons it becomes an anion.
• • A monatomic ion contains only one atom
  • A polyatomic ion contains more than one atom
• Formulas and Models:

  1. Molecular formula
  2. Structural formula
  3. Ball-and-stick model
  4. Space-filling model
• ionic compounds consist of a combination of cations and an anions

  • The formula is usually the same as the empirical formula
  • The sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero
• The most reactive metals and nonmetals combine to form ionic compounds.

  Metals: Li, Na, Mg, Al, K, Ca, Rb, Sr, Cs, Ba

  Nonmetals: N, O, F, S, Cl, Br I
• Types of Chemical Bonds:

  1. Covalent Bond

  • attraction between the nucleus of the 1st atom and the e-’s of the 2nd atom; and the attraction of the nucleus of the 2nd atom and the e-’s of the 1st atom
  • sharing of e-
  • atoms of non-metals combine
  • electronegativity difference is 0 to <2

  2. Ionic Bond

  • attraction between cations and anions
  • atoms of metal and nonmetal combine
  • atoms with a large difference in electronegativities (≥ 2)
  • metals lose e- (cations), nonmetals gain e- (anions) and the total net charge is 0
• Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond.

  • Electronegativity - relative, F is highest
  • Increasing electronegativity - Up and Right
• Chemical Bonds - net forces of attraction that hold atoms together
• Properties of Covalent Compounds:

  • intermolecular forces of attraction is weak
  • gas, liquid or low-mp solid
  • insoluble in H2O (mostly)
  • aqueous solutions do not conduct electricity
• Solid - Molecules in rows (table sugar)

  Liquid - Molecules moving around (rubbing alcohol)

  Gas - Molecules flying around (carbon monoxide)
• Valence electrons are the outer shell electrons of an atom. The valence electrons are the electrons that participate in chemical bonding.
• Group e- configuration # of valence e

  1A ns1 1

  2A ns2 2

  3A ns2np1 3

  4A ns2np2 4

  5A ns2np3 5

  6A ns2np4 6

  7A ns2np5 7
• Lewis Dot Symbol

  • Consists of the symbol of an element and 1 dot for each valence e- in an atom of the element
  • For representative elements only (s and p blocks)
  • Transition and inner transition metals have incompletely filled inner shells
• Properties: Bond Energy

  • amount of energy involved when bond is broken
  • amount of energy released when bond is formed
  • strong bond; high bond energy
• Properties: Bond Length

  • distance between the nuclei of atoms forming the bond
  • strong bond; low bond length
• Properties: Bond Order

  • # of bonds between atoms
  • single, double or triple
  • strong bond; low bond length; high bond order
• The Octet Rule

  • Formulated by Lewis
  • Observed tendency of atoms (representative elements) to lose , gain or share e- in order to acquire an octet e- in their outermost main energy level
  • Noble Gas Rule
• Valence Shell Electron Pair Repulsion (VSEPR) Theory - Determines the shape of the molecule.
• Polar Molecules

  • Polar molecules possess polar bond.
  • A bond is polar when the two atoms that are participating in the bond formation have different electronegativities. In polar molecule, all the bonds collectively should produce a polarity.
  • 0.4 < electronegativity difference < 1.8
  • Factors: shape of the molecules; polarity of the bonds
• Causes of Polarity

  • Asymmetrical shape (Bent, Trigonal Pyramidal)
  • Unshared electrons on the central atom
  • Polar bonds
  • In tetrahedral molecule, one substituent is different.
• Intermolecular Forces of Attraction (IMFA)

  • Attractive forces between molecules
  • Versus intramolecular forces of attraction: covalent or ionic
  • Covalent bond - strong
  • Intermolecular - weak
• Intermolecular Forces of Attraction

  1. Dipole-dipole forces
  2. Ion-dipole forces
  3. London dispersion forces (induced dipole forces)
  4. Ion-ion forces
  5. Hydrogen bonding
• Dipole-dipole forces

  • between polar (covalent) molecules
  • 0.4 < electronegativity difference < 1.8
  • The larger the dipole moment, the greater the force
• Ion-dipole forces

  • attraction between an ion(cation or anion) and a polar molecule
  • Depends on the charge and size of the ion and on the magnitude of the dipole moment and size of the molecule
• Dispersion forces, Ion-dipole forces, and dipole-dipole forces are collectively known as Van der Waals forces of attraction.
• Ion-ion forces

  • Electrostatic forces
  • attractive forces between cations and anions in ionic compounds
• Hydrogen bond

  • special type of dipole-dipole interaction between the H atom in a polar bond and an electronegative O, N or F atom