Chemistry Flashcards
What are compounds
Substances in which atoms of two or more elements are chemically combined
What does chemical bonding involve
Either transferring or sharing electrons in the highest occupied energy levels (shells) of atoms in order to achieve the electronic structure of a noble gas
When are ions formed
When atoms form chemical bonds by transferring electrons
What are positively charged ions
Atoms that lost electrons
What are negatively charged ions
Atoms that gained electrons
What are alkali metals
The elements in Group 1
What do alkali metals all react with non metal elements to form
Ionic compounds in which the metal ion has single positive charge
What are halogens
The elements in Group 7
What do halogens all react with alkali metals to form
Ionic compounds in which the halide ions have a single negative charge
What is an ionic compound
A giant structure of ions
What are ionic compounds held together by
Strong electrostatic forces of attraction between oppositely charged ions that act in all directions of the lattice
When are covalent bonds formed
When atoms share pairs of electrons. These bonds between atoms are strong
What are examples of simple molecules that some covalently bonded substances consist of
H2, Cl2, O2, HCl, H2O, NH3, CH4
What are examples of macromolecules
Diamond and silicon dioxide
What are macromolecules
Substances that have giant covalent structures
What do metals consist of
Giant structures of atoms arranged in a regular pattern
What can the electrons in the highest occupied energy levels do as a result of being delocalised
Be free to move through the whole structure. This corresponds to a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions
What substances have relatively low melting and boiling points
Substances that consist of simple molecules
How strong are the intermolecular forces of simple molecules
Weak. It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils
Why don’t substances that consist of simple molecules conduct electricity
Because the molecules do not have an overall electric charge
What are giant ionic lattices
Ionic compounds that have regular structures
Why do giant ionic lattices have high melting and boiling points
Because of the large amounts of energy needed to break the many strong bonds
What do ionic compounds do when melted or dissolved in water
Conduct electricity because the ions are free to move and carry the current
How are macromolecules formed
By atoms that share electrons
Why is diamond very hard
Because each carbon atom in diamond forms four covalent bonds with other carbon atoms in a giant covalent
Why is graphite soft and slippery
Because in graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between them
Why is graphite able to conduct heat and electricity
Because in graphite one electron from each carbon atom is delocalised. It is these delocalised that allow graphite to conduct heat and electricity
Why is graphite similar to metals
It has delocalised electrons
What is the structure of fullerenes based on
Hexagonal rings of carbon atoms
What can fullerenes be used for
Drug delivery into the body
In lubricants
As catalysts
In nanotubes for reinforcing materials e.g. in tennis rackets
Why do metals conduct heat and electricity
Because of the delocalised electrons in their structures
Why can metals be bent and shaped
The layers of atoms in metals are able to slide over each other
What are alloys made of
2 or more metals
Why are alloys harder than pure metals
The different sized atoms of the metals distort the layers in the structure, making it harder for them to slide over each other
What can shape memory alloys do
Return to their original shape after bring deformed, e.g. Nitinol used in dental braces
What do the properties of polymers depend on
What they’re made of and the conditions under which they are made, e.g. low density and high density poly(ethene) are produced using different catalysts and reaction condition
What do thermosetting polymers consist of
Individual, tangled polymer chains with cross-links between them so that they do not melt when heated
What does nanoscience refer to
Structures that are 1-100nm in size, of the order of a few hundred atoms
What do nanoparticles show
Different properties to the same materials in bulk
What can nanoparticles lead to the development of
New computers New catalysts New coatings Highly selective sensors Stronger and lighter construction materials New cosmetics e.g. sun tan creams
Why are nanoparticles able to lead to the development of various items
Nanoparticles have a high surface area to volume ratio
What are isotopes
Atoms of the same element that have a different number of neutrons
What is a mole
The relative formula mass of a substance in grams
How can elements and compounds be detected and identified
Using instrumental methods. They are accurate, sensitive, rapid and are particularly useful when the sample is small
What can chemical analysis be used to do
Identify additives in foods
How can artificial colours be detected and identified
By paper chromatography
What is an example of an instrumental method
(GC-MS) Gas chromatography linked to mass spectroscopy
What does gas chromatography allow
The separation of a mixture of compounds
What helps to identify the substance in gas chromatography
The time taken for a substance to travel through the column
What can the mass spectrometer do
Give the relative molecular mass of each of the substances separated in the column
Identify substances very quickly and accurately and can detect small quantities
What can be used to identify the substances leaving the end of the column
The output from the gas chromatography that can be linked to a mass spectrometer
How does gas chromatography work
Different substances, carried by a gas, travel through a column packed with a solid material at different speeds, so that they become separated
What does the number of peaks on the output of a gas chromatograph show
The number of compounds present
What does the position of the peaks on the output show
The retention time
How is the molecular mass given
By the molecular ion peak on the ouput
Why is not possible to obtain the calculated amount of a product
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 from the expected reaction.
How can the rate of reaction be calculated
Amount of reactant used / time
Amount of product formed / time
When only can chemical reactions occur
When reacting particles collide with each other and with sufficient energy
What is the activation energy
The minimum amount of energy particles must have to react
Why does increasing the temperature increase the rate of reaction
It increases the speed of the reacting particles so that they collide more frequently and more energetically
Why does increasing the pressure of reacting gases increase the rate of reaction
It increases the frequency of collisions
Why does increasing the concentration of reactants in solutions increase the rate of reactions
It increases the frequency of collisions
Why does increasing the surface area of solid reactants increase the rate of reaction
It increases the frequency of collisions
What do catalysts do
Change the rate of chemical reactions but are not used up during the reaction
What do different reactions need
Different catalysts
Why are catalysts important
They increase the rates of chemical reactions used in industrial processes to reduce costs
What happens when chemical reactions occur
Energy is transferred to or from the surroundings
What is an exothermic reaction
One that transfers energy to the surroundings, e.g. combustion, many oxidation reactions and neutralisation
What are everyday uses of exothermic reactions
Self-heating can (e.g. for coffee) and hand warmers
What is an endothermic reaction
One that takes in energy from the surroundings
What does endothermic reactions include
Thermal decomposition and sports injury packs
If a reversible reaction is exothermic in one direction …
…it is endothermic in the opposite direction. The same amount of energy is transferred in each case
What are the state symbols
(s), (l), (g) and (aq)
Soluble salts can be made by reacting acids with:
Metals - not all are suitable (too reactive or not enough)
Insoluble bases - the base is added to the acid until no more will react and the excess solid is filtered off
Alkalis - an indicator can be used to show when the acid and alkali have reacted to make a salt solution
Salt solutions can be …
…crystallised to produce solid salts
How can insoluble salts be made…
… By mixing appropriate solutions of ions so that a precipitate is formed
What can precipitation be used to do
Remove unwanted ions from solutions, for example in treating water for drinking or in treating effluent
What are bases
Metal oxides and hydroxides
What are alkalis
Soluble hydroxides
What does the particular salt produced in any reaction between an acid and a base or alkali depends on
The acid used (HCl produces chlorides, NH3 produces nitrates, H2SO4 produces sulfates)
The metal in the base or alkali
Ammonia dissolves in water to produce …
An alkaline solution. It is used to produce ammonium salts
What are ammonium salts important as
Fertilisers
What do hydrogen ions do
Make solutions acidic
What do hydroxide ions do
Make solutions alkaline
What happens in neutralisation reactions
Hydrogen ions with hydroxide ions to produce water
H+ + OH- = H2O
What happens when an ionic substance is melted or dissolved in water
The ions are free to move about within the liquid or solution
What is electrolysis
Passing an electric current through ionic substances that are molten, e.g. lead bromide or in solution breaks them down into elements
What is the electrolyte
The substance that is broken down
What happens during electrolysis
Positively charged ions move to the negative electrode, and negatively charged ions move to the positive electrode.
What is electrolysis used to do
Electroplate objects. This may be for a variety of reasons and includes copper plating and silver plating
What is reduction
When positively charged ions gain electrons at the negative electrode
What is oxidation
When negatively charged ions lose electrons at the positive electrode
What happens if there is a mixture of ions
The products formed depend on the reactivity of the elements involved
How can reactions at electrodes be represented by
Half equations
How is aluminium manufactured
By the electrolysis of a molten mixture of aluminium oxide and cryolite.
Aluminium forms at the negative electrode and oxygen at the positive electrode.
The positive electrode is made of carbon, which reacts with the oxygen to produce carbon dioxide
What does the electrolysis of sodium chloride produce
Hydrogen, chlorine and sodium hydroxide solution.
Why are the products of electrolysis of sodium chloride important reagents for the chemical industry
Sodium hydroxide for the production of soap
Chlorine for the production of bleach and plastics
What is the formula of sulphuric acid
H2SO4
What is the formula of nitric acid
HNO3
What is the formula of sodium chloride
NaCl
What is the formula of sodium carbonate
Na2CO3
What is the formula of sodium nitrate
NaNO3
Sodium sulfate
Na2SO4
Magnesium hydroxide
Mg(OH)2
Isotopes
Different atomic forms of the same element, which have the same number of protons but a different number of neutrons
Differences in LD and HD polythene
LD - made by heating ethene to 200C and has a high pressure
HD - Made at a lower pressure and temperature and uses a catalyst
What is LD polythene used for
Bags and bottles
What is HD polythene used for
Water tanks and pipeline
Acid + Metal Oxide ->
Salt + Water
Acid + Metal hydroxide ->
Salt + Water
