chemical bonding Flashcards
1
Q
compound
A
substance that is made up of two or more DIFFERENT elements combined together chemically
2
Q
octet rule
A
when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell
3
Q
an ion
A
a charged atom or group of atoms
4
Q
an ionic bond
A
the force of attraction between oppositely charged ions in a compound
5
Q
transition metal
A
one that forms at least one ion with a partially filled sublevel
6
Q
molecule
A
group of atoms joined together. It is the smaller particle of an element or compound that can exist independently
7
Q
valency of an element
A
defined as the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
8
Q
electronegativity
A
a measure of the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond
9
Q
electronegativity differences
A
- difference > 1.7 indicates ionic bonding in a compound
- difference ≤ 1.7 indicates covalent bonding in a compound
10
Q
the value of electronegativity
A
- decreases down groups in Periodic Table. (Bc of increasing atomic radius, screening effect of inner electrons)
- increases across table (bc of increasing nuclear charge, decreasing atomic radius)
11
Q
the most electronegative element
A
F
12
Q
halogens
A
decrease in reducing power down group due to drop in electronegativity values
13
Q
noble gases
A
- have 8 electrons on their outer shell + are quite stable
- generally unreactive
14
Q
uses of noble gases
A
helium
argon
15
Q
helium
A
used in airships as it is lighter than air
not as light as hydrogen (twice as heavy per volume) but does not burn
16
Q
argon
A
most common noble gas
used to fill normal light bulbs to stop them imploding
17
Q
limitations of the octet rule
A
hydrogen
lithium
transition metals
18
Q
valency
A
the number of bonds an atom makes when it reacts
19
Q
how to get valency
A
- can be worked out calculating the number of electrons an atom needs to lose/gain to have 8e⁻ on outer shell
- can be predicted from periodic table
20
Q
examples of valency numbers
A
ammonia (contains only nitrogen and hydrogen)
methane (contains only carbon and hydrogen)
calcium bromide
silicon fluroide
21
Q
transition metals (info)
A
- transition elements have variable valency
- form coloured compounds
- used as catalysts
- exceptions: zinc (Zn), scandium (Sc)
22
Q
ionic bonding
A
-transfer of electrons
-ions are formed
-ionic bonding usually between Groups I and II (metals)
and groups VI and VII (non-metals)
23
Q
cation
A
positive (+)
24
Q
anion
A
negative (-)
25
crystal lattice
ionic substances usually form a structure called a crystal lattice
26
eg of crystal lattice
NaCl
27
why ionic substances form crystals
ionic substances form crystals bc positive ions attract negative ions in all directions
28
what shape do crystals form?
a lattice structure
29
characteristics of ionic substances
- strong forces between ions -> v. hard to break up the lattice structure
- high melting + boiling points
- usually solid at room temp
- cannot conduct electricity when solid (ions not free -> move and carry electricity)
- most dissolve in water (when dissolved, ions can conduct electricity)
30
examples of everyday ionic substances
- table salt (sodium chloride NaCl)
| - fluoridation in water to prevent tooth decay (sodium fluoride NaF)
31
complex ions table
in hardback
32
covalent bonding
formed when atoms share electrons
eg. hydrogen molecule, chlorine molecule
33
types of covalent bonds
single
| double triple
34
covalents bonds - single
1 pair of electron shared
eg. H₂
35
covalents bonds - double
2 pairs of electrons shared
eg. O₂
36
covalents bonds - triple
3 pairs of electrons shared
eg. N₂
37
bonding pairs
shared electron pairs that form covalent bonds
38
lone pairs
electron pairs not involved in bonding
39
oribitals in a covalent bond
in a covalent bond, orbitals overlap
40
sigma bond
formed by the head-on overlap of two orbitals (can be s-orbitals or p-orbitals)
41
pi bond
formed by the sideways overlap of p-orbitals
42
which is stronger between sigma and pi bonds?
sigma bonds are stronger than pi bonds as there is more overlap between orbitals
43
sigma and pi bonds - double bonds
one sigma, one pi
44
sigma and pi bonds - triple bonds
one sigma, two pi
45
ionic bonds (facts)
- transfer of electrons
- ions formed
- high melting point + boiling points
- usually solid at room temp
- conduct electricity when dissolved in water or molten (ions are free to move in these states)
46
covalent bonds (facts)
- sharing electrons
- covalent bonds formed
- usually low melting + boiling points
- usually liquid or gaseous at room temp
- do not conduct electricity (no ions present)
47
sigma bonds (facts)
- stronger
- more overlap
- both s and p orbitals
- head on overlap
48
pi bonds (facts)
- weaker
- less overlap
- only p overlap
- sideways overlap
49
test for anions experiment
in hback
50
electronegativity differences - polarity
0 - 0.4 -> non-polar
0. 4 - 1.7 -> polar
1. 7 - 4 -> ionic
51
explain, in terms of atomic orbitals, how single bonds are formed
sigma, head-on overlap of atomic orbitals
52
explain, in terms of atomic orbitals, how double bonds are formed
sigma: head-on overlap of p orbitals
pi: sideways overlap of p orabitals
53
distinguish between sigma and pi covalent bonding
- sigma bond formed by head on overlap of atomic orbitals
| - pi bonds formed by sideways overlap of atomic orbitals
54
identify in ammonia the type of (i) intramolecular (ii) intermolecular forces, present
intramolecular: polar (covalent) bonds within ammonia molecules
intermolecular: hydrogen bonds between ammonia molecules
55
account for the difference in the shapes of the BF3 (boron trifluoride) and NH3 (ammonia) molecule
Boron trifluoride has three bond pairs of electrons and no lone pair
Ammonia has three bond pairs of electrons and one lone pair
56
Ammonia (NH3) and Silane (SiH4) - account for difference in bond angles between them
- Ammonia has 3 bond pairs and a lone pair whereas silane has 4 bond pairs (no lone pair)
- Lone pair of electrons has greater repelling power than a bond pair of electrons
57
When hydrogen bonding occurs
when hydrogen bonded to nitrogen, oxygen, or fluorine
58
reasons why can a molecule with polar bonds be non-polar
- centres of positive and negative charge coincide
- dipole moments cancel
- symmetrical distribution of bonds in 3-dimensional space around central atom / cancels due to symmetry of molecules
59
In terms of bonding/forces, why is the boiling point of hydrogen lower than that of oxygen?
hydrogen has fewer electrons, (therefore) weaker intermolecular forces
60
bonding/forces: why does iodine have a very low solubility in water?
- iodine pure covalent (non-polar)
- water is a polar solvent
- intermolecular forces between iodine and water very waek
61
bonding/forces: explain why: when a charged rod is held close to a thin stream of water flowing, the stream of water is deflected
-charge on rod attracts opposite charge on polar (dipole of) water molecule
62
Ionic bonding definition
-Bond/Force of attraction betwen oppositely-charged ions
/
-Bond involving transfer (loss and gain) of electrons
63
Covalent bonding definition
-Unequal sharing of bonding electrons
/
-Bond has slight positive (δ⁺) and slight negative (δ⁻) ends
64
Why do ionic substances conduct electriity when molten or dissolved in water but not in the solid state?
- Molten/dissolved: ions free to move
| - Solid: ions not free to move/ions locked in position
65
ammonia is polar covalent and is water-soluble.
| Show that the molecule has polar covalent bonding
- there is an electronegativity difference between N and H, showing unequal sharing
- show electroneg diff.
66
describe the processes involved when ammonia dissolves in water
- hydrogen bonds between the slightly negative O of water and H of ammonia
- and between the slightly H of water and N of ammonia
OR
- breaking of hydrogen bonds in water
- forming of hydrogen bonds between ammonia and water
67
why boiling point of one molecule with hydrogen bonding can be smaller than boiling point of another with hydrogen bonding
- weaker hydrogen bonding in one and stronger in another
| - smaller electronegativity difference for (eg. NH) bond, while bigger electronegativity difference for (eg. OH) bond
68
use electron pair repulsion theory to determine shape of the ammonia molecule and why bond angle is 107°
- three bonding and one lone pair
- giving bond arrangement to be pyramidal
-greater repelling power of lone pair pushes bonds closer
69
illustrate hydrogen bonding in ammonia
know how to illustrate
(occurs between H of one ammonia molecule and the N of another)
-2009 qs has diagram
70
why does methane have a low boiling point?
has weak intermolecular forces
71
why does water deflect towards a positively charged rod whereas cyclohexane doesn't?
what would happen if it was a negatively charged rod instead?
- polarity of water causes attraction to charged rod
- non-polarity of cyclohexane means it is not affected by charged rod
-stream of water still attracted to rod as molecules/dipoles arrange themselves with positive pole towards rod
72
water - polar or non polar
polar
73
when accounting for difference in boiling points
make sure to explain for both molecules.
eg. x has hydrogen bonds, while y has weak intermolecular forces
74
why would something be non-soluble in water?
- non-polar
| - does not form hydrogen bonds with water
75
conditions ionic compounds can conduct electricity
- in solution/in water
| - in the molten state
76
label clearly any tetrahedrally bonded carbon atom in the molecule
just label which C atoms have a tetrahedral shape
77
what type of intermolecular forces would you expect to find in nitrogen gas?
molecule is non-polar
78
would you expect GeH₄ to be water soluble?
no, as GeH₄ is non-polar
79
why the bonding in a molecule could be different from bonding in other molecules listed
- might be non-polar
- might be polar
- might have hydrogen bonding
80
properties affected by presence of hydrogen bonding
- boiling point
- melting point
- solubility in water
- surface tension
- specific heat
81
state how PH3 differs from other hydrides in terms of bonding (2012 qs)
virtually non-polar, due to tiny electronegativity difference between P and H in PH3, bigger electronegativity value differences in other hydrides
82
"identify the molecule or molecules where there is hydrogen bonding"
list ALL the molecules with hydrogen bonding, not just one of them
83
BCl3:
polar or non polar?: + why
B-Cl bond
BCl3 molecule -
B-Cl: polar, due to unequal sharing of electrons
BCl3 molecule: non-polar, cancels due to symmetry of molecule
84
why boiling point of ammonia lower than bp of water
weaker h bonding in ammonia / smaller electroneg diff for NH bond
85
account for diff in bond angle between methane (109.5) and water (104.5)
lone pairs in water have greater repelling power/push bonds closer
86
why bp of water is higher than methane
stronger h bonds between water molecules
87
diagram of bonds in magnesium chloride
ionic bond
88
how to know if bond is ionic
check electronegativity
89
drawing ionic bonds
know how to draw ionic bond diagrams
90
when asked to draw dot and cross diagram
-check electronegativity first to check if bond is ionic or covalent
91
hydrogen sulfide chemical formula
H2S
92
why H2S bp is lower than water
- h bonds in water
| - weak intermolecular forces in H2S
93
what type of intermolecular forces would you expect in nitrogen molecules? why
- van der waals
| - bc molecule is non polar
