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Chemistry > Unit 1: Section 3 - Bonding > Flashcards

Unit 1: Section 3 - Bonding Flashcards

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1
Q

What are the compound ions to remember?

A

Sulfate - SO4^2-
Hydroxide - OH-
Nitrate - NO3-
Carbonate - CO3^2-
Ammonium - NH4+

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2
Q

What is an ionic crystal?

A

They are giant lattices of ions.
A lattice is just a regular structure
It’s called giant because it’s made up of the same basic unit repeated over and over again
Different ionic compounds have different shaped structures

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3
Q

Do ionic compounds conduct electricity?

A

They do when they’re molten or dissolved but not when they’re solid
The ions in a liquid are free to move and carry a charge
In a solid the ions are fixed in position by strong ionic bonds

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4
Q

What are the melting points of ionic compounds like?

A

High melting points
Giant ionic lattices are held together by strong electrostatic forces
It takes lots of energy to overcome these forces

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5
Q

Do ionic compounds dissolve in water?

A

They tend to, yes
Water molecules are polar, these charged parts pull ions away from the lattice causing it to dissolve

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6
Q

What are molecules?

A

Form when 2 or more atoms bonded together
Held together by strong covalent bonds

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7
Q

What are giant covalent structures?

A

Macromolecular structures which have a huge network of covalently bonded atoms

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8
Q

What is the structure and what are the properties of graphite?

A
  1. The weak bonds between the layers in graphite are easily broken, so the sheets can slide over each other - used as a dry lubricant and in pencils
  2. The delocalised electrons are free to move along the sheets carrying a charge, so it’s an electrical conductor
  3. The layers are quite far apart compared to the length of the covalent bonds, therefore has a low density - used to make strong, lightweight sport equipment
  4. Due to the strong covalent bonds in the hexagon sheets graphite has a very high melting point (sublimes over 3900K)
  5. Insoluble in any solvent, as the covalent bonds in the sheets are too strong to break
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9
Q

What are the properties of diamond?

A
  1. Very high melting point (also sublimes over 3900K)
  2. Extremely hard - used in diamond-tipped drills and saws
    3.. Vibrations travel easily through the stiff lattice so it’s a good thermal conductor
  3. Can’t conduct electricity because all the outer electrons are held in localised bonds
  4. Won’t dissolve in any solvent
  5. It can be cut to form gemstones, its structure makes it refract light a lot which is why it sparkles
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10
Q

What is dative covalent bonding?

A

Forms when an atom provides both of the shared electrons

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11
Q

What are charge clouds?

A

An area where you have a high chance of finding an electron pair, the electrons don’t stay still, thy whizz around inside the charge cloud

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12
Q

What is Valence-shell electron-pair repulsion theory?

A

This is how much electron charge clouds repel each other`
Lone pair - lone pair repulsion > Lone pair - bonded pair > Bonded pair - bonded pair

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13
Q

How to predict the shape of a molecule

A
  1. Work out what the central atom is
  2. Use the periodic table to work out the number of electrons in the outer shell of the central atom
  3. Work out how many of those electrons are in a covalent bond, that’s the number of bonding pairs
  4. The remaining electrons around the central atom divide by t 2 and they’re the lone pairs
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14
Q

What is the shape when a molecule has 2 electron pairs?

A

0LP Shape - Linear Bond Angle - 180°

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15
Q

What is the shape when a molecule has 3 electron pairs?

A

0LP Shape - Trigonal planar Bond Angle - 120°

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16
Q

What are the shapes when a molecule has 4 electron pairs?

A

0LP Shape - Tetrahedral Bond Angle - 109.5°
1LP Shape -Trigonal pyramidal Bond Angle - 107°
2LP Shape - Bent Bond Angle - 104.5°

17
Q

What are the shapes when a molecule has 5 electron pairs?

A

0LP Shape - Bipyramidal Bond Angle - 120° and 90°
1LP Shape - Seesaw Bond Angle - 102° and 87°
2LP Shape - T-shaped Bond Angle - 88°

18
Q

What are the shapes when a molecule has 6 electron pairs?

A

0LP Shape - Octahedral Bond Angle - 90°
1LP Shape - Square pyramidal Bond Angle - 90°
2LP Shape - Square planar Bond Angle - 90°

19
Q

What is electronegativity?

A

An atom’s ability to attract the electron pair in a covalent bond
Fluorine is the most electronegative

20
Q

Why are some bonds polar?

A
  1. A covalent bond between 2 atoms of the same element is non-polar because the atom shave equal electronegativities, so the electrons are equally attracted to both nuclei
  2. Some elements have similar electronegativities, so the bonds between them are essentially non-polar
  3. In a polar bond, the difference in electronegativity between the 2 atoms causes a permanent dipole
  4. The greater the difference in electronegativity, the more polar the bond
21
Q

What is a dipole?

A

A difference in charge between 2 atoms caused by a shift in electron density in the bond

22
Q

How can a molecule be polar?

A

When a molecule contains polar bonds with an uneven distribution of charge across the whole molecule, the molecule is polar
If the polar bonds are arranged symmetrically in a molecule, then the charges cancel out and there is no permanent dipole

23
Q

What are permanent dipole-dipole forces?

A

In a substance made up of molecules that have permanent dipoles, there will be weak electrostatic forces of attraction between the delta+ and delta-charges on neighbouring molecules

24
Q

What are the 3 types of intermolecular forces in order of strength?

A
  1. Induced dipole-dipole or Van der Waals forces
  2. Permanent dipole-dipole forces
  3. Hydrogen bonding
25
Q

How do Van der Waals forces arise?

A
  1. Electrons in charge clouds are always moving really quickly, at any moment, the electrons in an atom are likely to be more to one side than the other, at this moment the atom would have a temporary dipole
  2. This dipole can induce another temporary dipole of the opposite charge on a neighbouring atom, the 2 dipoles are then attracted to each other
  3. Because the electrons are constantly moving, the dipoles are being created and destroyed all the time, even though the dipoles keep changing, the overall effect is for the atoms to be attracted to each other
26
Q

What is hydrogen bonding?

A

Strongest type of intermolecular forces
1. Only happens when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
2. F, N and O are very electronegative, so they draw bonding electrons away from the hydrogen atom
3. The bond is polarised, and hydrogen has such a high charge density (because it’s so small), that the hydrogen atoms form weak bonds with lone pairs of electrons on the F, N or O atom sof other molecules

27
Q

What is the effect of hydrogen bonding on the properties of substances?

A
  1. Substances with hydrogen bonds have higher boiling and melting points than other similar molecules because of the extra energy needed to break the hydrogen bonds
  2. As liquid cools to form ice, the molecules make more hydrogen bonds and arrange themselves into a regular lattice structure, in this regular structure the H2O molecules are further apart on average than the molecules in liquid water - so ice is less dense than liquid water
28
Q

How do metals exist, and what is metallic bonding?

A

Metals exist as giant metallic lattice structures
1. The outermost shell of electrons of a metal atom are delocalised and are free to move about the metal
2. The positive metal ions are attracted to the delocalised negative electrons, they form a lattice of closely packed positive ions in a sea of delocalised electrons

29
Q

How does metallic bonding explain the properties of metals/

A
  1. Metals have a high melting point because of the strong electrostatic forces of attraction between the positive metal ions and the sea of delocalised electrons
  2. The number of delocalised electrons per atom affects the melting point, the more there are, the stronger the bonding will be and the higher the melting point
  3. The delocalised electrons can pass kinetic energy to each other, making metals good thermal conductors
  4. Metals are good electrical conductors because the delocalised electrons can move and carry a current
  5. Metals are insoluble (except in liquid metals) because of the strength of the metallic bonds
30
Q

What are the properties of solids?

A

Particles are very close together - high density and incompressible, the particles vibrate around a fixed point and can’t move about freely

31
Q

What are the properties of liquids?

A

Has a similar density to a solid and is virtually incompressible, the particles move about freely and randomly within the liquid, allowing it to flow

32
Q

What are the properties of gases?

A

The particles have lots more energy and are further apart, so the density is very low and it’s compressible, the particles move about freely with not a lot of attraction between them, so they’ll quickly diffuse to fill a container

33
Q

Why do simple covalent structures have low melting and boiling points?

A

You only have to overcome the weak intermolecular forces and not the strong covalent bonds

34
Q

Why do giant covalent structures have high melting and boiling points?

A

You have to break the covalent bonds between atoms, it tends to sublime rather than melt

35
Q

What are the properties of ionic bonding?

A

Melting and boiling points - High
Typical state at room temperature and pressure - Solid
Does solid conduct electricity - No
Does liquid conduct electricity - Yes
Is it soluble in water - Yes

36
Q

What are the properties of simple covalent structures (molecular)?

A

Melting and boiling points - Low
Typical state at room temperature and pressure - May be solid like I2 but usually liquid or gas
Does solid conduct electricity - No
Does liquid conduct electricity - No
Is it soluble in water - Depends on how polarised the molecule is

37
Q

What are the properties of giant covalent structures (macromolecular)?

A

Melting and boiling points - High
Typical state at room temperature and pressure - Solid
Does solid conduct electricity - No (except graphite)
Does liquid conduct electricity - N/a sublimes rather than melting
Is it soluble in water - No

38
Q

What are the properties of metallic structures?

A

Melting and boiling points - High
Typical state at room temperature and pressure - Solid
Does solid conduct electricity - Yes
Does liquid conduct electricity - Yes
Is it soluble in water - No

Chemistry (12 decks)

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