CH121- Chapter 4
What is an example of a covalent molecule? N2 PtO2 NaNO3 Sr(OH)2
N2 N2 is a covalent molecule (nonmetal + nonmetal).
Identify the compound with the pure covalent bond. O2 HCl SO2 all of the above
O2 O2 has a pure covalent bond because the atoms it contains are identical and thus the electrons in this bond are shared equally.
A Lewis symbol with no dots must be a:
cation Lewis symbols show the valence electrons, so if a Lewis symbol has no dots, the atom must have lost its valence electrons and will therefore be a positively charged cation.
What is the correct molecular formula for silicon tetrachloride?
SiCl4
What is the formula for aluminum sulfite?
The sulfite ion has one fewer oxygen than the sulfate ion, so it will be SO2−3. Aluminum forms ions with a charge of 3+. Therefore, the compound will contain 2 aluminum ions and 3 sulfite ions such that the compound has a net charge of zero. The formula is Al2(SO3)3.
Which is NOT a typical cation of chromium? 2+ 3+ 5+ 6+
5+ Most transition metals will readily form 2+ and 3+ ions. The electron configuration for neutral chromium is 1s22s22p63s23p64s13d5. Chromium is a d-block transition metal, and so the valence electrons are removed from the s subshell before they are removed from the d subshell. Therefore, Chromium would lose its one s electron first and a d electron to form Cr2+, which is only stable in the absence of air. Chromium can lose two more d electrons to become Cr3+, which is the most stable oxidation state for chromium. Chromium can also lose all the remaining valence electrons to become Cr6+. Chromium is seen in this oxidation state in chromium(VI) sulfide Cr2S3.
A sulfur atom can make up to ____ bonds in a Lewis structure.
6- expanded octet
Aluminum oxide has the formula __________.
Al_2O_3 Aluminum will tend to lose its three valence electrons to achieve a complete octet, thus forming 3+ ions. Oxygen will tend to gain two electrons to achieve a complete octet, thus forming 2− ions. Therefore, Al3+ and O2− will combine in a 2:3 ratio so that the charges cancel out. Therefore the formula for aluminum oxide is Al2O3.
Which of the following is a characteristic of ionic solids? Their ionic bonds are very strong Ionic solids are poor conductors of electricity Ionic solids dissolve easily in water All of the above
All of the above The properties of ionic compounds shed some light on the nature of ionic bonds. Ionic solids exhibit a crystalline structure and tend to be rigid and brittle; they also tend to have high melting and boiling points, which suggests that ionic bonds are very strong. Ionic solids are also poor conductors of electricity for the same reason. Most ionic solids, however, dissolve readily in water.
Which of the following is very reactive and can readily combine with molecules containing atoms with lone pairs?
Electron Deficient Molecules An electron-deficient molecule will react with electron excess, namely a lone pair from some other molecule, like ammonia.
Which of the following elements can NOT form hypervalent molecules? (select all that apply)
Elements in the second period of the periodic table (n=2) can accommodate only eight electrons in their valence shell orbitals because they have only four valence orbitals (one 2s and three 2p orbitals). Elements in the third and higher periods (n≥3) have more than four valence orbitals and can share more than four pairs of electrons with other atoms because they have empty d orbitals in the same shell. Therefore, of the elements listed above boron and nitrogen can not form hypervalent molecules.
What is the name of the compound with the formula Fe(OH)3?
Iron has two possible oxidation states. In this example, we know there are three hydroxides, each with a charge of -1. This totals to a charge of -3. In order to balance the formula charge, iron must have a charge of +3. Therefore, the first part of the name is iron(III). The second part of the name is hydroxide, the name of the polyatomic ion. The name of this compound is iron(III) hydroxide.
Which of the following statements about nonmetal anions are true? -Nonmetals tend to form anions by gaining electrons to form a noble gas configuration. -Nonmetals do not tend to form anions. -Anions of nonmetals tend to be isoelectronic with a noble gas. -Nonmetals tend to form anions by losing electrons to form a noble gas configuration.
Nonmetals tend to form anions by gaining electrons to form a noble gas configuration. Anions of nonmetals tend to be isoelectronic with a noble gas. Most monatomic anions form when a neutral nonmetal atom gains enough electrons to completely fill its outer s and p orbitals (valence orbitals), thereby reaching the electron configuration of the next noble gas. Anions that have the same number of electrons as the next noble gas makes the anion isoelectronic with the noble gas.
If there are multiple resonance structures of a molecule with a formal negative charge that can end up on different atoms, placing the negative formal charge on which of the following elements generally gives the most stable resonance structure?
O The negative charge is most stabilized when it is on the most electronegative atom. Of the above options, that would be oxygen.
sulfur hexafluoride
SF6 Sulfur hexafluoride is SF6 because the name indicates 1 sulfur atom and 6 fluorine atoms.
What is the abbreviated electron configuration of Mn2+?
The abbreviated electron configuration of Mn is [Ar]4s23d5. Because Mn is a d-block transition metal, the electrons of the s subshell are removed before the (n−1)d electrons. Thus the abbreviated electron configuration for Mn2+ is [Ar]3d5.
What is true about the covalent bonds in the nitrite ion, NO−2?
They are of equal length
What is the electronic structure of V2+?
Vanadium's electron configuration is 1s22s22p63s23p64s23d3. Vanadium is a d-block transition metal, therefore we remove the two valence electrons from the 4s subshell to form vanadium(II), giving us 1s22s22p63s23p63d3. Alternatively, this can be written using the symbol [Ar] to represent the noble gas core; [Ar]3d3.
When comparing H2 and HCl, the hydrogen atom in the HCl molecule will:
be surrounded by less electron density A chlorine atom will draw electron density away from the hydrogen atom, so hydrogen will have lost some electron density in the HCl molecule, whereas in a hydrogen molecule, each hydrogen has the same amount of electron density.
CuOH is called
copper(I) hydroxide As the hydroxide has a charge of 1−, the copper atom must have a charge of 1+, thus we use the roman numeral I.
N2O5 is called
dinitrogen pentoxide. The name of the more metallic element (the one farther to the left and/or bottom of the periodic table) is first, followed by the name of the more nonmetallic element (the one farther to the right and/or top) with its ending changed to the suffix -ide. The numbers of atoms of each element are designated by the Greek prefixes shown below.
When covalent bonds break: energy is absorbed energy is released mass is gained mass is lost
energy is absorbed Energy must be added to break covalent bonds (endothermic), whereas forming covalent bonds releases energy (exothermic).
An alternative name for iron(II) chloride is:
ferrous chloride The word ferrous implies the Fe2+ ion.
Formula for Lithium Phosphate
$Li_3PO_4$Li3PO4 Step 1: Identify the symbol of the cation. The cation is lithium, which is written as Li+. Step 2: Identify the formula of the anion. The anion is phosphate, which is written as PO3−4. Step 3: Use the minimum number of cations and anions needed to make the sum of all charges in the formula equal to zero. The Li+ cation has a 1+ charge and the PO3−4 has a 3− charge. In order to balance the charges, three Li+ cations are needed for every PO3−4 anion. Therefore, the formula for lithium phosphate is Li3PO4.
What is the name of SnO2
tin (IV) oxide SnO2 is an ionic compound with a tin cation and the oxide anion. Tin can have multiple charges, so the name must indicate the charge with a roman numeral. To find the charge on the tin cation, use the fact that oxide has a charge of −2. There are two oxide anions, so the charge on the tin cation must be +4 in order to give a neutral charge overall. 1(+4)+2(−2)=0. Therefore, the name of the compound is tin (IV) oxide.
The elements that are most likely to have multiple oxidation states are:
transition metals The transition metals have a tendency to form more than one ion per element.
The element with the highest electronegativity is: helium neon carbon fluorine
fluorine Fluorine is at the upper right hand corner of the table, excluding the noble gases, which do not receive electronegativity values.
Au2O3 is called:
gold(III) oxide We must specify the oxidation state of the gold atoms, and if oxygen is 2−, gold must be 3+, hence the roman numeral III.
Ionic compounds tend to form between a nonmetal with ________ and a metal with __________.
high electron affinity, low ionization energy Nonmetals tend to have a high electron affinity whereas metals tend to have low ionization energies. A metal with a low ionization energy can easily lose an electron. A nonmetal with a high electron affinity can easily gain an electron. Thus if these elements come into contact, an electron will transfer from the metal to the nonmetal, forming an ionic compound as a result.
The greater the electronegativity difference, the more the bond will exhibit:
ionic character As the difference in electronegativity increases, the ionic character of the bond increases.
Which of the following correctly pairs the ion name with the ion symbol?
lithium cation, Li+ The correct pairing of the monoatomic ion with its formula is lithium ion with Li+.
MgCl2 is called __________.
magnesium chloride When combining a metal plus a non-metal for ionic compounds, we do not need a prefix for magnesium, and chlorine will become chloride, giving us magnesium chloride.
In a polar covalent bond, the more electronegative atom will bear a:
partial negative charge The more electronegative atom will be partially negative.
What is the chemical formula for chromium(III) phosphate? (hint: phosphate has a 3− charge)
$CrPO_4$CrPO4 Cr3+ and (PO4)3− will combine in a 1:1 ratio.
resonance structure
A molecule whose Lewis structure could be described by more than one resonance structure possesses an electronic structure equal to that of a combination of the resonance structures, with the more stable structures contributing more to the average structure. Resonance structures all contribute to the overall electronic structure of a molecules. They do not fluctuate over time, and they do not represent exact structures of different compounds. Instead, for any given arrangement of atoms in a molecule, the most stable arrangement of multiple bonds and formal charges may not represent a single Lewis structure, but an average over multiple stable resonance structures.
Which bond is NOT an example of a pure covalent bond? H-H C-C C-O Cl-Cl
C-O When the covalent bond is between two identical atoms, the electrons must be shared precisely evenly, but if the atoms differ, the electrons may skew closer to one atom than the other.
Which of the following characteristics would be preferred for a better resonance structure?
Formal charges indicate the stability of a Lewis structure. Because resonance forms are the various arrangements of atoms for lewis structures, we can determine the more stable/preferred resonance structure by considering the structure with minimal formal charges, maximized bond strength, and negative formal charges on the most electronegative atom. These factors all indicate stability.
Use the figure provided to determine which of the following has bonds with the greatest bond-polarity. HCl NO2 NH3 H2O
H2O Calculating the difference between the electronegativities for each element of each molecules, we find that H and O have the greatest difference, so H2O has bonds with the greatest polarity.
Ions typically have:
properties that are dramatically different from those of the corresponding neutral atom By definition of an ion, they will always bear an electrical charge, either positive or negative. Sodium and chlorine are excellent examples of how properties of individual ions correspond to the properties of the ionic compound. Both sodium and chlorine are toxic elements individually, but once ionized, are harmless components of table salt. Therefore, ions typically exhibit dramatically different properties from those of the corresponding neutral compound.
Hypervalent molecules require that central atoms access:
s, p and d orbitals All of the above orbitals are required if a central atom hopes to make more than four bonds to other atoms.
Which of the following is named using the unmodified element name and adding the word "ion"?
simple cations (monatomic cations of elements of only one possible charge) Simple cations are named with their elemental name followed by the word "ion." For instance, the Na+ is named the sodium ion.
What is the correct name of the following compound: NaNO3?
sodium nitrate Step 1: Identify the cation. Result of this step = Na+ is sodium.Step 2: Identify the anion. Result of this step = NO−3 is nitrate.The resulting name of this compound is sodium nitrate.
For a polyatomic ion, the sum of the formal charges present is equal to:
the charge of the ion The sum of the formal charges on each atom is equal to the charge of the ion.
On an energy diagram representing the distance between two hydrogen atoms, what does the lowest energy represent?
the ideal covalent bond length When a covalent bond forms, each electron interacts with each nucleus, which brings the system to a lower energy. The ideal bond length is determined by the lowest energy that can be attained as the atoms approach each other.
When drawing a Lewis structure for a free radical, which type of atom is more likely to receive the unpaired electron?
the less electronegative element A more electronegative element is more likely to be surrounded by more electrons and fulfill its octet. A less electronegative element is more likely to have the electron deficiency, in this case the unpaired electron. Recall that free radicals are electron deficient and display the same stability trends as electron deficient cations, like carbocations.
In a polar covalent bond, the atom that attracts the electrons less strongly has:
the partial positive charge In a polar covalent bond, the atom that attracts the electrons less strongly has the partial positive charge because the other atom holds on more tightly to the negative electrons.
A covalent bond holds two atoms near each other because
the two electrons that form the bond are attracted to both nuclei. When two electrons from two different atoms each feel the attraction of the other atom's nucleus, a covalent bond can form.
In a Lewis structure involving iodine and fluorine, if the central iodine atom has exactly one lone pair, how many fluorine atoms must be present?
Iodine has 7 valence electrons, and since it is a fifth period element, it can exceed the octet rule when it binds to a more electronegative element like fluorine. Fluorine also has 7 valence electrons, but cannot exceed an octet because it is in the second period. Each fluorine atom can therefore only form a single bond to the central iodine atom, and each single bond between iodine and fluorine accounts for 1 of iodine's valence electrons. Since there is a lone pair (or non-bonding pair) of electrons on the iodine, that means precisely 2 of the 7 valence electrons are not shared with a fluorine atom, and the remaining 5 are each shared with 1 fluorine atom, so there must be 5 fuorine atoms surrounding central iodine atom.
What is used to describe valence electron configurations of atoms and monatomic ions?
Lewis symbols are used to describe valence electron configurations of atoms and monatomic ions. They are drawn by writing the element's symbol, and placing dots around the symbol that represent the number of valence electrons it has.
When naming binary covalent compounds, the element listed first will be the one that is
More metallic The atom farther to the left on the periodic table, which will be the one with more metallic character, will be listed first.
Ionic compounds tend to be:
Neutral By definition, ionic compounds are composed of both positive cations and negative anions and bear a neutral overall charge. Therefore, these ions must come together in a particular ratio so as to result in a neutral substance.
Which of the following anions is most likely to form? Br2− S− Se3− Te2−
Te2− Tellurium will tend to gain two electrons to fill its valence shell. Sulfur and selenium also should become 2−, while bromine should become 1−.
What is the electron configuration of Cl−?
1s^2 2s^2 2p^6 3s^2 3p^6 [Ne]3s^2 3p^6 Due to Cl gaining an electron
Determine the electron configuration of the sulfur ion (S−2).
1s22s22p63s23p6 Sulfur has a configuration of 1s22s22p63s23p4 which means it's 2 away from having a noble gas configuration (its charge is −2) so the ion's configuration is 1s22s22p63s23p6. Alternatively, this can be written as [Ne]3s23p6 or [Ar].
What is the charge of a yttrium cation? Only enter the charge of the cation, do NOT enter the element symbol.
Yttrium has three valence electrons, and it will typically lose all three to become the 3+ ion. As Y is 3rd group and d block element.