chemistry exam

content through all of the booklets

atomic model: greek

principal characteristics: atoms are indivisible and indestructible

evidence: thoughts

atomic model: daltons

description of experiment:

law of conservation of mass compared to total mass before and after experiments

law of define proportions - measured mass of elements in the same compound

gas behaviour experiments

patterns in reactions

key findings:

atoms are re-arranged not destroyed

compounds form in fixed ratios of atoms

atoms combine in whole numbers

matter must be made of tiny particles

elements have unique identical atoms

atomic model: thomsons model

description of experiment:

Thomson discovered the electron by experimenting with cathode ray tubes, finding that rays were composed of negatively charged particles with very high charge - to - mass ratio.

using vacuum tube, electric plates, and magnetic fields, he determined these particles over 1000 times lighter than hydrogen proving atoms are divisible.

key findings:

atoms consist of positively charged ‘pudding’ or sphere, which spread throughout atom.

negatively charged electrons embedded randomly within this positive sphere

total positive charge are equal, making atom equally neutral

atomic model: rutherford

description of experiment:

beam of alpha particles from lead block containing radium (the radioactive alpha particle emitting source) targeted at very thin sheet of gold foil. the scattered alpha particles observed through microscope as cause flash light when strike the ZnS coated screen. most alpha particles in beam pass through gold foil undetected, some show slight deflection and very small deflected backwards.

key findings:

the nucleus incredibly small compared to total size of atom

proposed electron orbit nucleus at large distance with electrostatic attractive providing stability.

atomic model: bohr

description of experiment:

shined light through an element (gas) through a triangular prism giving off colours of light where he was able to measure wavelengths.

analysed the hydrogen emission spectrum to determine that electrons orbit the nucleus in specific quantised energy levels

key findings:

electrons orbit a positive nucleus in specific discrete circular orbits associated with fixed energy levels and electrons don’t radiate energy while occupying “stationary states”

explained spectral lines of hydrogen by introducing the concept of quantised energy levels.

atomic model: schrondinger

description of experiment:

any moving particle is associated with wave character

the schrondingers cat experiment absurdity of quantum super position.

key findings:

electrons behave as waves rather than particles.

replaced boars fixed orbits with orbitals three-dimensional mathematically defined regions of space representing probability of finding electron rather than specific path.

atomic model: Chadwick

description of experiment:

James Chadwick discovered the neutron by repeating a popular experiment that produced unknown radiation. placed polonium in a vacuum - sealed box which radiated alpha particles through a piece of beryllium, caused unknown radiation to accelerate out.

key findings:

neutron present in nucleus

neutrons and protons make nucleus mass

explanation of isotopes atoms of same element with same protons but different neutrons therefore unstable.

isotope

the number of neutrons of an element can vary, producing atoms that are slightly different.

isotopes have some chemical properties which are determined by their electron configuration eg. combustibility, flammability, reactivity.

different physical properties due to different mass eg. density melting boiling point.

forces in atom

electrostatic attraction: between the negative electrons and positive protons

electrostatic repulsion between the positive charged protons together in the nucleus. counteracted by the strong nuclear force acting between all nuclear particles

stable atoms has all these forces in balance

electron arrangement

electrons arranged in energy levels which are further organised in s p d and f orbitals

noble gases

unreactive inert gases found in group 18 full outer shell.

electron dot diagram

shows the number of valence electrons. known as lewis structures.

emission spectra and AAS

heating element vigorously can cause electron to absorb energy jump to higher energy state

as electron falls lower shell emits energy in form light corresponding to exact difference in energy between higher and lower energy.

electron may return directly to ground state or may move energy levels before returning.

as energy levels represent distinct quantised energies, each transition the electron makes is association with emission of a different quantity of energy in form different colours.

individual colour of light emitted by hydrogen atoms known as emission lines and collectively form emission spectrum.

atomic absorption spectroscopy is analytical technique that uses light absorption to measure the concentration of a metal in a sample.

AAS adresses limitation of flame test

AAS provides both quantitative and qualitative test

more than 70 elements can be analysed by AAS

AAS can detect elements in concentration as low as micrograms per litre

AAS highly selective and regularly used with mixtures

use of AAS

used in particularly for deflecting the concentrations of metal ions in solutions.

mining- metal concentration in mineral samples

water analysis- have metals, metal ions

biological tissues or fluids- heavy metals, toxicity levels

agriculture- trace elements in soil

determining concentration in AAS

create calibration curve by measuring absorbance of standard solutions of known concentration (absorbance y axis concentration on x axis) the standard solution should produce a straight line.

mass spectrometry

heat vaporising the sample- separating the individual isotopes in the sample

ionisation: positive ions are formed as the vapour passes through a high energy electron beam

acceleration: an electric field accelerates the ions to the same high kinetic energy

trends in periodic table

arranged by increasing atomic number (protons) so that similar electron configurations and hence chemical properties are together in columns and the same energy levels (shells) are together in a row.

valency

describes the combining power of an atom – how many atoms or groups that it would be capable of chemically bonding with.

atomic radius

represents the size of an atom usually measured in pm (10-12m). It is difficult to measure the radius of atoms in a consistent manner. Their size will depend on their state and whether they are an isolated or bonded atom.

ionisation energy

refers to the amount of energy required to remove an electron from an atom (in the gaseous state). It is measured in kJ/mol (electron removing energy).

electronegativity

describes the ability of an atom to attract the electrons of another atom in a bond (electron attracting power).

core charge

is an expression of the attractive force experienced by the valence electrons to the core (nucleus) of an atom. Core charge = number of protons – number of inner electrons

explain the trends of the atomic radium within a periodic table

Radius increases down a group:

extra energy level/shell is added which is further from the nucleus the radius increases

Radius decreases across a period:

within an energy level or shell as more protons are added the core charge increases. This increases the electrostatic attraction between the nucleus and valence electrons pulling the valence electrons closer and decreasing the radius

explain the trends of the ionisation energy within a periodic table

Ionisation energy decreases down a group:

valence electrons further from nucleus so experience a weaker attractive force. easier to remove as they are not held as tightly so ionisation energy is lower

Ionisation energy increases across a period:

atomic radii gets smaller across a period and the attractive forces are stronger due to the increased core charge (protons). Because the valence electrons are closer and held more tightly more energy required to overcome force and remove them. The ionisation energy increases.

Metals have low ionisation energies and non-metals have high ionisation energies.

explain the trends of electronegativity within a periodic table

Electronegativity increases across a period:

Across a period atoms smaller, have a more positive nucleus (core charge). able to exert greater attractive force on the electrons shared with another atom, pulling the electrons towards the more electronegative atom.

Electronegativity decreases down a group:

Down a group the radius increases so the attractive force of the nucleus must act over a larger distance. This results in a decreased attractive force acting on the shared electrons so a lower electronegativity.

Metals have low electronegativities and nonmetals have high electronegativities.

explain the trends of the core charge within a periodic table

larger core charge occurs across a period indicating a larger attractive force is acting to pull the outer electrons closer decreasing atomic radius.

also means that ionisation energy is increasing as more energy is needed to overcome this attractive force to remove an electron.

increase in electronegativity as the power to attract other electrons is also increasing.

groups within periodic table

alkali metals: group 1 highly reactive, soft, low density

alkali earth metals: group 2 shiny, highly reactive low density high electrical conductivity, high melting boiling point.

transitional metals: group 3-12 high melting/boiling points, high densities, and strong, hard, malleable structures

metals: group 13-16 high electrical and thermal conductivity, metallic lustre (shininess), high density, and high melting points

halogens: group 17 highly reactive

noble gases: group 18 odourless, colourless, nonflammable, and monatomic gases with extremely low chemical reactivity due to their complete valence electron shells

different types of bonding

metallic

ionic

covalent molecular

covalent network

allotropes of carbon

graphite

structure: covalent network, each carbon bonded to three other carbons, one delocalised electron per carbon atom.

properties: conductive, slippery, soft, greasy material.

uses: lubricant, pencils

diamond

structure: covalent network lattice, each carbon surrounded by four other carbon atoms in a tetrahedral arrangement.

properties: very hard, sublimes, non-conductor, brittle.

uses: jewellery, cutting tools, drills.

amorphous

structure: no crystalline structure. Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. As with other amorphous solids, some short-range order can be observed.

properties: conductive, non-crystalline, cheap.

uses: printing ink, carbon black filler, activated charcoal, photocopying

buckyball

structure: hollow, spherical, cage like structure. hexagonal lattice. 3 covalent bonds to each carbon atom. delocalised electrons.

properties: dark brown to black, highly symmetrical, stable, strong, incompressible.

uses: radical scavenger and antioxidant, used in organic solar cells.

(fullerene) nanotubes

structure: hollow cylindrical structure, with walls that are only one atom thick. hexagonal lattice, similar to graphene.

properties: highly elastic, high thermal conductivity and low density.

uses: batteries, solar panels, LED’s, sensors.

graphene

structure: single layer of carbon atoms, tightly bound in a hexagonal honeycomb lattice “one” instead of “its” indicates presence of double bonds within carbon structure.

properties: tough, flexible, light with a high resistance

uses: replace silicon as the basis for computer chips and circuits due to its high conductivity

can be used in organic photovoltaic cells

ionic compounds

ionic compounds can be represented using electron dot diagrams. ions tend to form based on the octet rule, that is most atoms will lose or gain electrons to achieve a more stable valence electron configuration of 8.

covalent compounds

covalent compounds form between non-metal atoms as the atoms have high electronnegativities. atoms will share electrons in order to fulfil the octet rule.lectrone

electron dot diagram for ionic compounds

electron dot diagram for covalent molecular compounds

electron dot diagram for metallic bonding

just the symbol

non octet compounds

there are some compounds that do not follow the octet rule. these occur in compounds when there are an odd number of valence electrons, where there are too few valence electrons or when there are too many valence electrons.

define nanomaterials

a substance containing particles which range in size from 1 to 100 nanometres (nm)

1nm= 10 to the power of -9 metres ( a billionth of a metre )

examples of nano materials

spider silk

carbon fullerens

graphene

concerns of using nano materials

health hazards: inhaled nanoparticles may reach deep in the lung and travel to other organs

environmental persistence: many engineered nano materials do not easily degrade

workplace exposure: production of dry powders pose high risk for inhalation

uncertain toxicology: their small size allows them to pass through biological membranes

materials

a substance that has mass/ occupies space and is used for a purpose due to its particular qualities.

pure substance

made only of 1 type of particle ie. elements and compounds

mixtures

matter that contains 2 or more different materials or substances with varying composition

homogeneous

having uniform composition aka not a mixture

heterogenous

having non-uniform/ varying composition aka bread

elements

a pure substance which is only composed of atoms of the same atomic number

compounds

a pure substance composes of more than one type of atom chemically combined in fixed proportions. ie. has a set formula

physical change

change to the physical properties so chemical composition remains the same

physical properties

properties observed without changing the chemical identity eg. hardness, density, colour, boiling point.

chemical change

involves a chemical reaction so the chemical composition (formula) changes.

chemical properties

properties observed by preforming a chemical reaction eg. flammability, oxidation, heat of a reaction, reaction with acids.

what characteristics determine how matter is classified

particle type present- one type or multiple types

arrangement of particles- uniform or varied

physical properties- fixed or varied/ range

key ideas about chemical and physical properties and changes

properties help determine if a substance is pure or a mixture

pure substances have properties that don’t vary

the properties of a mixture will vary depending on the mixture’s specific composition

mixtures can be separated into their components using physical changes. these are known as separation techniques including processes such as filtration, distillation and evaporation.

electrostatic seperation

method of separation

properties used in separation- difference in electrical charge

explanation/description- charged particles attracted to charged plates and uncharged particles move past

example- separating waste gas products from chimney. particles are attached to charged plates

magnetic seperation

method of seperation

properties used in separation- magnetic susceptibility (force of attraction to a magnetic field)

explanation/description- a process that uses powerful magnets to separate magnetic, ferocious materials form non-magnetic materials

examples- recovery of steel or iron, such as crushed food cans, scrap metal.

filtration and serving

method of separation

property used in separation- difference in particles size

explanation/description- used to seperate a mixture of solid particles form a liquid or gas. passing mixtures through the mesh or filter papers.

example- pool filters, coffee, pasta sieve/ strainers.

vaporisation (evaporating/boiling)

property used in separation- boiling point

explanation/ description- the compound with lower Bp evaporates off and it is lost to the atmosphere solid residue remains (solvent is evaporated off)

example- salt from water, production from crystals, distillation

distillation and fractional distillation

seperation method

properties used in sepration- boiling point

description/ explanation- the component with the lowest Bp evaporates first then re-condenses and is collected

example- canola oil, alcohol

decantation/ sedimentation

separation method

properties used in separation- density

description/ explanation- more dense component sticks to the bottom

example- stock preparation

separating funnel/ solvent extraction

separation method

properties used in separation- solubility in 2 immiscible liquids

explanation/ description- one component of the mixture dissolves into the top layer, another component into the bottom layer

example- oil and water

centrifuge

separation method

properties used in separation- density (faster sedimentation)

explanation- centrifuge force pushes the dense component to the bottom of the tube

example- blood cells

chromatography

seperation method

properties used in separation- adhesion (how well it sticks to the surface)

explanation- component that adheres more than one substance/ paper faster.

example- seperate dyes in ink

moles calculation

a mole is a convenient quantity for counting particles. the mole is given the symbol n and unit mol.

one mole is defined as the amount of substance that contains the same number of (specified) particles as there are atoms in 12g of carbon-12

the number of particles in 1 mol given symbol “N”. this is known as abagadros number and has the numerical value 6.022 × 10 to the power of 23.

the molar mass of an element or compound is the mass, in grams, of 1 mole of that element or compound. Molar mass is given the symbol M and the unit gmol-1

the molar mass of an element or compound has the same numerical value as the relative mass of the element or compound.

formula for the mass of moles in grams

m= n x M

formula for the number of moles

n= m/M

formula for the number of moles from the number of particles given

n= N/abagadros number

formula for the number of particles

N= n x abagadros number

interpreting formula

the chemical formula tells us what atoms are needed and how many. we can also work in moles rather than individual atoms. the formula tells us the proportion of each element requires in the compound.

what is stociochemistry

derived from the greek word “Stoicheion” or element

it is about being able to predict quantities of a product or reactant in a chemical reaction

to do this a balanced equation is required and a quantity needs to be known in moles

a conversion factor known as a more ratio enables on e quantity in a reaction to be predicted from another

balancing chemical equations

follow the law of conservation of mass ( equal on both sides)

the number of atoms of each type are equal on each side of the reaction

the formulae cannot be changed only coefficients can be added

it represents how many of each molecule or atom reacts

to determine the moles of one compound (unknown) when given the moles of another (known) what is the formula

stochiochemistry steps

write a balanced equation

calculate the moles of the known compound using n = m/M

determine the moles of the unknown compound using the mole ratio

answer question by converting mass m= n x M and rounding the correct number

percentage composition

the percentage composition of a compound gives the percentage by mass of each element in the compound.

what is the flame test

qualitative, analytical chemistry procedure used to detect the presence of specific metal ions based on the characteristic colors they emit when heated in a Bunsen burner flame

how can the flame test be used

identify an element/ which particular metal ion is present

why is distilled rather than tap water used

contamination so no other metal ions are present

relative atomic mass calculation

diagram for the separation technique electrostatic separation

 

diagram for the separation technique magnetic separation

 

diagram for the separation technique filtration and serving

diagram for the separation technique vaporisation

diagram for the separation technique distillation and fraction distillation

diagram for the separation technique decantation/ sedimentation

diagram for the separation technique funnel/ solvent extraction

diagram for the separation technique centrifuge

diagram for the separation technique chromatography