1. No category

Chemistry 11 – Unit 5 Forero Name: ______________________________ Date: ___________ Blk: _____
NOTES: BONDING
Examine your periodic table to answer these questions and fill-in-the-blanks. Use
drawings to support your answers where needed:
I. IONIC BONDING
Ionic bond: formed by the attraction of _______________ ions to ______________ ions.
1. Examine the Lewis structure examples above. When is an ionic bond formed?
2. All the electrostatic attraction in an ionic bond depends on the _________________
separating the central charges: the greater the _________________, the
_________________the attraction.
3. What TWO trends found in the periodic table are responsible for ionic bonds?
4. How to predict when an ionic bond will form:
IONIC BONDS are formed when elements from _________________of the
periodic table are combined à when a _________________ and
_________________ are combined.
Chemistry 11 – Unit 5 Forero 5. Which of the following atom pairs would you expect to form ionic bonds?
(a) Ba and S
(b) P and Cl
(c) Ca and O (d) Rb and I
(e) O and H
(f) S and O
The strength of ionic bonds can be estimated by examining the MELTING
TEMPERATURES of ionic compounds.
6. Look at the melting temperatures of some ionic substances:
- LiF = 845°C
- KCl = 770°C
- LiCl = 605°C
- NaF = 993°C
What can you conclude about the strength of ionic bonds? Why?
Recall what you know about the trend of atomic radius on the periodic table to answer the
following questions.
7. (a) Which compound has the smaller distance between the nuclei of the two ions
involved: NaCl or KBr?
(b) What happens to the force of electrostatic attraction between the two ions in an ionic
bond as the ions get smaller?
(c) What happens to the strength of an ionic bond as the ions involved gets smaller?
What happens to the melting temperature?
8. Mg2+ and Na+ have roughly the same ionic radius. O2- and F- have roughly the same
ionic radius. Which substance should have a higher melting temperature: NaF or MgO?
Chemistry 11 – Unit 5 Forero 9. Which member of each of the following pairs would you expect to have the higher
melting temperature?
i. CaO or RbI
ii. BeO or BN
iii. LiF or NaCl
iv. CsCl or BaS
v. RbI or KCl
vi. BeO or Mg
II. ION SIZE
Negative ions: assume extra electrons are added to a neutral atom of O to make O2-.
The resulting ion has the same positive nuclear charge and an increased number of
negative electrons surrounding the nucleus (recall the fire/shading analogy).
1. What happens to the amount of electrostatic repulsion existing between the electrons?
2. What happens to the volume occupied by the electrons due to the change in the amount
of electron-electron repulsion?
3. Fill in the appropriate word:
NEGATIVE IONS are _________________ than the corresponding neutral atom.
Positive ions: assume extra electrons are removed to a neutral atom of Mg to make Mg2+.
The resulting ion has the same positive nuclear charge and a decreased number of
negative electrons surrounding the nucleus.
1. What happens to the amount of electrostatic repulsion existing between the electrons?
2. What happens to the volume occupied by the electrons due to the change in the amount
of electron-electron repulsion?
3. Fill in the appropriate word:
NEGATIVE IONS are _________________ than the corresponding neutral atom.
4. Examine the diagram below, which shows a section of crystal NaCl.
Which circles represent Na+: the larger or smaller ones?
Chemistry 11 – Unit 5 Forero III. COVALENT BONDING
Covalent bond: A bond that involves the equal sharing of electrons.
Octet Rule: Atoms in families 14 to 17 of the periodic table tend to form covalent bonds
so as to have eight electrons in their valence shells.
1. What trend found in the periodic table is responsible for ionic bonds?
2. How to predict when an ionic bond will form:
COVALENT BONDS are formed when a _________________combines with
another _________________.
3. Which of the following atom pairs would you expect to form ionic bonds?
(a) S and O
(b) Ba and O (c) Fe and Cl (d) N and O
(e) H and S
(f) C and H
4. Look at the melting temperatures of some covalent crystals:
- BN = 3000°C
- SiC = 2700°C
- C (diamond) = 3550°C
What can you conclude about the strength of covalent bonds? Why?
It is very tempting to say that “covalent compounds have high melting temperatures”, but
look at the melting temperatures of the following covalent compounds:
- CH4 = -182°C
- O2 = -218°C
- HCl = -114°C
Chemistry 11 – Unit 5 Forero 5. Why do you think these covalent compounds have such low melting points?
IV. LONDON FORCES
Individual molecules are held together by strong covalent bonds between the atoms in the
molecule. Such bonds are called INTRAMOLECULAR FORCES (intra = within).
There are weak forces that hold one complete, neutral molecule next to another such
molecule. These INTERMOLECULAR FORCES (inter = between) are called LONDON
FORCES.
The London dispersion force is the weakest intermolecular force.
Dipole: partial separation of charge which exists when one end of a molecule has a slight
excess of positive charge and the other end of the molecule has a slight excess of negative
charge.
London force: a temporary attractive force that results when the electrons in two adjacent
atoms occupy positions that make the atoms form temporary dipoles.
London forces are the attractive forces that cause nonpolar substances to condense to
liquids and to freeze into solids when the temperature is lowered sufficiently.
Because of the constant motion of the electrons, an atom or molecule can develop a
temporary (instantaneous) dipole when its electrons are distributed unsymmetrically
about the nucleus.
Chemistry 11 – Unit 5 Forero A second atom or molecule, in turn, can be distorted by the appearance of the dipole in
the first atom or molecule (because electrons repel one another), which leads to an
electrostatic attraction between the two atoms or molecules.
Dispersion forces are present between all molecules, whether they are polar or nonpolar.
The more electrons an atom or molecule has altogether, the stronger the London forces
existing between I and a neighbouring atom or molecule.
1. What happens to the strength of the London forces between two identical atoms going:
(a) down a family of the periodic table? Why?
(b) left to right across a period of the periodic table? Why?
The ease with which the electron distribution around an atom or molecule can be
distorted is called the polarizability.
2. In response to a request to “write an equation showing what happens when H2(s) melts”,
a student writes the following:
H2(s) à 2 H(l)
What does this equation incorrectly imply about the bonds & forces in a sample of H2(s)?