Chemistry transition work!!! Flashcards
test on second lesson
What charge do electrons have?
-1
What charge will an ion of lithium take?
1+ (needs to loose on electron on outer shell)
What charge will an ion of beryllium take?
2+ (needs to loose the 2 electrons in outer shell)
What charge will an ion of barium take
2+(in group 2 so needs to loose both electrons )
What will an ion of fluorine take?
1- (7 electrons on outer shell so needs to gain one)
If something gains electrons what charge does it need to take?
a Negative charge
If something has lost electrons what charge will it have?
A positive charge
What charge will an ion of oxygen take?
2- (because is has 6 electrons on its outer shell so needs to gain two)
What charge will an ion of selenium take?
2- (group 6 so it has 6 electrons in it outer shell and needs to gain two)
Why do atoms transfer electrons in ionic bonding
So that they can have full outer shells
Explain in terms of electrons what occurs when lithiums bonds with fluorine
One electron transferred from lithium to fluorine
Explain in terms of electrons what occurs when magnesium bonds with oxygen
Two electrons transferred from magnesium to oxygen
Explain in terms of electrons what occurs when magnesium bonds with chlorine
One electron is transferred from magnesium to two different chlorine atoms
Explain in terms of electrons what occurs when sodium bonds with oxygen?
Two electrons from two different sodium atoms are transferred to an oxygen atom
Why do sodium ions and chlorine ions form an ionic bond?
There is an electrostatic force of attraction between oppositely charged ions
Why don’t sulphide ions and oxide ions form ionic bonds with each other?
Both have negative charges so would repel
What is the name for a substance made of billions of oppositely charged ions joined together?
Giant ionic lattice
State the melting points of ionic substances
High
Explain why ionic substances have high melting points.
Strong forces of attraction between oppositely charged ions require high amounts of energy to overcome
Will NaCI(s) conduct electricity?
No
Will NaCI (aq) conduct electricity?
Yes (aq stands for aqueous which means it is dissolved in water)
Will NaCI (I) conduct electricity?
Yes
What does molten mean
Melted
Explain why ionic compounds do not conduct electricity when solid
Because the ions are not free to move
Explain why ionic compounds conduct electricity in solution
Because the ions are free to move and carry charge
Explain why ionic compounds conduct electricity when molten
Because the ions are free to move and carry charge
What does soluble mean?
Dissolves in water
What does insoluble mean?
Does not dissolve in water
Magnesium carbonate is insoluble. What do you need to do before it will conduct electricity?
Melt it
Sodium fluoride is soluble.
Explain what the easiest way for it to conduct electricity
Dissolve it in water because this does not require high temperatures
Explain why chlorine and fluorine form covalent bonds
They are both non-metals
Complete the sentence: In covalent bonds, electrons
are
Shared
In ionic bonds, electrons
are
Transferred
What is the name given to the structure of diamond, graphite and silicon dioxide?
Giant covalent
Draw a dot and cross diagram for methane CH4
[draw it]
How many bonds does each carbon have in diamond?
4
Explain why diamond has a high melting point
It has a giant covalent structure so contains strong covalent bonds between the atoms. This requires a lot of energy to break
Explain why most giant covalent substances do not conduct electricity
There are no electrons/ions/charged particles that are free to move
Explain why graphite conducts electricity
Graphite has delocalised electrons between the layers that can move through the structure and carry charge
Explain why graphite can act as a lubricant
Weak forces between layers which are free to slide over each other
What is graphene?
One layer of graphite
What is a fullerene?
Substance made of carbon atoms arranged in a cage
What type of substance are methane and water?
Simple molecular (or simple molecules)
What is a molecule?
A group of atoms chemically bonded together
Describe the structure of simple covalent molecules
Strong covalent bonds between atoms, weak forces holding the molecules together
What are intermolecular forces?
Weak forces between molecules which hold them together
Explain why methane has a low melting point
It is a simple molecular substance with weak forces between the molecules (which are easy to break)
Describe the main features of metals in terms of their structure
Positive metal ions arranged in layers surrounded by delocalised electrons
Explain why metals can conduct electricity
Delocalised electrons are free to carry charge
What is crude oil?
A mixture of hydrocarbons
What is crude oil formed from?
The remains of ancient biomass (mostly plankton)
that was buried in mud
What is a hydrocarbon?
A compound made of atoms of carbon and hydrogen only
What is a general formula?
A mathematical formula which allows you to work out the chemical formula of a substance
What is an alkane?
A hydrocarbon with only single bonds
What is meant by the term saturated?
A compound that contains single bonds only
Name the first four alkanes
Methane, ethane, propane, butane
What is the general formula for alkanes?
CnH2n+2
How does boiling point change with the length of an alkane?
The longer the alkane, the higher its boiling point
How does viscosity change with the length of an alkane?
The longer the alkane, the more viscous (the thicker) it is
How does flammability change with the length of an alkane?
The longer the alkane, the less flammable it is
What is fractional distillation?
A process used to separate mixtures of substances with different boiling points
State the meaning of the term fraction
A group of hydrocarbons with similar boiling points
What are the steps involved in fractional distillation?
1) Crude oil is heated and vaporised, different molecules rise up the fractionating column and cool down.
2) There is a temperature gradient in the column so the column is hotter at the bottom and colder at the top.
3) The different fractions condense at different points on the column due to their different boiling points.
4) Long chain hydrocarbons condense at the bottom and shorter chain hydrocarbons condense further up.
Why is fractional distillation important?
Because the different fractions have different Uses
What is a fuel?
A substance which when reacted with oxygen releases energy
Name five fuels we obtain from crude oil
Petrol, diesel, kerosene, heavy fuel oil and liquefied petroleum gases
What is combustion?
The reaction of a fuel with oxygen
What are the products of complete
combustion?
Carbon dioxide and water
When does incomplete combustion occur
When there is not enough oxygen present
What is cracking?
The process of breaking down a long hydrocarbon into smaller hydrocarbons
What are the products of cracking?
Short alkanes and alkenes
Why is cracking important?
Because smaller hydrocarbons are more in demand
What are the two types of cracking?
Catalytic and thermal cracking
What catalyst is used in catalytic
cracking?
Zeolite
What is the pressure for catalytic
cracking?
Moderate pressure
What are the conditions for thermal cracking?
High temperature and high pressure
What bonds are broken in cracking?
C-C bonds
What is the major product formed
through thermal cracking?
Alkenes
What are the major products formed through catalytic cracking?
Aromatic hydrocarbons and motor fuels
How do you test for an alkene?
React it with bromine water
What is the colour change when an alkene reacts with bromine water?
Turns from orange to colourless
What type of polymerization do alkenes undergo?
Addition polymerisation
Why is it beneficial for some polymers to be biodegradable?
To prevent the build up of waste in landfills
Explain how oxides of nitrogen are formed in car engines
Nitrogen from the air reacts with oxygen at high temperatures
State why it is desirable to decrease emissions of oxides of nitrogen from vehicles
To reduce the formation of acid rain and to decrease respiratory problems
Explain why sulfur compounds should be removed from fractions before they are used for central heating fuel
On combustion, sulfur compounds produce SO2 which causes acid rain
