C2a Flashcards
What is the mass number?
The total number of protons and neutrons
What’s the atomic number?
The number of protons
How are compounds formed?
When atoms of 2 or more elements are chemically combined together
What’s an isotope?
Different atomic forms of the same element, which have the same number of protons but a different number of neutrons. They have the same atomic number but different mass numbers
Give an example of an isotope?
Carbon 12 and carbon 14
What happens in ionic bonding?
Atoms lose or gain electrons to form charged particles (ions) which are attracted to eachother
Shells with one or two electrons want to do what?
Get rid of the extra electron to have a full outer shell
Shells that are nearly full want to do what?
Gain an electron so they have a full outer shell, they then latch onto the ion that gave them the electron
Give an example of ionic bonding
The reaction of sodium and chlorine
What are the properties of an ionic compound’s structure?
Giant ionic lattices, closely packed lattice arrangement, strong electrostatic forces of attraction between ions
What are the general properties of an ionic compound?
High melting points and boiling points (strong attraction between the ions), when melted they’ll carry electric current, they dissolve in water (also carry electric current)
Which groups in the periodic table are most likely to form ions?
Groups 1, 2, 6 and 7
Ions have the electronic structure of a…
Noble gas
Group 1 and 2 metals lose an electron to form…
positive ions
Group 6 and 7 non metals gain electrons to form…
negative ions
The + and - charges just tell you what?
The type of ion the atom will form in a chemical reaction
The overall charge of any compund is?
Zero
What is covalent bonding?
Where atoms share electorons in their outer shells, but bond so they both have the same electron in the outer shell. They feel like they have full outer shells (think venn diagram)
Some examples of covalent bonds:
Hydrogen (H2), Chlorine (Cl2), Ammonia (NH3), Water (H2O), Oxygen (O2)
Properties of covalent substances (simple molecular):
Weak forces of attraction between molecules, low melting and boiling points, gases or liquids at room temperaature, don’t conduct electricity
What are giant covalent structures called?
Macromolecules
What are the properties of a giant covalent substance?
High melting and boiling points, don’t conduct electricity, no charged ions
Examples of giant covalent substances (structure and their uses):
Diamond- rigid giant covalent structure, hardest natural substance, used for drill tips
Graphite- layers that are free to slide over eachother, weak intermolecular forces between layers, good conductor of heat and electricity, used in pencils
Metal properties are all due to:
The sea of free electrons
Why are metals good conductors of heat and electricity?
They have free electrons that are free to move through the whole structure.
What do delocalised electrons allow layers of atoms to do?
Slide over eachother, allowing metals to be bent and shaped
What is an alloy?
A mixture of two or more metals
Alloys are harder than pure metals, true or false?
True
Give an example of a smart material, it’s properties and uses
Nitinol: A shape memory alloy, half nickel, half titanium. When cool it can be twisted and bent like rubber, if bent too far it stays bent. When heated it goes back to a ‘remembered shape’. Used for glasses frames and dental braces.
What is a nanoparticle and its properties?
A really tiny particle (1-100 nanometers across). It contains a a few hundred atoms and include fullerenes.
What are fullerenes?
Molecules of carbon shaped like a hollow balls or closed tubes- the carbon atoms are arranged in hexagonal rings. Different fullerenes contain different numbers of carbon atoms.
Nanoparticles have different properties from the bulk chemical they’re made from, true or false?
True
What’s a nanotube and what can it be used for?
A series of fullerenes joined together, used to reinforce graphite in tennis rackets, used in tiny electric circuits, used to make stronger/lighter building materials
What is nanoscience?
The use of nanoparticles
Why are nanoparticles good industrial catalysts?
They have a huge surface area to volume ratio
What can nanoparticles be used for?
To make sensors to detect one type of molecule and nothing else, used to test water purity. They can be used to make new cosmetics ( sun cream and deodrant) that don’t leave white marks
What are the properties of thermosoftening polymers?
WEAK INTERMOLECULAR FORCES.
- Don’t have cross linking between polymer chains
- The forces between the chains are easy to overcome so it’s easy to melt the plastic
- When it cools it hardens into a new shape (can be remoulded)
What are the properties of thermosetting polymers?
STRONG INTERMOLECULAR FORCES.
- Have cross links between polymer chains, holding the chains together in a solid structure
- It doesn’t soften when heated
- Strong, hard and rigid
Name the 2 different conditions in which polythene can be made?
Low density polythene: made using ethene to 200 degrees under high pressure- flexible, used for bags and bottles
High density polythene: made at lower temperature and pressure with a catalyst- more rigid used for water tanks and drain pipes
What is the relative atomic mass? (Ar)
How heavy different atoms are compared with the mass of an atom (SAME AS THE MASS NUMBER)
What is the relative formula mass? (Mr)
All the relative atomic masses added up
What is one mole of a substance equal to?
Its relative formula mass in grams
What is the formula for the number of moles?
Number of moles = Mass in g (of element or compound) / Mr (of the element or compound)
What is the equation for the percentage mass of an element in a compound?
(Ar x No.of atoms (of that element ÷ Mr (of the whole compound)) x 100
What does using the empirical formula find?
The formula of a compound
What is percentage yield and its formula?
Percentage yield compares actual and predicted yield and can be calculated from the balanced reaction equation The formula: Actual yield (g) ÷ predicted yield (g)
Why are yields always less than 100%?
Some product or reactant is always lost along the way
What’s a reversible reaction?
One where the products of the reaction can themselves react to produce the original reactants
How are resources saved?
Using little energy as possibe to create the highest product yield
What does a low yield mean?
Wasted chemicals- not sustainable
What is paper chromatography used for?
Seperating artificial colours
Explain briefly the process of paper chromatography using food colouring:
- Extract the colour from a food sample by putting in a cup with solvent
- Put spots of coloured solution on filter paper
- Roll up the sheet and put in a beaker with solvent
- Solvent will seep up the paper taking the dyes with it
What are the advantages of using paper chromatography?
Machines can analyse unknown substances, it’s very sensitive- can detect the tiniest amounts of substances, very fast- tests can be auutomated and are very accurate
What is gas chromatography used for?
Indentifying substances
Explain briefly the process of gas chromatography:
- A gas is used to carry substance through a column packed with solid material
- The substances travel through the tube at different speeds: they’re seperated
- The retention time (time taken to reach the detector) can be used to identify the substances
- The recorder draws a gas chromatograph
What do the number of peaks on a gas chromatograph show?
The number of different compounds in the sample
What do the position of the peaks on a gas chromatograph show?
The retention time of each substance
What can linking a mass spectrometer to a gas chromatograph do?
Identify the substances leaving the column very accurately
