Nafui

What charge does Al typically have in ionic compounds, and why?

+3 , because it has three valence electrons.

What is the valence configuration for Lv?

7s2 7p4

The elements C and Se have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from C and Se is most likely to be true?

A molecule of the compound will have a partial negative charge on the carbon atom.

Rb reacts with O in a mole ratio of 2 to 1, forming the ionic compound Rb2O. Which of the following elements will react with O in a mole ratio of 2 to 1, forming an ionic compound, and why?

Cs , because it is in the same group as Rb.

A student obtains a 10.0g sample of a white powder labeled as BaCl2. After completely dissolving the powder in 50.0mL of distilled water, the student adds excess Na2SO4(s), which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s), rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment? Ba2+(aq)+SO42−(aq)→BaSO4(s)

Is the BaCl2(s) used in the experiment pure?

The first ionization energy of polonium, Po, is 812 kJ/mol. Is the first ionization energy of Lv expected to be greater than, less than, or equal to that of Po? Justify your answer in terms of Coulomb's law.

Less than that of Po. The two atoms have comparable effective nuclear charges, but the valence electrons in Lv would be at a greater distance from the nucleus than those in Po. By Coulomb's law, the attractive force between the valence electrons and the nucleus decreases by the inverse square of the distance between them.

A jar labeled NaCl contains a powder. The table above contains information determined by analyzing a sample of the powder in the laboratory. What information in the table is the most helpful in determining whether the powder is pure NaCl?

Mass percent of Na

A jar labeled NaCl contains a powder. The table above contains information determined by analyzing a sample of the powder in the laboratory. What information in the table is the most helpful in determining whether the powder is pure NaCl? Mass Mass Percent of Na Density Color :: 27.3g 35.2% 2.05g cm−3 White

Mass percent of Na

A student obtains a sample of a pure solid compound. In addition to Avogadro's number, which of the following must the student know in order to determine how many molecules are in the sample?

Molar mass of the compound, mass of the sample

Which pair of elements is likely to produce a nearly nonpolar covalent bond

N and F

Element N P As Sb Bi :: Atomic Radius (picometers) 65 100 115 145 160 :: The atomic radii of the elements in the nitrogen group in the periodic table are given in the table above. Which of the following best helps explain the trend of increasing atomic radius from N to Bi?

The attractive force between the valence electrons and the nuclei of the atoms decreases.

The atomic radii of the elements in the nitrogen group in the periodic table are given in the table above. Which of the following best helps explain the trend of increasing atomic radius from N to Bi?

The attractive force between the valence electrons and the nuclei of the atoms decreases.

Which of the following best helps to explain why the atomic radius of K is greater than that of Br?

The effective nuclear charge experienced by valence electrons is smaller for K than for Br . Which of the following best helps explain why the first ionization energy of K is less than that of Ca? The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca .

What best explains the following trend: Melting point order: LiF > NaCl > KBr > Csl

The greater radii of the larger ions result in smaller lattice energies, leading to lower melting points

In a lab a student is given a 21g sample of pure Cu metal. Which of the following pieces of information is most useful for determining the number of Cu atoms in the sample? Assume that the pressure and temperature in the lab are 1.0atm and 25°C.

The molar mass of Cu

A vessel contains a mixture of gases. The mass of each gas used to make the mixture is known. Which of the following information is needed to determine the mole fraction of each gas in the mixture?

The molar mass of each gas

A student obtains a mixture of the chlorides of two unknown metals, X and Z. The percent by mass of X and the percent by mass of Z in the mixture is known. Which of the following additional information is most helpful in calculating the mole percent of XCl(s) and of ZCl(s) in the mixture?

The molar masses of X and Z

Which of the following best helps explain why the first ionization energy of K is less than that of Ca?

The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca .

Which of the following best explains the difference in the melting points of MgO (2852C) ans NaF (1819C)

There are greater Coulombic attractions in McO due to the greater charges on the ions

Which of the following claims about a binary compound in which the bonding is ionic is most likely to be scientifically valid?

There is equal sharing of electrons between the atoms of the elements in the compound.

A 42.0g sample of compound containing only C and H was analyzed. The results showed that the sample contained 36.0g of C and 6.0g of H. Which of the following questions about the compound can be answered using the results of the analysis?

What is the empirical formula of the compound?

A student measures the mass of a sample of a metallic element, M. Then the student heats the sample in air, where it completely reacts to form the compound MO. The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment?

What is the molar mass of M ?

A student has samples of two pure compounds, XClO3 and ZClO3 , which contain unknown alkali metals X and Z . The student measures the mass of each sample and then strongly heats the samples to drive off all the oxygen, leaving solid residues of XCl and ZCl . The student measures the mass of the solid residue from each sample. Which of the following questions can be answered from the results of the experiment?

Which has the greater molar mass, X or Z ?

The compound K2O2 also exists. A chemist can determine the mass of K in a sample of known mass that consists of either pure K2O or pure K2O2. From this information, can the chemist answer the question of which compound is in the sample? Indicate yes or no, and explain.

the chemist can determine the identity of the compound. If the mass of K in a sample of the compound is determined, then the percent mass of K in the compound can be calculated and the compound identified because the percent mass is different (or known) for the two compounds.