Units of Measurement in Chemistry

Units of Measurement

• Units are standard quantities used to define measurements, which are crucial in chemistry.
• There are three common systems of units: English system, Metric system, and International System of Units (SI).
• SI system is based on the metric system and preferred by scientists.
• The metric system uses one unit for each type of measurement:
  • Length: meter (m)
  • Volume: liter (L)
  • Mass: gram (g)
  • Temperature: Celsius (°C)
  • Time: second (s)

Measuring Length

• Length is the distance between two points.
• A meter stick is used to measure length.
• Centimeters (cm) are used for smaller lengths.

Measuring Mass

• Mass measures the amount of matter in an object.
• The mass of an object is measured using a balance.

Prefixes

• Prefixes adjust the size of a unit.
• Students should memorize the prefixes, their symbols, and their factors.
• Prefixes that increase the size of the unit: kilo-, mega-, giga-, tera-, peta-
• Prefixes that decrease the size of the unit: deci-, centi-, milli-, micro-, nano-, pico-

Density

• Density of a material is its mass per unit volume.
• Density is typically measured in units of g/L, g/mL, or g/cm3.
• Formula for density: Density = Mass / Volume.

History of Atomic Structure

• The atom comes from the Greek word "atomos," meaning indivisible.
• An atom consists of a nucleus (protons and neutrons) and surrounding electrons.

Molecular Elements

• Molecular Elements occur as multi-atom molecules, with atoms of the same element bonded by covalent bonds.
• Examples: H2, O2, N2, Cl2, P4, S8, Se8

Molecular Compounds

• Molecular Compounds are formed by molecules made of only nonmetals, bonded by covalent bonds.
• Examples: H2O, NH3, HCl, CH4

Ionic Compounds

• Ionic Compounds have particles made of metal cations and nonmetal anions, bonded by ionic bonds.
• Examples: NaCl, AlF3, Fe2O3, Mg2S

Classification of Elements

• Atomic Elements: Composed of individual atoms.
• Molecular Elements: Composed of molecules where atoms of the same element are bonded.
• Molecular Compounds: Composed of molecules where atoms of different elements are bonded.
• Ionic Compounds: Composed of ions of different elements.

Formula Mass and Molar Mass

• Formula mass (amu) is the mass of an individual molecule or formula unit, expressed in atomic mass units (amu).
• Molar mass is the mass of one mole of a substance.

Types of Chemical Equations

• Molecular equations: Show the formulas of compounds as if they existed as molecules.
• Ionic equations: Show the ionic forms of strong electrolytes in solution.
• Net ionic equations: Eliminate spectator ions (those that do not participate in chemical reactions) from the ionic equation, showing only the reacting species.

Writing Net Ionic Equations

• To Write a net ionic equation:
  1. Balance the molecular equation.
  2. Write the ionic equation for strong electrolytes.
  3. Identify precipitates using solubility rules.
  4. Cancel identical ions on both sides of the ionic equation.

Chemical Bonds

• Compounds are formed by atoms held together by bonds.
• Chemical bonds are attractive forces between atoms.
• Bonds form because they lower the potential energy between charged particles (protons and electrons).

Types of Chemical Bonds

• Ionic bonds: formed when electrons transfer between atoms, resulting in oppositely charged ions.
• Covalent bonds: formed by sharing electrons between atoms.
• Metallic bonds: formed by the attraction of delocalized electrons to a lattice of metal atoms.

This quiz focuses on the essential units of measurement used in chemistry, including the English, Metric, and SI systems. It covers measuring length, mass, and the important prefixes that adjust unit sizes. Test your knowledge on the fundamental concepts of measurement!