CHEM1003 - 27 Feb 20-s1-low

Lecture Overview

  • Focus on the techniques and theories within chemistry

  • Lecture covers physical and chemical reactions, mixtures, elements, compounds, and atomic theory

Recap from Previous Lecture

  • Physical Reactions

    • Discussed distillation, electrolysis, filtration, and chromatography

  • Filtration

    • Process of separating a solid from a liquid using filter paper and a funnel

    • Mixture poured into filter paper; solid is trapped while liquid passes through

    • Setup:

      • Circular filter paper folded into a cone

      • Placed in a funnel, then lowered into a beaker

  • Chromatography

    • Technique for separating components of a mixture based on solubility

    • Paper chromatography involves placing a dye or ink on paper and placing it in a solvent

    • Process:

      • Solvent moves up the paper, separating colors

      • Each component's movement measured as RF values (ratio of distances traveled)

Mixtures and Pure Substances

  • Understanding the difference between mixtures and pure substances

  • Mixtures

    • Can be separated into pure substances (physically)

  • Pure Substances

    • Can be classified into compounds and elements

    • Compounds have fixed ratios of elements (e.g., water is H2O)

    • Elements

      • Examples include oxygen (O2), iron (Fe), and aluminum (Al)

Types of Mixtures

  • Homogeneous Mixtures

    • Uniform composition (e.g., saltwater)

  • Heterogeneous Mixtures

    • Non-uniform composition (e.g., salad dressing with oil and herbs)

Elements and Their Classifications

  • Current knowledge of elements:

    • 118 known elements, 88 occur in nature

  • Element Symbols:

    • Example symbols: Au (gold), C (carbon), H (hydrogen), O (oxygen)

    • Symbols often derived from Latin or Greek origins

  • Atomic Types:

    • Monatomic: exists as single atoms (e.g., helium, neon)

    • Diatomic: consists of two atoms of the same element (e.g., N2, O2)

    • Triatomic: consists of three atoms (e.g., O3 for ozone)

    • Polyatomic: consists of many atoms (e.g., S8)

Dalton's Atomic Theory

  • Postulates of Dalton:

    1. Elements are made of tiny particles called atoms

    2. All atoms of a given element are identical

    3. Atoms of different elements are distinguishable

    4. Atoms can combine to form compounds with fixed ratios

    5. Atoms are indivisible in chemical processes (matter is neither created nor destroyed)

  • Impact on Periodic Table:

    • Elements grouped based on properties

Chemical Formulas and Compounds

  • Chemical Formulas

    • Describe composition of compounds, showing types of atoms and ratios

  • Unit Representation:

    • Example: H2O indicates 2 hydrogen atoms and 1 oxygen atom

  • Subscripts indicate the number of each type of atom

    • Example: CCl2 (two chlorine atoms with carbon)

Atomic Structure

  • Components of an Atom:

    • Nucleus: contains protons (positive) and neutrons (neutral)

    • Electrons: negatively charged particles, found outside the nucleus

  • Size Comparison:

    • Nucleus: 10^-15 meters, electron cloud: 10^-10 meters

Isotopes and Atomic Mass

  • Definition of Isotopes:

    • Atoms with the same atomic number but different masses due to varying neutrons

  • Examples in Nature:

    • Carbon-13 (6 protons, 7 neutrons), Carbon-14 (6 protons, 8 neutrons)

  • Atomic Mass Unit (AMU): average of all isotopes' masses

  • Chlorine Isotopes:

    • Chlorine-35 (75.77% abundance) and Chlorine-37 (24.23% abundance)

Conclusion and Next Steps

  • The next session will involve a workshop

  • Students encouraged to review lecture notes and textbook for deeper understanding of concepts

  • Importance of understanding both theoretical and practical aspects of chemistry in preparation for exams.