1. Bonding, structure and properties of matter

Question 1

What are the three types of strong chemical bonds? Describe them briefly, and what elements they occur in.

Answer 1

There are three types of strong chemical bonds: ionic, covalent and metallic.
For ionic bonding the particles are oppositely charged ions.
For covalent bonding the particles are atoms which share pairs of electrons.
For metallic bonding the particles are atoms which share delocalised electrons.

Ionic bonding occurs in compounds formed from metals combined with non-metals.

Covalent bonding occurs in most non-metallic elements and in compounds of non-metals.

Metallic bonding occurs in metallic elements and alloys.

Students should be able to explain chemical bonding in terms of
electrostatic forces and the transfer or sharing of electrons.

Question 2

What reacts together to form an ionic structure and how?

Answer 2

When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred. Metal atoms lose electrons to become positively charged ions. Non-metal atoms gain electrons to become negatively charged ions. The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).

Question 3

Draw a dot and cross diagran for the formation of Magnesium chloride, sodium chloride, nad aluminium oxide.

Question 4

What is an ionic compound?

Answer 4

Ionic compounds are formed from metals bonding with non-metals.

Solid ionic compounds are giant structures of ions.
Oppositely charged ions are regularly arranged in a specific ratio, e.g 1:1 for Sodium and Chloride ions.

Question 5

What is the empirical formula?

Answer 5

The empirical formula is the simplest ratio of elemnts in a compound.

Question 6

What is ionic bonding?

Answer 6

Ionic bonding is the strong electrostatic force of attraction between oppositely charged ions (cations and anions) in all directions.

Spec:
Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.

Question 7

Explain the properties of ionic compounds.

Answer 7

When an ionic compound metls, strong ionic bonds between the ions are broken. Ionic compounds have high melting and boiling points as it takes a lot of energy to break the stron oinic bonds between the oppositely charged ions in the giant structure.

Question 8

Why don’t ionic compounds conduct electricity in a solid state?

Answer 8

The ions are held strongly together in the giant structure.
Therefore the ions cannot move the charge through the structure.

Question 9

Why do ionic compounds conduct electricity when molten or in solution?

Answer 9

The ions are not held strongly together in the 3D lattice. Therefore, the ions CAN move to carry charge through the structure.

Question 10

What are the limitations of the ball and stick model?

Answer 10

This model suggests that:
ionic bonding occurs between oppositely charged ions in a few directions, but actually it is in all directions.
The model suggests that there is a lot of empty space between ions, but there isn’t.

Question 11

What are the limitations of 2D and 3D models of ionic compounds?

Answer 11

A 2D model shows the arrangement of one layer of ions but it does have a major additional limitation - it does not show where the ions are located on the other layers. This is important because there are different possible arrangements of ions.

A 3D construction model shows how the ions are arranged in a lattice structure. These models usually use coloured balls to represent the ions. Some use sticks to show the ionic bonds.

A 3D construction model still has limitations:
it is not to scale
it gives no information about the forces of attraction between the ions, or the movement of electrons to form the ions

A dot and cross diagram for sodium chloride suggests that it is made up of pairs of sodium and chloride ions. It is not.

Question 12

What are the chemical formulae of the following complex ions: hydroxide, nitrate, sulphate, carbonate, ammonia, ammonium

Answer 12

hydroxide: OH-
nitrate: NO3-
Sulphate: SO4 2-
Carbonate: CO3 2-
Ammonia: NH3 (neutral)
Ammonium: NH4+

Question 13

What is a covalent bond?

Answer 13

When atoms share pairs of electrons, they form covalent bonds.
These bonds between atoms are strong.

A covalent bond involves sharing a pair of electrons between atoms of non-metlas.

A covalent bond is the electrostatic force of attraction between a shared pair of electrons and two nuclei.

Question 14

Draw a dot and cross diagram for ammonia.

Question 15

Give some examples of covalently bonded substances that have giant covalent structures.

How do you recognise that a covalently bonded compound is a simple molecule?

Answer 15

Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.

Some covalently bonded substances have very large molecules, such as polymers. (not the same as a giant covalent structure though).

Covalently bonded substances may consist of small molecules.

Students should be able to recognise common substances that consist of small molecules from their chemical formula.

Question 16

What is the structure of a metal?

Answer 16

Metals consist of giant structures of atoms arranged in a regular
pattern.

In metals, the atoms are built up layer upon layer in a regular arrangement to form a giant strucure.

The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds.

Question 17

What is chemical bonding?

Answer 17

Chemical bonding is an electrostatic interaction betwen positive and negative charge.

Question 18

What is metallic bonding?

Answer 18

The electrostatic attraction between metal cations and delocalised outer electrons holds the metallic structure together.

Question 19

What are the three states of matter and what are the names when you change between them?

Answer 19

The three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing
take place at the boiling point.

Sublimation: solid to gas
Deposition: gas to solid

Question 20

What things contribute to the state of matter of a substance?

Answer 20

The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance.

The nature of the particles involved depends on the type of bonding and the structure of the substance.
The stronger the forces between the particles the higher the melting point and boiling point of the substance.

Question 21

What are limitations of particle models?

Answer 21

Real particles are not rigid spheres, they are elastic and different size and shapes (eg ions or molecules).

Forces between particles are not shown, even though they exist.

Real particles are not “solid”, since atoms are mostly empty space.

Limitations of the simple model above include that in the model there are no forces, that all particles are represented as
spheres and that the spheres are solid.

Students should be able to:
* predict the states of substances at different temperatures
given appropriate data
* explain the different temperatures at which changes of state
occur in terms of energy transfers and types of bonding
* recognise that atoms themselves do not have the bulk
properties of materials
* (HT only) explain the limitations of the particle theory in
relation to changes of state when particles are represented by
solid inelastic spheres which have no forces between them.

Question 22

What are the different state symbols in an equation?

Answer 22

In chemical equations, the three states of matter are shown as (s),
(l) and (g), with (aq) for aqueous solutions

Question 23

What are the properties of ionic compounds? (spec)

Answer 23

Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.

These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.

When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.

Question 24

What are the properties of small molecules? Why do larger molecules have a higher melting and boiling point?

Answer 24

Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points.

These substances have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.

The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.

These substances do not conduct electricity because the molecules do not have an overall electric charge.

Question 25

What is the bonding in polymers?

Answer 25

Polymers have very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.

Question 26

What are the properties of giant covalent structures?

Answer 26

Substances that consist of giant covalent structures are solids with very high melting points. All of the atoms in these structures are linked to other atoms by strong covalent bonds. These bonds must be overcome to melt or boil these substances. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures.

Question 27

Compare simple molecular structures to giant structures.

Answer 27

Giant structures: Made from a huge number of atoms all covalently bonded together. Examples: Diamond, Graphite, Silicion Dioxide (Silica), Silicion Simple molecular structures: Composed of lots of small molecules that contain relatively few atoms with weak intermolecular forces between molecules. Examples: Carbon dioxide, Water, SULPHUR dioxide, Ammonia Similarities: Atoms (not ions) Strong covalent bonds between ATOMS Differences: Weak intermolecular forces between molecules to form structure vs. storng covalent bonds in giant structure

Question 28

What are the properties of simple molecular structures?

Answer 28

1. Cannot conduct electricity 2. (very) low melting and boiling points Simple covalent molecules have low melting nad boiling points because it does not take much energy to break the weak intermolecular forces between the MOLECULES (not strong covalent bonds between atoms that break). Simple covalent molecules don't conduct electricity as there are no mobile carriers of charge (no electrons/ions).

Question 29

What is the structure of a metal?

Answer 29

Metals have giant structures of atoms with strong metallic bonding (regular arrangement of metal cations as they repel each other since are positive). Delocalised outer electrons free to move through strucutre and carry a charge. This means that most metals have high melting and boiling points.

Question 30

What are the properties of metals?

Answer 30

Metals have high melting and boiling points becuase metals have giant structures and it takes a lot of energy to overcome the strong all directional metallic bonds. Metals conduct electricity and htermal energy because the delocalised outer electrons are free to move through the structure to carry charge. Metlas are malleable and ductile because the regular layers of metal cations can slide over one another.

Question 31

What is an alloy?

Answer 31

Alloys are mixtures of two or more elements, at least one of which is metal.

Question 32

Why are alloys and not pure metals often used (so why are pure metals mixed with alloys)?

Answer 32

In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped. Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder. Alloys are harder than pure substances because atoms of different elements have different sizes: this DISTORTS the layers making it harder for them to slide over each other.

Question 33

Why are metals good conductors of electricity and thermal energy?

Answer 33

Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal. Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons.

Question 34

What is the structure of diamond?

Answer 34

In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity.

Question 35

Using their structures, explain the propertie sof diamond and silicon dioxide

Answer 35

Structure: atoms bonded by strong covalent bond Properties: solubility - most will not dissolve in water. Have very high melting and boiling points. BECAUSE they have giant structures with strong covalent bonds between the atoms that take a lot of energy to overcome. Very hard: It has a giant structure with strng covalent bonds that take a lot of energy to overcome. No electrical conductivity: do not conduct electriciyt because has no mobile carriers of charge.

Question 36

Describe the structure and properties of graphite.

Answer 36

In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers. In graphite, one electron from each carbon atom is delocalised. Strucutre: strong covalent bonds betwen carbon atoms but weak forces between layers. Very high melting and boiling point: beccuase has a giant structure with strong covalent bonds between the atoms that take a lot of energy to overcome. Electricial conductivity: each carbon atom forms 3 covalent bonds with with three other carbon atoms, and so 1 outer lectron PER CARBON ATOM is delocalised and free to carry charge through the LAYERS (not structure). Slippery: The layers can slide over one another as the weak forces between the layers take little energy to overcome.

Question 37

What is graphene? What is its structure and bonding?

Answer 37

Graphene is a single layer of graphite and has properties that make it useful in electronics and composites. Each carbon atom is covalently bonded with 3 other carbon atoms, forming hexagonal rings so one electron per carbon atom is delocalised, meaning it can conduct electricity. Strong covalent bonds between carbon atoms: high melting and boiling point. One layer of graphite: thin and flexible.

Question 38

What are the properties of graphene?

Answer 38

Very strong: each carbon atom forms strong covalent bonds with three other carbon atoms that take a lot of energy to break. Light, transparent and flexible: Graphene is just one lyaer of graphite, which is one atom thick. Conducts heat and electricity: Each carbon atom forms bonds to 3 other carbon atoms meaning each carbon atom has one outer electron that becomes delocalised and is free to move through the structure to carry charge.

Question 39

What are fullerens and what are they used for?

Answer 39

Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms. The first fullerene to be discovered was Buckminsterfullerene (C60) which has a spherical shape. Fullerenes are molecuels of carbon with shapes of a hollow sphere or tube. Because they are hollow, fullerenes can be used to trap drugs for targeted drug delivery. Because they have a larg surface area, fullerenes can be used to trap catalysts on their surface to incrase reaciton rates. Because there are only weak intermolecular forces between fullerenes they can roll over one another so are good lubricants (eg for machinery).

Question 40

What is a nanotube and what are its properties?

Answer 40

Graphene can also be rolled into a cylinder to produce a nanotube. They are hollow. Nanotubes have the same properties of graphene, but also have high tensile strength, which means they can stretch and not break. They are also used in composites, electronics and naotechnology. Nanotubes are a type of fullerene. Size: 1-100nm (1x10-9 to 1x10-7m)

Question 41

What are the difference in sizes between nanoparticles, fine particles and coarse particles? What are examples of them>?

Answer 41

Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms. Nanoparticles, are smaller than fine particles (PM2.5) Fine particles have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m). Coarse particles (PM10) have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust.

Question 42

What is the relationship between size of a cube and its surface area?

Answer 42

As the side of cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of 10.

Question 43

What is so special about nanoparticles?

Answer 43

Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio. It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes.

Question 44

What are uses of nanoparticles?

Answer 44

Nanoparticles have many applications in medicine, in electronics, in cosmetics and sun creams, as deodorants, and as catalysts. New applications for nanoparticulate materials are an important area of research. Medicines Suncreams Cosmetics Deodorants Electronics Catalysts Small quantity of nano particles needed as large SA:V ratio

Question 45

What are risks of nanoparticles?

Answer 45

It is possible that nanoparticles can be absorbed into our body and enter our cells. No one knows the potential long-term effects of this on our health. Nanoparticles can enter our water system. No one knows the potential long-term effects of this on the environment and wildlife. It is therefore important that nanoparticles are studied and carefully used.