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C3: STRUCTURE AND BONDING (States of Matter (The simple particle model of…
C3: STRUCTURE AND BONDING
States of Matter
The 3 states of matter are liquid, solid and gas
The particles in a solid are packed closely together and vibrate around fixed positions
The particles in a solid are close together, but can slip and slide over each other in random motion
The particles in a gas have (on average) lots of space in between them and zoom around randomly
In melting and boiling, energy is transferred from the surrounding to the substance. In freezing and condensing, energy is transferred from the substance to the surroundings
The simple particle model of solids, liquids and gases is useful but has its limitations
This is because the atoms, molecules and ions that make up all substances are not solid spheres with no forces between them
Atoms Into Ions
Elements react together to form compounds by gaining or losing electrons or by sharing electrons
Elements in group 1 and group 7 react together. As they react, atoms of group 1 elements can each lose one electron to gain the stable electronic structure of a noble gas.
This electron can be given to an atom in group 7, which the also achieves the stable electronic structure of a noble gas
Ionic Bonding
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 can form ionic compounds include those from group 2 (forming 2+ ions) and group 6 (forming 2- ions)
Giant Ionic Structures
It take a lot of energy to break the many strong ionic bonds, operating in all directions, that hold a giant ionic lattice together, therefor ionic compounds have high melting points and are solids at room temperature
Ionic compound conduct electricity when molten or dissolved in water. This is because their ions can can then become mobile and can carry charge through the liquid
Covalent Bonding
Covalent bonds are formed when atoms of non-metals share pairs of electrons with each other
Each shared pair of electrons is a covalent bond
Many substances containing covalent bonds consist of simple molecules but some have giant covalent structures
Giant Covalent Structures
Some covalently bonded substances have giant structures. These substances have very high melting points and boiling points
Graphite contains giant layers of covalently bonded carbon atoms. However, there are no covalent bonds between the layers
This means they can slide over each other, making graphite soft and slippery
The carbon atoms in diamonds have a rigid giant covalent structure, making it a very hard substance
Graphite can conduct electricity and thermal energy because of the delocalised electrons that can move along its layers
Fullerenes and Graphenes
As well as diamond and graphite, carbon also exists as fullerenes, which can form large cage like structures and tubes, based on hexagonal rings of carbon atoms
The fullerenes are finding uses as a transport mechanism for drugs to specific sites in the body, as catalysts, and as reinforcement for composite materials
Graphene is a single layer of graphite and so is just one atom thick. Its properties, such as excellent electrical conductivity, will help create new developments in the electronics industry in the future
Bonding in Metals
The atoms in metals 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
Giant Metallic Structures
Metals can be bent and shaped because the layers 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 of alloy
Nanoparticles
1 nanometer = one billionth of a metre
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 happens because nanoparticles have a high surface area to volume ratio, with a high percentage of their atoms exposed at their surface
Nanoparticles may result in smaller quantities of materials, suck as catalysts, being needed for industrial processes
Applications of Nanoparticles
New developments in nanoparticulate materials are very exciting and could improve many aspects of modern life
Titanium oxide nanoparticles are also used in modern sunscreens
The cosmetics industry uses nanoparticles in face creams, to make them absorb deeper into the skin
The increased use of nanoparticles needs more research into possible issues that might arise in terms of health and the environment