Unit 1 - Bonding Flashcards
(36 cards)
What is a covalent bond?
A shared pair of electrons, between two positively charged nuclei.
Arrange ionic, polar, and pure bonds in a bonding continuum in order of increasing difference in electronegativity.
At the start, there’s pure covalent, zero difference.
In the middle, there’s polar covalent, low difference.
At the end, there’s ionic, high difference.
https://prnt.sc/LwOMDjHIssa6
What are the types of bonding & structure that can exist in elements?
Ionic Bonds
Pure Covalent Molecular
Polar Covalent Molecular
Covalent Network
Metallic
Draw a diagram to show metallic bonding, and describe why metals conduct electricity.
https://prnt.sc/1MCqQXfgozEI
(Positive metal ions interlaced with a sea of free moving electrons)
They can conduct, since electrons are delocalised, so they can move freely within the metal structure.
Describe a pure covalent bond, and provide an example.
Pure covalent bonds are covalent bonds that exist between two atoms with the same electronegativities.
Any of the diatomic molecules are good examples, e.g. H-H
Describe a polar covalent bond, and provide an example.
Polar covalent bonds form when a shaired pair of electrons are not shared equally, due to one element having a higher electronegativity than the other.
An example can be H - Br where H has an electronegativity of 2.2, and Br has an electronegativity of 3.0
Draw a molecule of HCl and label the partial charges present
https://prnt.sc/EGE0Gyx6JwZH
(Don’t need to draw the larger size of the other)
When will an ionic bond be formed?
When do they usually form?
Ionic bonds when there is a high enough difference in electronegativities, higher than polar covalent bonds.
They usually occur between metals and non-metals with high differences in electronegativities
e.g. Sodium chloride
How are ionic compounds held together and what type of structure will they have?
The electrostatic force of attraction between the oppositely charged ions in the lattice.
Which elements in the first 20 have a metallic structure?
Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, and Calcium.
Which elements in the first 20 have a covalent network structure?
Boron, Carbon (in the form of graphite, or diamond), Silicon.
Which elements in the first 20 have a covalent molecular structure?
Phosphorus, Sulfur, Fullerenes
How do London Dispersion Forces arise?
LDFs are caused by an uneven distribution of electrons within an atom.
This gives rise to temporary dipoles.
Which elements in the first 20 have a monatomic structure?
Noble Gases (Helium, Neon, Argon)
What happens to the strength of LDFs as the size of the atom/molecule increases?
Why does this happen?
Larger atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones.
This is because, in a larger atom/molecule valence (outer) electrons are farther from the nucleui than smaller ones, they’re less tightly held so can form a temporary dipole easier.
How does a dipole form?
When an atom or molecules electrons are distributed unsymmetrically about the nucleus.
What are permanent dipole - permanent dipole interactions? How do they compare to LDFs?
An intermolecular bond stronger than LDFs that form in polar molecules.
Compared to LDFs, they are permanent due to the polarity, and are stronger than them.
Why do some substances with polar bonding not have dipoles?
If we take the vectors of the bond dipoles and draw them out,
If we draw out CO2, the C-O bond dipoles are equal in magnitude but oriented oppositely, and so their vector sum is zero.
Whereas H2O, O-H bonds are also equal in magnitude, but are oriented 104.5degrees to each other, hence why their vector sum is not zero.
https://prnt.sc/Zkd9FFG3k_Lg
Which of the following will be polar, explain.
CCl4
CH4
HCl4
CCl4 is non polar, this is because it’s net dipole is zero, as the geometrical structure is symmetrical.
In CH4 (non polar), the net dipole is zero, as the geometrical structure is symmetrical.
In H-Cl (polar), the net dipole is more than zero, and the geometrical structure is not symmetrical.
Which of the following will be polar, explain.
Carbon dioxide
Chloromethane
Hexane
Carbon dioxide is non polar, because the net dipole is zero, as the geometrical structure is symmetrical.
Chloromethane is polar, because the net dipole is more than zero, with an unsymmetrical geometrical structure.
Hexane is nonpolar because of its symmetrical structure (net dipole 0), but carbon and hydrogen also have low electronegativity differences.
When will hydrogen bonding occur? Give three compounds that will exhibit hydrogen bonding.
Hydrogen bonding occurs when a hydrogen atom is covalently bonded to a highly electronegative element such as nitrogen, oxygen, or flourine.
They work like PD-PD interactions
H2O, NH3, CHCl3
What anomalous properties of water arise from hydrogen bonding?
Ice is less dense than water, since hydrogen bonds create an open lattice structure
Relatively high melting point, since more energy is required to overcome hydrogen bonds because hydrogen bonds are strong.
What anomalous properties of water arise from hydrogen bonding?
Ice is less dense than water, since hydrogen bonds create an open lattice structure
Relatively high melting point, since more energy is required to overcome hydrogen bonds because hydrogen bonds are strong.
List the Van Der Waal forces in order of strength starting from weakest
- London Dispersion Forces
- Permanent Dipole - Permanent Dipole Interactions
- Hydrogen bonding
