C2 - Bonding, Structure and The Properties of Matter

What are the types of atom bonds?

• ionic

• covalent

• metallic

What are the characteristics of ionic bond?

• metals and non-metals

• electron transfer occurs, forming ions

• oppositely charged ions attract through electrostatic attraction

What are the characteristics of covalent bond?

• non-metal atoms

• share a pair of electrons

What are the characteristics of metallic bond?

• occurs in metals and metal alloys

• delocalised electrons hold 2 metal ions together

What is the negative ion name and how have them become like this?

called anions, have gained electron(s)

What is the positive ion name and how have them become like this?

called cations, have lost electron(s)

What is the outer shell and outer electrons called?

valance shell and valance electrons

How to describe an ionic bond - Method

1. State how many electrons the metal has lost and its new charge.

2. State how many electrons the non-metal has gained and its new charge.

3. State that oppositely charged ions are held together by strong forces of electrostatic attraction in ionic bonds.

Electrostatic forces are…

…strong, acting in all directions and so they form the basis of an ionic bond.

What is the arrangement of lattices formed by ionic compounds?

A regular arrangement of alternating positive and negative ions which the ions are tightly packed together. Strong electrostatic forces hold the lattice together.

Why do ionic lattice compounds have high melting andf boiling points?

As a result of so many electrostatic forces existing in this lattice structure.

What is a molecule?

2 or more atoms covalently bonded together.

What are the strengths of the bonds in covalent bonding? (paragraph)

They have very strong covalent bonds to hold atoms together in a molecule, but the intermolecular forces between individual molecules is very weak. This is why simple covalent structures can be easily seperated without breaking bonds but giant covalent lattices involve breaking bonds when separating as molecules are bonded together bu covalent bonds.

Different names of electrons - Covalent Bonds

• electrons on the valance shell wjich atre not involved in the covalent bond are non-bonding electrons

• electrons which are shared are bonding electrons

Examples of simple covalent molecules:

• O₂

• H₂

• Cl₂

• N₂

• HCl

• H₂O

• NH₃

• CH₄

N₂ Bond Diagram - Dot and Cross

Examples of large Covalent molecules / structures

• polymers

• giant covalent structures

Examples of polymers with Covalent Bonds

• polythene - used in plastic bags

• polyvinyl chloride (PVC) - has many industrial applications, mostly water pipes

Advantage and Disadvantage of Dot and Cross Diagram

• Useful for illustrating the transfer of electrons

• fails to illustrate 3D arrangement of atoms

Advantage and Disadvantage of Ball and Stick Diagram

• useful for visualizing shape of the atom

• shows large gaps in between atoms, which in reality is not the case as gaps are miniscule

Advantage and Disadvantage of 2D Representation of Molecule Diagram

• indicate which atoms are in molecule and how they’re connected in a simple way

• fail to illustrate relative size of atoms and bonds

Metals consist of…

…giant structures of atoms arranged in a regular pattern.

How is a metal lattice formed?

Each metal atom loses its valance electrons, which become delocalised. This means there are negative electrons and positive ions in the lattice. The negative electrons are attracted to the positive ions and vice versa, so they’re all bonded to form a lattice. Individual metal atoms are held together by strong metallic bonds forming a lattice structure.

Why can metals carry charge?

Because they have delocalised electrons which are free to move in the spaces between metal atoms’ nuclei.

Description of movement in the 3 states.

• Solid: vibrate around a fixed position

• Liquid: move around each other

• Gas: move quickly in all directions

Description of arrangement in the 3 states.

• Solid: regular arrangement

• Liquid: random arrangement

• Gas: random arrangement

Description of particle distance in the 3 states.

• Solid: very close together, tightly packed

• Liquid: fairly close

• Gas: far apart

The amount of energy needed to change the state from solid→liquid or liquid→gas depends on…

…the strength of the forces of attraction between the particles. (eg. bonds or intermolecular forces)

Changing state is a _______ change.

physical, as the particles and chemical properties of substance remain the same.

The change of state due to changes in temperature or pressure are called…

…interconversions of state.

What is the process of turning a substance from solid→gas called?

sublimination

Why are physical changes easy/hard to reverse?

easy, because no new substance is formed during interconversion of state.

Factors which affect evaporation…

• larger surface area

• higher temperature of liquid

Where does evaporation occur?

Only occurs at the surface of liquids where high energy particles can escape from the liquids surface at low temperatures, below the boiling point of the liquids

What happens during condensation?

When a gas is cooled at the particles collide, they do not have enough energy to bounce away so they make bonds and form a liquid.

Ionic Compounds Properties

• conducts electricity, but not in the solid state

• high melting/boiling points

Small Molecules (Covalent) Properties

• low melting and boiling points

• cannot conduct electricity

Giant Covalent Molecules Properties

• high melting and boiling points

• cannot conduct electricity (exception is graphite)

Examples of Giant Covalent Structures

• Diamond

• Graphite

• Graphene

• Fullerenes

• Polymers

Diamond Structure

• each carbon atom is bonded to 4 other carbon atoms by strong covalent bonds

• the carbon atoms form a regular tetrahedral network structure

• no free electrons (so doesn’t conduct electricity)

Diamond Properties and Uses

• Useful for cutting tools due to its hard strucutre

Graphite Structure

• each carbon atom is bonded to 3 other carbon atoms

• carbon atoms form layers of hexagonal rings

• no covalent bonds between layers, only intermolecular forces

• one delocalised electron from each atom

Graphene structure

A single layer of graphite.

Fullerenes Structure

• hexagonal rings of carbon atoms

• joined by covalent bonds

• some include rings with 5 or 7 carbon atoms

Graphite Uses

• conducts electricity, so useful for electrodes for batteries and electrolysis

• weak forces between layers means they can slide, so useful for pencils and lubricant

Graphene Properties and Uses

• high melting point

• very strong

• delocalised electrons free to move across its surface, so conducts electricity

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  These properties make graphene useful for making composites.

Fullerenes Definition and Examples

These are molecules of carbon atoms with hollow shapes. Buckminsterfullerene and Nanotubes.

Composites Definition

Material made from 2 or more different materials with contrasting properties.

Buckminsterfullerene Description

• 1st fullerene to be discovered

• made up of 60 carbon atoms (C) joined together by strong covalent bonds

• spherical

• weak intermolecular forces, so slippery and low melting point

Nanotube Structure , Properties and Uses

• layer of graphene rolled into a cylinder

• length is much longer than width, so have a high length:diametre ratio

• high tensile strength - strong in tension and can resist being stretched

• strong because of delocalised electrons

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  These properties make them useful in nanotechnology, electronics and specialised materials.

Tensile Strength Definition

The tension a material can withstand without breaking.

What is common between all polymers?

They’re all made up of smaller molecules called monomers.

Polymers - Boiling/Melting Ppoint explanation

Although they have strong covalent bonds, these are not what we need to break when changing state, but we need to break the intermolecular forces between the molecules. These require less energy to break, but because the polymers are so long with such a high surface area, there are many of these intermolecular forces, so it still requires quite a lot of energy to change their state.

Therefore, although they have lower melting points that giant covalent and giant ionic structures, they have higher melting points than simple molecular substances.

Why are metals conductors?

• Electrical Conductors - delocalised electrons carry charge through the metal

• Thermal Conductors - delocalised electrons transfer energy

• High Melting/Boiling Points - metallic bonding is very strong so large amounts of energy are needed to overcome these bonds.

Alloy Definition

A mixture of at lease 2 or more elements, at least 1 of which is a metal.

Why can alloys be useful?

Many pure metals are too soft for many uses, so they’re made harder by adding another element, forming an alloy.

Why is an alloy harder than a pure metal?

• Pure metals- giant metallic structure in solid state, and are arranged in layers which slide over each other when force is applied. In a pure metal, it requires little force for layers to slide.

• Alloys - the atoms are of different sizes, so the smaller or bigger atoms distort the layers of atoms in the pure metal, meaning a greater force is required for the layers to sli9de over each other. This means it’s harder and stronger.

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  The greater the force needed, the harder and stronger the metal.

Nanoscience Definition

The study of structures that are between 1 and 100 nanometers in size.

Diameter of Atoms and Small Molecules

0.1nm

Diameter of Nanoparticles

1 - 100nm

Diameter of Fine Particles

100 - 2,500nm

Diameter of Coarse Particles

2,500 - 10,000 nm

Thickness of Paper

100,000 nm

Nanoparticles have very _____ surface area to volume ratios.

large

For a solid, the ________ its particles, the greater the surface area to volume ratio.

smaller

Surface Area to Volume ratio Equation

surface area (nm²) / volume (nm³)

A substance that consists of nanoparticles is described as ____________.

nanoparticulate

Uses of Nanoparticles

• medical treatments

• cosmetics, deodorants and sunscreens

• electronics

• catalysts

How are nanoparticles used in suscreens?

Sunscreens block harmful ultraviolet light from the sun reaching the skin. Zinc oxide blocks ultraviolet, so it is used in sunscreens, but it is used asd nanoparticles because it is white in bulk and invisible on skin as nanoparticles.

How are nanoparticles used as catalysts?

As they have a high surface area to volume ratio due to their small size, they are more efficient catalysts than larger catalyst molecules.

Self-cleaning window panes have nanoparticle coatings, acting as catalysts in the breakdown of dirth through the presence of sunlight.

Risks of Nanoparticles

• There are concerns about them being breathed in and entering cells.

• They could then catalyse harmful reactions in the body.

• Toxic substances could bind to them because of their large SA:V, harming health.

• Modern nanoparticle materials have only become common recently, so it is difficult to determine their risks.