Why does this structure make sense? 2. Why does this structure make sense? Why does this structure make sense? 4. Why does this structure make sense?
252
Appendix X: Text R–Elaborative Interrogation Treatment
NOTE: An important guideline to follow in drawing Lewis structures is called the octet rule which states that atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons.
1. Hydrogen fluoride, HF, is composed of a hydrogen atom and a fluorine atom. In the Lewis
structure, the two atoms are connected by a single bond and the fluorine has three unshared pairs of electrons. Being a particle with no net charge and having all electrons in pairs, HF is classified as a
molecule. In Lewis structures, a hydrogen atom forms only one covalent bond and has no unshared pairs of electrons. The Lewis structure of HF is drawn as:
GO TO QUESTION 1 Æ
2. The phosphorus hexafluoride ion, PF
6 -
, contains one phosphorus atom and six fluorine atoms. In the Lewis structure, the central phosphorus has a single bond to each fluorine, each of which has three
unshared pairs of electrons. Being a particle with a net charge of 1–, PF
6 -
is classified as a polyatomic anion and the 1– charge or simply “–” is written to the upper right side of brackets drawn around the
structure. Like other period 3 elements with d orbitals available for bonding, phosphorus can exceed an octet in structures such as this. The Lewis structure of PF
6 -
is drawn as:
GO TO QUESTION 2 Æ
H F
: ..
..
:
F
: :
F F
:
P
:
F F
: :
F
: ..
.. ..
.. ..
.. ..
.. ..
..
1. Why does this structure make sense? 2. Why does this structure make sense?
3. Methane, CH
4
, consists of one carbon atom and four hydrogen atoms. In the Lewis structure, four hydrogens are connected by single bonds to the central carbon. Being a particle with no net charge and
having all electrons in pairs, CH
4
is classified as a molecule. The four valence electrons on carbon an element in group 4A are shared, one at a time, with the one valence electron from each hydrogen an
element in group 1A. The Lewis structure of CH
4
is drawn as:
GO TO QUESTION 3 Æ
4. The aluminum chloride ion, AlCl
4 -
, is composed of one aluminum and four chlorine atoms. In the Lewis structure, the central aluminum has a single bond to each chlorine, each of which has three
unshared pairs of electrons. Being a particle with a net charge of 1–, AlCl
4 -
is classified as a polyatomic anion and the 1– charge is written to the upper right side of brackets drawn around the structure. This is
the first structure of this exercise in which all atoms exactly obey the octet rule. The Lewis structure of AlCl
4 -
is drawn as:
GO TO QUESTION 4 Æ
H H C H
H
.. :
Cl
: :
Cl Al
Cl
: :
Cl
: ..
.. ..
.. ..
–
3. Why does this structure make sense? 4. Why does this structure make sense?
Y O U R I N S T R U C T I O
N S :
R e a d e a c h p a r a g r a p h O N C E . A n s w e r t h e q u e s t i o n s i n t h e r i g h t m a r g i n w h e n d i r e c t e d
.
C o n t i n u e a n s w e r s o n b a c k i f n e c e s s a r y .
253
5. Phosphorus trichloride, PCl
3
, contains one phosphorus atom and three chlorine atoms. In the Lewis structure, a central phosphorus is bonded to three chlorine atoms, each of which has three unshared
pairs of electrons. Being a particle with no net charge and having all electrons in pairs, PCl
3
is classified as a molecule. Nitrogen, another element in group 5A on the periodic table, also forms a similar molecule
with chlorine, NCl
3
. The Lewis structure of PCl
3
is drawn as:
GO TO QUESTION 5 Æ
6. Chlorine trifluoride, ClF
3
, consists of a chlorine atom and three fluorine atoms. In the Lewis structure, each fluorine is joined by a single bond to the chlorine, which has two unshared pairs of
electrons. Each fluorine atom has three unshared pairs. Being a particle with no net charge and having all electrons in pairs, ClF
3
is classified as a molecule. Like other period 3 elements with d orbitals available for bonding, chlorine is capable of exceeding an octet in certain instances. The Lewis structure of ClF
3
is drawn as:
GO TO QUESTION 6 Æ
:
Cl P Cl
: :
Cl
: ..
.. ..
.. ..
..
:
F Cl F
: :
F
: ..
.. ..
.. ..
5. Why does this structure make sense? 6. Why does this structure make sense?