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GOB Chemistry Key Concepts (Ch 1-5)

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  • What is chemistry?

    Chemistry is the study of the composition, structure, properties, and reactions of matter.

  • What defines a chemical?

    A chemical always has the same composition and properties wherever it is found.

  • What is the scientific method?

    The scientific method is a process starting with observations, forming a hypothesis, performing experiments, and drawing conclusions after repeated success.

  • How is scientific notation written?

    Scientific notation has two parts: a coefficient and a power of 10. Numbers >1 have positive powers; numbers <1 have negative powers.

  • Name common SI units for volume, length, mass, temperature, and time.

    Volume: liter (L), Length: meter (m), Mass: gram (g) or kilogram (kg), Temperature: degree Celsius (\(\degree C\)) or kelvin (K), Time: second (s).

  • What is the difference between measured and exact numbers?

    Measured numbers come from instruments; exact numbers come from counting or definitions and have no uncertainty.

  • How do you determine significant figures in calculations?

    For multiplication/division, use the fewest significant figures; for addition/subtraction, use the fewest decimal places.

  • What do metric prefixes represent?

    Metric prefixes change unit size by powers of 10: centi, milli, micro for smaller units; kilo, mega, tera for larger units.

  • How are conversion factors used?

    Conversion factors express relationships between units as fractions to convert quantities from one unit to another.

  • How is density defined and used?

    Density is mass divided by volume (g/mL or g/cm\(^3\)). It can convert between mass and volume.

  • What distinguishes pure substances from mixtures?

    Pure substances have fixed composition (elements or compounds); mixtures have variable composition and can be separated physically.

  • What are physical and chemical properties?

    Physical properties can be observed without changing identity; chemical properties describe a substance's ability to change into another substance.

  • How do you convert temperatures between Celsius, Fahrenheit, and Kelvin?

    \(T_F=1.8T_C+32\) converts Celsius to Fahrenheit; \(T_K=T_C+273\) converts Celsius to Kelvin.

  • What is the difference between potential and kinetic energy?

    Potential energy is stored energy; kinetic energy is energy of motion.

  • How is specific heat used to calculate heat change?

    Heat change = mass × specific heat × temperature change; specific heat is energy to raise 1 g by 1\(\degree C\).

  • What are the main states of matter and their changes?

    States: solid, liquid, gas. Changes include melting, evaporation, boiling, sublimation, each involving energy absorption or release.

  • How are elements represented on the periodic table?

    Elements have symbols; arranged by atomic number in periods (rows) and groups (columns) with metals on left, nonmetals on right, and metalloids along the zigzag line.

  • What are the charges and locations of protons, neutrons, and electrons?

    Protons: positive charge, in nucleus; Neutrons: neutral, in nucleus; Electrons: negative charge, outside nucleus.

  • How do you find the number of protons, neutrons, and electrons from atomic and mass numbers?

    Protons = atomic number; Neutrons = mass number − atomic number; Electrons = protons in neutral atoms.

  • What are isotopes?

    Atoms with the same number of protons but different numbers of neutrons.

  • How are electron arrangements written for the first 20 elements?

    Electrons fill energy levels: 1st level holds 2, 2nd holds 8, 3rd holds up to 18 electrons, arranged from lowest to higher energy levels.

  • What trends are observed in the periodic table?

    Atomic size increases down groups, decreases across periods; ionization energy and metallic character decrease down groups, increase across periods.

  • What types of radiation do radioactive isotopes emit?

    Alpha (α), beta (β), positron (β+), and gamma (γ) radiation.

  • What is a balanced nuclear equation?

    An equation showing mass and atomic numbers balanced for reactants and products during radioactive decay.

  • How is radiation detected and measured?

    Detected by Geiger counters; measured in curies (Ci), becquerels (Bq), rads, grays (Gy), rems, and sieverts (Sv).

  • What is half-life in radioisotopes?

    Time for half of a radioactive sample to decay; varies from seconds to billions of years depending on isotope.

  • How are radioisotopes used in medicine?

    Used for diagnosis by tracking radiation in the body and for treatment by applying higher radiation doses to destroy tumors.

  • What are nuclear fission and fusion?

    Fission: splitting large nuclei into smaller ones releasing energy; Fusion: combining small nuclei into larger ones releasing energy.