Chemistry AP Study

atomic mass (amu)

(mass)(percentage) + (mass)(percentage) = amu

3 peaks - first two double the size of third

1 single electron in 2p subshell

Based on the Lewis diagram for NH3, shown above, the H-N-H bond angle is closest to which of the following?

109.5°

Which of the following best helps explain why an atom of Rb gas more easily loses an electron in a chemical reaction than an atom of Li gas?

In the Rb atom the valence electron is farther from its nucleus than the valence electron of Li is from its nucleus.

substitutional alloy

some of the host metal atoms are replaced by other metal atoms of similar sizes

brittleness

the property of a material that fractures when subjected to stress but has a little tendency to deform before rupture

mass percent is most helpful in determining

whether a powder is pure

x is 1s electron bc strongest attraction to the nucleus

x and y peaks with x being taller than y & having stronger attraction

In terms of atomic structure, explain why the first-ionization energy K is less than that of Ca.

Ca+ has more shells and shielding than K+ . This outweighs the fact that Ca+ has more protons in the nucleus, meaning means there is a weaker attraction between the nucleus and the electron to be removed, meaning less energy is required to remove it.

Which of the diagrams above best represents the CH2O molecule, and why?

Diagram 2, because all atoms have a formal charge of 0.

Ba2+(aq)+SO42−(aq)→BaSO4(s) 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?

Is the BaCl2(s)BaCl2(s) used in the experiment pure? The calculated number of moles of BaBa in the precipitate can be compared with the expected number of moles of BaBa in 10.0g10.0g of BaCl2BaCl2. The presence of fewer moles of in the precipitate would imply that the BaCl2BaCl2 was not pure.

Which of the following indicates whether the solid substance represented by the particulate diagram shown above conducts electricity and explains why or why not?

It conducts electricity because electrons are free to move through the substance.

Molten (liquid) NaCl is represented by the particulate diagram shown above. Which of the following indicates whether NaCl(l) conducts electricity and best explains why or why not?

It conducts electricity because ions are free to move.

The diagram above best illustrates which of the following phenomena associated with solids that have metallic bonding?

Malleability, because it shows how adjacent layers of positive ions can move relative to one another while remaining in full contact with the electron sea.

K forms the compound K2O, which is an ionic compound that is brittle. Identify another element, M, that is likely to form a brittle, ionic compound with the formula M2O. Justify your answer in terms of periodic trends.

Na₂O will also form a brittle ionic compound. Sodium is located in the same group as Potassium: Alkali Metals. This is because both elements have similar chemical properties. In term of their electronegativity, both elements are very close. Na has an electronegativity of 0.93, while K has an electronegativity of 0.82. This makes both ideal elements to create ionic compounds with Oxygen.

atomic radius increases down a group and left of period

The attractive force btwn the valence electrons & the nuclei of the atoms decreases

Which of the following claims about a binary compound composed of elements with the same electronegativity is most likely to be true?

The bonding in the compound is nonpolar covalent.

why is atomic radius of k greater than Br?

The effective nuclear charge experienced by valence electrons is smaller for K than for Br.

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

The electronegativity difference between the elements in the compound is relatively large.

why is 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.

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 MM? The number of moles of OO in the compound is equal to the number of moles of MM and can be calculated using the difference in the masses of the sample and the compound. The molar mass of MM is calculated by dividing the mass of the sample of MM by the number of moles of MM.

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 molar mass of the compound? The results of the analysis can be used to determine the empirical formula of the compound, but more information is needed to determine the chemical formula and the molar mass of the compound. The number of moles of CC and HH is calculated by dividing the masses of each element in the compound and their respective molar masses. The ratio of the number of moles of CC to HH can be used to determine the empirical formula of the compound.

Based on formal charges, which of the following is the best Lewis electron-dot diagram for H3NO?

When the formal charge of each atom in this diagram is determined using the rule ((formal charge of an atom == the number of valence electrons of the atom −− ((the number of electrons in lone pairs ++ half the number of electrons in bonds with other atoms)))), the sum of the formal charges on all the atoms in H3NOH3NO is equal to zero. A sum of formal charges on all atoms equal to zero is preferable.

In terms of atomic structure, explain why the atomic radius of K is larger than that of Na.

Within a period of elements, each new electron is added to the same shell. When an electron is added, a new proton is also added to the nucleus, which gives the nucleus a stronger positive charge and a greater nuclear attraction. For each group you move down, the atom gets an additional electron shell. Each new shell is further away from the nucleus of the atom, which increases the atomic radius.

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

Yes, the chemist can determine which compound is in the sample. In 1 mole of K₂O, the mass of K is 2 × 39.1 g = 78.2 g and the mass of K₂O is 94.2 g. The mass ratio of K to K₂O is 78.2 g / 94.2 g = 0.830. In 1 mole of K₂O₂, the mass of K is 2 × 39.1 g = 78.2 g and the mass of K₂O₂ is 110.2 g. The mass ratio of K to K₂O₂ is 78.2 g / 110.2 g = 0.710. If the chemist knows the mass of K and the mass of the sample, he or she must calculate the mass ratio of K to the sample. If the ratio is 0.830, the compound is pure K₂O. If the ratio is 0.710, the compound is pure K₂O₂. If the ratio is not 0.830 or 0.710, the sample is a mixture.

interstitial alloy

a mixture formed when small atoms fill holes in a metallic crystal

1s^2 2s^2 2p^6 3s^2 3p^6 3d^10

arrows up then down

The particulate-level diagram shown above best helps to explain which of the following properties of ionic solids?

brittleness

mass to moles

g x 1 mole/g = mol

How to determine # of atoms in a sample

grams/ molar mass x 6.022E23

to calculate mole percent

mass % = mass of solute/ mass of solution x 100 mole percent/fraction = # of moles/ total # of moles of all substances x 100 The molar mass (massmoles)(massmoles) is the quantity that establishes the ratio of the mass of a pure substance in a mixture to its number of moles. This ratio can be used to calculate the mole percent of either XClXCl or ZClZCl in the mixture.

moles to mass

mol x g/1 mol = g