EL - Covalent bonding Flashcards
What is covalent bonding?
When atoms share electrons with one another so they’ve got a full outer shell.
What do covalent bonds do?
Hold atoms in molecules together.
How are molecules formed?
When 2 or more atoms bond together, and are held together by covalent bonds.
What doesn’t matter in a molecule?
Doesn’t matter if the atoms are the same or different.
For a covalent bond to be maintained, what does there have to be a balance between?
The electrostatic attraction between the nuclei and the electrons and the repulsion between the positive nuclei.
What does covalent bonding happen between?
2 non-metals.
What are the typical properties of molecular substances?
Fairly low melting points and boiling points.
Don’t conduct electricity.
Usually insoluble in water (or only very slightly soluble).
Why do molecular substances have fairly low melting and boiling points?
There is no giant structure that needs to be broken down.
What state are molecular substance at standard temperature and pressure (usually)?
Usually liquids or gases.
Why don’t molecular substances conduct electricity?
There are no charge carriers that are free to move.
Why are molecular substances usually insoluble in water?
The polar water molecules are more attracted to each other than the molecular substance and so tend to leave it alone.
What has to happen to melt or boil a simple molecular compound?
You only have to overcome the intermolecular forces between the molecules. These are weak compared to ionic or covalent bonds. You don’t need to overcome the much stronger covalent bonds that hold the atoms together in the molecule.
What diagram can be used to show how electrons behave in covalent bonds?
Dot-and-cross diagrams.
How are the bonded molecules drawn in a dot-and-cross diagram for to show covalent bonds?
Drawn with their outer atomic orbitals overlapping. The shared electrons that make up the covalent bond are drawn within the overlapping area.
Which electrons are shown in dot-and-cross diagrams?
Electrons in the outer shells.
How many electrons does the central atom end up with most of the time?
8 electrons in its outer shell - Good for the atom as it is a very stable arrangement.
How many electrons do atoms share with each other?
Depends. Atoms don’t have to stick to forming single bonds (one pair), you can get atoms sharing multiple pairs of electrons (e.g. 2 or 3 - double or triple bonds).
What is it called if a there is a bond containing two electron pairs?
A double bond.
What is it called if a there is a bond containing three electron pairs?
A triple bond.
How is a double bond formed?
If a there is a bond containing two electron pairs.
How is a triple bond formed?
If a there is a bond containing three electron pairs.
What is dative covalent bonding?
Where both electrons come from one atom.
Where one atom donates both electrons to a bond.
What is a dative bond also called?
A coordinate bond.
What are examples of molecules that contain dative bonds?
Carbon monoxide, CO.
Ammonium ion, NH4+.
Why are some covalent compounds special cases - what doesn’t need to happen?
Not all atoms need 8 electrons in their outer shell to be happy - some have more, and some have less.
What does it mean if some atoms use the d-orbitals to ‘expand the octet’?
Means they have more than 8 electrons in their outer shell.
How do some atoms have more than 8 electrons in their outer shell?
In a few compounds, some atoms use the d orbitals to ‘expand the octet’.
