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3. Bonding Flashcards

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0
Q

Nobel gases…

A

Have full outer main levels of electrons and are very unreactive

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1
Q

Which electrons do the bonds between atoms always involve?

A

The outer electrons

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2
Q

Name the three strong chemical bonds

A
  • Ionic
  • Covalent
  • Metallic
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3
Q

How many electrons do metals have in their outer main levels?

A

One, two or three electrons.

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4
Q

Metals have either one, two or three electrons in their outer shells. What is the easiest way for them to attain the electron structure of a nobel gas?

A

To loose their outer electrons.

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5
Q

Which type of bonding occurs between metals and non-metals?

A

Ionic bonding

Electrons are transferred from metal atoms to non-metal atoms
Positive and negative ions are formed

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6
Q

The positive and negative ions formed in an ionic bond are attracted to each other by which force?

A

Electrostatic force

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7
Q

In ionic bonding how far does the electrostatic force extend?

A

The attraction extends throughout the compound. Every positive ion attracts every negative ion and vice versa.

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8
Q

What repulsive force exists in an ionic bond?

A

The repulsive force between all the ions of the same charge.

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9
Q

What is the structure in which all ionic compounds exist? How are the forces distributed in this?

A

A lattice

The attractive forces and the repulsive forces are balanced

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10
Q

What is the state of an ionic lattice at room temperature?

A

Solid, they have high melting temperatures because of their giant structures.

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11
Q

To melt a lattice of ions, what would you have to do?

A

Supply enough energy to break up the lattice of ions.

I.e break the electromagnetic forces of attraction.

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12
Q

Do ionic compounds conduct electricity?

A

Ionic compounds conduct electricity when molten or dissolved in water (aqueous) but not when solid.

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13
Q

Why do ionic compounds conduct when they are molten/aqueous but not when they are solid?

A

The ions that carry the current are free to move in the liquid state but they are not free in the solid state.

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14
Q

Ionic compounds are…

A

Brittle and shatter easily when given a sharp blow.

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15
Q

Why do ionic compounds shatter when given a sharp blow?

A

Because they form a lattice of alternating positive and negative ions, a blow may move e ions and produce contact between ions with like charges.

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16
Q

Do non-metals need to loose or receive electrons to gain electron structures of nobel gases?

A

Non-metal atoms need to receive electrons to fill the spaces in their outer shells.

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17
Q

Which type of bond is formed between a pair of non-metals?

A

A covalent bond

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18
Q

What is a covalent bond?

A

A shared pair of electrons

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19
Q

What is a small group of covalently bonded molecules called?

A

A molecule

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20
Q

How are covalent molecules neutral?

A

Because no electrons have been transferred from one atom to another

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21
Q

How does sharing electrons hold atoms together in covalent bonds?

A

Atoms with covalent bonds are held together by the electrostatic attraction between the nuclei and the shared electrons.

(The molecules are not strongly attracted to each other).

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22
Q

What kind of melting point do substances composed of molecules have?

A

Substances composed of molecules are gases, liquids or solids with low melting points

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23
Q

Why do substances composed of molecules have low melting points?

A

Because the strong covalent bonds are only between the atoms within the molecules. There is only weak attraction between the molecules which do not take much energy to overcome.

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24
Are substances composed of molecules good conductors?
They are poor conductors of electricity because the molecules are neutral overall. There are no changed particles to carry the current. (Even when aqueous).
25
What is co-ordinate bonding/dative covalent bonding?
When one atom provides both electrons in a covalent bond.
26
What do we call the atom that accepts the electron pair in a co-ordinate bond?
Electron-deficient
27
What are two spare electrons on an atom not being used in a bond called?
A lone pair
28
Co-ordinate covalent bonds are represented by what?
An arrow pointing towards the atom which is accepting the electron pair.
29
A molecule with a co-ordinate bond (and other covalent bonds) has bonds of what strength?
All the bonds have exactly the same strength and length. The molecule is symmetrical.m
30
What is electronegativity?
The power of an atom to attract the electrons in a covalent bond.
31
What is the word used to describe the way the negative change is distributed in a molecule?
The electron density
32
Which scale is used as a measure of electronegativity?
The Pauling scale
33
What numbers does the Pauling scale range?
0-4 (4 has the greatest electronegativity)
34
Which group of elements have no number on the Pauling scale?
The nobel gases, because they do not form covalent bonds
35
List three things electronegativity depends on?
1. The nuclear charge 2. The distance between the nucleus and the outer shell electrons 3. The shielding of the nuclear charge by electrons in inner shells.
36
What is the trend in electronegativity as we go up a group in the periodic table?
It increases as there is less shielding by electrons in inner shells.
37
What is the trend in electronegativity as we go across a period in the periodic table?
The electronegativity increases. The nuclear charge increases, the number of inner main levels stays the same and the atoms become smaller.
38
N the periodic table where are the most electronegative atoms found?
At the top right-hand corner
39
Which are the three most electronegative atoms?
Fluorine, oxygen and nitrogen (then chlorine)
40
What is polarity?
The unequal sharing of the electrons between atoms that are bonded together covalently.
41
When both atoms are the same, how are the electrons in the bond shared?
They are shared equally- they have the same electronegativity - the bond is non-polar
42
When the atoms are different, how are the electrons in the bond shared?
The electrons in the bond will not be shared equally . One of the atoms will have a positive partial charge, the other will have a negative partial charge. It is a polar bond.
43
The greater the difference in electronegativity between two atoms in a covalent bond...
The greater the polarity of the the bond is.
44
How are d+ and d- charges pronounced?
Delta plus and delta minus
45
Do atoms in a metal element transfer electrons?
No, they cannot transfer electrons unless there is a non-metal atom present to receive them.
46
What happens to the electrons in a metal element?
The outer main levels of the atoms merge. The outer electrons are no longer associated with any particular atom.
47
Describe metallic bonding
Metals consist of a lattice of positive ions in a sea of delocalised electrons.
48
In a metal, which ions tend to repel one another? How is this balanced?
The positive ions, this is balanced by the electrostatic attraction of these positive ions for the sea of delocalised electrons.
49
What do the number of delocalised electrons depend on in a metal?
How many electrons have been lost by each metal atom.
50
How far does the metallic bonding spread in the metal?
Throughout the structure (hence, metals have giant structures).
51
Can metals conduct electricity?
They are good conductors of electricity. Electrons from a power supply can join the sea of delocalised electrons and leave at the end terminal. The delocalised electrons flow through the structure carrying charge.
52
Are metals good conductors of heat?
Yes, they have high thermal conductivities, energy spreads by the vibration of the closely packed ions.
53
What does the strength of a metallic bond depend on?
- The charge of the ion, the greater the charge on the ion, the greater the number of delocalised electrons and the stronger the attraction between the positive ions and the electrons. - The size of the ion, the smaller the ion, the closer the electrons are to the positive nucleus.
54
What two distinct properties do metals have?
They are malleable and ductile.
55
What doe a it mean to be malleable?
They can be beaten into shape.
56
What does it mean to be ductile?
They can be pulled into thin wires.
57
Explain how metals are ductile and malleable.
After a small distortion each metal ion is still in exactly the same environment so the new shape is maintained.
58
What kind of melting points do metals have?
They generally have high melting and boiling points because they have giant structures. The metallic bond makes the atoms difficult to separate.
59
Molecules and separate atoms are attracted to one another by other weaker forces called...
Intermolecular forces
60
List the three types of intermolecular forces in order of increasing strength.
van der Waals forces Dipole-dipole forces Hydrogen bonding
61
Where do van der Waals forces act?
They act between all atoms and molecules
62
Dipole-dipole forces act between molecules that....
Have permanent dipoles. E.g polar molecules
63
Where does Hydrogen boning take place?
When you have... - A hydrogen atom which is bonded to a very electronegative atom. (Produces strong partial charge on the hydrogen). - A very electronegative atom with a lone pair of electrons. These will be attracted to the partially charged hydrogen atom in the other molecule.
64
Polarity can cancel in certain circumstances when...
Molecules with more than one polar bond have cancellation effects.
65
Two molecules which both have dipoles will...
Attract one another, the molecules with dipoles flip to give an arrangement where the two molecules attract.
66
An atom as a whole is neutral but at any moment in time the electrons could be anywhere. What does this result in?
This means the distribution of charge is changing at every instant.
67
As the electron distribution of the original atom changes what will it induce?
It will induce new dipoles in the atoms around it which will be attracted to the original one.
68
What are van der Waals forces also named?
Instantaneous dipole-induced dipole forces
69
The more electrons there are, the ................... the instantaneous dipole and the ............. the van der Waals force.
The more electrons there are, the larger the instantaneous dipole and the stronger the van der Waals forces.
70
Give two examples of evidence for the size of van der Waals forces increasing with the number of electrons present.
1. The boiling point of the nobel gases increase as the atomic numbers of the nobel gases increase. 2. The boiling points of hydrocarbons increase with increased chain length.
71
Is water polar?
Yes
72
How many times weaker are hydrogen bonds than covalent bonds?
Ten times weaker
73
What are hydrogen bonds represented by?
Dashes: ---------
74
Which atoms are electronegative enough to by the 'electronegative atoms' in hydrogen bonding (they are COVALENTLY bonded to the hydrogen atom(s))?
Nitrogen Oxygen Fluorine
75
Hydrides with N,O or F in them have higher boiling points than other hydrides... True of false? Explain why.
True. Hydrides containing N,O or F can make hydrogen bonds.
76
What is relevant about ice floating on water?
Hydrogen bonding takes place in water. When water is in it's liquid form the hydrogen bonds break and reform easily as the molecules are moving about. When water freezes the water molecules are no longer free to move about and the hydrogen binds hold the molecules in fixed positions. In this structure the molecules are slightly less closely packed than in liquid water. This means ice is less dense than water and floats on it.
77
Give some examples of the application of hydrogen bonds.
1. Bonds between biological proteins 2. Hydrogen bonds forming in materials when we iron them 3. DNA replication
78
How does a solid expand?
When we heat a solid and supply energy to the particles it makes them vibrate more about a fixed position. This slightly increases the average distance between the particles and so the solid expands.
79
What is the amount of energy needed to weaken the forces that act between solid particles when melting a substance called?
The latent heat of fusion or the enthalpy change of fusion
80
While a solid is melting how does the temperature change?
It does not change because the heat energy provided is absorbed as the forces between particles are weakened.
81
What is the energy required to turn a liquid into a gas called?
Latent heat of vapourish action or the enthalpy change of vaporisation.
82
List the four basic crystal types
Ionic, metallic, molecular and macromolecular
83
Describe some of the properties of an ionic crystal
- They have strong electrostatic attractions between oppositely charged ions which extend throughout the structure. - They have high melting points.
84
Give an example of an ionic crystal.
Sodium chloride
85
Describe some of the properties of metallic crystals
- High melting point - strong electrostatic forces of attraction between electrons and positive ions. (Extends throughout the crystal)
86
Describe some of the properties of molecular crystals
- Molecular crystals consist of molecules held in a regular array by one or more of the three types of intermolecular forces. Covalent bonds within the molecules hold the atoms together but they do not act between the molecules. - They therefore have low melting points
87
Give an example of a molecular crystal
Iodine
88
I2 molecules in iodine are held together by van der Waals forces which properties does this give them?
- It's crystals are soft and break easily - It has a low melting temperature and sublimes readily to form gaseous iodine molecules - It does not conduct electricity because there are no charged particles to carry charge
89
Describe the properties of macromolecular crystals
- Covalent bonds extend throughout the compound (hence high melting points) (giant structure).
90
Give two examples of macromolecular crystals
Diamond and graphite (allotropes or polymorphs of carbon)
91
Describe the structure of diamond
A carbon atom has four electrons in its outer shell. In diamond each carbon atom forms four single covalent bonds with other carbon atoms. These four electron pairs repel each other due to electron pair repulsion. (Tetrahedron: bond angles of 109.5)
92
Describe the properties of diamond
- It is a very hard material - It has a very high melting point (over 3700K) - It does not conduct electricity because they're no free charged particles to carry charge.
93
Describe the structure of graphite
In graphite each carbon atom forms three single covalent bonds to other carbon atoms. There form a flat trigonal planar arrangement due to electron pair repulsion. (120 degrees) Each carbon atom has a spare electron in the p orbital. All the p orbitals merge above and below the layers of carbon. And form a sea do delocalised electrons.
94
What is the intermolecular forces act in graphite?
There is no covalent bonding between the layers of carbon atoms they are held together be much weaker van der Waals forces. The layers can therefore, slide across each other making graphite soft and flaky.
95
Give the properties of graphite
Graphite is a soft material It has a high melting temperature due to the strong network of covalent bonds. It conducts electricity along the planes of the hexagons
96
See bond angles and shape questions on mixed questions
See bond angles and shape questions on mixed questions
97
How many degrees do lone pairs of electrons repel other bonds down?
2 degrees
98
How many bonds are double bonds counted for when finding the shape of a molecule?
Double bonds are counted as one bond when finding the shape of certain molecules.

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