C3 Flashcards
Alloy
A mixture of two or more elements, at least one of which is a metal
Covalent bond
The bond between two non-metal atoms that share one or more pairs of electrons
Covalent bonding
The attraction between two non-metal atoms that share one or more pairs of electrons
Fullerene
Molecules of carbon that can exist as large cage-like structures, based on hexagonal rings of carbon atoms, carbon molecules shaped like closed tubes/hollow balls
Giant covalent structure
A huge 3D network of covalently bonded atoms
Giant lattice
A huge 3D network of atoms or ions
Intermolecular forces
The attraction between the individual molecules in a covalently bonded substance
Ionic bond
The electrostatic force of attraction between positively and negatively charged ions
Polymer
A substance made from very large molecules made of many repeating units
Ions
Charged particles, as single atoms or broup of atoms
Limitations of dot and cross diagrams
They don’t show:
The structure of the compound
The relative sizes size of the ions/atoms
How ions/atoms are arrangedin space
Ionic lattice
The structure of ionic compounds where there are strong electrostatic forces of attraction between oppositely charged ions, in all directions
Properties of ionic compounds
They have high melting points and boiling points due to the strong bonds between the ions.
When they’re solid, the ions are held in place, so the compounds can’t conduct electricity, but when ionic compounds melts, the ions are free to move and they’ll carry electric charge
Some ionic compounds dissolve in water
Why are covalent bonds strong?
The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong
Advantages of displayed formulas
Good at showing how atoms are connected in large molecules
Disadvantages of displayed formula
Don’t show the 3D structure of the molecule
Don’t show the atoms the electrons in the covalent bond have come from
Advantages of 3D models
Show atoms, covalent bonds and arrangement in space next to each other
Disadvantages of 3D models
Confusing for large molecules where there are lots of atoms to include - don’t show where the electrons in the bond have come from, either
Advantages of dot and cross diagrams
Show the arrangement of electrons in an atom/ion, show which atom the electrons in an ion originally come from
Examples of simple molecular substances
Hydrogen
Chlorine
Oxygen
Nitrogen
Methane
Water
Hydrogen chloride
Properties of Simple Molecular substances
Weak intermolecular forces
Strong covalent bonds between atoms in molecules
Low melting/boiling points
Don’t conduct electricity - aren’t charged
What are the atoms in a polymer joined by?
Strong covalent bonds
Properties of polymers
The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy’s needed to break down. This means most polymers are solid at room temperature.
The intermolecular forces are still weaker than ionic/covalent bonds, so have lower boiling points than ionic/giant molecular compounds
Properties of giant covalent structures
All the atoms are bonded to each other by strong covalent bonds
High melting + boiling points
Don’t contain charged particles so never conduct electricity
Are also macromolecules
Examples of giant covalent structures
Diamond
Graphite
Silicon dioxide
Structure of diamond
Each carbon atom forms four covalent bonds in a very rigid giant covalent structure
Structure of graphite
Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom has one delocalised(free) electron
Structure of silicon dioxide
What sand is made of, each grain of sand is one giant structure of silicon and oxygen
Properties of diamond
Hard - is a giant covalent structure
High melting point - strong covalent bonds take a lot of energy to break
It doesn’t conduct electricity because it has no free electrons or ions
Properties of graphene
Graphene is a sheet of carbon atoms joined together in hexagons which is just one atom thick, making it a two-dimensional substance
Very strong due to network of covalent bonds
Light, is added to composite materials to improve strength
Like graphite, contains delocalised electrons so can conduct electricity through the whole structure
Uses of graphene
Electronics
Added to composite materials
Properties of graphite
Each carbon atom only forms three covalent bonds, creating sheets of carnon atoms arranged in hexagons
Aren’t any covalent bonds between layers so they can move over each other, making graphite soft and slippery, so it’s ideal as a lubricant
High melting points - covalent bonds in layers need lots of energy to break
A thermal/electrical conductor - each carbon atom has one delocalised(free) electron
Properties of fullerenes
Form around another atom/molecule, which is trapped inside - delivers a drug into the body
Have a huge surface area, so can make great individual catalysts and make great lubricants
Can form tiny carbon cylinders called nanotubes
Properties of nanotubes
Conduct electricity and thermal energy
High tensile strength(don’t break when stretched)
Very thin cylinders
Nanotubes are used in electrons to strengthen material without adding much weight
Allotropes
Different structural forms of the same element in the same physical state
Examples of carbon allotropes
Diamond
Graphite
Graphene
Fullerenes
Metallic bonding structure
There are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons in the outer shell of the metal atoms, which are delocalised(free to move around).
Properties of metals
High melting and boiling points, solid at room temperature, strong electrostatic forces between the metal atoms and delicalised sea of electrons
Good electrical and thermal conductors due to delocalised electrons
Malleable - layers of atom in a metal can slide over each other
Properties of alloys compared to pure metals
Alloys are harder than pure metals, as when another element is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, so it’s difficult for the, to slide over each other. Meanwhile, pure metals are too soft. This makes alloys more useful than pure metals
Advantages of particle theory
Good at explaining how the particles in a material behave in a solid, liquid or gas
Disadvantages of the particle theory
In reality, the particles aren’t solid, inelastic spheres, they’re atoms/ions/molecules,
The model doesn’t show the forces between particles - we don’t know how strong they are
Solid particle theory
Strong forces of attraction hold particles in fixed positions to form regular lattice arrangement
Definite shape and volume as particles don’t move from position
The hotter the solid is, the more particles vibrate about their positions
Liquid particle theory
Particles randomly arranged and free to move past each other due to weak forces of attraction, but are close
Definite volume, no definite shape as they flow to take the shape of their container
Particles constantly move with random motion, move faster when hotter to expand slightly
Gas particle theory
Weak forced of attraction mean particles are free to move and are far apart(move in straight lines)
No definite shape/volume
Particles move constantly eith random motion and move faster at higher temperatures, which increases gas pressure/causes gases to expand
What occurs in melting?
At the melting point, particles have enough energy to break free from their positions - the solid becomes a liquid
What happens in boiling/evaporating
The liquid particles have enough energy to break their bonds - the liquid becomes a gas
What happens in condensing?
At the boiling point, so many bonds have formed between the particles since the particles don’t have the energy to overcome the forces of attraction, that the gas becomes a liquid
What hapoens in freezing?
At the melting point, so many bonds have formed between the particles due to not enough energy to overcome this attraction, that the particles are held in place. The liquid becomes a solid
Molecular formula of polythene
(C2H4)n
Buckminster fullerene
One type of fullerene, with medium electrical conductivity due to some non-bonding electrons and some double(C=C) covalent bonds
