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Bonding Flashcards

(72 cards)

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1
Q

How does the size of electronegitivity affect type of bond formed?

A

Pure covalent = <0.4
Polar covalent = 0.4 - 1.8
Ionic = > 1.8

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2
Q

What is a lone pair?

A

When an electron is not used for bonding it is know as a lone pair

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3
Q

Octet rule

A

Unpaired electrons pair up to obey the octet rule but this is not always possible as there may not be enough electrons avaliable.

Where 4 or more electrons pair up to bond it is called expansion of the octet and only occurs from period 3 and above due to more stable electrons

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4
Q

Metallic bonding

A

Metals loose electrons to become ions and electrons are delocalised so metals form a lattice of positive ions surrounded by a sea of electrons.

-positive ions repel but is balanced via electrostatic attraction from electrons
-number of delocalised electrons depends on amount lost by each metal atom
-metallic bonding spreads throughout so metals have giant structures
-attraction is high so metals have high melting and boiling points
-metallic compounds are not soluble

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5
Q

Why are metals good conductors of electricity?

A

Delocalised electrons more diectionally towards positive terminal inducing a current.

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6
Q

Why are metals good conductors of heat?

A

They have high thermal conductivity as energy is spread via vibrations of closely packed particles and rapidly moving electrons

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7
Q

Why do metals have high melting points?

A

Giant structure with large attraction so needs alot of energy to overcome

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8
Q

What does the strength of a metal depend on?

A

The strength of the attraction controlled via:
-charge on ion (greater no. of electrons, stronger the attraction)
-size of ion ( electrons are closer to the positive nucleus in a small ion so stronger bond)

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9
Q

Why are metals malleable and ducticle?

A

When metal is subjected to stress layer slide over eachother due to lattice causing manipulation. Will not occur in alloys.

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10
Q

What is charge density?

A

Charge of ion/volume

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11
Q

What is ionic bonding?

A

Occurs between a metal and a non-metal

-electrons are transferred from the metal with low electronegativity to non-metals with high electronegativity
-metals form cations and non-metals form anions
-ions are attracted to each other via electrostatic forces of attraction

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12
Q

Properties on an ionic bond

A

-form ionic lattice due to non-directional bonding
-form cubic crystals due to the lattice structure
-high melting point due to large electrostatic forces of attraction
-conduct electricity when molten as ions are free to move

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13
Q

Covalent Bonding

A

Mostly occurs between metals and non-metal

-sharing of electrons in the outer shell so each atoms has a stable configuration
-atoms remain neutral
-forces of electrostatic attraction occur between the nucleus of each atom and shared electrons

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14
Q

Dative Covalent Bonding

A

-where both electrons in the covalent bond comes from one atom
-represented by an arrow from electron donor
-atom that accepts is electron deficient
-same strength and length as normal covalent bonds

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15
Q

Properties of covalent bonds

A

-low melting points as there is weak attraction between molecules
-poor conductors due to no free charged particles
-dissolve in water and remain as molecules

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16
Q

3 types of intermolecular forces

A

-van der val
- dipole dipole
-hydrogen

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17
Q

Heating solids

A

Heating a solid will supply energy to the particles causing more vibrations which will lead to increasing distance causing the solid to expand

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18
Q

Solid to Liquid

A

-energy needed to weaken forces between molecules
enthalpy change of melting
-temperature does not change as heat energy is absorbed as forces weaken

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19
Q

Heating a liquid

A

-supply energy to particles to make them move quicker. liquids also expand

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20
Q

Liquid to gas

A

-break all intermolecular forces
enthalpy change of vapourisation

no tempreture change

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21
Q

Heating a gas

A

gain kinetic energy and move faster to expand

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22
Q

What are crystals?

A

solids that have a regular arrangement that are held together via attraction of forces.

The strength of the forces determines the physical properties of the crystal

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23
Q

Ionic Crystals

A

-strong electrostatic forces of attraction so have high melting point
-cannot conduct electricity as ions are fixed as a solid

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24
Q

Metallic Crystals

A

-lattice of positive ions with sea of delocalised electrons
-high melting point
-conduct electricity and heat
-ductile

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25
Molecular Crystals
-consist of molecules held together via intermolecular forces (covalent bonds within molecules) -low melting points due to weak intermolecular forces -soft -does not conduct electricity
26
Macromolecule crystals
-covalent bonds extend throughout structure and cause giant structure with strong bonds so has high melting points
27
Diamonds
-carbon forms 4 bonds forming giant structure -bond angle 109.5 -tetrahedron -hard -high melting point >3700 K -does not conduct electricity
28
Graphite
-carbon forms 3 bonds -bonding angle 120 -trigonal planar -strong covalent with weaker van der vals between layers -layers held via van der vals so they slide over each other -high melting point -soft -conducts electricity due to delocalised electron from p orbitals which flow along planes.
29
Giant footballs
forms of carbon known as nanotubes or buckyballs that can be used in sports equipment or for medical treatments
30
Electron Pair Repulsion
-each pair of electrons around an atom will repel all other electron pairs -pairs of electrons will take up space as far apart as possible to minimise repulsion -pairs may be shared or lone
31
VSESPR theory
1) identify central atom 2) count number of outer shell electrons 3) add 1 electron for each bonding atom 4) add/subtract electrons for any charges 5) divide total by 2 to find total number of electron pairs 6) work out bonding and lone pairs (how many bonds are formed) 7) use numbers to predict a shape
32
Explain in terms of intermolecular forces present why HF has a higher boiling point than HCl.
-HF contains hydrogen bonding of which is occurring between the H and F -HCL only contains slight dipole dipole charges and vdws -these are weaker and therefore require less energy to be broken
33
Predict the shape of an AlH4- ion and explain why it has that shape
-tetrahedral shape -equal repulsion between the 4 bonding pairs that surround Al
34
Suggest why graphite has a very high melting and boiling point
-have very strong covalent bonds -macromolecular
35
Explain the movement of atoms in a crystalline solid
vibrate about a fixed position
36
What is ionic bonding?
The electrostatic force of attraction between oppositely charged ions formed via electron transfer.
37
What structure do ionic crystals have?
Giant lattices of ions
38
What affects the melting and boiling points of ionic bonding?
The bonds are stronger and the melting points are higher when the ions are smaller or have higher charges.
39
Explain the difference in size of a positive ion and an atom
Positive ions are smaller compared to their atoms because they have one less shell of electrons and the ratio of protons to electrons has increased so there is greater net force on remaining electrons holding them more closely.
40
Explain the difference in size of a negative ion and an atom
The negative ions formed from groups five to seven are larger than the corresponding atoms. The negative ion has more electrons than the corresponding atom but the same number of protons. So the pull of the nucleus is shared over more electrons and the attraction per electron is less, making the ion bigger
41
State how the size of ionic radii changes in a group.
Within a group the size of the ionic radii increases going down the group. This is because as one goes down the group the ions have more shells of electrons
42
What is a covalent bond?
A shared pair of electrons.
43
Describe a dative covalent bond
A dative covalent bond forms when the shared pair of electrons in the covalent bond come from only one of the bonding atoms. A dative covalent bond is also called co-ordinate bonding
44
Give some common examples of compounds that have dative covalent bonds.
NH4+ H3O+ NH3BF3
45
Define metallic bonding
The electrostatic force of attraction between the positive metal ions and the delocalised electrons.
46
What are the three main factors that affect the strength of metallic bonding?
1. Number of protons/ Strength of nuclear attraction. The more protons the stronger the bond 2. Number of delocalised electrons per atom (the outer shell electrons are delocalised) The more delocalised electrons the stronger the bond 3. Size of ion. The smaller the ion, the stronger the bond
47
State the structure of covalent molecules
Simple molecular: With intermolecular forces (van der Waals, permanent dipoles, hydrogen bonds) between molecules Macromolecular: giant covalent structure
48
Give an example of substances that have a covalent simple molecular structure.
Ice and Iodine
49
Give an example of substances that have a covalent macromolecular structure.
Diamond and Graphite
50
Describe the structure of compounds formed via metallic bonding and give an example.
Giant metallic lattice (all metals such as magnesium)
51
How can you explain the shape of a molecule in 5 steps?
1. State number of bonding pairs and lone pairs of electrons. 2. State that electron pairs repel and try to get as far apart as possible (or to a position of minimum repulsion.) 3. If there are no lone pairs state that the electron pairs repel equally 4. If there are lone pairs of electrons, then state that lone pairs repel more than bonding pairs. 5. State actual shape and bond angle.
52
How do lone pairs affect bonding pairs?
They repel more so reduce bond angles by around 2.5 degrees.
53
Define electronegativity
Electronegativity is the relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself. Greater the electronegativity of an atom the more it attracts electrons towards it.
54
What are the factors which effect electronegativity?
Electronegativity increases across a period as the number of protons increases and the atomic radius decreases because the electrons in the same shell are pulled in more. It decreases down a group because the distance between the nucleus and the outer electrons increases and the shielding of inner shell electrons increases
55
What are the most electronegative atoms?
F, O, N and Cl are the most electronegative atoms
56
How does the electronegativity of 2 elements affect bonding type?
A compound containing elements of similar electronegativity and hence a small electronegativity difference will be purely covalent. A compound containing elements of very different electronegativity and hence a very large electronegativity difference (> 1.7) will be ionic
57
Explain the formation of a permanent dipole.
A polar covalent bond forms when the elements in the bond have different electronegativities . (Of around 0.3 to 1.7) When a bond is a polar covalent bond it has an unequal distribution of electrons in the bond and produces a charge separation, (dipole) δ+ δ ends.
58
Why are symmetrical molecules non-polar?
A symmetric molecule (all bonds identical and no lone pairs) will not be polar even if individual bonds within the molecular are polar. The individual dipoles on the bonds ‘cancel out’ due to the symmetrical shape of the molecule.There is no net dipole moment.
59
What are Van der Wal forces?
In any molecule the electrons are moving constantly and randomly. Causes the electron density to fluctuate and parts of the molecule become more or less negative i.e. small temporary or transient dipoles form. These instantaneous dipoles can cause dipoles to form in neighbouring molecules. These are called induced dipoles. The induced dipole is always the opposite sign to the original one. A temporary dipole forms between the ∂+ in one molecule and the ∂- in a neighbouring molecule
59
Where do Van der Wal forces occur?
Van der Waals forces occur between all molecular substances and noble gases. They do not occur in ionic substances.
60
How does the shape of the molecule affect Van der Wal forces?
Long chain alkanes have a larger surface area of contact between molecules for Van der Waals to form than compared to spherical shaped branched alkanes and so have stronger Van der Waals.
60
What is the main factor effecting the size of Van der Wal forces?
The more electrons there are in the molecule the higher the chance that temporary dipoles will form. This makes the Van der Waals stronger between the molecules and so boiling points will be greater.
61
What is permanent dipole-dipole forces?
*Permanent dipole-dipole forces occurs between polar molecules *They are stronger than Van der Waals and so the compounds have higher boiling points *Polar molecules have a permanent dipole. (commonly compounds with C-Cl, C-F, C-Br H-Cl, C=O bonds) *Polar molecules are asymmetrical and have a bond where there is a significant difference in electronegativity between the atoms.
62
What is hydrogen bonding?
It occurs in compounds that have a hydrogen atom attached to one of the three most electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of electrons. e.g. a –O-H -N-H F- H bond. There is a large electronegativity difference between the H and the O,N,F.
63
What substances form hydrogen bonding?
Alcohols, carboxylic acids, proteins, amides all can form hydrogen bonds
64
Name the 4 types of crystal structures
ionic,metallic,simple molecular, macromolecular
65
Describe the structure of an ionic crystal
Giant Ionic lattice showing alternate ions held via electrostatic forces
66
Describe the structure of a metallic crystal
Giant metallic lattice showing close packing metal ions with delocalised electrons
67
Describe the structure of ice
The main point to show is a central water molecule with two ordinary covalent bonds and two hydrogen bonds in a tetrahedral arrangement. The molecules are held further apart than in liquid water and this explains the lower density of ice
68
Describe the structure of diamond
Tetrahedral arrangement of carbon atoms. 4 covalent bonds per atom
69
Describe the structure of graphite
Planar arrangement of carbon atoms in layers. 3 covalent bonds per atom in each layer. 4th outer electron per atom is delocalised. Delocalised electrons between layers.
70
State the properties of a macromolecular substance
macromolecular structures have very high melting points because of strong covalent forces in the giant structure. It takes a lot of energy to break the many strong covalent bonds.

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