Chemistry 2a (need to improve) Flashcards
The mass number is the top number on the periodic table, what does it tell you?
The total number of protons and neutrons (both added together)
What are the three particles in an atom
Protons, neutrons and electrons
The atomic number is the bottom number on the periodic table, what does it tell you?
The number of protons.
How do you work out the number of neutrons?
By taking the atomic number away from the mass number
Why aren’t electrons counted in the mass number?
Because their relative mass is very small
How are compounds formed?
They are formed when atoms of two or more elects are chemically combined together eg carbon dioxide is formed via a chemical reaction between carbon and oxygen. It’d difficult to separate the original elements after
Explain what is meant by the term isotope?
Isotopes are different forms of the same element which have the same number of protons but a different number of neutrons
Do isotopes have the same mass number or atomic number?
Isotopes must have the same atomic number but different mass numbers
What is an example of a pair of isotopes?
Carbon-12 and carbon-14. They both have six protons and six electrons but carbon-12 has 6 neutrons while carbon-14 had 8 neutrons
What happens in ionic bonding?
Atoms lose or gain electrons to form charged particles (ions) which are then strongly attracted to each other because they have opposite charges, + and -
Turn over the card for a fact about ionic bonding…fun :)
A shell with one electron wants to get rid of that one, and a nearly full shell wants to gain one
Eg sodium gives up its outer electron and gives it to chlorine so they both now have full outer shells and they are now sodium chloride
What sort of structure do ionic compounds have?
They have a regular lattice structure. They always have giant ionic lattices
Name some facts about lattices
The ions are closely packed
There are very strong electrostatic forces of attraction between opposite charges in all directions
Why are salt crystals often cuboid in shape?
Because a single crystal of sodium chloride is one giant ionic lattice
What are similar properties all ionic compounds have?
They all have high melting and high boiling points due to their strong attraction between the ions. When they melt, the ions are free to move and carry electric currents.
They dissolve easily in water, the ions separate and are free to move so they’ll carry an electric current
What groups are most likely to form ions?
Groups 1&2 and 6&7
Ions have the electronic structure of a noble gas, true or false?
True
Do group 1 and 2 metals lose or gain electrons?
Group 1 and 2 are metals so they lose electrons to form positive ions
What do group 1 alkali metals form ionic compounds with?
Non-metals
What group is the non metals?
Group 6 and 7. They gain electrons to form negative ions
Turn over for another “cool” fact about ionic bonding…
The charge on the positive ions is the same as the group number of the element. Any positive ion can combine with any negative ions to form an ionic compound
What is the overall charge of any compound?
Zero, all the negative charges must balance all the positive charges
What are two examples of how you can work out the formula of an ionic compound?
Sodium chloride= Na+ and Cl-
(+1) + (-1) = 0 so sodium chloride =NaCl
Magnesium chloride=Mg2+ and Cl-
You then need two chlorines to balance out the 2+ charge of the magnesium so the formula is
MgCl2
What is covalent bonding?
It is where atoms share electrons with each other to complete both if their outer shells
What are the seven examples of covalent?
Hydrogen-Between two hydrogens
Chlorine-Between two chlorines
Methane-Between one carbon and four hydrogens
Hydrogen Chloride-Between one hydrogen and one chlorine
Ammonia-Between one nitrogen and three hydrogens
Water-Between one oxygen and two hydrogens
Oxygen-Between two oxygens
Substances with covalent bonds can either be_____or_____?
Simple molecules or giant structures
Is the force of attraction between two atoms in covalent bonding strong or weak?
Very weak
In simple covalent bonding, why are the melting and boiling points very low?
Because the intermolecular force is weak means the molecules are easily parted from each other. The force is broken when simple molecular substances melt or boil
What are most molecular substances at room temperature?
Liquids or gasses but they can be solids
Do most molecular substances conduct electricity?
No, because there are no ions so there is no electrical charge
What are giant covalent structures?
Macromolecules
Giant covalent structures are like lattices, but why are they different?
Because there are no charges ions
Why do giant covalent structures have high melting and boiling points?
Because all the atoms are bonded to each other by strong covalent bonds
Do giant covalent structures conduct electricity?
No, not even when molten, except for graphite
What are the examples of giant covalent structure?
Diamond, graphite (both made only from carbon atoms) and silicon dioxide (silica)
Explain about diamond as a giant covalent structure
Each carbon atom forms four covalent bonds, the structure makes diamond the hardest natural substance so its used for drill tips
Explain silicon dioxide as a giant covalent structures
Sometimes called silica, which is what sand is made of. Each grain of sand is one giant structures of silicon and oxygen
Explain graphite as a giant covalent structure
Each carbon atom forms three covalent bonds. It has layers which slide over each other making it soft and slippery. The layers are loose so it can slide off on paper (pencils) as there is a weak intermolecular force between the layers. It is the only non-metal that is a good conductor of heat and electricity as each carbon atom has a delocalised electron which conducts heat and electricity
What structure do metals have?
Metals have a giant structure
What creates all the properties of metals?
Delocalised electrons on the outer shell of every metal atom in the structure
Why are metals good conductors of heat and electricity?
Because the free electrons are free to move through the whole structure
FACT
These electrons hold the atoms together in a regular structure. There are strong electrostatic forces of attraction between the positive metal ions and negative electrons
Why can metals be malleable?
Because their layers of atoms can slide over each other, allowing them to be bent and shaped
Why can alloys be good for certain jobs?
Because they can be made so that they have all the right properties needed as they are a mixture of different metals
Why are alloys harder than pure metals?
Because the atoms are different sizes so it is harder for the layers to slide over each other, making them harder
LEARN THE PROPERTIES OF GIANT IONIC, SIMPLE MOLECULAR, GIANT COVALENT AND GIANT METALLIC SO YOU CAN IDENTIFY THEM WHEN GIVEN THE PROPERTIES LIKE ON PAGE 49!
!!!
What makes smart materials behave differently?
They behave differently depending on the conditions eg, temperature
What is an example of a smart material?
Nitinol-Shape memory alloy
Half nickel, half titanium
Can be bent and twisted when cool, but then returns to original shape at a certain temperature which is why it is good for dental braces and glasses frames, incase they get bent
How small are nano particles?
1-100 nanometers
1 nanometer=0.000000001 meter
Roughly how many atoms do nanoparticles contain?
Roughly a few hundread
Nanoparticles contain fullerenes, what are they?
Fullerenes are molecules of carbon shaped like hollow balls or closed tubes, the carbon atoms are arranged in hexagonal rings. Different fullerenes contain different numbers of carbon atoms
What are nanotubes?
Fullerenes can be joined to form carbon nanotubes. They are very strong as there are many covalent bonds. They can be used to reinforce graphite in tennis rackets
What is the study of nanoparticles called?
Nano Science
What are the new uses being developed for nano particles?
The huge surface area to volume ratio can mean they can be made into industrial catalysts
They can make sensors to detect only one type of molecule, can be used to test water purity
Nanotubes can be stronger, lighter building materials
New cosmetics eg deodorant and sun cream that doesn’t leave white marks
Nano Medicine to deliver drugs to the right cells
What do forces between molecules determine when talking about polymers?
They determine the different properties
What sort of bond holds polymers together?
Strong covalent bonds that hold the atoms together in long chains but its the bonds between different molecule chains that determines the properties
Explain weak forces (polymers)
Individual tangled polymer chains held together by weak intermolecular forces. They are free to slide over eachother
Weak forces explain thermosoftening polymers, what are they?
They don’t have cross links between chains, the force is easy to overcome so it’s easy to melt. When it cools, it hardens into a new shape so they can be melted then remoulded as many times
Explain strong forces (polymers)
They have strong intermolecular forces between polymer chains called cross links that hold the chains firmly together
Strong forces explain thermosetting polymers, what are they?
They have crosslinks so the chains are held together in a solid structure. They don’t soften when heated. They are strong, hard and rigid
The starting materials and reaction conditions affect the properties of a polymer, what are the two types of polythene/poly(ethene) that can be made by using different conditions?
Low density polythene made by heating ethene to 200 degrees under high pressure. It is flexible and used for bags and bottles.
High density polythene is made at lower temperatures and pressures with a catalyst. They are more rigid and are used for water tanks and drain pipes
What is relative atomic mass?
How heavy different atoms are compared with the mass of an atom of carbon-12. Carbon 12’s Ar is exactly 12
What is relative atomic mass usually the same as?
Usually the same as the mass number of the element
What is relative formula mass?
All the relative atomic masses added together
Work out the relative formula mass, Mr of MgCl2
Mg Cl2
24 + 35.5 x 2 = 95
35.5 is multiplied by two because there are to chlorines.
The relative formula of MgCl2 is 95
What is one mole of a substance equal to?
It is equal to its Mr in grams (relative formula mass in grams)
Examples of moles…
Iron has an Ar of 56 so one mole of iron weighs 56 grams
Nitrogen gas has an Mr of 28 so one mole weighs 28 grams
What is the formula to convert between moles and grams?
Mass in g(of element or compound)
Number of moles=_____________________________
Mr (of element or compound)
How many moles are there in 42 g of carbon?
42 divided by 12 = 3.5 moles
What is the formula for calculating percentage mass of an element in a compound?
Percentage mass| Ar x no. of atoms of that element
of an element =_____________________________
in a compound| Mr of whole compound
THEN MULTIPLY THE ANSWER BY 100!
How do you find the empirical formula (from masses or percentages)?
1) list all the elements in the compound
2) Then write their masses or percentages
3) Divide each mass or percentage by the Ar for that particular element
4) Turn the numbers into a ratio by multiplying and/or dividing them by well chosen numbers
5) Get the ration into it’s simplest form then you have the empirical formula!
Work out the empirical formula for iron oxide
Iron oxide= iron and oxygen iron =44.8 and oxygen= 19.2 44.8 divided by 56= 0.8 19.2 divided by 16=1.2 Multiply by ten to make 8 and 12 then divide by 4 to get 2 and 3 Iron oxide = 2:3 so the empirical formula =Fe2O3
How do you calculate the masses in ractions?
1) Write out the balanced equation
2) Work out the Mr, just for the two parts you need
3) Divide to get one, then multiply to get all
What mass of magnesium oxide is produced when 60g of magnesium is burned in air?
2Mg + 2O —> 2MgO
2x24 —>2x (24 + 16)
48 —> 80
48g of mg = 80 g MgO
1g of mg=1.67g MgO (divide both sides by 48)
60g of mg=100g MgO (multiply both sides by 60)
What does percentage yield do?
It compares actual yield and predicted yield
What is the formula to work out percentage yield?
Actual yield (grams)
Percentage Yield=\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ x 100
Predicted yield (grams)Why are yields always less than 100%?
Because some of the product or reactant is always lost during the reaction
NO ATOMS ARE GAINED OR LOST!
What are some of the reasons why some of the product or reactant is lost?
If the reaction is reversible the reactants will never be completely converted to products as the reaction goes both ways. Some of the product is always reacting to change back to the original reactants
When you filter a liquid to remove solid particles liquid or solid is lost
Also unexpected reactions can occur which use up the reactants
Artificial colours can be separated using paper chromatography, how?
An extract of the colour is placed in a cup with a solvent (water, ethanol etc)
Spots of the coloured solution are placed on a pencil baseline on filter paper, not pen as is may dissolve and confuse the results
Place the rolled up paper in a beaker with the solvent, keeping the baseline above the solvent
The solvent seeps up the paper carrying the dye up into different places showing you how many dyes there are at least, there could be more dyes than dots though
What are advantages of using machines to analyse unknown substances?
They are:
Very sensitive so can detect even the tiniest amounts of a substance
Very fast and tests can be automated
Very accurate
Explain gas chromatography?
Gas caries substances through column packed with solid material
It travels though tube at different speeds so it separates
Substances are identified at the detector (retention time)
Recorder draws a gas chromatograph, the number of peaks shows the number of different compounds and the position shows the retention time
The electrons further away from the nucleus have more or less energy?
They have more energy than those closer to the nucleus
All elements in the same group of the periodic table have the same number of what?
Electrons in their outer shell
Why are group 1 metals more reactive as you go down the table?
Because as you go down the table, they have more shells, meaning the outer electrons are further away from the nucleus, making them more reactive
Why is group 8 stable
Because they have 8 electrons in their outer shell-they have a full outer shell
