Intro to Chem
Define the difference between accuracy and precision and give a classroom example of each.
Accuracy = closeness to true value; Precision = reproducibility. Example: darts clustered together but off-center = precise, not accurate.
State what the atomic number and mass number represent for an atom.
Atomic number = number of protons; mass number = protons + neutrons
Describe the difference between ground state and excited state for an electron.
Ground = lowest energy; excited = electron promoted to higher energy level after absorption.
Define ionic bond and covalent bond and give one example of each.
Ionic: transfer of electrons, e.g., NaCl. Covalent: sharing electrons, e.g., Cl2
Define hydrofracking (hydraulic fracturing) in one or two sentences.
Hydrofracking: injection of high-pressure fluid into rock to create fractures and release natural gas.
Define matter, element, compound, and mixture with one-sentence definitions for each.
Matter = anything with mass and volume. Element = pure substance of one type of atom. Compound = substance of two or more elements chemically combined. Mixture = physical combination of substances.
Convert 21 days21 days into seconds and write the answer in scientific notation.
1.8144×106 seconds.
Explain what an isotope is and give two examples of isotopes of the same element using hyphen notation.
Isotopes: same Z, different N. Examples: Carbon-12 (C-12) and Carbon-14 (C-14)
Write the electron configuration and noble-gas shorthand for nitrogen.
Nitrogen: 1s22s22p31s22s22p3;
noble-gas shorthand: [He]2s22p3
Using electronegativity values, explain how to decide whether a bond is ionic, polar covalent, or pure covalent. Give an example for each category.
Use electronegativity difference: large (≈>1.7) ionic, moderate polar covalent, near zero pure covalent. Examples: Na–Cl ionic, H–Cl polar covalent, Cl–Cl pure covalent.
List two advantages and two disadvantages of hydrofracking for natural gas production.
Advantages: increased natural gas supply, economic benefits. Disadvantages: groundwater contamination risk, induced seismicity, methane leaks.
Determine the number of significant figures in: 3.01, 850, 7,102.0, 0.009903.01, 850, 7,102.0, 0.00990.
Significant figures:
3.01 → 3 sf
850 → 2 sf
7,102.0 → 5 sf
0.009900 → 4 sf
A lab set of five measurements of a length are: 2.01 cm, 2.03 cm, 1.98 cm, 2.00 cm, 2.02 cm2.01 cm, 2.03 cm, 1.98 cm, 2.00 cm, 2.02 cm. Calculate the average and the percent error if the accepted value is 2.05 cm2.05 cm.
2.008 cm
2.05%
Draw or describe a Bohr model for potassium-39 and identify number of protons, neutrons, and electrons.
K-39: protons = 1919, neutrons = 2020, electrons = 1919. Bohr: nucleus with 19p/20n; shells: 2,8,8,1.
Explain how Coulomb’s law relates to atomic radius and ionization energy trends across a period.
Coulomb’s law: greater effective nuclear charge pulls electrons closer (smaller atomic radius) and increases ionization energy across a period
Draw the Lewis structure for PCl3, state electron domains and lone pairs, and predict the molecular shape using VSEPR.
PCl3: Lewis: P central with 3 Cl, one lone pair; electron domains = 4; shape = trigonal pyramidal.
Explain, in basic terms, how mass spectrometry can be used to distinguish between biogenic and thermogenic methane.
Mass spectrometry measures isotopic ratios (e.g., carbon and hydrogen isotopes); thermogenic methane shows different isotope signatures than biogenic methane.
Balance and name the ionic compound formed between aluminum and sulfate; provide the chemical formula and name.
Al2(SO4)3, aluminum sulfate.
Given a plastic with mass 15 g that displaces water from 32 mL to 52 mL, calculate its density and classify whether density is an intensive or extensive property.
0.75 g/mL
intensive
Explain why elements in the same group share similar chemical properties. Name the group that is inert in nature and explain why.
Elements in same group have same valence electron count causing similar chemistry. Noble gases are inert due to full valence shells.
Given two waves: Wave A has wavelength λ=400, Wave B has wavelength λ=700. Which has greater frequency and which has greater energy?
Higher energy: shorter wavelength means higher frequency and energy. Using c=λν, so Wave A (400 nm) has greater frequency and energy than Wave B (700 nm).
Compare metallic bonding to ionic and covalent bonding. Explain why metals conduct electricity using the “sea of electrons” concept.
Metallic bonding: delocalized electrons across metal lattice; electrons move under potential difference → conductivity
Summarize how mining activities can lead to lead contamination in a watershed and name one major health effect of lead exposure in children.
Mining can release lead into tailings and runoff entering watershed; children: neurodevelopmental effects, cognitive deficits.
Given the molecular formula Ca(ClO3)2, list the number of atoms of each element present.
Ca = 1 atom; Cl = 2 atoms; O = 3×2=6 atoms.
Design a brief experimental outline (IV, DV, at least two constants, and safety considerations) to test how concentration of salt affects boiling point elevation of water. Include how you would organize data and what graphical analysis you would use.
many correct answers possible
atomic number = 16, mass number = 34,
determine the number of protons, neutrons, electrons, and write the most common isotope in nuclear notation. Also classify if this atom is likely to gain or lose electrons and why.
For Z=16, protons=16, neutrons=18, electrons=16. Nuclear notation: 3416S. Sulfur tends to gain electrons (form anions) to fill valence
Write the electron configuration (long form) for iodine
Iodine long-form: 1s22s22p63s23p63d104s24p64d105s25p5
For a diatomic bond between atoms with atomic radii leading to short bond length and high bond enthalpy, predict whether the bond is strong or weak
Short bond length and high bond enthalpy → strong bond. Smaller atomic radius generally yields shorter bond length if bonding orbitals overlap more.
Describe the principle of atomic absorption spectroscopy (AA) for lead determination and outline phytoremediation (phytoaccumulation) as a remediation strategy, including one limitation of phytoaccumulation.
AA: atomize sample, measure absorption at element-specific wavelength to determine concentration. Phytoaccumulation: plants uptake contaminants; limitation: slow and depth-limited uptake, disposal of biomass.
Explain what PFAS/PFOA (“forever chemicals”) are, describe why the C–F bond contributes to persistence, and name one health outcome that has been associated with PFOA exposure.
PFAS/PFOA: fluorinated compounds resistant to degradation; C–F bond is very strong giving persistence; health outcomes associated with PFOA include increased risk of certain cancers and thyroid disease (refer to epidemiological sources).