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Bonding Flashcards

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1
Q

What are the diagrams used to show ionic bonding called?

A

Dot and cross diagrams

The dots and crosses are used to represent the origin of each electron

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2
Q

How are positive and negative ions held together?

A

By a force of electrostatic attraction

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3
Q

For an ion that is made from two or more brackets how do you show that the charge acts over the whole ion?

A

You use square brackets, e.g. [HCO3]-

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4
Q

What structure do ionic compounds take?

A

They form a giant lattice structure with a regular, repeating pattern of ions

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5
Q

What groups will form which ions?

A

1) +1
2) +2
3) +3

5) -3
6) -2
7) -1

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6
Q

What are common compound ions?

A
  • Hydroxide: OH-
  • hydrogen carbonate: HCO3-
  • nitrate: NO3-
  • ammonium: NH4+
  • sulfate: SO42-
  • sulfite: SO32-
  • carbonate: CO32-
  • phosphate: PO43-
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7
Q

How do you use charges to work out the formula of a compound?

A

The charges must balance out

E..g. caesium forms ions with a 1+ charge, oxygen forms ions with a 2- charge. Two caesium ions are needee to give two positive charges to balance oxygen so the formula is Cs2O

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8
Q

What happens in a covalent bond?

A
  • electrons are shared to complete electron shells

* the positively charged nuclei attracts the negative charge of the bonding pair of electrons (shared pair of electron)

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9
Q

How would you draw the covalent bond in the hydrogen molecule?

A

H-H

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10
Q

What is the structure of covalent molecules?

A
  • they have no overall charge
  • they exist as individual molecules
  • or if many covalent bonds are formed they can form a giant covalent structure such as diamond or graphene
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11
Q

What is the number and type of atoms from which a molecule is made given by?

A

Its molecular formula

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12
Q

What is a double covalent bond (double bond) and how can you write this?

A

Four electrons are shared so there are two bonding pairs in each double bond

C=C

Or with a dot and ceoss diagram

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13
Q

What is a triple covalent bond?

A

The triple bond contains six electrons to give three bonding pairs

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14
Q

What is a co-ordinate or dative bond and how is it written?

A

When both shared electrons in a covalent bond come from the same atom

It can be written like: N->H with an arrow representing the dative bond or with a dot and cross diagram

The result will be an ion with the ssme charge as the molecule recieving the electrons

You can get triple bonds with one dative covalent bond and two normal covalent bonds

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15
Q

What is the bonding in metals called?

A

Metallic bonding

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16
Q

How do metallic bonds work?

A
  • In a lump of solid metal the metal will be present as ions
  • each atom transfers it’s outer electrons ro make a ‘sea’ of delocalised electrons that surround the regularly spaced ions and are free to move about the metal
  • the attraction between the positive metal ions and the delocalised electrons holds the metal together in the solid state
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17
Q

What do the properties of a particular substance depend on?

A

How the atoms from which it is made bond to one another

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18
Q

What is attraction between one molecule and another called?

A

Intermolecular bonding

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19
Q

The structure of a solid may be crystalline or amorphous. What does this mean?

A
  • in a crystalline structure the different types of particle are arranged inna fixed repeating pattern
  • in an amorphous solid there is no regular pattern to the way the particles are arranged
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20
Q

What are the four types of crystal structure?

A
  • Ionic: compounds containing ions form ionic crystals
  • Metallic: metals have a metallic crystal structure when solid
  • macromolecular (giant covalent): non-metals form macromolecular crystals
  • molecular: some molecules with intermolecular forces between them form molecular crystals
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21
Q

What are ionic crystals and what are their properties?

A
  • they consist of a lattice of positive and negative ions
  • an ionic crystal melts when enough energy is transferred to it to overcome the strong electrostatic attractions between the ions. The energy is transferred by heating
  • because their electrostatic attractions are strong the melting points are high
  • ionic crystals don’t conduct electricity when solid, but when melted or dissolved in water they do as the ions are free to move and carry the charge
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22
Q

What are metallic crystals and their properties?

A
  • metal ions are held in place by a sea of delocalised electrons with the ions packed together as closely as possible
  • the ions will have a basic pattern (e.g. hexagonal close packed) that is repeated in the metals structure, making up small crystals or grains
  • metallic bonds are strong bonds as there is a strong electrostatic attraction between the ions and sea of delocalised electrons throughout the structure. A lot of energy is needed to break these bonds and so metals usually have high melting points.
  • the more outer electrons that the atom loses the higher the electron density. This means that the metallic bonds are stronger.
  • ions with a smaller radius will have stronger metalluc bonding as the delocalised electrons are more strongly attracted to the metal ions as they are closer together
  • they have free delocalised electrons that can move throughout the structure, and so therefore metals conduct electricity, even when solid
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23
Q

What are allotropes?

A

Allotropes of an element have different structures but are the same state

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24
Q

What is the structure and properties of diamond?

A
  • each carbon atom forms four covalent bonds with four other carbon atoms giving a tetrahedral structure
  • the regular symmetrical pattern makes diamond the hardest naturally occuring substance
  • when diamond melts, covalent bonds between the carbon atoms are broken and the carbon atoms become free to move
  • diamond has a very high melting point (3500°c) because it has very strong covalent bonds
  • diamond doesn’t conduct electricity as it has no charged particles
25
Q

What is the structure and properties of graphite?

A
  • has a giant covalent structure
  • consists of flat sheets of carbon atoms covalently bonded together into hexagonal rings
  • each carbon is bonded to three other carbon atoms. The fourth carbon electron makes up part of a cloud of delocalised electrons between the layers
  • the delocalised electrons hold the structure together by intermolecular forces called van der waal forces
  • large amounts of energy are needed to break the covalent bonds in graphite so it has a high melting point
  • graphite conducts electricity because its delocalised electrons are free to move
26
Q

What are molecular crystals and their properties?

A
  • contain molecules held together by intermolecular forces
  • they normally have a regular pattern
  • crystals such as iodine which are just held together by van der waal forces have a low melting point as these intermolecular forces are easily broken
  • molecular crystals normally don’t have any charged particles to carry an electric current and are non-conductors
27
Q

What is the shape of a simple molecule determined by?

A

The number of electron pairs that surround the central atom. Electron pairs repel eachother and arrange themselves to be as far apart as possible. This determines the shape of a covalently bonded molecule

28
Q

What are the two types of electron pairs atoms have in molecules?

A
  • Bonding pairs: pair of electrons involved in a chemical bond
  • lone pair (non-bonding pair): pair of electrons not involved in bonding
29
Q

Why do lone pairs of electrons have a greater repulsion than bonding pairs?

A

Because they are closer to the nucleus than bonding pairs

30
Q

What order does the repulsion between electron pairs around an atom increase in?

A

Bonding pair-bonding pair < lone pair-bonding pair < lone pair-lone pair

31
Q

How do you predict the shape of molecules?

A

1) determine the number of electron pairs (the bond structure will give you this)
2) Identify the basic shape
3) look for lone pairs (these are the electron pairs not involved in bonding)
4) Apply the rule for the order of increasing repulsion between electron pairs
5) draw out the shape of the molecule, adding the bond angle

32
Q

What shape are the molecules with 2,3,4,5 and 6 pairs of bonding electrons and their angles?

A

2) linear (180°)
3) trigonal planar (120°)
4) tetrahedral (109.5°)
5) trigonal bypyramidal (90°/120°)
6) octahedral (90°)

33
Q

In a covalent bond between two hydrogen atoms how are the electrons distributed?

A

Evenly between the two hydrogen atoms. The electron density is symmetrical because each hydrogen nucleus has the same power of attraction

34
Q

In a covalent bond between a hydrogen and a fluorine atom how are the electrons distributed?

A

The electrons are drawn closer to the fluorine atom. The electron density is unsymmetrical because the fluorine nucleus attracts the bonding electrons more strongly than the hydrogen nucleus does. This means that the negative charge from the bonding pair of electrons is closer to the fluorine atom. The fluorine end of the molecule is now more negative than the hydrogen end.

The hydrogen end is delta positive and the fluorine end is delta negative

35
Q

What is electronegativity?

A

The ability of the nucleus to attract the bonding pair of electrons

36
Q

What is a polar bond?

A

When the bonding pair of electrons lies closer to atoms nucleus than the other. They have a large difference in their electronegativity and so have dipoles

37
Q

What is the most and least electronegative elements?

A

Fluorine is the most and caesium and francium are the least

38
Q

Why does electronegativity increase across the periodic table?

A

It increases as atomic number increases and atomic radius decreases. The larger the nuclear charge and the smaller the atomic radius the greater the attraction for the electron pair in the covalent bond

39
Q

What two factors decide the electronegativity of an atom and why?

A
  • the atomic radius - if atoms are small, the nucleus can get close to the bonding pair of electrons and attract them more strongly
  • the nuclear charge - the total positive charge on the nucleus. Since the number of protons increases across a period the nuclear charge also increases. For atoms in a period those with a higher nuclear charge will attract the bonding pair of electrons more strongly and will be more electronegative
40
Q

What happens if a molecule has a permenant dipole

A

One side will be slightly positive and the other side slightly negative

41
Q

Is the molecule polar if there are delta negative charges all on the outside?

A

No, for a molecule to have a permenant dipole one side will be slightly positive and the other slightly negative

42
Q

What are forces that can exist between molecules called and what is their strength?

A

Intermolecular forces that are very weak

43
Q

What is an instanteous dipole?

A

Electrons that are in constant motion and at any particular instant may not be evenly distributed. This means one end of the molecule may have a more negative charge than the other end. This dipole only lasts for an instant

44
Q

What is an induced dipole?

A

If a non-polar molecule is next to a polar molecule with a permenant or instaneous dipole an induced dipole is created in that molecule. The small negative charge on the polarised molecule is enough to repel the electrons in an adjacent unpolarised molecule and induce a dipole

45
Q

What are the three types of attracrion with intermolecular forces?

A
  • permanent dipole - permenant dipole
  • permanent dipole - induced dipole
  • induced dipole - induced dipole (van der waal)
46
Q

When do van der waal forces form?

A

When an instanteous dipole induces a dipole in an adjacent non-polar molecule. They are very weak intermolecular forces

47
Q

How do van der waal forces affect melting point

A
  • in longer molecules more van der waal forces can operate so the molecules are more strongly attracted to eachother so the boiling point is higher
  • with branched chain molecules the molecules cannot lie close together and parallel so there are fewer van der waal forces and less energy is needed to melt them
48
Q

What three features does a hydrogen bond depend on?

A
  • a highly polar bond between a hydrogen atom and a highly electronegative atom such as oxygen, nitrogen or fluorine
  • the small hydrogen atom can get close to other atoms
  • a lone pair of electrons on an oxygen, nitrogen or fluorine atom of one molecule can attract the positive charge of the hydrogen atom on the adjacent molecule
49
Q

How are hydrogen bonds formed?

A
  • the large difference in electronegativity between a hydrogen and a nitrogen, oxygen or fluorine atom means that strongly polar bonds are formed which gives the molecules a large permenant dipole
  • when two molecules are close enough, an attraction is set up between the positive end of one and the negative end of the other. This attraction is called hydrogen bonding.
  • the two highly electronegative atoms in adjacent molecules and the hydrogen atoms are always in a straight line. The arrangement is X-H-X. It is linear and hydrogen bonds are described as being directional
50
Q

How is a hydrogen bond different to other dipole-dipole forces?

A

Hydrogen has no inner non-bonding electrons so the proton of the hydrogen nucleus is exposed. Without non-bonding electrons to repel the lone pair of electrons in nitrogen, oxygen or fluorine, the proton is attracted strongly to their lone pair of electrons. It is embedded in the lone pair forming a hydrogen bond

51
Q

What is the bonding in water molecules?

A

• oxygen is more electronegative than hydrogen and strongly attracts the shared pair of electrons in a covalent bond. This makes the O-H bond highly polar and strong hydrogen bonds form between the water molecules

52
Q

What are hydrides?

A

Compounds that contain hydrogen plus one other element

53
Q

What is the trend in boiling points for the hydrides in group 6 and 7?

A
  • from period 3 down each group to period 5 there is a steady increase because the molecules get larger as you go down the group
  • water and hydrogen fluoride do not follow the same pattern because the hydrogen bonds present attract the molecules very strongly to eachother making the boiling point higher
54
Q

What shape is a water molecule?

A

V shaped

55
Q

What happens as you heat water?

A

The molecules gain energy, move more rapidly and become slightly further apart as their motion offsets the attraction of the hydrogen bonds. The water becomes less dense as its volume increases

56
Q

What happens as you cool water?

A
  • It becomes more dense as the molecules move closer together. This is until about 4°c when it is at its most dense.
  • from 4°- 0° the proportion of hydrogen-bonded molecules increases and the molecules start to form a lattice structure very similar to that carbon in diamond. The effect is that the molecules are set slightly further apart and the water becomes less dense.
  • at 0°c all the molecules are fixed in hydrogen-bonded positions making a rigid 3D lattice structure. The water has now frozen and become ice
57
Q

How can pond organisms survive?

A

Because when water freezes and becomes less dense it rises to the top of the pond leaving liquid water below

58
Q

What are the names and angles for the shapes with 6,5,4 and 3 electron pairs with one lone pair?

A
  • 6: Square pyramid (90°)
  • 5: see saw (90/118°)
  • 4: trigonal pyramidal (107°)
  • 3: bent (118°)
59
Q

What are the names and bond angles for the molecules with 6,5 and 4 electrob pairs with two lone pairs of electrons

A
  • 6: square planar (90°)
  • 5: t shape or trigonal planar (90° or 120°)
  • 4: bent (104.5°)

Chemistry (15 decks)

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