Bonding & Structure Flashcards
What is ionic bonding?
Ionic bonding is the electrostatic attraction between positive and negative
ions.
It is a relatively strong attraction.
How are ionic compounds held together?
● They are held together in a giant lattice.
● It’s a regular structure that extends in all directions in a
substance.
● Electrostatic attraction between positive and negative ions holds
the structure together.
State properties of ionic substances
● High melting and boiling point (strong electrostatic forces between
oppositely charged ions)
● Do not conduct electricity when solid (ions in fixed positions).
● Conduct when molten or dissolved in water - ions are free to move.
Give 5 examples of positive ions and 5 examples
of negative ions (give names of negative anions).
What is important when working out a formula of an ionic compound?
E.g. Positive: Na+, Mg2+, Al3+, Ca2+, Rb+
, E.g. Negative: Cl−, Br−, SO4 2−, NO3
−, OH− (chloride, bromide, sulfate, nitrate,
hydroxide). Ionic compounds are electrically neutral, i.e. positive and negative charges
balance each other.
How are ionic compounds formed? Explain in
terms of MgO case.
Reaction of a metal with a non-metal.
Electron transfer occurs - metal gives away its outer shell electrons to
non-metal.
Mg is in Group II, so has 2 available outer shell electrons.
O is in Group VI, so can accept 2 electrons to get a full outer shell
configuration.
Mg becomes Mg2+ and O becomes O2− (oxide).
What is a covalent bond?
Covalent bond is a shared pair of electrons between two atoms.
Describe the structure and properties of simple
molecular covalent substances
- Do not conduct electricity (no ions)
- Small molecules
- Weak intermolecular forces, therefore:
- Low melting and boiling points
How do intermolecular forces change as the
mass/size of the molecule increases?
They increase. That causes melting/boiling points to increase as well (more
energy needed to overcome these forces).
What are polymers? What are thermosoftening polymers?
Polymers are very large molecules (>100s, 1000s of atoms) with atoms linked by
covalent bonds.
Thermosoftening polymers - special type of polymers; they melt/soften when
heated. There are no bonds between polymer chains. Weak intermolecular forces
ensure that the structure is solid at room temperature. These forces are overcome
with heating - polymer melts.
What are giant covalent substances? Give examples
- Solids, atoms covalently bonded together in a giant lattice.
- High melting/boiling points – strong covalent bonds.
- Mostly don’t conduct electricity (no delocalised e−)
- Diamond, graphite, silicon dioxide.
Describe and explain the properties of allotropes of carbon.
Diamond
– four, strong covalent bonds for each carbon atom
– very hard (Strong bonds)
– very high melting point (strong bonds)
– does not conduct (no delocalised electrons)
Graphite
– three covalent bonds for each carbon atom
– layers of hexagonal rings
– high melting point
– layers free to slide as weak intermolecular forces
between layers; soft, can be used as a lubricant
– conduct thermal and electricity due to one delocalised
electron per each carbon atom
Fullerenes
– hollow shaped molecules
– based on hexagonal rings but may have
5/7-carbon rings
– C60 has spherical shape, simple
molecular structure (Buckminsterfullerene)
Nanotubes
– cylindrical fullerene with high length to
diameter ratio
- High tensile strength (strong bonds)
- Conductivity (deloc. electrons)
Graphene - a single layer of graphite.
What is metallic bonding?
Forces of attraction between delocalised electrons and nuclei of metal
ions.
Describe properties of metals
- High melting/boiling points (strong forces of attraction)
- Good conductors of heat and electricity (delocalised electrons)
- Malleable, soft (layers of atoms can slide over each other whilst maintaining
the attraction forces)
What are alloys? Why are they harder than pure
metals?
Alloys:
- mixtures of metal with other elements, usually metals
- different sizes of atoms distorts the layers, so they can’t slide over each other,
therefore alloys are harder than pure metals
What are the limitations of the simple model?
There are no forces between spheres and atoms, molecules and ions are solid
spheres – this is not true
What does the amount of energy needed to
change state from solid to liquid or liquid to gas
depend on?
The strength of the forces between the particles of the substance. The
nature of the particles involved depends on the type of bonding and the
structure of the substance. The stronger the forces between the particles
the higher the melting point and boiling point of the substance
A pure substance will melt or boil at…?
A fixed temperature.
A mixture will melt over a range of temperatures.
What are the three states of matter?
Solid, liquid and gas
What is nanoscience?
Science that studies particles that are 1 - 100nm in size
State the uses of nanoparticles
Medicine (drug delivery systems)
- Electronics
- Deodorants
- Sun creams (better skin coverage and more effective protection
against cell damage)
What are fine and coarse particles?
- Fine particles (soot), 100-2500 nm diameter
- Coarse particles (dust), 2500-10^5 nm diameter
Why do nanoparticles have properties different from
those for the same materials in bulk?
High surface area to volume ratio
What is the law of conservation of mass?
The law of conservation of mass states that no atoms are lost or made
during a chemical reaction so the mass of the products equals the mass
of the reactants.
Define relative atomic mass and relative formula
mass.
RAM - average mass of atoms in an element taking into account masses
and abundance of its isotopes, relative to 12C.
RFM - sum of RAM’s of all atoms in the formula
The following reaction occurs in a test tube under a Bunsen
Burner:
4 MgO(s) + CH4(g) → 4 Mg(s) + 2 H2O(g) + CO2(g)
The carbon dioxide and water escape from the test tube.
Use the equation to explain why.
They are both gases
What is Avogadro’s constant?
The number of atoms, molecules or ions in a mole of a given substance.
The value of the constant is 6.02 x 10^23
.
What is the formula that links mass, molecular mass and moles
together
Mass = Mr x Moles
What is the mass of 20 moles of calcium carbonate, CaCO3
Mass = Mr x Moles
Mr = 100
100 x 20 = 2000 g
Calculate the amount of carbon dioxide
in moles in 0.32 g of carbon dioxide.
Relative atomic masses (Ar): carbon =
12, oxygen = 16
Moles = Mass / Mr
0.32 / 44 = 0.007
Nitrogen and hydrogen form ammonia shown by the following
equation:
N2(g) + 3 H2(g) ⇌ 2 NH3(g)
Calculate the mass of nitrogen needed to form 6.8 tonnes of
ammonia.
Relative atomic masses (A
r): H = 1; N = 14
Step 1 - Work out the number of number of moles of ammonia (Mr of ammonia = 17)
6800000 / 17 = 400000 moles of ammonia
Step 2 - Use the balanced equation and number of moles of ammonia to work out the number of moles of
nitrogen
The ratio of nitrogen to ammonia is 1:2
Therefore the number of moles of nitrogen is 400000/2 = 200000
Step 3 - Work out the mass of nitrogen (Mr of N2 is 28)
200000 x 28 = 5600000 g = 5.6 tonnes.
State what we mean by a limiting reactant in a chemical reaction
In a chemical reaction involving two reactants, it is common to use an
excess of one of the reactants to ensure that all of the other reactant is
used. The reactant that is completely used up is called the limiting
reactant because it limits the amount of products.
Hydrogen peroxide decomposes in
water to form water and oxygen. How
many grams of oxygen gas will be
given off from 40.8 g of hydrogen
peroxide?
Step 1: Write the balanced equation 2 H2O2(l) → 2 H2O + O2(g) Step 2: Number of moles in 40.8 g : 40.8/34 = 1.2 moles
Ratio in the balanced equation of H2O2 : O2 = 2:1
Step 3 :Therefore number of moles of O2 = 0.6 moles
Step 4: Mass of oxygen = 0.6 x 32 (Mr of O2) = 19.2
Mr of H2O2 = 34
Write down the two formulae that link concentration, mole/mass
and volume together.
Concentration (g per dm3) = Mass (g)/Volume (dm3)
Concentration (mol per dm3) = nr of moles/volume (dm3)
What is the molar volume of a gas at room
temperature and pressure?
1 mole of a gas at room temperature and pressure occupies 24 dm^3
What is titration?
A technique for finding the concentration of a solution by reacting a known
volume of this solution with a solution of known concentration.
How do you conduct a titration?
Rinse the pipette with a solution of unknown concentration. Use the pipette to
measure out the known volume of this solution.
Add an indicator (a substance that changes colour at the end of titration)
Rinse the burette with a solution of known concentration. Discard the liquid.
Use a burette to gradually add the solution of a known concentration.
When indicator changes colour (at the end point), the volume added is
recorded
It is important to get concordant volume results - they have to lie close to each
other
Suitable calculations are performed to find the concentration.
Why is it not always possible to obtain the theoretical amount of product in
a chemical reaction?
● The reaction may not go to completion because it is reversible.
● Some of the product may be lost when it is separated from the
reaction mixture.
● Some of the reactants may react in ways different to the expected
reaction (side reactions may occur).
https://bit.ly/pmt-edu
How is the percentage yield of a product in a chemical
reaction?
% Yield = Actual mass of a product over
Maximum theoretical mass of product x 100
What is atom economy?
A measure of the amount of starting materials that end up as useful products.
It is a ratio of the relative formula mass of desired product to the sum of relative
formula masses of reactants.
