Unit 2.5 - simple molecules & covalent bonds Flashcards
What is a covalent bond?
A pair of electrons shared between 2 atoms; occurs when two or more non-metallic atoms bond together and share electrons in order to achieve a full valence shell.
Name the different types of covalent bonds
Singular: 1 pair of electrons shared. Represented by a single line between symbols. E.g. H-H
Double: 2 pairs of electrons shared. Represented by two lines between symbols. E.g. Cl=Cl
Triple: 3 pairs of electrons shared. Maximum amount. Represented by 3 lines between symbols. E.g. N☰N
How to draw covalent bonding in diagram?
- Draw two atoms as usual with a + in between them. Draw arrows to the right
- Draw the 2(or more) in a Venn diagram, so that their valence shells overlap
- Draw a dot and cross diagram, and put as many electrons in the intersection between the 2 atoms as needed for both to have a full valence shell.
- Label that molecule
What type of structure do covalent substances have?
Simple molecular/covalent -
1. weak intermolecular forces between molecules
2. strong covalent forces within molecules between atoms
How do you name a molecular compound?
The element closes to metals in the periodic table is named first.
Ending of second element is changed to -ide.
Prefixes: Mono = 1, Di = 2, 3 = Tri, 4 = Tetra
How many bonds must common atoms make?
Hydrogen and chlorine : 1
Oxygen: 2
Carbon: 4
Properties of covalent molecules
- volatile: low mp because the weak intermolecular forces between molecules require little energy to break. Strong molecular/covalent forces do NOT BREAK when a molecular substance changes state
- insoluble in water but soluble in organic solvents (oil)
- do not conduct electricity as they are made of neutral molecules
Important rules for dot and cross covalent bonds diagram
- Each atom must share the same number of electrons
- Each atom in the molecule must have a full valence shell
- Only show valence shell
