C2: Bonding, structure and properties of matter Flashcards
What is covalent bonding?
Atoms share pairs of electrons to become more stable.
What type of elements bond covalently?
Non-metals.
Are covalent bonds strong or weak? Why?
Strong; the positive nuclei are attracted to the shared pairs of electrons (electrostatic forces).
Give 7 examples of simple covalent substances (name and symbol).
Hydrogen - H2 Methane - CH4 Nitrogen - N2 Hydrogen chloride - HCl Oxygen - O2 Chlorine - Cl2 Water - H2 O
Describe the bond(s) in oxygen. What is this type of compound called?
Double covalent bond.
Diatomic, and simple molecular/covalent structure.
Describe the bond(s) in Hydrogen. What is this type of compound called?
Single covalent bond.
Diatomic, and simple molecular/covalent structure.
What are the bonds between atoms called?
Intramolecular.
What are the bonds between molecules called?
Intermolecular.
List and explain the properties of simple covalent substances.
~Low melting and boiling points: gases/liquids at room temperature - molecules easily parted (weak intermolecular forces).
~The more there is of the substance, the stronger - cumulative intermolecular forces increase; more energy needed to break bonds.
~Never conduct electricity - no charge or free ions/electrons.
What is a polymer?
A long chain of repeating units: monomers.
Lots of monomers are linked (bonded covalently and strongly) to form a long molecule with repeating sections- the polymer.
How can a polymer be realistically drawn? Draw poly(ethene).
( H H ) Shown in the brackets is the monomer.
( | | ) The lines through the brackets show where it
-(–C–C–)- joins to the next unit.
( | | )
( H H )n
How are molecular formulae of polymers written?
Formula of monomer in brackets.
“n” or a given number outside the right bracket, in subscript.
E.g. (C2 H4)n
How do the forces in polymers compare to those in other types of substance?
Larger than simple covalent molecules. More cumulative intramolecular force so more energy needed to break them. Usually solids at room temperature.
These forces are still weaker than ionic or giant covalent compounds so they generally have lower melting/boiling points.
What is another term for giant covalent structures?
How are these formed?
Macromolecules.
All the atoms are linked by strong covalent bonds.
What are the properties of macromolecules and why?
Very high melting/boiling points - lots of energy needed to break the intramolecular forces.
Don’t conduct electricity, except graphite - no ions/electrons able to more and no charge.
Give the 3 main macromolecules.
Diamond, graphite and silicon dioxide/silica/sand.
What is the term used to describe each of at least 2 different physical forms in which an element can exist?
Give an example.
An allotrope.
E.g. allotropes of carbon are diamond, graphite and graphene.
Describe the structure and properties of diamond.
Diamond is a rigid, giant covalent lattice made of carbon. Each carbon atoms forms 4 covalent bonds, making it a rigid tetrahedral structure whose strong covalent bonds require large amounts of energy to overcome, giving it a high melting/boiling point.
Diamond does not conduct electricity because it has no mobile electrons or ions to carry current.
Describe the structure and properties of graphite.
Each carbon atom forms 3 covalent bonds, creating sheets of hexagons. 3 out of 4 of graphite’s outer electrons are bonded, leaving one delocalised electron per atom. It can conduct electricity and heat because of this.
No covalent bonds between layers; they are held together weakly and can slide over each other. It is therefore soft and slippery.
High melting/boiling point - strong covalent bonds need lots of energy to be broken.
Describe the structure and properties of graphene.
One layer of hexagonally arranged carbon atoms. Only one atom thick; it is a 2D compound.
Covalent bonds make it strong, though it is light, so can be added to other materials to add strength but not much weight.
3 out of 4 outer electrons are bonded, leaving one delocalised electron per atom. It can conduct electricity and heat because of this.
What are fullerenes?
Molecules of carbon shaped like closed tubes or hollow balls. Can be made of carbon heptagons or pentagons- but usually hexagons.
What are the 2 types of fullerene?
Nanotubes - tiny cylinders.
Bucky balls - hollow balls.
Describe the structure and uses of fullerenes.
They can cage molecules so could deliver a drug into a specific location in the body.
Large surface area so catalyst molecules could be attached to them for industrial purposes.
They can make good lubricants.
Nanotubes have a high ratio of length to diameter so they do not break when stretched. They can also conduct heat and electricity.
What is the name for technology that uses very small particles, such as fullerenes? Why are they useful?
Nanotechnology.
They can add strength but minimal weight, amongst other uses.
Describe the structure of metals.
Positive metal nuclei (ions), arranged in layers, are surrounded by a sea of delocalised electrons; this is a metallic lattice. The strong electrostatic forces of attraction between the cations and electrons makes metals strong.
Give and explain 3 properties of metals.
Usually solids at room temperature- high melting/boiling points: strong electrostatic forces of attraction between the cations and electrons need lots of energy to be broken.
Conduct electricity and heat: delocalised electrons are free to move and carry charge.
Malleable (can be deformed into shapes or into thin sheets) and ductile (can be made into wires): layers of nuclei can slide over each other while electrons hold the structure together.
What is an alloy?
A mixture of a metal and another metal/different element.
Why do alloys have a useful property and what is it?
They are harder and therefore stronger.
Different elements have atoms of different sizes so introducing a different particle to a metallic lattice distorts the layers of metal nuclei. This makes it harder for them to slide over each other.
What is an ion?
A charged particle- an atom which has either lost or gained electrons to obtain a full outer shell/stable electronic structure, like a noble gas.
What reacts in ionic bonding?
A metal and non-metal.
What charge do metal ions have? What can these be called?
Positive - cations.
What charge do non-metal ions have? What can these be called?
Negative - anions.
Describe the process of ionic bonding.
A metal and non-metal react. The metal loses electrons to form a positive ion. The non-metal gains these electrons to become a negative ion. These have opposite charges so are attracted to each other by strong electrostatic forces. This is an ionic bond. Many of these ions are closely packed to form a giant structure: an ionic lattice.
Which groups in the periodic table are most likely to form ions?
1 and 2 (metals).
6 and 7 (non-metals).
What are the pros and cons of dot and cross diagrams?
Pro- clearly shows how compounds are formed.
Cons- no structure of the compound.
-doesn’t show the size of ions.
-doesn’t show the arrangement of the compound.
Give and explain 4 properties of ionic compounds.
High melting/boiling points - need lots of energy to overcome strong electrostatic forces between ions.
Don’t conduct as solids - ions are closely packed so cannot move and carry the charge.
Conduct as liquids - ions can move around and are charged so will carry electrical current.
Dissolve easily in water and will conduct - ions separate and can move. They are charged so will carry electrical current.
What is the term to describe when there is a 1:1 ratio of ions in a lattice? What can be drawn from this?
A regular ionic lattice. The ions must have equal but opposite charges.
What is meant by the empirical formula of an ionic compound?
An equation where the ions are balanced so that the overall charge is neutral.
What is the term for an equation where the ions are balanced so that the overall charge is neutral?
The empirical formula.
What 3 factors affect the physical state of a substance?
- The strength of the material.
- Temperature.
- Pressure.
How can the state of a substance be shown in an equation? What are these symbols called?
Solid = (s)* Liquid = (l) Gas = (g) Aqueous = (aq) *These would be in subscript. These are state symbols.
Solid -> liquid =
Melting.
Liquid -> gas =
Boiling/evaporating.
Gas -> liquid =
Condensing.
Liquid -> solid =
Freezing.
Gas -> solid =
Deposition.
Solid -> gas =
Sublimation.
write the word equation and balanced symbol equation for the reaction between lithium oxide and sulfuric acid.
lithium oxide + sulfuric acid —> lithium sulfate + water
