CHEM EXAM 2 - Kallevig UMD

Identify the intermolecular forces present in: HCL

- Dipole-dipole -LDF Because the H is not bonded to an N O F

Identify the intermolecular forces present in: NH3

- Hydrogen bonding -Dipole-dipole -LDF

Identify the intermolecular forces present in: CO

-Dipole-dipole -LDF Because CO has a slightly positive and negative charge it is dipole-dipole

Rank these compounds from highest to lowest boiling point:

-Hexane = HIGHEST -Pentane -Neuropentane =LOWEST

Identify the intermolecular forces present in: HCN

-LDF -Dipole- dipole

Identify the intermolecular forces present in: CH3OH

-LDF -Dipole-dipole -Hydrogren

Identify the intermolecular forces present in: CO2

-LDF only Because it is non-polar and is structured in an 180 degrees, indicating non polar

What 3 things have the same increasing trend on periodic table? Which one is opposite?

1.) electron affinity (EA) 2.) ionization energy 3.) electronegativity

Small molecules with smaller molar masses, arrange these intermolecular forces by strength

1st -Hydrogen = strongest 2nd- Dipole-dipole = middle 3rd - LDF = WEAKEST

Unequal sharing of electrons in a covalent bond indicates:

A dipole Polar + / -

Chiral.

A molecule is chiral if it is not superimposable on its mirror image. Most chiral molecules can be identified by their lack of symmetry or a center of symmetry. YOU NEED 4 DIFFERENT BONDS Your hand is a chiral object,

What are the ideal bond angles around a central atom with a steric number of 4?

All 109.5 degrees

What are the ideal bond angles around a central atom with a steric number of 3?

All 120 degrees

What are the ideal bond angles around a central atom with a steric number of 2?

All 180 degrees

What are the ideal bond angles around a central atom with a steric number of 6?

All 90 degrees

Which compound is Ionic? -SO3 -CF3 -BaCl2 -H2S

BaCl2

Acetone can form hydrogen bonds with water. Select the options below that shows the correct hydrogen bonding between acetone and water

C

Atoms, molecule and compound simplification

C or He = Atom C2 or He2 = Molecule C2H or C2H3 = Compound

Insoluble in water

C6H14 = Non-polar liquid C = Graphite, Non-polar solid CH4 = Non-polar gas * Very low in solubility is for Non-polar substances

Which molecule is polar? -CF4 -CS2 -SiH4 -CO2 -CH2Cl

CH2Cl2 C = 0 H2= +2 Cl2= -2

Which of the following molecules can form hydrogen bonds? -CH3OH -CH4 -H2 -HF

CH3OH and HF Hydrogen bonds form only when the H is attached to an N, O, or F

Calcium Nitrate

Ca (NO3) 2 = the charge on it

Electron Affinity - Negative

Change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) When an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron

AS BOND ANGLE INCREASES DUE TO:

DECREASE IN NUMBER OF LONE PAIRS

Internuclear distance

Distance between the centers of adjacent ions Size of ions affects this

What are the ideal bond angles around a central atom with a steric number of 5?

Either 90 degrees or 120

In the VSEPR theory, molecular geometry is determined by:

Electron- electron REPULSIVE forces

Which of the following properties is used to predict the type of bond that forms between 2 elements?

Electronegativity

Molecular compounds consist of

Equal balanced equations

Iron (II) Carbonate

Fe CO3

Water is a polar molecule, meaning it carries partial (+/-) charges on opposite sides. For Nacl - GROUPING OF WATER MOLECULES White dots are H Red dots are O

For a molecule to be polar, it must have a positive and negative charge.

In an ionic compound, the size of the Ions affect the internuclear distance. Based on ion SIZES, rank these compounds by their expected solubilities in water

HEAVIER the Ion, the more soluble it is

Nitric acid formula

HNO3

Methanol - CH3OH

Has a polar region that overshadows the effect of the non polar region Polar

For a molecule to exhibit dipole-dipole interactions must

Have a permanent dipole moment

Which of the following exhibit ONLY London Dispersion forces? -H2O -He -HCl -Cl2

He and Cl2 Because H2O is a hydrogen bond and Cl2 is non-polar since the charges cancel out Only LDF because LDF can have polar and non-polar molecules, unlike dipole having only polar bonds

Highest to lowest solubilities can be ranked from:

Heaviest to lightest molar masses Lighter the molecule, the less soluble it is in water Heavier the molecule, more soluble it is in water

Non Metals

High Ionization energy High electronegativity High negative electron affinity

Arrange these compounds from highest to lowest expected boiling point -CH3OH -CH3Cl -CH4

Highest boiling point = Heaviest

Highest boiling point

Highest electronegativity

Highest electronegativity

Highest molar mass / viscosity

Increasing electronegativity trend

In < Ga < Al < C

One reason electronegativity increases from left to right across a period is because

Increase in number of protons in the nucleus

Ion dipole forces always require

Ion and polar molecule

Covalent compounds DO NOT dissolve in water unless it is Sugar or Ethanol

Ionic compounds DO dissolve in water and break apart

Water - H2O

Is polar and has NO non polar regions

Potassium Oxide

K2O

Metals

Low ionization energy Low electronegativity Low negative EA - electron affinity

Lattice energy

Measure of force needed to pull ions apart

Ionic compounds consist of

Metals and Non metals

Which of the following substances have polar interactions (dipole-dipole forces) between molecules? - Cl2 - NF3 - F2 - CIF

NF3 and CIF Because there is unequal charges between them (+/-) they become polar

Ammonium chloride

NH4 Cl

Soluble in water

NO2 = Polar gas C2H5OH = Polar liquid NaCl = Ionic solid * Soluble if it is polar or ionic compound

Red orange on a dipole

Negative end

Ionic comounds = Metal and Non metal

No sharing of electrons Losing or gaining

Ethanol - C2H5OH

Non polar region that overshadows the effect of the polar region MISABICLE / Mixable

Bond order

Number of bonds / number of atoms bonded

Dissolve "like to like"

Polar dissolves polar Non- polar dissolves Non polar

Blue green on a dipole

Positive end

Platinum (II) fluoride

PtF2

Disulfur tetroxide

S2 O4

Covalent (molecular) = Two Non-metals

Sharing of electrons

SIGMA BONDS EVERYWHERE

Sigma bond is between every bond line BUT if there is more than one line, it is a Pi bond after that

Resonance Delocalizes

Stabilizes molecules

Pi bonds

The 2nd line on a bond and more 2 lines = one is sigma 3 lines = two is sigma

Most important rule in hydrogen bonding is:

The H must be attached to an -N -O -F

Electronegativity:

The ability of an atom in a molecule to attract bonding electrons to itself

Electron affinity:

The energy change when a neutral atom attracts an electron to become negative

Ionization energy:

The energy required to remove an electron from a neural atom

Which alcohol should be most soluble in a non polar solvent such as hexane - C6H14

The longest chain possible

Which of the following compounds is most soluble in water?

The one with an OH hydrogen bond on both ends of the molecule

T/F) Dipole-dipole only involve polar interactions

True

Electronegativity

Unequal sharing of COVALENT bonds that leads to polar covalent

For each solute, identify the BETTER solvent: Carbon tetrachloride (heavy) or Water (light)

Water is better solvent for KF and NH3 (lightest) Carbon Tetrachloride is a better solvent for Br2 (heaviest)

Highest boiling point = highest energy to break

biggest electronegativity