Simple Molecular Substances

Question 1

what is a covalent bond?

Answer 1

bond (formed) between two atoms in which electron pairs are shared

Question 2

what is a molecule?

Answer 2

a collection of two or more atoms held together by chemical bonds

Question 3

what do molecules of the same element or compound have in terms of size?

Answer 3

a set size

Question 4

what can be used to model the transfer of electrons in covalent bonds?

Answer 4

a dot and cross diagram

Question 5

which 2 diagrams could be used to model molecules?

Answer 5

• dot and cross diagram

- drawing structures

Question 6

what is the number of covalent bonds an atom has the same as?

Answer 6

the number of electrons needed to get a full outer shell.

Question 7

what does a double-bond consist of? and a triple bond?

Answer 7

• two shared pairs of electrons

- three shared pairs of electrons

Question 8

explain why simple covalent compounds have low melting and boiling points: (4)
+ what is not broken during these state changes?

Answer 8

• there are intermolecular forces between simple molecules.
• intermolecular forces much weaker than strong covalent bonds in molecules.
• When molten or boiled, it is these weak intermolecular forces that are overcome.
• Very little energy is needed to overcome the intermolecular forces, so simple molecular substances/ simple covalent compounds usually have low melting and boiling points.

-covalent bonds are not broken.

Question 9

under what two circumstances can a substance conduct electricity? (2)

Answer 9

• it contains charged particles

- these particles are free to move from place to place

Question 10

explain why simple covalent compounds cannot conduct electricity: (2)

Answer 10

• simple molecules have no overall charge, or charged particles that are free to move
• so simple molecular substances cannot conduct electricity, even when liquid or dissolved in water.