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Introduction to Chemistry - Lecture 2 Key Concepts

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Termini in questo insieme (27)

  • Atomic number

    The number of protons in an element's nucleus; defines the element and increases sequentially across the periodic table.

  • Atomic weight

    The weighted average mass of an element's atoms, measured in grams per mole (g/mol); shown at the bottom of each element box.

  • Mole

    A fixed number, \(6 \times 10^{23}\), representing a large quantity of particles, similar to a dozen but much larger.

  • Diatomic elements

    Elements that naturally exist as molecules of two atoms at room temperature: H2, N2, O2, F2, Cl2, Br2, I2.

  • Ionic compounds

    Compounds containing metals that dissociate into ions in water, e.g., NaCl breaks into Na+ and Cl-.

  • Molecular (covalent) compounds

    Compounds with no metals that do not dissociate into ions in water, e.g., CO2 and H2O.

  • Scientific method steps

    Observe, hypothesize, design experiment, conduct experiment, analyze data objectively, refine/repeat if needed.

  • Theory vs. Law

    Theory: widely accepted explanation; Law: universal rule with no exceptions.

  • Mass vs. Weight

    Mass: amount of matter, constant everywhere; Weight: force due to gravity, varies by location.

  • SI unit for amount of substance

    The mole (mol) is the SI unit for amount of substance, distinct from mass units like grams.

  • Elements liquid at room temperature

    Only bromine (Br) and mercury (Hg) are liquids at normal room temperature and pressure.

  • Why some element symbols differ from English names

    Some symbols come from Latin or old names, e.g., Fe for iron (ferrous), Au for gold (aureus), Na for sodium (natrium).

  • Groups 1 and 2 on the periodic table

    Group 1: Alkali metals (except hydrogen); Group 2: Alkaline earth metals.

  • Halogens and noble gases groups

    Group 7: Halogens (e.g., fluorine, chlorine); Group 8: Noble gases (e.g., helium, neon).

  • Mnemonic for elements 27–30

    "Connie cousin" helps remember Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn).

  • Definition of a compound

    A pure substance made of two or more different elements chemically combined, e.g., NaCl or CO2.

  • Importance of reproducibility in science

    Experiments must be repeatable by others to verify results and maintain scientific integrity.

  • Metric prefixes kilo, mega, giga

    Kilo (k) = ×103, Mega (M) = ×106, Giga (G) = ×109.

  • Metric prefixes milli, micro, nano

    Milli (m) = ×10-3, Micro (µ) = ×10-6, Nano (n) = ×10-9.

  • Why 'chemical' does not mean dangerous

    All matter is chemical; toxicity depends on dose, not mere presence of a chemical.

  • Example of a drug with mirror-image forms

    Thalidomide had two forms: one safe for nausea, the other caused birth defects.

  • SI unit for temperature

    Kelvin (K) is the SI unit for temperature, used in chemistry and physics formulas.

  • Difference between mass and weight units

    Mass is measured in grams/kilograms; weight is a force measured in newtons (N).

  • Role of the periodic table groups and periods

    Groups are vertical columns with similar properties; periods are horizontal rows with no inherent similarity.

  • Why atomic weight may be in parentheses

    Parentheses indicate the element is radioactive and atomic weight is not precisely known.

  • Examples of transition metals to know

    Mercury (Hg), Palladium (Pd), Platinum (Pt), Silver (Ag), Gold (Au), Molybdenum (Mo), Tungsten (W).

  • Scientific dishonesty consequences

    Falsifying data can end careers and cause serious real-world consequences.