CHE 100 - Ch. 10

The octet rule predicts that fluorine will tend to make ____ bond(s).

1 With three lone pairs and one unpaired electron, fluorine will gain an octet by making one covalent bond.

How many electrons does hydrogen need to gain to fill its outermost shell?

1 The outermost shell (and, in fact, the only valence shell) of hydrogen is n=1, which can only hold two electrons. So hydrogen needs to gain 1 electron to fill its outermost shell.

How many valence electrons does the cyanide ion (CN−) have? How many bonds are present in its Lewis structure?

10,3 The cyanide ion (CN−) has a total of 10 valence electrons. Carbon has 4 valence electrons. Nitrogen has 5 valence electrons. Adding the the valence electrons from carbon and nitrogen, we get 9 total valence electrons. However, because the ion has a negative charge, we add an addition electron, giving us a total of 10 valence electrons. We follow the steps below to construct the Lewis structure for CN− which has 3 bonds (a triple bond). Determine the total number of valence (outer shell) electrons. For cations, subtract one electron for each positive charge. For anions, add one electron for each negative charge. Draw a skeleton structure of the molecule or ion, arranging the atoms around a central atom. (Generally, the least electronegative element should be placed in the center.) Connect each atom to the central atom with a single bond (one electron pair). Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom. Place all remaining electrons on the central atom. Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible.

How many shared electrons and lone pairs does the following molecule have?

12 shared electrons, 0 lone pairs Each line in the Lewis structure is a bond representing a shared pair of electrons. There are 4 single bonds and 1 double bond which contain 12 shared electrons. There are no lone pairs in this Lewis structure because all of the valence electrons are being shared in bonds.

Of the 5 molecules on this slide (CH4, CH3F, CH2F2, CHF3, CF4), how many are polar?

3

O3 has how many electron groups around it's central atom?

3 yes, 2 bonds (a single and a double) plus 1 lone pair = 3 electron groups

How many electron groups does H2S (shown here) have around its central atom?

4

Lead (Pb) is a group 14 element which has 4 valence electrons. How many bonds does this element usually form?

4 Lead has 4 valence electrons, following the octet rule it wants to reach a total of 8 electrons to be stable. To do this it needs 4 more electrons, which means it usually forms four bonds such is the case with lead tetrafluoride (PbF4).

In the Lewis structure below, with how many valence electrons does nitrogen interact?

8 The N atom interacts with 8 valence electrons: the 2 electrons in the lone pairs and the 6 in each single bond.

In the Lewis structure below, the carbon atom has _____ shared electrons(s) and ____ lone pair(s).

8, 0 Each pair of dots is a lone pair of electrons. Each line is a bond representing a shared pair of electrons. Therefore, there are 2 double bonds which contain 8 shared electrons and 0 lone pair for the C atom in this polyatomic ion. Recall, that carbon only has 4 valence electrons. All of its electrons are being shared in covalent bonds; thus, carbon has 0 available valence electrons to form lone pairs.

Create the Lewis structure of SeCl+3.

A Lewis structure is shown. In the center is an Se atom, with one lone pair of electrons, single-bonded to 3 C l atoms. Each C l atom has 3 pairs of electrons. The overall charge is +1. We count valence electrons (6+3(7)−1)=26 and draw a skeleton with single bonds. We then distribute 3 lone pairs to each Cl and the remaining electrons to the central atom.

Identify the correct Lewis structure of aluminum fluoride.

Aluminum comes in with three valence electrons, and each fluorine comes in with seven valence electrons. Each F receives one electron from the Al atom, so three fluorine atoms are required.

What is the Lewis symbol for Be2+?

Be has 2 valence electrons, but Be2+ has lost those valence electrons so its Lewis symbol would not have any dots (2−2=0).

Compare Cl to Br. Which is more electronegative?

Br Electronegativity decreases down the PT because larger atoms are not holding on to electrons as well...they are "less selfish" with electrons, so to speak.

Which choice correctly assigns δ+ and δ− to the atoms in the bonds?

C-N, where C is δ+ and N is δ− The correct δ+ and δ− assignment is given for the C-N bond, C is the element with the δ+ and N is the element with the δ−. This is because N is the more electronegative element of the two. Review the following bond polarities and electronegativity differences. Bond Difference ΔEN Polarity C-N 3.0−2.5 0.5 Cδ+−Nδ− N-H 3.0−2.1 0.9 Nδ−−Hδ+ C-O 3.5−2.5 1.0 Cδ+−Oδ− O-H 3.5−2.1 1.4 Oδ−−Hδ+

What does the equation represent? ⋅Ca⋅→Ca2++2e−

Cations are formed by losing valence electrons. The equation ⋅Ca⋅→Ca2++2e− shows calcium cations formed by losing two valence electrons. To represent this with a Lewis structure, the dots around the atomic symbol are removed.

Compare C and F. Which is more electronegative?

F Electronegativity increases across the PT because smaller atoms are holding on to electrons better...they are "more selfish" with electrons, so to speak.

Which of the following is the correct the Lewis structure for carbon dioxide CO2?

Follow the steps below to construct the Lewis structure. Determine the total number of valence (outer shell) electrons. For cations, subtract one electron for each positive charge. For anions, add one electron for each negative charge. Draw a skeleton structure of the molecule or ion, arranging the atoms around a central atom. (Generally, the least electronegative element should be placed in the center.) Connect each atom to the central atom with a single bond (one electron pair). Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom. Place all remaining electrons on the central atom. Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible. Note: Most people forget about the double bond between carbon and oxygen. This is formed because it helps carbon become a full octet.

Which of the following will have the greatest electronegativity?

H Electronegativity increases as you move up and to the right on the periodic table (the same as the ionization trend).

Which molecule will have a double bond?

H2COH2CO In H2COH2CO, carbon and oxygen form a double bond in order to satisfy the octet rule. Carbon atom connected to two hydrogen atoms by single bonds and one oxygen atom by double bond. The oxygen atom has four electrons surrounding the atomic symbol. In COCO, carbon and oxygen must form a triple bond to satisfy the octet rule. Carbon atom connected to one oxygen atom by triple bond. The oxygen and carbon atoms each have two electrons surrounding the atom symbol. In OF2OF2 and CCl4CCl4, there are only single bonds. Oxygen atom connected to two fluorine atoms by single bond. The oxygen atom has four electrons surrounding the atom symbol and each fluorine has six electrons surrounding the atom symbol..

Use the figure provided to determine which of the following has bonds with the greatest bond-polarity?

H2O Calculating the difference between the electronegativities for the elements in each molecule, we find that H and O have the greatest difference, so H2O has bonds with the greatest polarity.

Identify the compound(s) with polar covalent bonds.

H2O NO2 H2O and NO2 feature polar covalent bonds because the electronegativities of the two elements involved in each bond are different. Cl2 is a diatomic molecule; therefore, the electronegativities of the two atoms are the same, making this a non-polar covalent bond. AlBr3 is an ionic compound because it consists of a metal and a nonmetal joined by ionic bonds.

Identify the compound(s) containing polar covalent bonds.

HBr, CO2 All choices are covalent compounds and, thus, contain covalent bonds. However, only HBr and CO2 feature polar covalent bonds because the pairs of atoms in each bond have different electronegativities.

Which molecule has the most lone pairs?

HF The hydrogen fluoride atom will have three lone pairs, whereas water has two, ammonia has one, and methane has none.

Use the figure provided to determine which of the following is the least polar.

ICl The least polar bonds are formed between elements with the smallest difference in their electronegativities. In this case, ICl, has the smallest difference of 0.5.

How do we know CO2 has a linear molecular shape? (Note: if you're paying attention, you should note that BeF2 is an exception to the octet rule. No need to worry about that in this course.)

It has 2 electron groups around it's central atom and no lone pairs.

Identify the Lewis structure of potassium sulfide.

K+2[:S:⋅⋅⋅⋅]2− Potassium has one valence electron, so each potassium loses its one valence electron to form K+. Sulfur atoms have six valence electrons, so they will add two electrons to form S2− , which has eight valence electrons. In order to form a compound with neutral charge, the resulting ionic compound must have a formula of K2S. The resulting Lewis structure is K+2[:S:⋅⋅⋅⋅]2−.

Use the image below to answer the question that follows. Two Lewis structures are shown. The left-hand structure shows two H atoms connected by a single bond. The right-hand structure shows two C l atoms connected by a single bond and each surrounded by six dots. Which of the following is an appropriate key for the image above?

Lewis structures and diagrams show electrons, not protons. The electrons that are not used in bonding are called lone pairs, and are represented by two dots. A line represents a shared pair of electrons (2 electrons), participating in a single bond.

What does the equation represent? :S⋅⋅⋅⋅+2e−→[:S⋅⋅⋅⋅:]2−

Lewis structures for anions are shown by adding additional electron dots to the atomic Lewis structure, as shown by the example for sulfur. Anions are formed by gaining valence electrons, and in most cases, the stable anion can be predicted by the number of electrons it takes to reach eight valence electrons. The equation shows the example of adding two electron dots to the Lewis structure for the sulfur atom to form [:S⋅⋅⋅⋅:]2−.

Which molecule contains only single bonds?

NH3 CO2 and C2H4 contain double bonds, while HCN contains a triple bond, but ammonia has only single bonds.

What is the Lewis symbol for I−?

Neutral iodine has 7 valence electrons. The 1− charge indicates that Iodine has acquired an additional electron, giving it 8 valence electrons. The correct Lewis structure is shown below. :I⋅⋅⋅⋅:-

Identify the molecules(s) containing non-polar covalent bonds.

O2 H2 All choices are covalent molecules and, thus, contain covalent bonds. Remember that the absolute value of the difference in electronegativity (ΔEN)(ΔEN) of two bonded atoms provides a rough measure of the bond polarity. The difference in electronegativity in the S−F bonds in SF6 is 4.0−2.5=1.5. Therefore, the S−F bonds are considered to be polar covalent bonds. The difference in electronegativity in the N−O bonds in NO2 is 3.5−3.0=0.5. Therefore, the N−O bonds are considered to be polar covalent bonds. Thus, only the diatomic molecules O2 and H2 feature non-polar covalent bonds because both atoms have the same electronegativity.

Which molecule will have an oxygen atom as the central atom?

OF2 Oxygen is less electronegative than fluorine, so this molecule is the only example where oxygen will be the central atom.

Which molecule will have a net dipole?

SO2 has polar bonds and a bent structure, so it will have a net dipole. CO2 and BF3 have polar bonds but molecular structures in which the polarity cancels, producing no net dipole. CH4 has non-polar bonds, so regardless of the molecule structure, it has no net dipole.

Two of the top 50 chemicals produced in the United States, ammonium nitrate and ammonium sulfate (both used as fertilizers), contain the ammonium ion: NH+4. Predict the molecular structure of NH+4 ,whose Lewis structure is pictured below.

Tetrahedral We can see that NH+4 contains four bonds from the nitrogen atom to the four hydrogen atoms, and no lone pairs. We thus expect the four regions of high electron density to arrange themselves so that they point to the corners of a tetrahedron, with the central nitrogen atom in the middle (see the chart provided in the question). Therefore, the molecular structure of NH+4 is tetrahedral.

What is the Lewis structure of C2H6?

The center of the structure is 2 C atoms, with one pair of electrons between them. Each C atom is surrounded by 3 H atoms. There is a pair of electrons between each C and H atom. We count valence electrons (2(4)+6(1) = 14) and draw a skeleton with bonds to the central atom (hydrogen is never the central atom).

Which best describes the *electron group geometry* around NH3?

There are 4 groups of electrons and we call this tetrahedral. 3 bonds + 1 lone pair = 4 electron groups around the central atom. The name for 4 electron groups is tetrahedral.

What is the Lewis structure of CO?

We count valence electrons (4+6=10) and draw a skeleton with single bonds. We then distribute electrons and create multiple bonds in order to achieve an octet. We use a triple bond and have a lone pair on each atom in order for each atom to have the correct number of electrons.

Even though H2S has 4 electron groups and it's *electron* group geometry is tetrahedral, what is the name of it's molecular shape?

bent

even though O3 has trigonal planar *electron group geometry*, what is the name of it's molecular shape since one of those electron groups is a lone pair?

bent

What is the molecular structure of O3?

bent There are two resonance structures for O3, so the central O has two outer O's at equal length. The central O has one nonbonding pair so there are three electron domains, which means the electron-pair geometry is trigonal planar and the molecular structure is bent.

A Lewis symbol that has a non-noble gas element and no electrons represents a:

cation Lewis symbols show the valence electrons. If a Lewis symbol has no dots, the atom must have lost its valence electrons, and will therefore be a positively charged cation.

Which of the following is a step in predicting electron pair geometry and molecular structure using VSPER theory?

count the number of regions of electron density around the central atom write the Lewis structure of the molecule use the number of lone pairs to determine the molecular structure identify the electron-pair geometry based on the number of regions of electron density VSEPR theory can be used to determine both the electron-pair geometry and the molecular structure. First, we write the Lewis structure of the molecule, and then count the number of electron dense regions around the central atom. Single bonds, double bonds, triple bonds, and lone pairs each count as one electron dense region. After determining the electron dense regions, the electron-pair geometry can be determined based on the number of regions. Finally, we can use the number of lone pairs to determine the molecular structure by focusing on minimizing repulsions.

Which of the following is NOT a step in constructing Lewis structures?

draw a skeletal structure with the most electronegative atom in the middle We will put the least electronegative atom in the middle when we draw the skeletal structure.

The number of electron domains surrounding an atom will determine the:

electron-pair geometry Each number of electron domains will correspond with a specific electron-pair geometry.

VSEPR theory considers which of the following?

electron-pair repulsions VSEPR theory considers electron-pair repulsions in that it predicts molecular structure based on electron pairs minimizing their repulsions from each other in order to achieve the most stable structure.

Which statement is true about BF2Cl? (Note: he was accidentally mis-pronouncing "Boron" has "borine".)

it contains polar bonds and is a polar molecule overall.

Which statement is true about BF3?

it contains polar bonds but is a non-polar molecule overall.

Which statement is true about CO2?

it contains polar bonds but is a non-polar molecule overall.

Which electron-pair geometry involves fewer than five regions of electron density and a 180∘ bond angle?

linear Two regions of electron density around a central atom in a molecule form a linear geometry with a 180∘ bond angle.

Which pair of electron domains generates the most repulsion?

lone pair - lone pair Lone pairs generate the most repulsion as they take up a larger region of space than a bonding pair.

The more electronegative an atom is the _____________

more it attracts electrons towards itself in a bond

Question 1 of 1 Molecules are ___________ but polarity occurs when there is an _____________ distribution of charge on the molecule.

neutral, uneven

If two atoms have precisely the same electronegativity, the type of bond they will form will be

nonpolar covalent. If two atoms have precisely the same electronegativity, the electrons in the covalent bond will be shared precisely evenly, and will therefore be a nonpolar covalent bond.

An electrically charged object can be used to attract:

polar molecules In electric fields, polar molecules align with the molecule's positive end pointed toward a negative plate and the negative end of the molecule aligned toward the positive plate. Because of this tendency toward alignment, an electrically charged object can be used to attract polar molecules.

And what name is used for 4 electron groups?

tetrahedral

The central atom in a Lewis structure will tend to be:

the least electronegative The central atom will be the most metallic, or the least electronegative atom.

We can predict the number of bonds an atom can form from:

the number of electrons needed to form an octet We can predict the number of bonds an atom can form from the number of electrons needed to form an octet.

What is the name of the *electron group geometry* for 3 electron groups?

trigonal planar

What is the molecular shape of NH3?

trigonal pyramidal Since one of the 4 electron groups is a lone pair, the molecular shape has a different name than its electron group geometry.

What is the molecular structure of SnCl−3?

trigonal pyramidal SnCl−3 has four electron regions with one resulting from a nonbonding pair. The electron-pair geometry is tetrahedral, and the molecular structure is trigonal pyramidal.

The dots in the image above represent:

valence electrons The image above is a Lewis symbol, and it is used to describe valence electron configurations of atoms and monatomic ions. A Lewis symbol consists of an elemental symbol surrounded by one dot for each of its valence electrons.

What can be used to represent bond dipole moments?

vector Vectors point from the less electronegative atom to the more electronegative atom to indicate the direction of the bond dipole moment. The vector shows that the electrons are pulled from the less electronegative atom toward the more electronegative atom. This separation of charges between the atoms produces a bond dipole moment.

The magnitude of a bond dipole moment is represented by the Greek letter mu (μ) and is a function of the magnitude of the partial charges (Q), and the distance between the charge (r). Which of the following equations accurately represents bond dipole moment?

μ=Qr The magnitude of a bond dipole moment (μ) is given by the formula shown below, where Q is the magnitude of the partial charges (determined by the electronegativity difference) and r is the distance between the charges. μ=Qr This bond dipole moment can be represented as a vector, a quantity having both direction and magnitude.