Chemistry - Topic 2 - Bonding, Structure and the Properties of Matter

What are the three types of strong chemical bonds and how do the particles bond?

• Ionic : The particles are oppositely charged ions

• Covalent : The particles are atoms which share pairs of electrons

• Metallic : The particles are atoms which share delocalised electrons

Where does ionic, covalent and metallic bonding occur?

• 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

What are electrostatic forces in chemical bonding?

Attractive forces between charged particles that hold bonds together.

What do atoms seek to achieve in terms of stability?

Atoms seek to achieve stable electron configurations.

What happens when a metal atom reacts with a non-metal atom?

• When a metal atom reacts with a non metal atom, electrons in the outer shell of the metal atom are transferred.

• The metal atom loose electrons to become positively charged

• Non metal atoms gain electrons to become negatively charged ions

What electronic structure do ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have?

The ions produced by metals in group 1 and 2 and by non metals in group 6 and 7 have the electronic structure of a noble gas (Group 0).

How does the charge on ions relate to the periodic table for metals in Groups 1 and 2 and non-metals in Groups 6 and 7?The

• The charge on the ions produced by metals in group 1 and 2 and by non metals in groups 6 and 7 relates to the group number of the element in the periodic table.

• Metals in group 1 and 2 typically form +1 and +2 ions

• Non metals in group 6 and 7 typically form -2 and -1 ions

What is an ionic compound and how are they held toegther?

• An ionic compound is a giant structure of ions.

• 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

What are the limitations of using dot and cross diagrams?

• They’re good for showing electron transfer.

• Limited in representing 3D structure and scale

What are the limitations of using ball and stick model?

• Show’s connectivity well

• May not accurately represent ion sizes or lack of distinct molecules

What are the limitations of using 2D diagrams?

• Easy to draw and understand

• Fails to show the full 3D nature of the structure

What are the limitations of using 3D diagrams?

• Better at showing overall structure.

• Can be complex and may not show all ions in the structure

How are covalent bonds formed?

• When atoms share a pair of electrons, they form covalent bonds.

• These bonds between atoms are strong

• Covalent bonded substances may consist of small molecules

In what forms can covalent bonds in molecules and giant structures be represented?

The covalent bonds in molecules and giant strcutures can be represesented in :

• Dot and croos diagrams

• Displayed formula

• Ball and stick Models

How are atoms arranged in metals and how are the bonds strong?

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

• 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.

What are the three states of matter and their transition points?

• 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.

• The three states of matter can be represented by a simple model.

How are particles represented in the simple model of matter?

• In this model particles are represented by small, solid spheres

• Particle theory can help to explain melting boiling , freezing and condensing

What determines the energy needed for state changes?

• 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 stronger the forces between particles, the higher the melting point and boiling point of the substance

What are the limitations of the simple particle model?

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

Do individual atoms possess bulk properties of materials?

Individual atoms don’t posses properties like ‘hardness’ or ‘fluidity’ that we associate with bulk materials. These properties emerge from the collective behaviour of many atoms or molecules.

What are state symbols?

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

What type of structure do ionic compounds have?

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

What are the melting and boiling points of ionic compounds?

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

How do ionic compounds conduct electricity?

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

What are the properties of substances that consist of small molecules?

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

• These substances have weak forces between the molecules (intermolecular forces)

• It’s these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils

How do intermolecular forces and size of molecules affect melting and boiling points?

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

• These substances do not conduct electricity because the molecules don’t have an overall charge.

What are the characteristics of polymers?

• 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.

What are the characteristics of substances that consist of giant covalent structures?

• 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.
  

What are the characteristics of metals and pure metals?

• Metals have giant structures of atoms with strong metallic bonding.

• This means that most metals have high melting and boiling points. 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.
  

Why are alloys harder than pure metals?

• Alloys are harder than pure metals because the introduction of different-sized atoms distorts the layers of atoms, making it more difficult for them to slide past one another.

Why are metals good conductors of electricity?

Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal.

Why are metals good conductors of thermal energy?

Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons.

What’s the characteristics of diamond in terms of structure and bonding?

• In diamond, each carbon atom forms 4 covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a high melting point and doesn’t conduct electricity.

What is the structure of graphite?

• 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.

What are the properties of graphite related to its structure?

• The presence of delocalised electrons allows it to conduct electricity

• While the weak forces between layers make it soft and slippery.

• The strong covalent bonds within the layers give graphite a high melting point.

What’s the structure of graphene?

• Graphene is a single layer of graphite and has properties that make it useful in electronics and composites.

• Each atom forms three covalent bonds between the carbon atoms.

What are the properties of graphene related to its structure?

• The delocalised electron allows for electrical conductivity

• It’s also very strong from the strong covalent bonds between the carbon atoms

• It also enables efficient heat dissipation through rapid energy transfer via delocalised electrons

• It’s large surface area also enhances reactivity, making it ideal for sensors.

What are fullerenes and what was the first one discovered?

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.

What are carbon nanotubes and what are their applications?

Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials.

What is the size range of nanostructures and how do they compare to fine and coarse particles?

• 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), which 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.

How does the surface area to volume ratio change as particle size decreases?

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

What are the properties and applications of nanoparticles?

• 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.

• 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.

What are the potential risks associated with nanoparticles?

• There are risks with using nanoparticles. it is possible that nanoparticles can be absorbed into our body, however nobody knows the potential long term effects of this.