Chemical Bonding Revision 1
Solutions
1) A compound is a substance that is made up of two or more different elements chemically
combined.
Salt – sodium chloride
Water – hydrogen oxide
Baking Powder – sodium hydrogen carbonate
2) An ionic bond is the force of attraction between oppositely charged ions in a compound.
An ion is a charged atom or group of atoms.
3) Sodium Hydroxide = NaOH
Sodium Carbonate = Na2CO3
Silver Nitrate = AgNO3
Calcium hydrogen carbonate = Ca(HCO3)2
Potassium Sulphite = K2SO3
Magnesium Sulphate = MgSO4
4) Ionic substances form crystals because they contain charged ions. In the crystal lattice
each positive ion is surrounded by negative ions, in all directions, and each negative ion is
surrounded by positive ions, in all directions, giving the substance a three dimensional
crystal lattice structure.
5) Nitrate ions – chemicals used = sodium nitrate, iron (II) sulphate, conc. sulphuric acid,
deionised water
- positive result for presence of nitrate ions = the formation of a brown ring.
Chloride ions – chemicals used = sodium chloride, silver nitrate solution, dilute ammonia
solution, deionised water
- positive result for presence of chloride ions = a white precipitate is
formed which is soluble in dilute ammonia solution
(Note: above is brief outline of tests these tests must be explained in more detail!!!)
6) Electronegativity is the relative attraction that an atom in a molecule has for the shared
pair of electrons in a covalent bond.
7) i) Electronegativity increases across a period.
ii) Electronegativity increases across a period because of:
1. Increasing effective nuclear charge – number of protons in nucleus is increasing
as move from left to right across a period. As a result, the attraction between the
nucleus and the outer electrons is increasing. Therefore the electrons involved in
bonding are being more strongly attracted to the nucleus i.e. electronegativity
increases
2.Decreasing atomic radius – atomic radius decreases from left to right so outer
electrons drawn closer to nucleus. Due to increased attraction between electron in
outermost shell and nucleus the electronegativity values increase.
8) Al2O3
Electronegativity Al = 1.61
Electronegativity O = 3.44
Difference = 1.83 therefore ionic bonding
H2 O
Electronegativity H = 2.2
Electronegativity O = 3.44
Difference = 1.24 therefore polar covalent
Hδ+ - OδHδ+
OF2
Electronegativity F = 3.98
Electronegativity O = 3.44
Difference =
0.54 therefore polar covalent Fδ-- Oδ+
Fδ-
9) KF – ionic compound
NO – polar covalent
Use electronegativity values to determine
Br2 – Non-polar (pure covalent)
polarity
IBr – slightly polar
CaO – ionic compound
i) Dissolve in water = KF & CaO
ii) Conduct electricity when dissolved = KF & CaO
iii) Dissolve in cyclohexane = NO, Br2, IBr
10) 5525Mn3+
55-25 = 30 neutrons
25 – 3 (lost 3 electrons) = 22 electrons
11) A covalent bond is the chemical bond formed by sharing a pair of electrons
A molecule is a group of atoms joined together. It is the smallest particle of an element
or compound that can exist independently.
12) When two pairs of electrons are shared (between two atoms), we say that a double bond
is formed.
13) KF – Ionic bonding (use electronegativity values)
14) i) Beryllium and Oxygen – BeO
ii) Hydrogen and Arsenic – AsH3
14) iii) Carbon and chlorine – CCl4
15) Sulphate and Sulphite ions – chemicals used = sodium sulphate, sodium sulphite,
barium chloride, dilute HCl, deionised water
Positive result for the presence of sulphate and sulphite ions = upon addition of barium
chloride a white precipitate is formed in both
Distinguishing test = upon addition of HCl precipitate in sulphite dissolves and in sulphate
remains
(Note: above is brief outline of test this test must be explained in more detail!!!)
16) Sodium Chloride is an ionic substance and will conduct electricity when either
dissolved in water or when molten (i.e. melted).
17) Electronegativity is the relative attraction that an atom in a molecule has for the shared
pair of electrons in a covalent bond.
Electronegativity decreases down a group because of:
1. Increasing atomic radius: - atomic radius increases – outermost electrons are
moving further away from attractive force of nucleus. Therefore smaller attraction
between the nucleus and the shared pair of electrons
2. Screening Effect: - inner electrons screen outer electrons from the positively
charged nucleus – since it is outermost electrons involved in bonding, the attraction
of the nucleus for these electrons decreases going down the group i.e.
electronegativity decreases.
18) GeS2
Electronegativity Ge = 2.01
Electronegativity S = 2.58
Difference =
0.57 therefore polar covalent Sδ- - Geδ+ - Sδ-
CaS
Electronegativity Ca = 1.00
Electronegativity S
= 2.58
Difference = 1.58 therefore ionic bonding
18) PBr3
Electronegativity P = 2.19
Electronegativity Br = 2.96
Difference = 0.77 therefore polar covalent Brδ-- Pδ+ - BrδBrδ19)
NaBr – ionic compound
HCl – polar covalent
Use electronegativity values to determine
F2 – non-polar (purely covalent)
polarity
MgS – ionic compound
CaCl2 – ionic compound
i) have high melting points – NaBr, MgS, CaCl2
ii) dissolve in water – NaBr, MgS, CaCl2
iii) do not conduct electricity – F2 (HCl – although this is a covalent substance it
DOES conduct electricity)
20) 168O216-8 = 8 neutrons
8 + 2( 2- indicates 2 electrons were gained) = 10 electrons