Unit 1: Atomic Structure and Properties

How many atoms in total are in 12.0 g of water, H₂O?

Four samples each have a mass of 10.0 g. Which sample contains the greatest total number of atoms?

What is the mass, in grams, of a single atom of silver, Ag?

The mass spectrum of a sample of element X is shown. What is the average atomic mass of X?

A student calculates an element's average atomic mass from its mass spectrum by weighting each isotope's mass by the height of its peak. Which assumption does this method rely on?

A mass spectrum of a pure element shows two peaks: 63 amu with relative abundance 69.2% and 65 amu with 30.8%. Which element is it?

Element Q has two isotopes, with masses of 10.0 amu and 11.0 amu. Its average atomic mass is 10.81 amu. What is the percent abundance of the isotope with mass 11.0 amu?

What is the percent by mass of nitrogen in ammonium sulfate, (NH₄)₂SO₄?

An oxide of phosphorus is 43.6% phosphorus and 56.4% oxygen by mass. What is its empirical formula?

A gaseous compound contains only nitrogen and oxygen and is 30.4% nitrogen by mass. Its molar mass is 92.0 g/mol. What is its molecular formula?

A chemist decomposes two samples of a black copper compound. Sample A gives 3.18 g of copper and 0.80 g of oxygen. Sample B, made by a different method, gives 6.36 g of copper and 1.60 g of oxygen. Which claim do the data best support?

A 10.0 g mixture of calcium carbonate, CaCO₃, and sodium chloride, NaCl, contains 2.40 g of calcium. What is the percent by mass of CaCO₃ in the mixture?

The particle diagrams show four samples. Which box represents a mixture of an element and a compound?

A white powder is either pure potassium chloride, KCl, or a mixture of KCl and sodium chloride, NaCl. Which measurement would best decide between the two?

A student wants to find the mass percent of water in a sample of a hydrated salt, such as CuSO₄·5H₂O. Which procedure gives the most reliable result?

In a simple model, the attraction between an electron and the nucleus follows Coulomb's law, F ∝ q₁q₂/r². Electron A is a distance r from a nucleus with an effective charge of +1. Electron B is a distance 2r from a nucleus with an effective charge of +2. What is the ratio of the force on B to the force on A?

What is the ground-state electron configuration of the Fe³⁺ ion?

Which species has the same ground-state electron configuration as a neon atom?

The photoelectron spectrum of a neutral atom is shown. Peaks are listed from highest to lowest binding energy, and each bar's height is proportional to the number of electrons. Which element is it?

In photoelectron spectra, the 1s peak of magnesium appears at a higher binding energy than the 1s peak of sodium. Which statement best explains this?

The ions S²⁻, Cl⁻, K⁺ and Ca²⁺ all have 18 electrons. Which ion has the largest radius?

The first four ionization energies of a period 3 element, X, are given in the table. What is the most likely formula of the oxide of X?

The first ionization energy of oxygen, 1,314 kJ/mol, is lower than that of nitrogen, 1,402 kJ/mol, even though oxygen has more protons. Which explanation is best?

The first ionization energies of three group 1 elements are lithium 520 kJ/mol, sodium 496 kJ/mol and potassium 419 kJ/mol. Which value is the best prediction for rubidium?

Element Z, a main-group metal, forms an oxide with the formula Z₂O₃. What is the most likely formula of the compound formed between Z and chlorine?

Which pair of elements is most likely to form an ionic compound with the formula XY₂, where X is the first element named?

A sodium atom is about twice as large as a chlorine atom, even though both have their valence electrons in the third shell. Which statement best explains the difference?