Hard Stuff Flashcards
What does the mass number tell you?
-The total number of protons and neutrons.
What does the atomic number tell you?
-The number of protons.
What is the relative mass of a proton?
-1.
What is the relative mass of a neutron?
-1.
What is the relative mass of an electron?
-Very small. Nearly 0.
What is a compound?
- A compound is formed when atoms of two or more elements are chemically combined together. For example, carbon dioxide is a compound formed from a chemical reaction between carbon and oxygen.
- It’s difficult to separate the two original elements out again.
What is an isotope?
-Isotopes are different atomic forms of the same element, which have the same number of protons but a different number of neutrons.
What is a popular pair of isotopes?
-Carbon-12 and Carbon-14.
What is ionic bonding?
-In ionic bonding, atoms lose or gain electrons to form charged particles (called ions) which are then strongly attracted to one another (because of the attraction from
What is an ion?
-A charged particle.
How does ionic bonding happen?
- Groups 1&2 (metals), e.g. sodium, potassium, calcium etc. only have 1 or 2 electrons in their outer shell, so therefore they want to get rid of this in order to get a full outer shell as this is desired by electron shells as they try to have the same electronic structure as a noble gas). So therefore, they get rid of the extra electron which leaves as an ion instead.
- Groups 6&7 (non-metals), such as oxygen and chlorine, have 6 or 7 electrons in their outer shells, so their outer shells are nearly full. So therefore, they’re pretty keen to gain that one extra one or two electrons to fill the shell up.
- When they do this, they become ions, and they have latched onto the atom (ion) that previously just gave away the electrons.
What is ionic bonding between?
-A metal and a non-metal.
What type of structures do ionic compounds have?
- Ionic compounds always have giant ionic lattices.
- The ions form a closely packed regular lattice arrangement.
- These are very strongly electrostatic forces of attraction between oppositely charged ions, in all directions.
What is a example of one giant ionic lattice?
-A single crystal of sodium chloride (salt) is one giant ionic lattice, which is why salt crystals tend to be in a cuboid shape. The Na+ and Cl- ions are held together in a regular lattice.
In a giant ionic lattice structure, what type of forces hold the atoms together?
-Very strong electrostatic forces of attraction between oppositely charged ions, in all directions.
What are the similar properties of ionic compounds?
- All ionic compounds have similar properties.
- They all have high melting points and high boiling points due to the strong attraction between the ions. It takes a large amount of energy to overcome this attraction.
- When ionic compounds melt, the ions are free to move and they’ll carry electric current.
- They do dissolve easily in water though. The ions separate and are all free to move in the solution, so they’ll carry electric current.
What type of ions do Group 1 and 2 metals form?
- Group 1 and 2 elements are metals and they lose electrons to form positive ions (losing electrons which are negatively charged).
- For example, Group 1 elements (the alkali metals) form ionic compounds with non-metals where the metal ion has a 1+ charge. E.g. K+Cl-
What type of ions do group 6 and 7 elements make?
- Group 6 and 7 elements are non-metals. They gain electrons to form negative ions.
- For example, Group 7 elements (the halogens) form ionic compounds with the alkali metals where the halide ion has a 1- charge. E.g. Na+Cl-.
How can you tell what the charge on positive ions is?
- The charge on positive ions is the same as the group number of the element.
- For example, Positive ions: Group 1: Li+, Na+ and K+. Group 2: Be^2+, Mg^2+ and Ca^2+.
- For negative ions, for example, Group 6: O^2-. For Group 7: F- and Cl-.
What elements can form ionic compounds?
- Only elements at opposite sides of the periodic table will form ionic compounds, e.g. Na and Cl, where one of them becomes a positive ion and one becomes a negative ion.
- Any of the positive ions in Group 1 and Group 2 can combine with any of the negative ions to form an ionic compound.
What do the + and - charges tell us?
-The + and - charges we talk about, e.g. Na+ for sodium, just tell you what type of ion the atom will form in a chemical reaction. In sodium metal there are only neutral sodium atoms, Na. The Na+ ions will only appear if the sodium metal reacts with something like water or chlorine.
What are ionic compounds made up of?
-A positively charged part and a negatively charged part.
What is the overall charge of any compound?
-The overall charge of any compound is zero.
How can you work out the formula for an ionic compound?
- You can use the charges on the individual ions present to work out the formula for the ionic compound.
- For example, Sodium chloride contains Na+ (+1) and Cl- (-1) ions. (+1) + (-1) = 0. Charges are balanced with one of each ion, so the formula for sodium chloride = NaCl.
- Another example, Magnesium chloride contains Mg^2+ (+2) and Cl- (-1) ions. Because a chloride ion only has a 1- charge we will need two of them to balance out the 2^+ charge of a magnesium ion. This gives us the formula MgCl2.
How do you draw the electronic structure of simple ions?
-Use a big square bracket and a + or - to show the charge.
What is covalent bonding?
- Where atoms share electrons with each other so that they’ve got full outer shells.
- They only share electrons in their outer shells (highest energy levels).
- This way both atoms feel that they have a full outer shell, making them happy as having a full outer shell gives them the electronic structure of a noble gas.
- Each covalent bond provides one extra shared electron for each atom.
- So, a covalent is a shared pair of electrons.
- Each atom involved has to make enough covalent bonds to fill up its outer shell.
How does Hydrogen bond with another Hydrogen and Chlorine with Chlorine (they go around in pairs)?
- Covalently.
- Hydrogen atoms have just one electron. They only need one more to complete the first shell.
- Chlorine atoms also need only one more electron.
- So they often form single covalent bonds.
What is the symbol to show a covalent bond?
—
What is the important thing to remember in a dot and cross diagram?
-In a dot and cross diagram (shows electrons) you only have to draw the outer shell of electrons.
What bonds make up methane?
- Covalent bonds.
- Carbon has four outer electrons, which is half a full shell. So it forms four covalent bonds to make up its outer shell.
What bonds make up Hydrogen Chloride?
- Covalent bonds.
- This is very similar to H2 and Cl2. Again, both atoms only need one more electron to complete their outer shells.
What bonds make up Ammonia (NH3)?
- Nitrogen has five outer electrons.
- So it needs to form three covalent bonds to make up the extra three electrons needed.
What bonds make up Water (H2O)?
- Oxygen atoms have six outer electrons.
- They sometimes form ionic bonds by taking two electrons to complete their outer shell (Not H2O).
- However they’ll also cheerfully form covalent bonds and share two electrons instead.
- In water molecules, the oxygen shares electrons with the two H atoms.
What bonds make up Oxygen (O2)?
- In oxygen gas, oxygen shares two electrons with another oxygen to get a full outer shell.
- A double covalent bond is formed.
What are simple molecular substances?
- The atoms form very strong covalent bonds to form small molecules of several atoms.
- By contrast, the forces of attraction between these molecules are very weak.
- The result of these feeble intermolecular forces is that the melting points are very low, because the molecules are easily parted from each other. It’s the intermolecular forces that get broken when simple molecular substances melt or boil - not the much stronger covalent bonds.
- Most molecular substances are gases or liquids at room temperature, but they can be solids.
- Molecular substances don’t conduct electricity - there are no ions so there’s no electrical charge.
What are giant covalent structures?
- Giant covalent structures are macromolecules.
- These are similar to giant ionic structures (lattices) except that there are no charged ions.
- All the atoms are bonded to each other by strong covalent bonds.
- This means that they have very high melting and boiling points.
- They don’t conduct electricity - not even when molten (except for graphite).
- The main examples are diamond and graphite, which are both made only from carbon atoms, and silicon dioxide (silica).
How is diamond structured?
- Each carbon atom forms four covalent bonds in a very rigid didn’t covalent structure.
- This structure makes diamond the hardest natural substance, so it’s used for drill tips.
- And it’s pretty and sparkly too.
How is Graphite structured?
- Each carbon atom only forms three covalent bonds.
- This creates layers which are free to slide over each other, like a pack of cards - so graphite is soft and slippery.
- The layers are held together so loosely that they can be rubbed off onto paper - that’s how a pencil works.
- This is because there are weak intermolecular forces between the layers.
- Graphite is the only non-metal which is a good conductor of heat and electricity.
- Each carbon atom has one delocalised (free) electron and it’s these free electrons that conduct heat and electricity.
What structures do metals have?
- Metals also consist of a giant structure (giant metallic).
- Metallic bonds involve ‘free electrons’ which produce all the properties of metals. These delocalised (free) electrons come from the outer shell of every metal atom in the structure.
- These electrons are free to move through the whole structure and so metals are good conductors of heat and electricity.
- These electrons also hold the atoms together in a regular structure. There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
- They also allow the layers of atoms to slide over each other, allowing metals to be bent and shaped.
What type of forces of attraction are involved in giant metallic?
-Electrostatic attraction forces.
What type of forces of attraction are involved in giant metallic and giant ionic structures?
-Electrostatic attraction forces.
What type of forces of attraction are involved in simple molecular and giant covalent?
-Intermolecular forces.
What physical properties do giant metallic structures have?
- Good conductors of heat and electricity because of delocalised (free) electrons.
- Regular structure due to electrostatic attraction between the positive metal ions and the negative electrons due to the delocalised (free) electrons.
- Layers of atoms can slide over each other, so metals can be bent and shaped due to the delocalised (free) electrons.
What are alloys?
- Pure metals often aren’t quite right for certain jobs. So scientists mix two or more metals together - creating an alloy with the properties they want.
- Different elements have different sized atoms. So, when another metal is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other. So alloys are harder.
What are the physical properties of giant ionic structures?
- High melting points.
- High boiling points.
- Can conduct electricity when molten.
What are the physical properties of simple molecular?
- Low melting points.
- Low boiling points.
- Can’t conduct electricity.
What are the physical properties of giant covalent structures?
- High melting points.
- High boiling points.
- Can’t conduct electricity.
What are the physical properties of giant metallic structures?
- High melting points.
- High boiling points.
- Can conduct electricity (delocalised electrons).
What are smart materials?
-Smart materials behave differently depending on the conditions, e.g. temperature.
What is a good example of a smart material?
- A good example is nitinol - a “shape memory alloy”. It’s a metal alloy (about half nickel, half titanium) but when it’s cool you can bend/twist it I’ve rubber. Bend it too far, though and it stays bent. But, if you heat it above a certain temperature, it goes back to a “remembered” shape.
- It’s really handy for glasses frames. If you accident,y bend them, you can just pop them into a bowl of hot water and they’ll jump back into shape.
- Nitinol is also used in dental braces. In the mouth it warms and tries to return to a ‘remembered’ shape, and so it gently pulls the teeth with it.
What are nanoparticles?
- Really tiny particles, 1-100 manometers across, are called ‘nanoparticles’ (1nm = 0.000 000 001m).
- Nanoparticles contain roughly a few hundred atoms.
- Nanoparticles include fullerenes.
- A nanoparticles has very different properties from the ‘bulk’ chemical that it’s made from - e.g. fullerenes have different properties from big lumps of carbon.
What are fullerenes?
-These are molecules of carbon, shaped like hollow balls or closed tubes. The carbon atom,s are arranged in hexagonal rings. Different fullerene contain different numbers of carbon atoms.
What are nanotubes?
- Fullerenes can be joined together to form nanotubes - teeny tiny hollow carbon tubes a few nanotubes across.
- All those covalent bonds make carbon nanotubes very strong. They can be used to reinforce graphite in tennis rackets.
What can nanotubes be used for?
-To reinforce graphite in tennis rackets.
What is using nanoparticles known as?
-Using nanoparticles is known as nanoscience.
What new uses of nanoparticles are being developed (7 points)?
- They have a huge surface area to volume ratio, so they could help make new industrial catalysts.
- You can use nanoparticles to make sensors to detect one type of molecule and nothing else. These highly specific sensors are already being used to test water purity.
- Nanotubes can be used to make stronger, lighter building materials.
- New cosmetics, e.g. sun tan cream and deodorant, have been made using nanoparticles. The small particles do their job but don’t leave white marks on the skin.
- Nanomedicine = hot topic. Idea = tiny fullerenes are absorbed more easily by the body than most particles. This means they could deliver drugs right into the cells where they’re needed.
- New lubricant coatings are being developed using fullerenes. These coatings reduce friction a bit like ball bearings and could be used in all sorts of places from artificial joints to gears.
- Nanotubes conduct electricity, so they can be used in tiny electric circuits for computer chips.
What are weak forces like in plastics?
-Individual tangled chains of polymers, held together by weak intermolecular forces,mare free to slide over each other.
What are strong forces like in plastics?
-Some plastics have stronger intermolecular forces between the polymer chains, called cross links, that hold the chains firmly together.
What are thermosoftening polymers?
- They don’t have cross-linking between chains. The forces between the chains are really easy to overcome, so it’s dead easy to melt the plastic.
- When it cools, the polymer hardens into a new shape.
- You can melt these plastics and remould them as many times as you like.
What are thermosetting polymers?
- They have crosslinks.
- These hold the chains together in a solid structure.
- The polymer doesn’t soften when it’s heated.
- Thermosetting polymers are the tough guys of the plastic world.
- They’re strong, hard and rigid.
How do you make polymers have different properties?
- How you make a polymer affects it’s properties.
- The starting materials and reaction conditions will affect the properties of a polymer.
What are the two types of polyethene that you can make?
-Low-density (LD) and High-density (HD) polyethene.
How is Low density (LD) polyethene made and what is it usually used for?
Low density (LD) polyethene is made by heating ethene to about 200degress under high pressure. -It's flexible and is used for bags and bottles.
How is high density (HD) polyethene made and what is it usually used for?
- High density (HD) polyethene is made at a lower temperature and pressure (with a catalyst).
- It’s more rigid and is used for water tanks and drainpipes.
What type of plastic would you use for a hot drink?
- Low cost (disposable).
- High melting point (for hot drinks).
What type of plastic would you use for clothing?
- Flexible (essential for clothing).
- Able to make into fibres (clothing is usually woven).
What type of plastic would you use for a measuring cylinder?
-Transparent and resistant to chemicals (you need to be able to see the liquid inside and the liquid and measuring cylinder mustn’t react with each other).
What is the relative atomic mass?
-Relative atomic mass Ar, is usually just the same as the mass number of the element.
What is relative formula mass?
- It is just all the relative atomic masses added together to get the relative formula mass - Mr.
- For example, MgCl2 is just 24 + (35.5 X 2) = 95. S Mr of MgCl2 is simply 95.
What is one mole of a substance known as?
-The relative formula mass (Ar or Mr) of a substance in grams is known as one mole of that substance.
What is the formula for the number of moles?
-Number of moles = Mass in g (of element or compound) divided by the Mr (of element or compound).
What is the formula for finding the percentage mass of an element in a compound?
-Percentage mass of an element in a compound = Ar x No. of atoms (of that element) divided by the Mr (of whole compound) x100.
What are the steps to finding the empirical formula of a compound (from masses or percentages)?
- List all the elements in the compound (there’s usually only two or three).
- Underneath them, write their experimental masses (ones given to you) or percentages.
- Divide each mass or percentage by the Ar for that particular element.
- Turn the numbers you get into a nice simple ratio by multiplying and/or dividing them by well-chosen numbers.
- Get the ratio in its simplest form, and that tells you the empirical formula of the compound.
What are the steps to calculating masses in reactions?
- Write out the balanced equation.
- Work out the Mr of the two bits you want.
- Apply the rule: Divide to get one, then multiply to get all (But you have to apply this first to the substances they give you information about, and then the other one.).
What is the yield?
-The amount of product you get is known as the yield.
How do you change the amount of yield you get?
-The more reactants you start with, the higher the actual yield will be.
What is the percentage yield?
- Percentage yield is given by the formula:
- Percentage yield = actual yield (grams) divided by predicted yield (grams) x 100.
What is percentage yield?
- Percentage yield is always somewhere between 0 and 100%.
- A 100% percentage yield means that you got all the product you expected to get.
- A 0% yield means that no reactants were converted into product, i.e. no product at all was made.
Why is a yield always less than 100% and never 100%? (3 points).
-The reaction is reversible. A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants. For examples ammonium chloride = (reversible reaction sign should be there
When is it important to think about the product yield?
-Thinking about product yield is important for sustainable development.