Chapter 3: Structure and bonding

Question 1

States of matter

Answer 1

• Particles in solid are closely packed together and vibrate around fixed positions. The particles in a liquid are also close together but can slip and slide over each other in random motion. The particles in a gas have on average lots of space between them and zoom around randomly
• In melting and boiling, energy is transferred from the surroundings to the substance (endothermic). In freezing and condensing, energy is transferred from the substance to the surroundings (exothermic)
• The simple particle model of solids liquids and ages is useful but its limitations because the atoms, molecules, and ions that make up all substances are not solid spheres with no forces between them.

Question 2

Atoms into ions

Answer 2

• Elements lose and gain electrons during reactions, forming compounds
• The elements in group 1 react with elements from group 7. As they react, atoms from group one can each lose one electron to gain the stable electronic structure of a noble gas. The electron is given to the element in group 7 to stabilise it

Question 3

Ionic bonding

Answer 3

• Ionic compounds are held together by strong forces of attraction between their oppositely charged ions. This is called ionic bonding.
• Besides the elements in group 1 and group 7, other elements that can form ionic compounds include those from group 2 (forming 2+ ions) and group 6 (forming 2- ions)

Question 4

Giant ionic structures

Answer 4

• It takes a lot of energy to break the many strong ionic bonds, operating in all directions, that hold a giant ionic lattice together, so ionic compounds have high melting points. They are all solids at room temperature
• Ionic compounds will conduct electricity when molten or dissolved in water. This is because their ions can become mobile and can carry charge through the liquid

Question 5

Covalent bonding

Answer 5

• Covalent bonds are formed when two non-metals share electrons
• Each shared pair of electrons is a covalent bond
• Many substances containing covalent bonds consist of simple molecules, but some have giant covalent strictures

Question 6

Structure of simple molecules

Answer 6

• Substances made up of simple molecules have low melting/boiling points
• The forces between simple molecules are weak. These weak intermolecular forces explain why substances made of simple molecules have low melting points and boiling points
• Simple molecules have no overall charge, so they cannot carry electrical charge. They can’t conduct electricity
• Models are used to help understand bonding, but each model has its limitations in representing reality

Question 7

Giant covalent structures

Answer 7

• Some covalently-bonded substances have giant structures. These substances have very high melting and boiling points
• Graphite contains giant layers of covalently bonded carbon atoms.
• However, there are no covalent bonds between layers. This means they can slide over each other, making graphite soft and slippery. The carbon atoms in diamond have a rigid giant covalent structure, making it very hard substances
• Graphite can conduct electricity and thermal energy because of the delocalised electrons that can move along it layers

Question 8

Fullerenes and graphite

Answer 8

• Carbon also exists as fullerenes, which can form large cage like structure and tubes, based on hexagonal rings of carbon atoms
• The fullerenes are finding uses as a transport method for drugs to specific site in the body, as catalysts, and as the reinforcement for composite materials
• Graphene is a single layer of graphite and so it just one atom thick. Its properties, such as its excellent electrical conductivity, will help create new developments in the electronics industry in the future

Question 9

Bonding in metals

Answer 9

• The atoms in metal s are closely packed together and arranged in regular layers
• You can think of metallic bonding as positively charged metal ions, which are held together by electrons from the outermost shell of each metal atom. These delocalised electrons are free to move throughout the giant metallic lattice.

Question 10

Giant metallic structures

Answer 10

• Metals can be bent and shaped because the layer of atoms (or positively charged ions) in a giant metallic structure can slide over each other
• Alloys are harder than pure metals because the regular layers in a pure metal are distorted by atoms of different sizes in an alloy.
• Delocalised electrons in metals enable electricity and thermal energy to be transferred through a metal easily

Question 11

Nanoparticles

Answer 11

• Nanoscience is the study of small particles that are between 1 and 100 nanometres in size
• Nanoparticles may have properties different from those for the same materials in bulk. This arises because nanoparticles have a high surface area to volume ration, with a high percentage of their atoms exposed at their surface
• Nanoparticles may result in smaller quantities of materials, such as catalysts, being needed for industrial purpose.
• 1 nanometre (1nm) = 1 x 10^-9 metres (= 0.000000001 or a billionth of a metre)

Question 12

Application of nanoparticles

Answer 12

• New developments in nanoparticulate materials are very exciting and could improve many aspects of modern life
• The increased use of nanoparticles needs more resea4rch into possible issues that might arise in terms of health and the environment