Unit 8: Bonding and Molecular Geometry Flashcards
What makes an ionic bond? And it’s characteristics?
- Metal and non-metal (element)
- Transfer of electrons
- Oppositely charged ions attract each other (form a bond)
- High melting point
- Dissolves in water
- Does not dissolve in ethyl alcohol
- Conducts electricity
What makes a covalent bond? And it’s characteristics?
- Non-metal and non-metal
- Electrons are shared
- No ions involved (orbitals from each atom overlap)
- Low melting point
- Polar dissolves in water, non-polar does not
- Non-polar dissolves in ethyl alcohol, polar does not
- does not conduct electricity
Why is it that atoms share electrons?
This happens when neither atom has enough attraction to take the other’s electron-so they share!
Definition of electronegativity?
The tendency of an atom to attract bonding electrons (pairs) to itself
How do you know if a bond is covalent?
Look at the difference in electronegativity. Difference < 1.7 = Covalent
What is the trend of electronegativity in the periodic table?
From left to right = electronegativity increases
From top to bottom = electronegativity decreases
What does it mean if a bond is a “Non-Polar (pure) Covalent Bond” ?
Attraction is equal between the two atoms
What does it mean if a bond is a “Polar Covalent Bond” ?
- Electrons shared, but not equally
- One atom attracts the electrons more strongly than the other
- STILL NO TRANSFER OF ELECTRONS
What does it mean if a bond is an “Ionic Bond” ?
- Attraction is so great from one atom in the bond that a complete transfer occurs.
- Ions formed/ NO SHARING!
- electronegativity difference is greater than 1.7
Difference in electronegativity:
- 0-0.5 = ?
- 0.6-1.6 = ?
- 1.7-? = ?
- Non-Polar Bond
- Polar Covalent Bond
- Ionic
What are the three exceptions to the Octet Rule?
- Total number of valence electrons is an odd number (Very rare)
- When a stable molecule has a central atom that is most stable with less than 8 valence electrons (Rare)
- When the stable molecule has a central atom that is most stable with a central atom that has more than eight valence electrons. (Not so rare)
What do you need to know about the first exception to the octet rule? (the very rare one)
*not too common.
just know it exists
What do you need to know about the second exception to the octet rule? (the rare one)
*Boron, as a central atom, is stable with 6 valence electrons
*Beryllium, as a central atom, is stable with 4 valence electrons
(will have to draw this!)
What doe you need to know about the third exception to the octet rule? (the not so rare one)
*Phosphorus, S, and Xe, as central atom, are examples of this exception.
(will have to draw this!)
Fill this in!
“the third exception to the octet rule can only happen to elements in periods ___ and down due to the presence of ‘__’ orbitals. Occurs most often when the central atom bonds to the most _______ elements”
- 3rd
- D
- electronegative
What is Bond Enthalpy?
The enthalpy change required to break a bond of one mole of a substance in its gaseous form.
True or False? The greater the bond enthalpy the stronger the bond.
TRUE!
What is an equation to find the change in energy or bond enthalpy?
ΔH = ΣD(Bonds broken) - ΣD(bonds formed)
D=# of moles
Fill in!
“As the number of bonds _____, the bond becomes ____ and _____”
- increases
- shorter
- stronger
Fill this in!
“the ____ the bond energy, the _____ the bond length”
- larger
2. shorter
What are the names of all the possible shapes an electron domain can have?
- Linear
- Trigonal Planar
- Tetrahedral
- Trigonal Bipyramidal
- Octahedral
What are the angles of Linear, Trigonal Planar, and Tetrahedral shapes?
- 180 degrees
- 120 degrees
- 109.5 degrees
What is the definition of crystal lattice?
3D array/ configuration of elements in an ionic compound
The formulation of an ionic compound is (exothermic or endothermic) and why?
Exothermic. The attraction between oppositely charged ions causes the ions to come together and release a large amount of energy.
if the formulation of an ionic compound is exothermic what does this lead to? (talking about physical changes, etc)
This causes them to form a sold, they become stable, and they create a strong bond which contributes to them being hard, brittle and to have high melting points.
What is the definition of lattice energy?
the amount of energy required to completely separate one mole of a solid ionic compound into its gaseous ions.
What is the equation to compare lattice energies?
E lattice = kQ1Q2 / d
k= 8.99 X 10 to the 9th power Jm/c^2
Q1 and Q2: the charges on the particles
d: the distance between their centers
What do we use to compare lattice energies of ionic compounds?
quantitative means
When do you get a high E lattice?
when you have a high charge and a small distance between ions (small radii)
What is the amount of lattice energy mainly dependent on?
the charge
What does VSEPR stand for? and what is if for?
“valence shell electron pair repulsion” and it predicts the general shape of atoms. Note: atoms and electrons try to stay away from each other when they bond
polar compounds dissolve….
non polar compounds dissolve….
- polar compounds
2. non polar compounds
+—–> the ‘arrow’ is towards the more ____?
the more electronegative side
What does intermolecular mean?
This means forces between molecules
What does intramolecular mean?
Forces within a single molecule
Why are intra-and intermolecular forces important?
These forces influence both physical and chemical properties of different molecules
Within gases, how do molecules look like?
Molecules in gases are far apart from each other which means a week attractive force between molecules
Within liquids, how molecules look like?
Molecules are closer together than in gases thus that bond is stronger than the gas.
In solids, how do molecules look like?
Molecules are the closest they can than in liquids and gases. this is the strongest force.
What does changing a “state” involve?
Changing the speed of molecules also known as the average kinetic energy this has to do with the intermolecular forces!
How do you change a state of a substance?
Heating or cooling a substance changes the average kinetic energy of the molecules and allow the forces of attraction to be more (solid) or less (gas) effective at holding the molecules close to each other
What are the four intermolecular forces of attraction?
- Ion dipole forces
- Dipole dipole forces
- London (dispersion) forces
- Hydrogen bonding forces
Are intermolecular forces stronger or weaker than intra-molecular forces?
Weaker
The ______ the MP or BP of a liquid the ______ the IMF that is involved between the molecules
Higher
stronger
True or false all four types of forces are electrostatic in nature?
True!!!!
To melt for you or vaporize a liquid or solid requires _____ energy than to break a covalent or ionic bond.
Less
Explain Ion dipole forces
Exist between a single ion and the partial charge on the end of a polar molecule
* note that the higher the charge the greater the attraction of the ion for the polar molecule
Explain what a dipole dipole force is.
Polar molecules attract each other when the positive end of one molecule is near the negative end of another.
Explain London forces A.K.A London dispersion forces.
Forces that occur between nonpolar atoms/molecules. Molecules have to be very close.
Do all molecules get London forces?
Yes!
what makes a stronger London force?
larger molecule or atom
Why do molecules get squished?
Because when molecules are very close together, electrons want to be far apart from each other so they create the squishiness
If molecules are very different in weights/sizes then London force attractions are ____ for the most massive/largest molecules.
Greatest
What is hydrogen bonding?
A special inter molecular attraction between the H bond in a polar bond and an unshared electron pair on a nearby small electronegative Ion or Atom
What are the most common polar bonds with hydrogen? And why are they?
H-F, H-O, and H-N
Because they are very electronegative
What does the small size of hydrogen allow it to do?
It allows you to get very close to the electronegative Atom and interact strongly with it.
why is it so easy for hydrogen to be attracted to electronegative atoms in nearby molecules?
Because hydrogen has no inner core electrons and it’s positive nucleus is exposed
List the IMF’s in order from weakest strongest
- London forces which are found in all substances
- Dipole dipole forces (add onto London forces)
- Ion dipole forces
- Hydrogen bonding
Why do atoms often gain lose or share electrons?
To achieve the same configuration as the nearest noble gas
Which Atoms are most stable with only two valence electrons?
Hydrogen, helium, lithium, beryllium, and boron
Which two elements are almost always in the middle of a Lewis dot structure?
Carbon and silicon
Which will never be a central Atom?
Hydrogen, column one, and column 17
How many bonds does hydrogen form?
One
How many bonds does oxygen form?
Two
How many bonds do halogens form?
One
How many bonds does nitrogen usually have?
Three
How many bonds can Carbon have up to?
Four
True or false: Covalent bonds can only be polar.
False! can be both polar or non-polar
What is a dipole?
It’s a region in a molecule that is either more positive or more negative
What determines if a bond is either polar or non-polar
Electronegativities
Definition of nonpolar
Electrons are not pulled closer to an atom so no dipole forms
When can nonpolar molecules happen?
When electrons are not pulled closer to any Atom or when polar bonds cancel each other out
Polarity allows for weak attraction of ions in ionic compounds causing dissociation. True or false
True
Which forces are van der waals forces
London forces dipole dipole forces hydrogen bonding and Ion dipole forces
