Key Concepts Flashcards
How did the atomic structure theory change?
- Dalton model (atoms as solid spheres)
- Plum pudding model (Thomson measurements of charge/mass showed electrons - positively charged pudding with electrons floating in)
- Nuclear atom (gold foil experiment showed alpha particles deflected - showing positive nucleus)
- Bohr model (introduced shells - atom would collapse in nuclear model as nucleus would attract electrons)
What is the Relative mass of an electron?
0.0005
should know mass and charge of all the others
How big is an atom?
10^-10 m (ten to the minus ten)
What is an isotope?
Different forms of the same element - have the same number of protons but a different number of neutrons
What is an example of an isotope?
Carbon-12 and Carbon-13
What is the RAM?
Relative Atomic Mass - average mass of an atom - isotopes make it decimal
How can the Ar be worked out from isotopic abundances?
- Multiply each isotopic mass by its isotopic abundance (given in Q) - add up the results
- Divide by the sum of the abundances (given in Q)
Who made the first periodic table?
Mendeleev (1869)
How did Mendeleev arrange elements?
Into groups based on similar properties - as he did this he realised he could put them in order of atomic mass and a pattern occurred - elements with similar properties could be put in columns - however some elements didn’t fit the pattern so he switched some around so he could keep them in the right columns - also left gaps to keep elements with similar properties together
How did Mendeleev predict undiscovered elements?
He used properties of of other elements in the columns with the gaps to predict the properties of undiscovered elements
What did John Dalton describe atoms as?
Solid spheres - different spheres made up different elements
How did Dalton’s ideas about atoms change?
JJ Thomson discovered from his measurements of charge and mass, that atoms must contain electrons - led to plum pudding model, positively charged atom with electrons loose
What did Rutherford do?
Conducted the gold foil experiment - positively charged alpha particles fired at a thin sheet of gold - some particles passed through but some were deflected backwards - theory of nuclear atom, positively charge nucleus surrounded by cloud of negative electrons
What did the Bohr Model do?
Put the electrons into shells - as the cloud of electrons would be attracted to the nucleus and collapse
What is the relative charge and mass of an electron?
Mass - 0.0005
Charge - -1
What is the relative charge and mass of a proton?
Mass - 1
Charge - +1
What is the relative charge and mass of a neutron?
Mass - 1
Charge - 0
what does aqueous mean?
dissolved in water
what is the chemical formula for water?
H2O
what is the chemical formula for carbon dioxide?
CO2
what is the chemical formula for chlorine?
Cl2
what is the chemical formula for ammonia?
NH2
what is the chemical formula for hydrogen?
H2
what is the chemical formula for oxygen?
02
what is the formula for an ammonium ion?
NH4+
what is the formula for a nitrate ion?
NO3-
what is the formula for a sulfate ion?
SO4 ²-
what is the formula for a hydroxide ion?
OH-
what is the formula for a carbonate ion?
CO3 ²-
what is included in an ionic equation?
- only the reacting particles (and the products they form)
- so when writing out the equation cross out anything that’s the same on both sides
- e.g. 2Na -> 2Na wouldn’t be included (but the chemicals which reacted together would)
do you understand how to write ionic equations in general?
pg 76
what is a hazard?
a hazard is anything that has the potential to cause harm or damage
what is a risk?
the probability or someone being harmed if they are exposed to a hazard
what does oxidising mean?
provides oxygen which allows other materials to burn more fiercely (symbol - circle with fire on like a hat)
what does harmful mean?
can cause irritation, reddening or blistering of the skin (symbol - !)
what does environmental hazard mean?
harmful to organisms and to the environment (fish and tree symbol)
what does highly flammable mean?
catches fire easily (fire symbol)
what does toxic mean?
can cause death (e.g. swallowing, breathing in, absorption through skin) (skull symbol)
what does corrosive mean?
destroys materials, including living tissues (e.g. eyes, skin) (test tube and hand symbol)
give an example of an oxidising substance
liquid oxygen
give an example of a harmful substance
bleach
give an example of an environmental hazard
mercury
give an example of a highly flammable substance
petrol
give an example of a toxic substance
hydrogen cyanide
give an example of a corrosive substance
concentrated sulfuric acid
a student is carrying out an experiment using two chemicals.
chemical A is corrosive while chemical B is highly flammable. suggest appropriate safety precautions the student could take to minimise the risk associated with the chemicals.
the student should wear gloves, a lab coat and goggles when handling chemical A (1 mark)
when handling chemical B the student should take care to keep it away from naked flames (1 mark)
How is the modern periodic table organised?
- Organised in order of ascending atomic number once protons/electrons discovered (fit the same patterns that mendeleev worked out)
- Elements with similar chemical properties form groups (columns)
- The group corresponds to the number of electrons in the outer shell (so group 7 elements have 7 electrons in outer shell)
- Rows are called periods (correspond to the number of shells of electrons an element has e.g. period 3 has 3 shells)
What are energy levels?
Shells (on atoms)
What is the electronic configuration of argon (18 electrons)?
2.8.8
What are ions?
Charged particles that form when atoms lose or gain electrons (to obtain a stable electronic structure)
When do negative ions form?
anions - form when atoms gain electrons
When do positive ions form?
cations - form when atoms lose electrons
What is the charge if 2 electrons are lost?
2+
Which elements form ions most readily?
Groups 1 & 2 and 6 & 7
What ions do group 1 and 2 elements form?
Group 1 = 1+ ions (cations)
Group 2 = 2+ ions (cations)
- they are metals and they lose electrons to form positive ions
What ions do group 6 and 7 elements form?
Group 6 = 2-
Group 7 = 1-
- they are non-metals and will gain electrons to form negative ions
What are ionic compounds?
Compounds made up of a positively charged part and a negatively charged part - but the overall charge is zero so the charges are balanced
What are ions with names ending in -ate (e.g. nitrate)?
negative ions containing oxygen and at least one other element
What are ions with names ending in -ide (e.g. chloride)?
Negative ions containing only one element (apart from hydroxide OH-)
How do you work out the formula of an ionic compound (e.g. calcium nitrate)?
- write out the formulas of the ions present
(Ca²+, NO3-) - overall charge must be zero so work out the ratio that gives a neutral charge
(Ca(NO3)2)
pg 93
What are the three types of bonding in particles?
ionic, covalent and metallic
When does ionic bonding occur?
When a metal and a non-metal react - the metal atom loses electrons (forming a cation) and non-metals gain these electrons - forming anions - these oppositely charged ions are strongly attracted to eachother by electrostatic forces (called an ionic bond)
Do you know how to draw ionic compounds using dot and cross diagrams?
(with the square brackets around the compounds that have been formed)
What structure do ionic compounds have?
A regular lattice structure - very strong electrostatic forces of attraction (between oppositely charged ions)
Give an example of a giant ionic lattice
Sodium chloride
What are the properties of ionic compounds?
- High melting/boiling points (due to strong attraction between ions takes large amount of energy to overcome)
- do not conduct electricity (ions fixed in place)
- melted ionic compounds have free moving ions so an electrical current can be carried
- many dissolve easily in water - ions separate so can carry electrical current
What are the advantages and disadvantages of using 2D representations of atoms?
- simply shows the atoms something contains
- shows how the atoms are connected
- don’t show shape of the substance
- don’t give idea of the size of atoms
(e. g. displayed formulas)
What are the advantages and disadvantages of using dot and cross diagrams to show atoms?
- show how compounds/molecules are formed
- show where electrons go in ions/bonds
- don’t give ideas about size or arrangement of atoms
What are the advantages and disadvantages of using 3D models to show atoms?
- show arrangement of ions
- only show outer layer of substance
What are the advantages and disadvantages of using ball and stick models to show atoms?
- help visualise structures (shape of the lattice/molecule in 3D)
- make it seem like there are gaps between atoms (but this is just where electron clouds interact)
- dont show correct scales of the atoms and ions (atoms and ions are different sizes)
What is a covalent bond?
A strong bond that forms when a pair of electrons is shared between two atoms - these bonds make up simple molecular substances
Do you know how to draw dot and cross diagrams for…
- H2
- HCl
- H2O
- O2
- CH4
- CO2
(its kinda obvious as long as you know how to draw covalent bonds - with the overlapping circles with the shared electrons inside)
How big are simple molecules?
10^-10
What are the properties of simple molecular structures (made up of covalent bonds)?
- atoms within the molecules are held together by very strong covalent bonds
- forces of attraction between the molecules are very weak
- very low melting/boiling points (molecules easily parted as weak forces of attraction)
- most are gases/liquids at room temp
- bigger molecules have stronger intermolecular forces (so more energy needed to separate them so boiling point will increase)
- dont conduct electricity - no free electrons/ions
- some are soluble in water
What are polymers?
Molecules made up of long chains of covalently bonded carbon atoms (e.g. polythene)
How are polymers formed?
When lots of small molecules (called monomers) join together
What are the properties of giant covalent structures?
- all atoms are bonded to each other (by strong covalent bonds)
- very high melting/boiling points (lots of energy needed to break bonds)
- dont conduct electricity (as don’t generally contain charged particles)
- aren’t soluble in water
What are some examples of carbon-based giant covalent structures?
Diamond, graphite and graphene
What are the properties of diamond? (a carbon-based giant covalent structure)
- made up of a network of carbon atoms that each form 4 covalent bonds
- very high melting point (as the strong covalent bonds take a lot of energy to break)
- the bonds hold the atoms in a rigid lattice structure, making diamond really hard - used for strengthening cutting tools
- no free electrons/ions so doesn’t conduct electricity
What are the properties of graphite? (a carbon-based giant covalent structure)
- each carbon atom forms 3 covalent bonds (creating sheets of carbon atoms arranged in hexagons)
- no covalent bonds between layers - only held weakly so are free to move over each other
- this means graphite is soft and slippery - so used as a lubricating material
- high melting point (the covalent bonds within the layers need lots of energy to break)
- carbon has 4 outer electrons - only 3 are used in graphite bonds - so each atom has a delocalised electron - meaning it conducts electricity
What are the properties of graphene? (a carbon-based giant covalent structure)
- graphene is one layer of graphite
- a sheet of carbon atoms joined in hexagons
- one atom thick sheet makes it two-dimensional
What are fullerenes?
- molecules of carbon shaped like closed tubes or hollow balls (so they are hollow)
- mainly made up of carbon atoms arranged in hexagons (but can contain pentagons or heptagons)
- used to “cage” other molecules - the fullerene structure forms around another atom (trapping it inside)
- could be used to deliver a drug directly to cells in the body
- have huge surface area - could help make great industrial catalysts (individual catalyst molecules could be attached to the fullerenes)
What are nanotubes?
a type of fullerene - like tiny cylinders of graphene (so conduct electricity) - high tensile strength (stretchy) so used to strengthen materials without adding much weight - e.g. strengthen sports equipment (so it is strong but light)
How is metallic bonding formed?
- consist of a giant structure
- electrons in outer shell are delocalised and shared between atoms - there is a strong electrostatic attraction between these Negative electrons and the Positive metal ions which means that the atoms are held together in a strong, regular structure
- compounds held together by metallic bonding are metallic elements and alloys
- lose electrons to gain full outer shell
What are the physical properties of metals?
- lots of energy needed to break the strong electrostatic force (between the positive metal ions and the delocalised electrons) - so high melting/boiling points
- shiny solids at room temp
- not soluble in water
- very dense as metallic structure is packed close together
- malleable - can be hammered/rolled into flat sheets as layers of atoms can slide over each other
- good conductors of electricity and heat - delocalised electrons carry the current and thermal energy through the material
What does it mean if mass is conserved?
- no atoms are destroyed/made during a chemical reaction so there is a same number of atoms on each side of a chemical equation (this can be seen if you do a reaction in a closed system)
What is an example of conservation of mass in action?
If you do a precipitation reaction:
- copper sulfate + sodium hydroxide react in an airtight test tube on a mass balance to form copper hydroxide (precipitate) + sodium sulfate - the mass doesn’t change
Why might the mass appear to increase in a reaction?
- if one of the reactants is a gas found in the air and the products are not gas
- e.g. when a metal in an unsealed container reacts with oxygen - the mass in the container increases - the mass of metal oxide produced is equal to the total mass of the metal and oxygen that reacted from the air
Why might the mass appear to decrease in a reaction?
- if one of the products is gas and the reaction is done in an unsealed reaction vessel
- e.g. when a metal carbonate thermally decomposes to form a metal oxide + carbon dioxide gas - the gas will escape and the mass will appear to decrease
Do you know how to find the relative formula mass of something?
(its literally just finding the mass of a compound from adding the masses of the original elements e.g. the mass of MgCl2)
What is the difference between the empirical formula and the molecular formula?
The molecular formula is the number of atoms in a molecule
The empirical formula is the simplest ratio of atoms
e.g. molecular formula of glucose = C6 H12 O6
empirical formula of glucose + C H2 0
How do you use Avogadro’s Constant to calculate the number of particles?
no. of particles =
avogadro’s constant x no. of moles
What is avogadro’s constant?
6.02 x 10^23
What is the equation for finding the mass in grams of a compound?
mass of compound =
no. of moles x relative atomic mass (or formula mass)
How do you find the concentration of a solution?
concentration = mass of solute (solid you’re dissolving)
volume of solution
How do you calculate the empirical formula?
- find the atomic mass of the elements involved
- divide the mass (g) given in the question by the atomic mass
- divide all your answers by the smallest answer
- this is your answer - you may need to multiply them all so you get whole numbers
How can you use an experiment to calculate the empirical formula of a metal oxide?
- heat a crucible until red rot (to clean it)
- leave the crucible to cool then weigh it
- add clean magnesium ribbon to the crucible and reweigh it
- heat the crucible containing the magnesium for 10 mins until the ribbon turns white - put on lid to stop any solid escaping but slightly ajar to let in oxygen
- allow to cool and weigh again to find the mass of magnesium oxide
- you can use the masses you found to calculate the mass of oxygen that was used - and in turn the empirical formula
What is a limiting reactant?
the reactant that is used up in a reaction - the others are said to be in excess
How can you calculate the amount of product formed from the limiting reactant?
- write the balanced equation
- work out the atomic masses of the reactant and product you’re interested in
- find how many moles there are of the substance you know the mass of
- use the balanced equation to work out the no. of moles in the other substance
- use the no. of moles to find the mass (pg 94)
How can you balance equations using reacting masses?
by using the empirical formula
