Atomic Theory
Which scientist is credited with discovering the nucleus during the gold foil experiment?
Ernest Rutherford.
Write the electron configuration for a neutral oxygen atom.
1s² 2s² 2p⁴
Name the compound MgCl₂.
Magnesium chloride
Draw the Lewis structure for CH₄.
Four single bonds connecting the carbon atom to each hydrogen atom.
Given the reaction C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, if 44.0 g of C₃H₈ reacts with 160.0 g of O₂, calculate the percent yield of water if 50.0 g of H₂O is produced.
Moles of C₃H₈ = 44.0 / 44.1 = 1.00.
Moles of O₂ = 160.0 / 32.0 = 5.00.
Limiting reactant is O₂ since 5.00 / 5 < 1.00 / 1.
Moles of H₂O = 5.00 / 5 × 4 = 4.00.
Mass of H₂O = 4.00 × 18.02 = 72.08 g.
Percent yield = (50.0 / 72.08) × 100 = 69.4%.
Calculate the average atomic mass of an element with two isotopes: 70% at 10.0 amu and 30% at 11.0 amu.
10.3amu.
Name a periodic trend that increases across a period and decreases down a group?
Ionization energy or electronegativity.
Write the formula for barium phosphate.
Ba₃(PO₄)₂
Identify the molecular geometry of SO₂.
Bent
Calculate the percent composition of carbon in C₃H₈.
(3 × 12.01) / 44.1 × 100 = 81.7%
A radioactive isotope has a half-life of 5 years. If you start with 200 grams, how much remains after 15 years?
200÷2÷2÷2=25grams.
Write the ground-state electron configuration for a manganese(II) ion (Mn²⁺).
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵
Name the compound Fe₂O₃.
Iron(III) oxide
Explain why water is a polar molecule, but CO₂ is not.
Water is polar because it has a bent geometry with an uneven distribution of electron density. CO₂ is nonpolar because it is linear, and the dipole moments cancel.
Determine the empirical formula of a compound that is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.
CH₂O
An atom has a mass number of 56 and 30 neutrons. Identify the element and write its isotope notation.
Protons = 56 - 30 = 26. The element is iron. Isotope notation: ⁵⁶₂₆Fe
Identify the shape of a molecule with a central atom bonded to four other atoms and no lone pairs.
Tetrahedral
Predict whether KCl or AlCl₃ will have a higher melting point and explain why.
AlCl₃ has a higher melting point because it has stronger ionic bonds due to the higher charge on aluminum ions compared to potassium ions.
Which intermolecular force is the strongest in NH₃?
Hydrogen bonding
A compound contains 85.6% carbon and 14.4% hydrogen by mass. Its molar mass is 56 g/mol. Determine its molecular formula.
Empirical formula = CH₂, Molecular formula = C₄H₈
A radioactive isotope of thorium-232 undergoes alpha decay, followed by beta decay, and then gamma decay. Identify the resulting isotope.
Alpha decay reduces the mass number by 4 and the atomic number by 2, resulting in radium-228. Beta decay increases the atomic number by 1, resulting in actinium-228. Gamma decay does not change the isotope. Final isotope: actinium-228.
Calculate the wavelength (in meters) of a photon with a frequency of 4.0 × 10¹⁴ Hz. Use c = 3.0 × 10⁸ m/s.
Wavelength λ = c / f = (3.0 × 10⁸) / (4.0 × 10¹⁴) = 7.5 × 10⁻⁷ m
A sample of MgSO₄·xH₂O is heated until all water is lost. If the starting mass is 5.00 g and the anhydrous residue is 3.10 g, determine the value of x.
Draw the resonance structures for the carbonate ion (CO₃²⁻).
Three resonance structures with one double bond to an oxygen atom and two single bonds to the other oxygen atoms, with the double bond rotating among the three oxygens.
Combustion of a 2.50 g sample of a hydrocarbon containing carbon, hydrogen, and oxygen produces 6.60 g of CO₂ and 2.70 g of H₂O. Determine the empirical formula of the hydrocarbon.
Calculate moles of carbon:
Moles of CO2 = 6.60 g / 44.01 g/mol = 0.150 mol.
Moles of carbon = 0.150 mol.
Calculate moles of hydrogen:
Moles of H2O = 2.70 g / 18.02 g/mol = 0.150 mol.
Moles of hydrogen = 0.150 mol x 2 = 0.300 mol.
Calculate mass of carbon and hydrogen:
Mass of carbon = 0.150 mol x 12.01 g/mol = 1.80 g.
Mass of hydrogen = 0.300 mol x 1.008 g/mol = 0.302 g.
Determine mass of oxygen:
Mass of oxygen = Total sample mass - Mass of carbon - Mass of hydrogen.
Mass of oxygen = 2.50 g - 1.80 g - 0.302 g = 0.398 g.
Calculate moles of oxygen:
Moles of oxygen = 0.398 g / 16.00 g/mol = 0.0249 mol.
Determine the ratio of elements:
C:H:O = 0.150 : 0.300 : 0.0249.
Simplify by dividing each by the smallest value (0.0249):
C:H:O = 6 : 12 : 1.
Empirical formula: C6H12O.