Chapter 3: Atomic Structure, Explaining the Properties … 2016_CH1010_Dr. Kreider-Mueller 1 of 11...

Fall 2016_CH1010_Dr. Kreider-Mueller

1 of 11

CH1010 Exam #2 Study Guide For reference see “Chemistry: An Atoms-focused Approach” by Gilbert, Kirss, and Foster

Chapter 3: Atomic Structure, Explaining the Properties of Elements

Trends to know (and be able to explain the trend…think about Zeff): o Effective Nuclear Charge (Zeff): the attraction toward the nucleus experienced by

an electron in an atom; the positive charge on the nucleus reduced by the extent to which other electron in the atom shield the electron from the nucleus

o Ionic radius (Figure 3.35 in textbook) When you form a cation, the radius shrinks (ex: the ionic radius of Na+ is

smaller than the atomic radius of Na). Why? When you form an anion, the radius expands (ex: the ionic radius of Cl− is

larger than the atomic radius of Cl). Why? o Ionization Energy

M + Energy M+ + e− M+ + Energy M2+ + e− M2+ + Energy M3+ + e− …and so forth Look at Figure Table 3.2 in your book (Think about when/why there are

large jumps between successive ionization energies) Be able to make predictions about ionization energies for various elements

o Electron Affinity Which group in the periodic table has the highest (most negative) electron

affinity? Which group(s) in the periodic table have the lowest (values close to zero) electron affinity

Look at Figure 3.37 in your book Be able to make predictions about electron affinities for various elements Group 1A elements have low electron affinities so they tend to lose their

ns1 electron Group 2A elements have low electron affinities so they tend to lose their

ns2 electrons Group 7A elements have large electron affinities so they tend to gain one

electron, adopting the electron configuration of the neighboring noble gas Group 8A elements are inert, and don’t generally gain or lose electrons

Chapter 4: Chemical Bonding Definitions to know:

o Molecule: unit of matter that results when 2 or more atoms are joined by covalent bonds.

o Ionic Bond: a bond resulting from the electrostatic attraction of a cation for an anion.

o Nonpolar Covalent Bond: a bond characterized by an even distribution of charge; electrons

in the bonds are shared equally by the two atoms.

o Polar Covalent Bond: a bond resulting from unequal sharing of bonding pairs of electrons

between two atoms.

o Polyatomic ions: charged group of more than one kind of atom joined together by covalent

bonds.


2 of 11

o Electrostatic Potential: the energy a charged particle has due to its position relative to another

charged particle.

Directly proportional to the product of the charges of the particles

Inversely proportional to the distance between the particles

o Lattice Energy: the energy released when 1 mole of an ionic compound forms from its free

ions in the gas phase.

o Bond Energy: the energy needed to break 1 mole of a particular covalent bond in a molecule

or polyatomic ion in the gas phase.

o Octet Rule: atoms of main group elements make bonds by gaining, losing, or sharing

electrons to achieve a valence shell containing 8 electrons, or four electron pairs.

o Bond Length: distance between the nuclear centers of two atoms joined together in a bond.

o Bonding Pair: a pair of electrons shared between two atoms.

o Lone Pair: a pair of electrons that is not shared between two atoms.

o Electronegativity: a relative measure of the ability of an atom in a bond to attract electrons to

itself when bonded to another atom.

o Resonance: characteristic of electron distributions when two or more equivalent Lewis

structures can be drawn for one compound.

o Resonance Structure: one of two or more Lewis structures with the same arrangement of

atoms but different arrangements of bonding pairs of electrons

o Resonance Stabilization: the stability of a molecular structure due to delocalization of its

electrons.

o Formal Charge: value calculated for an atom in a molecule or polyatomic ion by determining

the difference between the # of valence electrons in the free atom & the sum of lone-pair

electrons plus half of the electrons in the atom’s bonding pairs.

o Bond Order: the number of bonds between atoms: 1 for a single bond, 2 for a double bond, 3

for a triple bond.

Be able to Distinguish between the three different types of bonds

* Energy is released when bonds are formed, exothermic process*

* Energy is absorbed when bonds are broken, endothermic process*

1) Nonpolar Covalent Bond: two atoms evenly share 2 electrons

o Length and Strength of covalent bonds:

Double bond is shorter and stronger than a single bond

Triple bond is shorter and stronger than a double bond

The internuclear distance that corresponds to a potential energy minimum (point

“c” on the graph below) is the bond length between two atoms.


3 of 11

2) Polar Covalent Bond: two atoms share 2 electrons unevenly (unequal sharing). The

electrons are more attracted to the more electronegative atom.

3) Ionic Bond: complete transfer of one or more electrons from one atom to another occurs

resulting in the formation of 2 charged particles (ions)

o Ions of opposite charge attract one another Metals tend to form cations

We use a Roman numeral in parentheses to indicate # of charges on a cation

Ex: in Fe(II)Cl2 the iron has a 2+ charge, Fe2+

Ex: in Fe(III)Cl3 the iron has a 3+ charge, Fe3+

Nonmetals tend to form anions

Common polyatomic ions you should know:

NH4+, ammonium

NO3−, nitrate

ClO4−, perchlorate

CH3CO2−, acetate

OH−, hydroxide

PO43−, phosphate

CN−, cyanide

MnO4−, permanganate

SO32−, sulfite

NO2−, nitrite CO3

2−, carbonate

SO42−, sulfate

Be able to distinguish between ionic & molecular compounds in molecular level representations

Ionic Covalent

Be able to account for the differences in physical properties of ionic & covalent compounds. For

ex, see table 4.1 from General Chemistry: Atom’s First by McMurry & Fay

Trends to know (and be able to explain…think about Zeff):

o Lattice Energy

Depends on the charge of the ions and the size (radius) of the ions.

The smaller the radius, the higher the lattice energy

The larger the charge on the ions, the higher the lattice energy

The higher the lattice energy, the higher the melting point of the ionic solid


4 of 11

Be able to predict the magnitudes of lattice energy based on analogous compounds,

ionic charge, & ionic radius

For example, see the table below:

o Electronegativity

Look at Figures 4.8 & 4.9 in your textbook

Be able to predict the ionic/covalent character of bonds based on electronegativity

differences

Bonds between atoms w/ similar electronegativities are usually nonpolar

covalent

Bonds between atoms whose electronegativities differ by more than 2 units are

largely ionic

Bonds between atoms whose electronegativities differ by more than 0.4 units

but less than 2 units are usually polar covalent

Fluorine is the most electronegative (value of 4.0) atom

Oxygen is the second most electronegative (value of 3.5) atom

Bonding in molecules can be represented by using only valence electrons in electron dot (Lewis)

diagrams. Be able to draw electron dot structures:

o Section 4.3 of your book gives some steps for drawing electron dot structures

o Figure out how many valence electrons you need to account for in your structure

o Connect the atoms appropriately

o Remember the following:

Hydrogen does not follow the octet rule (only surrounded by 2 electrons)

C, O, N, and F follow the octet rule (boron often does not)

If an element is in period 3 or below, then you can expand the octet if necessary

Carbon likes to form 4 bonds

Nitrogen typically likes to form 3 bonds

Oxygen typically likes to form 2 bonds

Halogens typically like to form 1 bond

o Consider if you need any multiple bonds


5 of 11

o If there is more than one possible structure, you need to be able to determine which

structure is best based on the octet rule and formal charges

Formal Charge = (# of valence e−) – ½ (# of bonding e−) – (# of nonbonding e−)

The more formal charges there are on the atoms in your structure, the less the

structure contributes to the overall structure of the molecule (more formal charge =

worse structure)

o Consider if you can draw resonance structures for your compound (ex. Ozone, O3)

If you can draw different resonance structures, then the electrons are delocalized

within the compound

Delocalization reduces electrons’ potential energy making the molecule more stable

Be able to calculate bond orders for resonance hybrids

Chapter 5: Bonding Theories, Explaining Molecular Geometry *Bonding can be described using different models…each is useful & each has drawbacks. *

Definitions to know:

o Bond Angle: the angle (in degrees) defined by lines joining the centers of two atoms to a

third atom to which they are chemically bonded.

o Electronic Geometry: the 3D arrangement of bonding pairs & lone pairs of electrons

about a central atom.

o Molecular Geometry: the 3D arrangement of the atoms in a molecule.

o Bond Dipole: separation of electrical charge created when atoms with different

electronegativities form a covalent bond.

o Hybridization: in valence bond theory, the mixing of atomic orbitals to generate new sets

of orbitals that then are available to form covalent bonds with other atoms.

o Hybrid Atomic Orbital: in valence bond theory, one of a set of equivalent orbitals about

an atom created when specific atomic orbitals are mixed.

o Molecular Orbital: a region of characteristic shape and energy where electrons in a

molecule are located.

o Bonding Orbital: term in MO theory describing regions of increased electron density

between nuclear centers that serve to hold atoms together in molecules.

o Antibonding Orbital: term in MO theory describing regions of electron density in a

molecule that destabilize the molecule because they do not increase the electron density

between nuclear centers.

Understand the Valence-Shell Electron-Pair Repulsion (VSEPR) model

o Used to predict the shape of a molecule

o Electrons in bonds and in lone pairs are thought of as occupying “electron domains”

(regions of electron density) that repel one another and stay as far apart as possible,

causing the molecules to assume specific shapes

o When applying the VSEPR model:

Draw the electron-dot structure

Be able to predict the geometric arrangement of electron domains around each atom

by assuming that its electron domains are oriented in space as far away from one

another as possible

Know electron and molecular geometries for molecules with 2, 3, 4, 5, or 6 electron domains


6 of 11

o Be able to predict bond angles based on the shape of a molecule or polyatomic ion

For trigonal planar and tetrahedral electron geometries, as the # of lone pair

electrons increases, the bond angles become more compressed (bond angle

decreases)

Ex: CH4, NH3, and H2O all have a tetrahedral electronic geometry (4 electron

domains). CH4 has no lone pair electrons, and the H-C-H bond angle is about

109.5˚. NH3 has one set of lone pair electrons on the N, and the H-N-H bond angle

is about 107˚. H2O has 2 sets of lone pair electrons on the O, and the H-O-H bond

angle is about 104.5˚.

o Be able to identify simple polar molecules based on their molecular shape & bond polarity.

Polar Bonds: bond between 2 atoms that have a large difference in

electronegativity

Polar Molecule: A molecule that has a significant net dipole moment

A molecule that contains polar bonds may or may not be a polar molecule!!

You have to consider the geometry of a molecule in order to determine

if it has a net dipole moment

If a molecule contains polar bonds, but the dipole moments for those

bonds point equally in opposite directions, the dipole moments cancel

and there is no net dipole moment on the molecule (ex. CO2)

Examples of polar molecules: H2O, CH3OH, CH2Cl2, NH3

Examples of nonpolar molecules: CO2, SiH4, CH4, CCl4, CH3CH3

Valence Bond Theory: provides a readily visualized orbital picture of how electron pairs are

shared in a covalent bond (Section 5.4 of your book)


7 of 11

o Covalent bonds are formed by overlap of atomic orbitals, each of which contains 1 electron

of opposite spin. The 2 overlapping lobes must be of the same phase

o Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the

overlapping orbitals is shared by both atoms

o The greater the amount of orbital overlap, the stronger the bond

o Hybridization

What does the concept of hybridization help us explain?

Know about the shape (dumbbell shape with one large lobe & one small lobe) and

orientation of sp, sp2, and sp3 hybrid orbitals

Be able to identify the hybridization on a given atom in a molecule.

Ex: The carbon atom in CH4 is sp3 hybridized

Ex: Each of the carbon atoms in C2H4 are sp2 hybridized

Ex: each of the carbon atoms in C2H2 are sp hybridized

You can determine the hybridization of an atom based on the number of electron

domains (See Table 5.3 in your book)

If you have sp3 hybridization, you mixed 1 s atomic orbital with 3 p atomic

orbitals so you have no unhybridized p atomic orbitals

If you have sp2 hybridization, you mixed 1 s atomic orbital with 2 p atomic

orbitals so you have one unhybridized p atomic orbital

If you have sp hybridization, you mixed 1 s atomic orbital with 1 p atomic

orbitals so you have 2 unhybridized p atomic orbitals

Be able to identify the orbitals that overlap to give a specific bond in a molecule

A bond involves “head-on” overlap

A bond involves “side-on” overlap

A single bond consists of 1 bond

A double bond consists of 1 and 1 bond

A triple bond consists of 1 and 2 bonds

A π bond is weaker than a σ bond

Know a few basic things about Molecular Orbital Theory

o Atomic Orbital: a wave function whose square gives the probability of finding an electron

within a given region of space in an atom

o Molecular Orbital: A wave function whose square gives the probability of finding an

electron within a given region of space in a molecule

o Molecular orbitals are to molecules what atomic orbitals are to atoms o A molecular orbital describes a region of space in a molecule where electrons are most

likely to be found, and it has a specific size, shape, and energy level

o MO’s are formed by combining atomic orbitals on different atoms. The # of molecular

orbitals formed is the same as the # of atomic orbitals combined

o MO’s that are lower in energy than the starting atomic orbitals are bonding, and MO’s that

are higher in energy than the starting atomic orbitals are antibonding.

o Electrons occupy MO’s beginning with the MO of lowest energy. A maximum of 2

electrons can occupy each orbital, and their spins are paired

o Bond order can be calculated: B.O. = [(# bonding e−)-(# of antibonding e−)]/2

o Be familiar with the basic MO diagram: ex for H2, H2+, He2, Li2… etc

Combine the concepts of Valence Bond Theory and Molecular Orbital Theory to explain

resonance hybrids & the delocalization of electrons.


8 of 11

Chapter 6: Intermolecular Forces, Attractions Between Particles

Definitions to know:

o Intramolecular Forces: any force that holds together the atoms making up a molecule

or compound. They contain all types of chemical bonds.

o Intermolecular Forces: forces of attraction or repulsion between neighboring particles

o Dipole Moment: a quantitative expression of the polarity of a molecule.

o Temporary Dipole: an intermolecular force between nonpolar molecules caused by the

presence of temporary dipoles within the molecules.

o Permanent Dipole: permanent separation of electrical charge in a molecule due to

unequal distribution of bonding and/or lone pairs of electrons.

o Van der Waals Force: Any interaction between neutral atoms and molecules including

hydrogen bonds, other dipole-dipole interactions, and London dispersion forces. (Does

not apply to interactions involving ions)

o London Dispersion Force: an intermolecular force between molecules caused by the

presence of temporary dipoles in the molecules.

o Ion-Dipole Interaction: an attractive force between an ion and a molecule that has a

permanent dipole.

o Dipole-Dipole Interaction: an attraction between regions of polar molecules that have

partial charges of opposite sign.

o Hydrogen Bond: the strongest dipole-dipole interaction, which occurs between a

hydrogen atom bonded to a N, O, or F atom and another N, O, or F atom.

o Polarizability: the relative ease with which the electron cloud in a molecule, ion, or atom

can be distorted, inducing a temporary dipole.

o Sphere of Hydration: the cluster of water molecules surrounding an ion in an aqueous

solution.

o Alcohol: An organic compound whose molecular structure includes a hydroxyl group

bonded to a carbon atom that is not bonded to any other functional group(s).

o Solvent: the component of a solution that is present in the largest # of molecules.

o Solute: any component in a solution other than the solvent. A solution may contain one

or more solutes.

o Solubility: the maximum quantity of a substance that can dissolve in a given volume of

solution.

o Miscible: Liquids that are mutually soluble in any proportion.

o Hydrophobic: describes a “water-fearing” or repulsive interaction between a solute &

water that diminished water solubility.

o Hydrophilic: describes a “water-loving” or attractive interaction between a solute and

water that promotes water solubility.

Be able to do the following:

o Identify polar molecules based on their molecular shape and bond polarity

o Distinguish between intermolecular & intramolecular forces

Be able to identify the 4 kinds of intermolecular forces (IMF’s)


9 of 11

Ion-dipole

o Act between ions & molecules

o Result of electrical interactions between an ion & the partial charges

on a polar molecule

Dipole-Dipole (A Van der Waals force)

o Experienced by neutral but polar molecules

o Result of electrical interactions among dipoles of neighboring

molecules

o Strength of force increases as the polarity (net dipole moment) of

the molecule increases

London Dispersion (A Van der Waals force)

o Experienced by all atoms & molecules, regardless of structure

o Due to motion of electrons (instantaneous dipole)

o Magnitude of force depends on the polarizability of the molecule

o The larger/heavier the molecule, the more polarizable it is, & the

stronger the dispersion forces

o The more spread-out (longer chain) the molecule is, the more

surface area there is available for dispersion forces

o Generally, a weak force

Hydrogen Bonding (A Van der Waals force)

o Attractive force between a hydrogen atom bonded to a very

electronegative atom (O, N, F) & an electron-rich region elsewhere,

either in the same molecule or in a different molecule

o Be able to explain why hydrogen bonds are significantly stronger

than dipole-dipole forces

o Be able to discuss the significance of hydrogen bonding in water

o Understand the difference in strength of Hydrogen bonding

between ―OH group and ―NH group (―OH stronger than ―NH)

The table below presents a comparison between these forces

(Table from General Chemistry: Atom’s First by McMurry & Fay)


10 of 11

o IMF’s are responsible for physical properties of materials

o IMF’s can be predicted from molecular structure, shape, & bond polarity

o Physical properties can be predicted from molecular structure

As the strength of IMF’s increases, boiling point increases

Ex: the larger the atomic radius, the greater the polarizability of the

electron clouds. The greater the polarizability, the more likely the

atoms/molecules are to form temporary dipoles. The stronger the London

Dispersion Forces, the higher the boiling point. (Table 6.1 & 6.2)

o Ex: For a series of hydrocarbons, the longer the hydrocarbon chain, the greater the

polarizability of the electron clouds. The greater the polarizability, the more likely the

atoms/molecules are to form temporary dipoles. The stronger the London Dispersion

Forces, the higher the boiling point. See the figure below.

veryStrong

weak

moderate

strong


11 of 11

o As the strength of the London Dispersion forces increases, solubility in polar

solvents decreases and solubility in nonpolar solvents increases.

For example: be able to recognize solubility trends for alcohols

As the hydrocarbon chain length increases, the solubility in polar

solvents decreases

Alcohol Solubility in Water (g/100g)

CH3OH Infinitely soluble

CH3CH2OH Infinitely soluble

CH3CH2CH2OH Infinitely soluble

CH3CH2CH2CH2OH 9

CH3CH2CH2CH2CH2OH 2.7

CH3CH2CH2CH2CH2CH2OH 0.6

CH3CH2CH2CH2CH2CH2CH2OH 0.18

CH3CH2CH2CH2CH2CH2CH2CH2OH 0.054

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2OH Insoluble in water

Also Be able to: o Calculate grams of a compound if you are given moles of a compound

Moles can be used to convert between molecular level particles & macroscopic masses

of compounds

o Calculate moles of a compound if you are given grams of a compound

o Use the chemical formula of a compound to calculate the number of atoms in a sample of

a given compound

Be able to relate mass or moles of the compound to the mass or moles of the elements

that comprise the compound

Chapter 3: Atomic Structure, Explaining the Properties … 2016_CH1010_Dr. Kreider-Mueller 1 of 11...

Documents

Transcript of Chapter 3: Atomic Structure, Explaining the Properties … 2016_CH1010_Dr. Kreider-Mueller 1 of 11...