4.1 Covalent Bonding Flashcards
Define covalent bonding
Covalent bonding is the electrostatic attraction between protons in two nuclei and a shared pair of of electrons between them
Covalent bonds are formed between…
Non metals (share pairs of electrons to get a fully outer shell)
What is the process for determining the sharing of atoms in molecules with double or triple pairs? For e.g. what happens when S and F share?
- S has 6 in the outer-shell = needs to share two pairs
- F has 7 in the outer-shell = needs to share one pair
- So we need 2 x F and 1 x S
What is a simple molecule?
A small group of atoms held together by covalent bonds.
Is covalent bonding a strong or weak attraction?
Covalent bonding is a very strong attraction.
How do shared pairs of electrons contribute to bond formation between atoms?
The shared pair of electrons effectively pull the nuclei of the atoms closer together
What happens when simple molecular substances boil?
Weak intermolecular forces (IMFs) break between the molecules.
As molecular mass increases, what happens to the strength of weak intermolecular forces (IMFs)?
The strength of weak intermolecular forces (IMFs) increases. This results in the boiling point increasing.
Why don’t simple molecular substance conduct electricity?
Simple molecular substances do not conduct electricity because they lack charged particles necessary (molecules are neutral) for electrical conductivity.
C60 fullerene
C60 fullerene is a unique simple molecule composed of sixty carbon atoms in a ball.
What are properties of C60 fullerene?
Formula: C60
Molecular Mass: 720
Boiling Point: Above +600°C
Physical State: Soft and slippery solid
Electrical Conductivity: Insulator
Why is C60 fullerene a soft slippery solid?
-Because molecules can roll over eachother easily
Why is C60 an electrical insulator?
-Because the molecules are neutral
What is diamond?
Diamond is a form of pure carbon arranged into a giant lattice.
Why does diamond sublime at a high temperature?
- Covalent bonds are very strong
- There are lots of bonds in the giant lattice
- Lots of energy is required to break all the bonds
Why can’t diamond conduct electricity?
-because there are no freely-moving charged particles.
-All the atoms are neutral
-and all the electrons are stuck inside an atom or a bond
What is diamond used in and why?
-Used in cutting
-It is one of the hardest substances
What are the characteristics of diamond’s lattice structure?
- Every C makes 4 covalent bonds
- Tetrahedral shape
- Strong, grid-like arrangement
What is graphite?
Graphite is another form of pure carbon arranged into a giant lattice.
Why can graphite conduct electricity?
-Because inside the layers
-The delocalised electrons can move freely
Why does graphite sublime at a very high temperature?
(For the same reasons as diamond)
* Covalent bonds are very strong
* There are lots of bonds in the giant lattice
* Lots of energy is required to break all the bonds
What are the characteristics of graphite’s lattice structure?
- Layers of hexagons of C atoms
- Every C makes 3 covalent bonds (red)
- Weak intermolecular forces (IMFs) between layers (blue)
- Delocalised electrons inside each layer
What is graphite used in and why?
-Used as a solid lubricant
-It is soft and slippery because the layers can slide easily
What is silicon dioxide?
Silicon dioxide (SiO2) is also known as silica and has a giant covalent structure.
What are the characteristics of silicon dioxide’s lattice structure?
- Every Si makes 4 covalent bonds (black)
- Every O makes 2 covalent bonds (red)
- Tetrahedral shape (like diamond)
- Strong, grid-like arrangement
What properties of silicon dioxide are similar to diamond?
-Share similar bonding and structure.
Why is silicon dioxide much less expensive compared to diamond?
-It is much less rare.
What is the bonding ,structure and properties of Metal + Non-metal?
Bonding: Ionic
Structure: Giant lattice
Essential properties: -High MP/BP
-Insulator when (s)
-Conductor when (l)
-Conductor when (aq)
Other properties: -Brittle
-Usually soluble in water
-Crystalline
What is the bonding ,structure and properties of only Non-metals?
Bonding: Covalent
Structure: Simple molecules
Essential properties: -Low MP/BP
-Insulator
Other properties: -Usually insoluble in water
-Dull
What is the bonding ,structure and properties of only Metals?
Bonding: Metallic
Structure: Giant lattice
Essential properties: -High MP/BP
-Conductor
Other properties: -Malleable
-Ductile
-Shiny
Why do melting and boiling points of substances with simple molecular structures increase, in general, with increasing relative molecular mass?
-Larger molecules have more mass and more forces of attraction between them
-These forces, though weak, must be overcome for the substance to boil
-Larger molecules possess more attractions that need to be overcome
Do covalent compounds conduct electricity?
Covalent compounds do not conduct electricity
Explain the trend in reactivity in Group 7 in terms of electronic configurations
-Reactivity increases up Group 7 (halogens) of the periodic table.
-Halogens readily form ions by attracting passing electrons to fill their outer shell.
-Fluorine’s outer shell is close to the nucleus, resulting in strong attraction and high reactivity.
-lodine’s outer shell is farther from the nucleus, leading to weaker attraction and lower reactivity.
