Chemistry Unit 4 Flashcards
Bonding!
What allows ionic bonds to form?
Elements having a large difference in electronegativity
Define ionic bond
The electrostatic forces of attraction between oppositely-charged ions
How are ionic compounds arranged?
A 3D crystalline structure called an ionic lattice
What is a coordinate number?
The number of ions that surround a given ion in an ionic lattice
What is lattice enthalpy and what does it depend upon?
Lattice enthalpy is the strength of the force between ions in an ionic compound, and it depends upon the size of the ion and the charge
What is charge density?
The charge per unit volume of an ionic compound
Why do ionic compounds tend to have high melting and boiling points?
Because the electrostatic forces of attraction between ions is very strong and requires high amounts of energy to break
What two factors determine the melting point of an ionic compound?
Ionic radius and the charge on the ion
As ionic radius increases, melting point _______
Decreases!
As the charge on the ion increases, melting point ______
Increases!
Do ionic compounds tend to have high or low volatility, and why?
Low voltality because they have strong electrostatic forces of attraction
This means they do not readily escape to the vapor phase
What does electrical conductivity depend upon?
The fact that ions are able to carry a charge (freely moving charged particles)
Are ionic compounds usually brittle?
Yes! This means the crystals typically shatter when force is applies
What causes the crystal lattice to split when force is applied?
When force is applied, ions of the same charge get moved next to each other, so the repulsive forces exerted by the ions cause the lattice to split
If the difference in electronegativity increases, then ionic character ________
Increases!
What is bond length and what unit is it expressed in?
Bond length is the measure of the distance between two covalently bonded nuclei, and it is expressed in picometers (pm)
What is bond strength and what unit is it expressed in?
Bond strength is a measure of the energy required to break a covalent bond, and it is expressed in KJ/mol
Bond length and bond strength have what kind of relationship?
An inverse relationship
As you go from single to double to triple bonds, bond length (increases/decreases), and bond strength (increases/decreases)
Decreases; increases
Which bonds are stronger, shorter or longer bonds, and why?
Shorter bonds are stronger than weaker bonds because as bond length increases, the distance of the shared pair of electrons from the nucleus increases, which reduces the bond strength
What two values classify covalent bonds?
Bond length and bond strength
In a covalent bond, which side is always the slightly negative side?
The side with the atom that has a higher electronegativity because the electrons are being pulled in closer
What elements can exceed the octet rule?
Elements that are in period 3 or higher because they have d sublevels to hold “extra” electrons
When multiple atoms can exceed the octet rule, where should we place the extra lone pairs?
On the central atom
What does VSEPR stand for?
Valence Shell Electron Pair Repulsion
What is VSEPR
Not what it stands for, what it is
The shape of a molecule is due to repulsions between pairs of electrons outside the shell of the central atom
Molecules take shape to ____ repulsions
Minimize!
True or false: Bonded pairs repel more than lone pairs
False! Lone pairs repel more than bonded pairs
Do double and triple bonds repel more than single bonds?
No, they all repel the same amount
What are electron domains?
Places where bonds have formed or can form
What determines the electron geometry?
The number of electrons domains
What is the electron geometry for something with 2 domains?
Linear
What is the electron geometry for something with 3 domains?
Trigonal Planar
What is the electron geometry for something with 4 domains?
Tetrahedral
What is the electron geometry for something with 5 domains?
Trigonal Bipyramidal
What is the electron geometry for something with 6 domains?
Octahedral
What are the bond angles for a linear electron geometry?
180 degrees
What are the bond angles for a trigonal planar electron geometry?
120 degrees
What are the bond angles for a tetrahedral electron geometry?
109.5 degrees
What are the bonds angles for a trigonal bipyramidal electron geometry?
90 degrees (from top/bottom to side), 120 degrees (from side to side), and 180 degrees (from top to bottom)
What are the bond angles for an octahedral electron geometry?
90 degrees, and 180 from top to bottom
What does the bond angle become when there is one lone pair on a trigonal planar molecule?
117 degrees
What does the bond angle become when there is one lone pair on a tetrahedral molecule?
107 degrees
What does the bond angle become when there are two lone pairs on a tetrahedral molecule?
105 degrees
What are the domains around the middle called?
Equitorial
What are the domains on the top and the bottom called?
Axel
Where must you place lone pairs when drawing a trigonal bipyramidal molecule and why?
They must be put on one of the domains that is on the side, not on top or bottom. This is because lone pairs want space and these domains are furthest away from the others
What do the equitorial bond angles become on a trigonal bipyramidal when there is one lone pair present?
117 degrees because they are originally 120 degrees
What is the molecular geometry for a molecule with four domains, one of which is a lone pair?
Trigonal pyramidal
What is another name for a bent molecular geometry?
V-shape
What is the molecular geometry for a molecule with five domains, one of which is a lone pair?
Unsymmetrical tetrahedron or seesaw
What is the molecular geometry for a molecule with five domains, when two of them are lone pairs?
T-shape
Because it looks like a T
What does the equitorial bond angle become when there are two lone pairs of electrons on a molecule with five domains?
There isn’t a bond angle because there is only one equitorial bond
What is the molecular geometry for a molecule such as I3 -
Central iodine has five domains, and three lone pairs
Linear!
What do the bond angles become on a molecule with six domains, when there is one pair of lone electrons?
Less than 90 degrees
Where must you place the first two lone pairs of electrons on a molecule with 6 domains?
The top and the bottom
Which molecular shapes are symmetrical and will result in nonpolar molecules?
Linear, trigonal planar, tetrahedral, trigonal bipyramidal, square planar, octahedral
When a molecule has a charge, what will the formal charge always equal?
The charge of the molecule
Why are Boron and Beryllium considered Lewis acids?
They are electron deficient and seeking electrons
How many electrons does Boron want?
6
How many electrons does Beryllium want?
4
How many electrons is aluminum happy with?
6
What does aluminum do to form a more stable compound?
It reacts with itself (dimerizes)
What molecule dimerizes and why is it able to do this?
Other than aluminum
NO2 dimerizes to form N2O4. It is able to do this because the molecule has 1 lone electron (on the N) which makes it a free radical, and therefore it can bond with itself
If something has 1 lone electron, does that make it very reactive or not very reactive?
Very reactive
When beryllium or aluminum combine with chlorine, why is the bond covalent and not ionic?
Keep in mind, beryllium and aluminum are both metals
The difference in electronegativity makes the bonds ever so slightly covalent
Define hybridization
The mixing of atomic orbitals to form new hybrid orbitals which are used in bonding
What are degenerates?
Orbitals that all have the same amount of energy
What do hybrid orbitals form when they overlap?
Sigma bonds
Where is the electron density for sigma bonds?
Along the bonding axis
If something is sp3 hybridized, will it have more p or s characteristics?
p
What do unhybridized orbitals form?
pi bonds
Which orbitals can form pi bonds?
Its either p, s, or d
p orbitals
Where is the electron density for pi bonds?
Above and below the bond axis
This is why when you draw them, you must draw them twice, once on the top and once on the bottom
What is the hybridization for a linear electron geometry?
sp hybridized because it has 2 bonding sites
What is the hybridization for a trigonal planar electron geometry?
sp2 hybridized because it has 3 bonding sites
What is the hybridization for a tetrahedral electron geometry?
sp3 hybridized because it has 4 bonding sites
What is the hybridization for a trigonal bipyramidal electron geometry?
dsp3 hybridized because it has 5 bonding sites
What is the hybridization for an octahedral electron geometry?
d2sp3 hybridized because it has 6 bonding sites
What bonds (sigma/pi) do single bonds make?
One sigma bond
What bonds (sigma/pi) do double bonds make?
One sigma and one pi
What bonds (sigma/pi) do triple bonds make?
One sigma and two pi
When are resonance structures a thing?
When more than one equivalent Lewis structure is possible
When there is more than one position for the double bond
How do you find the bond order of a resonance structure?
Number of total bonds divided by number of bond positions
What does delocalized mean?
Not fixed in a specific location
True or false: electrons in a resonance structure are stuck in a certain location
False! They are delocalized and not fixed in a specific location
Which ones are stronger: sigma or pi bonds?
Sigma bonds
What are the characteristics of metals?
List 4
Malleable, ductile, conductors of heat and electricity, shine/luster
More valence electrons = more delocalized electrons = hardness and strength (increases/decreases)
Increases
Why do transition metals have more delocalized electrons?
They have 4s and 3d sublevels which causes them to have greater metallic bonding
What’s an alloy?
A homogeneous mixture of metals (always a solid solution)
How does combining metals to make an alloy change the properties of the original metal?
It makes them less malleable and stronger
What are the two types of alloys?
Interstitial and substitutional
What is an interstitial alloy?
Added atoms are smaller than the original metal atoms and fit into the spaces between metal atoms
What is an example of an interstitial alloy?
Steel (iron + carbon)
What is a substitutional alloy?
The added atoms are similar to the size of the original metal atoms and replace some of the original metal atoms
List two examples of substitutional alloys
Bronze (copper + tin) and brass (copper + zinc)
Define allotrope
A different form of an element in the same physical state with different bonding within the structure
List the four allotropes of carbon
Diamond, graphite, graphene, fullerene/Buckyball
What is the hybridization of diamond
sp3
What are the bond angles in diamond?
109.5
What is the shape of the carbons bonded in diamond?
Tetrahedral because four carbonds are bonded together
Does diamond have a high or low melting/boiling point?
High!
Which of the following is diamond a part of: Giant covalent molecules, network solid, macromolecules
Can select multiple
Giant covalent molecules, network solid, macromolecules
Can diamond conduct electricity?
No because it has fixed electrons
Can diamond conduct heat?
Yes! It is an excellent thermal conductor
What is the hybridization of graphite?
sp2
What are the bond angles of graphite?
120
What is the structure of the C’s in graphite?
Hexagonal structure
Which carbon allotrope is made up of many layers with weak bonds in between?
Graphite. The bonds are weak so when you write they just slide off
Does graphite have a high or low melting/boiling point
High melting/boiling point
Can graphite conduct electricity?
Yes, it has delocalized electrons
Can graphite conduct heat?
No!
Which carbon alloy is soft and slippery?
Graphite
What is the hybridization of graphene?
sp2 hybridized
What are the bond angles in graphene?
120
What is the structure of the carbons in graphene?
Hexagonal structure
Does graphene have a high or low melting/boiling point?
High melting/boiling point
Can graphene conduct electricity?
Yes, due to the delocalized electrons
Can graphene conduct heat?
Yes
What is graphene used in?
Photo-voltaic cells and electronics
Which carbon allotrope is very flexible and has high tensile strength?
Graphene
Tensile strength means it can bend without breaking btw
btdubs
Graphene is the ____ material to ever exist
thinnest
Is graphene stronger than steel and diamond?
Yes! It is 100 times stronger than steel and 40 times stronger than diamond
What is the formula for fullerene?
C60
How many pentagons and hexagons are in fullerene?
There are 12 pentagons and 20 hexagons
What is the hybridization of fullerene?
sp2 hybridized
Is fullerene a giant covalent molecule? Why or why not?
No because it has a fixed formula of C60
Is fullerene a conductor of electricity?
It is a semi-conductor due to some delocalized electrons in the hexagons
Does fullerene have high or low thermal conductivitiy
Low
Does fullerene have a high or low melting/boiling point
Low
Is fullerene flexible?
Yes!
What does fullerene look like?
It is a yellow crystalline solid
What is the difference between intermolecular and intramolecular forces?
Intermolecular means between molecules, intramolecular means inside of the molecule
What type of intermolecular forces exist in all types of covalent molecules?
London Dispersion Forces
What is the weakest IMF?
London Dispersion Forces
Do London Dispersion Forces become stronger or weaker as molecule size and mass increases?
Stronger!
Why can nonpolar molecules condense and freeze at low temperatures?
Because of London Dispersion Forces
What type of dipole do London Dispersion Forces create?
Temporary dipoles
In London Dispersion Forces, does more electrons mean higher or lower temporary dipoles?
Higher
How does dipole-dipole attraction work?
Opposite charges in neighboring molecules attract each other
Does greater polarity equal stronger or weaker dipole-dipole?
Stronger!
True or false: Hydrogen bonding is a type of dipole-dipole force
True!
Which three atoms, when bonded DIRECTLY to hydrogen can form hydrogen bonding?
Fluorine, oxygen, and nitrogen
Does hydrogen bonding result in very high or low boiling points?
Very high
What is the strongest type of IMF?
Hydrogen bonding!
What allows molecules to be more soluble in water?
List 2 things
Having more places for hydrogen bonding and being smaller
Do covalent compounds conduct? Why or why not?
No, because they have no mobile ions and the electrons are all fixed
Can molecules have multiple IMFs?
Yes!
What is the type of hybridization on the silicon and oxygen in silicon dioxide?
Sp3 cause its a network solid/giant covalent molecule/macromolecule
True or false: pi bonds are formed by the axial overlap of orbitals
False. They are formed by the sideways overlap of parallel orbitals
Why do molten ionic compounds have good electrical conductivity?
The ions are broken apart and they are mobile
What does it mean if the question says a molecule “possesses dipole moments”?
The molecule is polar
What is the bond order of N2?
Three
