Topic 1 - Key Concepts in Chemistry COMPLETE PK Flashcards
What are the symbol states and what do they stand for?
(s)- solid (l)- liquid (g)- gas (aq)- aqueous: dissolved in water
What are diatomic molecules?
Molecules that only contain two atoms
Name the formulae of the following ions: 1. ammonium 2. nitrate 3. sulfate 4. hydroxide 5. carbonate
- NH4+ 2. NO3- 3. SO42- 4. OH- 5. CO32-
Name the chemical formulae of the following molecules: 1. water 2. ammonia 3. carbon dioxide 4. hydrogen 5. chlorine 6. oxygen
- H2O 2. NH3 3. CO2 4. H2 5. Cl2 6. O2
How can you write an ionic equation?
- Write out the full balanced chemical equation. 2. Split any aqueous substances into their two separate ions. 3. Cross out any ions that are the same on both sides. 4. Write out anything that is left.
What is a hazard?
Anything that has the potential to cause harm or damage.
What is a risk?
The risk associated to a hazard is the probability of someone (or something) being harmed if they are exposed to the hazard.
What is an oxidising agent and what is its hazard symbol?
An oxidising agent provides oxygen which allows other materials to burn more fiercely e.g. liquid oxygen.
What is a harmful substance and what is its hazard symbol?
A harmful substance is a substance that can cause irritation and reddening and blistering of the skin e.g. bleach. The hazard symbol could be either an exclamation mark inside a rotated red square or a black cross inside an orange square.
What is an environmental hazard and what is its hazard symbol?
Any substance that is harmful to organisms and to the environment e.g. mercury.
What is a highly flammable substance and what is its hazard symbol?
A highly flammable substance is a substance that catches fire very easily e.g. petrol. The hazard symbol is a flame inside a red square that has been rotated.
What is a toxic substance and what is its hazard symbol?
A toxic substance is a substance that can cause death by being consumed in any way (swallowing - breathing in - absorption through skin etc.) e.g. hydrogen cyanide. The hazard symbol is a skull and cross bones inside a rotated red square.
What is a corrosive substance?
A substance that destroys materials - including living tissues (eyes & skin etc.) e.g. concentrated sulfuric acid.
What is a risk assessment?
It is a procedure that involves identifying all the hazards posed within a chemical experiment and what the risk is from each hazard; this includes working out how likely it is that something will go wrong and how serious it would be if it did. After this you must think of ways to reduce the risks.
Why are hazard symbols used?
They are used to indicate the dangers associated with the contents of the container and inform people about safe-working precautions with these substances in the laboratory.
How did John Dalton describe atoms at the start of the 19th century?
He described atoms as solid spheres and said that different spheres made up the different elements.
How did J J Thompson change this model?
From his experiments of charge and mass he concluded that atoms must contain smaller - negatively charged particles - electrons. He proposed the ‘plum pudding’ model.
How did Ernest Rutherford disprove the ‘plum pudding’ model?
In 1909 he conducted the gold foil experiment. They fired positively charged alpha particles at an extremely thin sheet of gold. Some passed through - some were slightly deflected but others were deflected backwards which meant that the positive charge of each atom could not be spread out as the ‘plum pudding’ model described. Rutherford proposed the theory of a nuclear atom: a tiny - positively charged nucleus surrounded by a ‘cloud’ of negative electrons.
What is the Bohr model?
Niels Bohr realised that electrons in a ‘cloud’ would be attracted to the nucleus - causing the atom to collapse so he proposed a new model where the electrons were contained in shells. he said that electrons can only exist in fixed shells which must have a fixed energy.
What is the current model of an atom?
It is a nucleus containing protons and neutrons surrounded by electrons in shells.
Describe the nucleus.
It contains protons and neutrons and is in the middle of an atom. It has a positive charge due to the protons and compared to the overall size of the atom - the nucleus is very small - so the mass of an atom is concentrated in the nucleus as electrons have hardly any mass.
Describe electrons.
They orbit the nucleus in electron shells (or energy levels) and have a negative charge (-1.) Although - they are very small - their orbits cover a large space and each electron has a negligible weight (roughly equal to 1/1835.)
Describe protons.
They are positively charged (+1) and are contained within the nucleus. They have a mass of 1.
Describe neutrons.
They are contained within the nucleus and do not have a relative charge. They have a relative mass of 1.
Why do atoms have the same number of protons and electrons?
Atoms are neutral so do not have a charge therefore they have the same number of electrons and protons as they are oppositely charged (-1 and +1 respectively.) The charges cancel each other to give 0.
What is the atomic number of an atom?
It is the number of protons (and therefore electrons) within an atom.
What is the mass number of an atom?
It gives the total number of protons and neutrons in an atom.
What are isotopes of an element?
They are different atoms of the same element that contain the same number of protons (as this is unique to the element) but a different number of neutrons in their nuclei so they have a different mass number.
What is the relative atomic mass (Ar) of an element?
It is the average mass of one atom of there element compared to 1/12 of the mass of one atom of carbon-12.
Why might the Ar of an element be a decimal?
If the element exists as more than one isotope, Ar is an average of the masses, considering how common they are.
How can Ar be worked out from isotopic abundances?
- Multiply each relative isotopic mass by its isotopic abundance 2. Add the results 3. Divide by the total of the abundances (100 if in percentages)
How did Dmitri Mendeleev the 50 or so known elements at the time (1868)?
Arranged into the Table of Elements by sorting them into groups based on properties of them and their compounds; realised that if put in order of atomic mass a pattern appeared- he could put elements with similar properties into columns.
What were the problems with Mendeleev’s arrangement of the elements?
Some elements ended up in the wrong columns and some’s atomic mass was wrong due to isotopes. Some because they didn’t fit pattern; he switched order to keep elements with similar properties in same columns.
What did Mendeleev also have to do to keep elements with similar properties together?
He had to leave gaps; he used properties of elements in same column to predict their properties; when they were found﹐ they fitted pattern; e.g. Mendeleev predicted chemical and physical properties of element called ekasilicon﹐ which we know today as germanium.
How is the periodic table arranged today?
- In order of atomic number rather than atomic mass once protons and electrons were discovered; fit same pattern that Mendeleev worked out 2. Columns called groups and have elements with similar chemical properties 3. Group number = number of electrons in outer shell; group 8 or 0 has full outer shell 4. Rows called periods and each one represents another full shell of electrons; period element is in = number of electron shells it has.
What are electron shells also known as?
Energy levels
How many electrons can be allowed in each shell?
- 2 2. 8 3. 8 4. 18
What are ions?
Charged particles- can be single atoms or groups of atoms
Why might atoms become ions?
They lose or gain electrons to have a full outer shell and so a stable electronic structure; usually metals.
What are anions?
Negative ions that form when atoms gain electrons; non-metals.
What are cations?
Positive ions that form when atoms lose electrons.
Which elements are the most likely to form ions?
Those in groups 1﹐ 2﹐ 6 and 7.
What are the three types of bonding?
- Ionic 2. Metallic 3. Covalent
What happens when a metal and a non-metal react with each other?
The metal atom loses electrons to form positive cation; non-metal gains these electrons to form negative anion; oppositely charged ions are strongly attracted to one another by electrostatic forces so bond ionically.
How can the arrangement of electrons in an atom or ion be shown?
Dot and cross diagram
How can you draw a dot and cross diagram for an ionic compound?
Use dots for electrons of one atom﹐ and crosses for the other; draw all electron shells and electrons and transfer electrons that are lost and gained; draw square brackets around ions in compound and write charge in top right corner.
What is the structure of ionic compounds?
A giant ionic lattice; ions form closely packed regular lattice; there are very strong electrostatic forces of attraction between oppositely charged ions in all directions.
What are the properties of ionic compounds?
- High melting and boiling points as large amount of energy needed to overcome strong attraction between ions 2. Don’t conduct electricity when solid as ions in fixed place and can’t move; when molten﹐ ions free to move and will carry an electric current 3. Dissolve easily in water- ions separate and move freely in solution so will carry an electric current
What are the advantages and disadvantages of 2D representations of molecules?
A. Simple; great at showing atoms the molecule contains and how atoms connected D. Don’t show shape of substance﹐ and don’t give indication of size of atoms
What are the advantages and disadvantages of dot and cross diagrams?
A. Useful for showing how compounds or molecules formed and where electrons in the bonds or ions came from D. Don’t usually show anything about size of atoms/ions or how they’re arranged
What are the advantages and disadvantages of 3D models of ionic solids?
A. Show arrangement of ions D. Only show outer layer of substance
What are the advantages and disadvantages of ball and stick models?
A. Help to visualise structure and show shape of lattice or molecule in 3D; more realistic than 2D drawings D. Misleading- make it look like there are big gaps between atoms but this is where electron clouds interact; don’t show correct scales of atoms/ions which are really different sizes.
What is a covalent bond?
A strong bond that forms when a pair of electrons is shared between two atoms; simple molecular substances are made up of molecules containing few atoms joined by covalent bonds.
Give some examples of simple molecular substances.
- Hydrogen﹐ H subscript 2 2. Hydrogen chloride﹐ HCl 3. Water﹐ H subscript 2 O 4. Oxygen﹐ O subscript 2 5. Methane﹐ CH subscript 6. Carbon dioxide﹐ CO subscript 2
How big are simple molecules generally?
10 superscript -10 m.
What is specific to the dot and cross diagrams of simple molecular substances?
They only show the electrons in the outer shell of each atom.
What are the properties of simple molecular substances?
- Usually have simple molecular structures 2. Atoms held together by very strong covalent bonds (intramolecular forces)﹐ whereas intermolecular forces between these molecules are very weak 3. Low melting and boiling points as little energy needed to break feeble intermolecular forces 4. Most are gases/liquids at room temperature 5. As molecules get bigger﹐ intermolecular forces get stronger to melting and boiling points increase 6. Don’t conduct electricity as don’t contain any free electrons or ions 7. Some soluble﹐ some aren’t
What are polymers?
Molecules made up of long chains of covalently bonded carbon atoms; formed when lots of small molecules called monomers join together.
Describe the structure of giant covalent molecules.
All the atoms are bonded to each other by strong covalent bonds.
Describe the properties of giant covalent structures.
- Very high melting points as lots of energy needed to break covalent bonds 2. Generally don’t conduct electricity as they don’t contain charged particles (except graphite and graphene) 3. Not soluble in water
Give some examples of carbon-based giant covalent structures.
- Diamond 2. Graphite 3. Graphene
Describe the properties of diamond.
- Made up of network of carbon atoms﹐ each forming four covalent bonds 2. High melting point as lots of energy needed to break strong covalent bonds 3. Really hard as strong covalent bonds hold atoms in rigid lattice structure- used to strengthen cutting tools 4. Doesn’t conduct electricity as no free electrons/ions
Describe the properties of graphite.
- Each carbon atom form three covalent bonds﹐ creating sheets of carbon atoms arranged in hexagons 2. No covalent bonds between layers﹐ only held together weakly so are free to move over each other- graphite soft and slippery used as lubricant 3. High melting point- due to strong covalent bonds 4. Conducts electricity as only three of each carbon’s outer four electrons are used in bonds so each atom has one delocalised electron that can move and carry a charge
Describe the properties of graphene.
- One layer of graphite- a type of fullerene 2. Sheet of carbon atoms joined in hexagons 3. Just one atom thick so a 2-dimensional compound
What are fullerenes?
Molecules of carbon﹐ shaped like closed tubes or hollow balls; mainly made of carbon atoms arranged in hexagons﹐ but can also be pentagons or heptagons.
Describe some uses of fullerenes.
- Can be used to cage other molecules﹐ trapping it inside- so could be used to deliver drug directly to cells in the body 2. Huge surface area so could make great industrial catalysts- individual catalyst molecules could be attached to fullerene
Describe the properties of buckminsterfullerene.
- Molecular formula = C subscript 60 2. Forms hollow sphere; made up of 20 hexagons and 12 pentagons. 3. Stable molecule that forms soft brownish-black crystals
Describe nanotubes (a type of fullerene).
- Tiny cylinders of graphene- so conduct electricity 2. High tensile strength so can be used to strengthen materials without adding much weight e.g. strengthen sports equipment that needs to be strong and lightweight i.e. tennis rackets
Describe metallic bonding.
- Metals consist of giant structure 2. Electrons in outer shell of metal atoms are delocalised 3. Strong forces of electrostatic attraction between positive metal ions and shared negative electrons 4. Used to hold together compounds of metallic elements and alloys
Why is metallic bonding very strong?
Electrostatic forces between metal ions and delocalised sea of electrons are very strong﹐ so need lots of energy to be broken.
Describe the physical properties of metals.
- Most compounds with metallic bonds have very high melting and boiling points due to structure so are usually shiny solids at room temperature 2. Not soluble in water 3. Generally more dense than non-metals as ions in metallic structure are packed closer together 4. Layers of atoms in pure metal can slide over each other﹐ making metals malleable- can be hammered or rolled into flat sheets 5. Delocalised electrons carry electrical current and thermal energy through material so they’re good conductors of electricity and heat
What is the conservation of mass?
During a chemical reaction﹐ no atoms are destroyed or created so there are the same number and types of atoms on each side of the equation and the total mass is conserved.
If a reaction causes a loss or gain of mass﹐ what can be deduced?
It is not a closed system.
Why might the mass seem to increase in an unsealed reaction vessel?
- Probably because at least one of products is a gas found in air and the products are solids﹐ liquids or aqueous 2. Before reaction﹐ gas is floating around in the air; it’s there but not contained in reaction vessel so its mass can’t be measured 3. When gas reacts to form part of product﹐ it becomes contained inside reaction vessel 4. So total mass inside vessel increases
Why might the mass seem to decrease in an unsealed reaction vessel?
- Probably because some or all of reactants are solids﹐ liquids or aqueous and at least one of the products is a gas 2. Before reaction﹐ all reactants contained in vessel so mass can be measured 3. If vessel isn’t enclosed﹐ gas can escape as it’s formed so its mass can’t be measured 4. Total mass inside vessel decreases
How can you work out the relative formula mass﹐ M subscript r﹐ of a compound?
Add the relative atomic masses﹐ A subscript r﹐ of all of the atoms within its formula.
What is the empirical formula of a compound?
The simplest whole number ratio of the atoms within the compound.
What is a mole?
An amount of particles (e.g. atoms﹐ molecules or ions) that is equal to Avogadro’s constant: 6.02 x 1023
How is the number of moles related to the mass of a substance?
One mole of atoms or molecules of any substance will have a mass in grams equal to the relative particle mass (A or M subscript r) for that substance.
What is the formula for working out the number of moles of a substance?
Moles = mass in grams (of element or compound)/ M or A subscript r of a compound or of an element
What is the concentration of a solution?
How crowded the particles are in the solution.
How can you convert cm cubed into dm cubed?
Divide by 1000
How can you calculate the empirical formula of a compound from the masses of the elements it contains?
- Work out how many moles of each element there are. 2. Put the number of moles into a ratio and simplify it as far as possible.
How could you use an experiment to find empirical formulae?
- Get crucible and heat until red hot to clean it from previous experiment 2. Leave to cool﹐ weight it﹐ along with its lid 3. Add magnesium ribbon and reweigh with crucible﹐ magnesium and lid 4. Magnesium mass is second mass minus the first mass 5. Heat crucible containing magnesium; put lid on to stop solid from escaping but leave gap to allow oxygen into crucible 6. Heat strongly for around 10 minutes or until ribbon has turned white 7. Allow to cool and reweigh crucible with lid and contents 8. Mass of magnesium oxide is this reading minus initial reading for crucible and lid.
How can empirical formulae be worked out from the magnesium ribbon experiment?
- Work out mass of oxygen as difference between mass of magnesium and magnesium oxide 2. Work out number of moles of magnesium and oxygen atoms involved 3. Divide both values by the lowest result to obtain the simplest ratio
What is a limiting reactant?
Reactant that is completely used up in a reaction - stopping the reaction.
How can the non-limiting reactants be described?
They are in excess
How is the amount of product formed related to the amount of the limited reactant used?
They are directly proportional as long as the other reactants are in excess.
The model of atoms has barely changed/changed quite a lot over time
changed quite a lot
Rutherford was responsible for discovering…
The nucleus and protons
Who discovered neutrons?
Chadwick
Who developed the current model of atoms?
Bohr
Where are electrons located in an atom?
On the outer shells
Where are protons located in an atom?
In the nucleus
Where are neutrons located in an atom?
In the nucleus
What is the mass of protons?
1
What is the charge of protons?
+1
What is the mass of neutrons?
1
What is the charge of neutrons?
0
What is the mass of electrons?
1/2000
What is the charge of electrons?
-1
The atomic number is the larger/smaller number shown with the element on the periodic table
smaller
The mass number is the larger/smaller number shown with the element on the periodic table
larger
What does the atomic number tell us?
The number of protons in an atom
What does the mass number tell us?
The number of protons + the number of neutrons
The number of electrons in an atom is equal to the number of…
protons
Protons = which number?
Atomic number
Electrons = which number?
Atomic number
The number of neutrons in an atom = …
Mass number - atomic number
What is an isotope?
Something that has the same number of protons but a different number of neutrons
A proton is what identifies…
The identity of an atom
Why do some elements have .5 mass?
The atomic mass is the relative abundance of all isotopes
The mas number of Chlorine is 35.5 because…
There are 2 main isotopes of chlorine, chlorine 35 and chlorine 37. 75% of naturally occurring isotopes are chlorine 35 and 25% are chlorine 37.
What are the 2 main isotopes of chlorine?
Chlorine 35 and chlorine 37
75% of naturally occurring isotopes of chlorine are…
chlorine 35
25% of naturally occurring isotopes of chlorine are…
chlorine 37
The periodic table is a list of all the ________ which are known to exist
elements
Elements are a single type of ____
atom
An atom is…
A very small thing
When they named atoms they thought they were the…
smallest things possible
True/False: There are still lots of elements yet to be discovered
True
What is a compound?
2 or more elements that are chemically bonded together
Who was the first attempt at a periodic table by?
Newland
What did Newland try to do when making the first periodic table?
Group things into octaves and rate them by pattern
What was the problem with Newland’s first periodic table, involving iron and oxygen?
They were in the same group - these have very different properties
Newland arranged elements in the periodic table by ____
mass
True/False: Newland left lots of gaps in his periodic table
False, he left no gaps
What did Newland do which meant his periodic table didn’t really work?
He tried to force things in to have similar patterns or properties as other things
Mendeleev’s periodic table came before/after Newland
after
How did Mendeleev arrange elements in his periodic table?
By mass
What did Mendeleev do in his periodic table which Newland hadn’t done?
Left gaps
In Mendeleev’s periodic table, he arranged things in groups with…
Similar patterns
Because Mendeleev left gaps in his periodic table and arranged things in groups with similar patterns, he could…
Predict the properties of elements that have yet to be discovered
Mendeleev was correct/incorrect with his predictions of elements yet to be discovered
Correct
A few years after Mendeleev had developed his periodic table, a couple new elements were discovered and they…
fitted in really neatly to his periodic table
After a few new elements were discovered and fitted really neatly in Mendeleev’s periodic table, his table was…
accepted
How has the periodic table changed since Mendeleev developed his version?
Things are now arranged by electronic arrangement
The periodic has changed lots/little in terms of its layout since Mendeleev developed his version
Little
Groups go ____ the periodic table
down
Periods go ______ the periodic table
across
The attached image shows what type of bonding?
Covalent
What does this dot and cross diagram show?
The covalent bonding of hydrogen and chlorine to make hydrochloric acid
What does this dot and cross diagram show?
The covalent bonding of nitrogen and hydrogen to make ammonia
What does this dot and cross diagram show?
The covalent bonding of carbon and hydrogen to make methane
What does this dot and cross diagram show?
The covalent bonding of two hydrogen atoms
What does this dot and cross diagram represent?
The covalent bonding of chlorine gas
What does this dot and cross diagram represent?
The covalent bonding of oxygen
Why are there 4 electons being shared in the middle?
Oxygen has a double bond
What does this dot and cross diagram represent?
The covalent bonding of two nitrogen atoms
Why are there 6 electons being shared in the middle?
Nitrogen has a triple bond
Label the formula
C5H12
Label the formula
C3H8O
Why is C5H12 incorrect for this formula?
The numbers are written too big
Why is C5H12 incorrect for this formula?
The numbers are in the wrong place
