1.4 EXERCISE 1 – trends in Period 3
1. State and explain the following trends:
a) atomic
size across Period 3
b) first
ionisation energy across Period 3
c) electronegativity
across Period 3
d) melting
point from sodium to aluminium
e) electrical
conductivity from sodium to aluminium
2. Explain the following:
a) the
melting point of silicon is the highest in Period 3
b) the
melting point of phosphorus is lower than silicon
c) the
melting point of phosphorus is lower than that of sulphur
d) the
boiling point of chlorine is greater than that of argon, but lower than that of
sulphur
e) neither
silicon nor sulphur conduct electricity
Answers to 1.4
exercises
1.4 Exercise 1
1. a) decreases
proton number increases
shielding stays the same
so attraction to nucleus
increases
b) increases
proton number increases
shielding stays the same
so attraction to nucleus
increases
so more energy required
to remove electron
c) increases
proton number increases
shielding stays the same
so ability to attract
electrons in a covalent bond increases
d) increases
size of ions decreases
and charge on ions
increases
so attraction between
ions and delocalised electrons increases
so more energy is
required to separate them
e) increases
number of delocalised
electrons per atom increases
so more electrons are
free to move
2. a) Si
has a giant covalent structure
every Si atom attached
to 4 others by covalent bonds
the covalent bonds are
strong
so a lot of energy is
required to break them
b) P
is simple molecular
Van der Waal’s forces
between P molecules are weaker
Than covalent bonds
between Si atoms
So much less energy is
required to break them
c) Phosphorus
contains P molecules
which have a smaller
surface area and less electrons
than the S molecules in sulphur
so the Van der Waal’s forces are weaker in
phosphorus
and less energy is required to overcome them
d) Chlorine
contains Cl molecules
which have a smaller
surface area and less electrons
than the S molecules in
sulphur
but a larger surface
area and more electrons
than the Ar atoms in
argon
so the energy required
to separate Cl molecules is greater
than the energy needed
to separated Ar atoms but less
than the energy needed
to separated S molecules
e) neither
silicon or sulphur contain ions or free electrons
A Few Practice Questions about Periodicity! NOTE: “more stable” = lower energy state.
“less stable” = higher energy state
1. The most important factor in determining the
variation in size of atoms as you move from left to right within a series is
the:
a.
increase in nuclear charge b. increase in number of valence electrons
c.
increase in the radii of electron shells d. increased shielding effect
e.
decrease in nuclear charge
2. The major contributing factor to the decrease
in ionization energy as you move to the bottom of a family is :
a.
nuclear charge b. valence electrons
c. more inner shell electrons d.
reduced shielding effect
3. As the atomic numbers of the elements in Group
16 (oxygen family)increase, the
shielding effect:
a.
decreases b. increases
c. remains the same d.
breaks
4. Ions formed by the gain of an electron are
always more _____ than the atom they came from.
a.
stable b. unstable
c.
electronegative d.I can't tell
because I don't know what the atom is.
5. The energy value for electron affinity within
a family generally becomes ______ with
increasing atomic number.
a. more negative b.
less negative c. constant
6. Based on valence electrons, what is the most
probable oxidation state of N?
a. -3 b. -2 c. +3 d. 0
7. You do an experiment which involves adding an
electron to an atom of He. You make the
following assumption in regard to its stability:
a.
the ion is more stable b. the ion is less stable c. the
stability doesn't change
d.
You can't tell what happened because this statement doesn't give enough
information.
8. Which of the following elements is most
metallic? a. He b.
F c. S
d. Te e. Sb
9. Which of the following has a larger
radius?
a.
chlorine atom b. chlorine anion c. chlorine cation d. they're the same
10. Which of the following is least likely to gain electrons in a
chemical reaction?
a.
potassium b.
aluminum c.
fluorine d. oxygen
11. High ionization energy is characteristic
of:
a. metals b. non-metals c.
metalloids d.
liquids
12. Which of the following trends generally have
an opposite pattern from atomic radius?
a.
electronegativity b. electron affinity c. ionization energy d.
all of these
e.
none of these
13. If energy is released during a process, the
resulting particle is:
a.
more stable b. less stable
c. about the same d.
irrelevant
14. An atom which lost energy during an electron
transfer:
a.
gained an electron b. lost an electron c. lost a proton
d.
there is insufficient information to answer this question.
15. Which of the following elements would you
expect to have a positive electron affinity?
a.
K b. Ne
c. O d.
F
16. Compared to the stability of the original
atom, the stability of its ion formed by the gain of an electron is:
a.
always less b. sometimes less c. the same
d. always greater
17. Which of the following has the largest
radius? a. Ne b. F- c. Na+ d. Mg++
18. Which element would form an ion which is
isoelectronic with Ne and would bond with oxygen in a 1:2 ratio:
a. F b. Na c. Mg d. Al e. K
19. The greatest increase in ionization energy
for the element B comes with the removal of the _________ electron?
a.
2nd b. 3rd c.
4th d.
5th e.
6th
20. An atom of Neon which gained energy during an
electron transfer:
a.
gained an electron b.
lost an electron
c.
lost a proton d. there is insufficient information to answer
this question.
21. What element will form an ion which is
isoelectronic with Ne and will combine with phosphorous in a 3 : 2 ratio? (2 atoms of phosphorous)
Answers: 1a 2c 3b 4d 5b 6a 7b 8e
9b 10a 11b 12d 13a 14a 15b 16b 17b 18b 19c 20d 21Mg
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