the chemical earth - unsw chemistry

The Chemical Earth

Assumed KnowledgeThe Essence of the New SyllabusThe New vs The OldResources

Assumed Knowledge✘ identify the atom as the smallest unit of an element and distinguish

between atoms and molecules (5.7.2a)

fundamental property: number of protonsmodel is Rutherford/Bohr - protons and neutrons in nucleus withelectrons surroundingatoms join together to form moleculesmolecule - two or more atoms bonded together

✘ identify that a new compound is formed by rearranging atoms ratherthan creating matter (5.7.3a)

compound - consists of atoms of two or more elements joinedchemicallysimple chemical reactions do not involve nuclear energy

Assumed Knowledge

✘ classify compounds into groups based on common chemicalcharacteristics (5.7.3b)

melting point, boiling point, conductivity, hardness, malleable,ductile, lustre, nature of aqueous solutions formed

✘ construct word equations from observations and written descriptions of arange of chemical reactions (5.7.3c)

state of matter important - great influence on whether a reaction occursor not.

Assumed Knowledge

✘ identify a range of common compounds using their commonnames and chemical formulae (5.7.3d)

students at University still have trouble with this.Basic ideas of stoichiometry weak - needs to be drilled

✘ qualitatively describe reactants and products in decompositionreactions (5.7.3e)

need to define clearly decomposition - one reactant forms two ormore products.Under specified conditions of decomposition - Products morestable than reactantspractical examples - fireworks

The Essence of the NewSyllabus

An understanding of atoms,elements and compounds

1. The living and non-living components of the Earthcontain mixtures

✘ recall the difference between elements, compounds and mixtures in termsof particle theory

what is particle theory and how does it apply to each of these

✘ recall that compounds are classified into groups based on commonchemical characteristics

melting point, boiling point, conductivity, hardness, malleable,ductile, lustre, nature of aqueous solutions formed


✘ identify that the biosphere, lithosphere, hydrosphere andatmosphere contain examples of mixtures of elements andcompounds

Biosphere - living organisms on earthLithosphere - the earths outer mantle and crustHydrosphere - the earths waterAtmosphere - the gases above the earths surface

✘ identify and describe uses of mixtures which are obtained from theAustralian environment and which are used without the need forseparation procedures

foodstuffs, bio derived materials eg wood, coal,


✘ explain why the elemental composition of the Earth is fixed in time

composition fixed at time of formation of planet.Some elements deca,y others (He) are lost from the atmosphere. So isthe composition really unchanging.

✘ identify and describe procedures that can be used to separate naturallyoccurring mixtures of:- solids of different sizes manual separation, mechanical- solids and liquids decantation- dissolved solids in liquids evaporation- liquids distillation ( freezing)- gases liquefaction,

effusion - uranium isotope separation


✘ assess separation techniques for their suitability in separatingexamples of earth materials, identifying the differences inproperties which enable these separations

element vs compounds, bonding, state,cost (plant, energy), purity of material required

✘ describe situations in which gravimetric analysis supplies usefuldata for chemists and other scientists

composition of material - material must contain species whichare isolable by gravimetric analysis - solubility. Mixture must notbe too complex


✘ apply systematic naming of inorganic compounds (binarycompounds, hydroxides, acids, salts of acids including thehydrogen salts of diprotic and triprotic acids) as they areintroduced in the laboratory

since no guidelines to range of compounds - need summary ofrules, common species. Students weak on arrival at University.Care as often non systematic names are the IUPAC names

✘ identify IUPAC names for carbon compounds as they areencountered

IUPAC name and systematic name not always the same. Careand common sense required as some names can be complex.Take note of latter statements on range of nomenclature thatmust be known in the organic module.

2. Although most elements are found in combinationson Earth, some elements are found uncombined

✘ identify the five most abundant (by weight) elements in each ofthe biosphere, lithosphere, hydrosphere and atmosphere anddescribe the most common physical and chemical forms inwhich they are found

SI data book invaluable

✘ recall the atom as the smallest unit of an element anddistinguish between atoms and molecules

definition of molecule: definition may be inconsistent with usagelatter in the syllabus

2. Although most elements are found in combinations onEarth, some elements are found uncombined

✘ explain the relationship between the reactivity of an element and thelikelihood of its existing as an uncombined element

ties into activity series in metals - reactive elements unlikely to befound as pure elements .CARE: eg oxygen is a reactive element yet often needs energy toinitiate reactions, 20 % of atmosphere is oxygen

✘ classify elements as metals, non-metals and semi-metals accordingto their physical properties

electrical conductivity, colour, physical state, reactivitycare as some of these properties change gradually across the table

2. Although most elements are found in combinationson Earth, some elements are found uncombined

✘ account for the uses of metals and non-metals in terms of theirphysical properties

strength - requires metals, alloys, polymerscorrosion resistance, conductivity, inertness, reactivity ( I2, Cl2)

✘ recall some relationships between elements using the PeriodicTable

trends??? - what is in 4/5 syllabus - need to be aware of whatyour group of students has done before.

3. Elements in Earth materials are present ascompounds because of interactions at the atomic level

✘ recall that matter is made of particles that are continuouslymoving and interacting

the students level of understanding will depend very much onwhat has been covered in stages 4/5. Teachers may need toreinforce ideas of vibrational and rotational movement in solidsand liquids.

✘ recall the model for atomic structure and the distribution ofelectrons, protons and neutrons

vague - several models will have been encountered. Modelused is mainly based on that of Rutherford. (Bohr gives usprinciple energy levels)


✘ describe qualitatively the energy levels of electrons in atoms

dealing mainly with the principle energy levels - statement isvague as can also talk about the sublevels in a qualitative sense

✘ describe the formation of ions in terms of atoms gaining orlosing electrons

straight forward! - completion of outer (valence) shell ofelectrons

Na X+XNa+

ClX+Cl_

X

XX

XX

XX


✘ apply the Periodic Table to predict the ions formed by atoms ofmetals and non-metals

completion of outer shell - easier for metals to give up electrons,non metals to gain electrons - related to ionisation energies andelectron affinities

✘ apply Lewis electron dot structures to visualise:- the formation of simple ions- the electron sharing in some simple molecules

implies do not need to know how to construct Lewis diagrams (seenext page) but simply to use them - care needs to be exercised inusing them for some systems which are not “simple”. Manysystems do not have an octet of electrons!

Rules for writing Lewis Diagrams

✘ Write the correct (sensible) arrangement of the atoms(electropositive atoms tend to be central atoms)

✘ Find the total number of valence electrons - total over all atoms,add for negative charge, subtract for positive charge

✘ Assign 2 electrons to each covalent bond

✘ distribute remaining electrons so each atom has the appropriatenumber

✘ examples: HCl, SiCl4, H2O, NH4+

✘ Atoms attain noble gas configuration


✘ recall that particles with opposite charges will attract each otherand identify that this attraction forms ionic compounds

basis for ALL bonds is an electrostatic interaction betweenspecies of opposite charge.

✘ explain why the formula for an ionic compound is empirical

structure of solid is a 3D array, formula reflects the ratio of theions in the lattice. Idea of 3D lattice comes latter


✘ describe molecules as particles which can move independently ofeach other

simplistic view - molecules have strong bonding within the moleculebut weak bonding interactions between molecules - intermolecularforces play an important role in determining properties - particles arenot really independent

✘ distinguish between molecules containing one atom (the noblegases) and molecules with more than one atom

grave concerns here - The statement is wrong!!!a molecule “ consists of TWO or more atoms bound togetherchemically”“interparticle interactions”


✘ describe the formation of covalent molecules in terms of sharing ofelectrons

electrostatic attraction for a shared pair of electronsinequality of attraction leads to polar bond formation

✘ construct formulae for compounds formed from- ions- atoms sharing electrons

relate to completion of valence shellsie loss of two electrons means formulae must be MX2 ( if X gains oneelectron) MX ( if X gains 2 electrons) for ionic systems.Stoichiometry of covalent systems can be determined by electronicand coordination requirements - care needed here. Care for 2nd and3rd row


✘ recall the construction of word equations from observations andwritten descriptions of a range of reactions

By this stage students should be less reliant on word equationsand start to use symbol equations as well

4. Energy is required to extract some elements fromtheir naturally occurring sources

✘ identify the differences between physical and chemical change interms of rearrangement of particles

physical relates to changes of statechemical involves making and/or breaking of bonds. New specieswith different chemical properties are produced.

✘ summarise the differences between the boiling and electrolysis ofwater as an example of the difference between physical and chemicalchange

boiling is a physical change - relatively, requires small amount ofenergy.electrolysis is a chemical change - bonds are broken/formed, muchenergy is required - water is decomposed to its constituent elements.Energy used to break bonds recovered on reacting H2 + O2.


✘ recall qualitative descriptions of reactants and products indecomposition reactions

✘ identify light, heat and electricity as the common forms of energythat may be released or absorbed during the decomposition orsynthesis of substances and identify examples of these changesoccurring in everyday life

photosynthesis, internal combustion engine, batteries


✘ explain that the amount of energy needed to separate atoms ina compound is an indication of the strength of the attraction, orbond, between them

can be related to melting and boiling points in ionic substances.tabulations of bond strengths would be useful here - can berelated to an experiment such as the water electrolysis vsboiling observed previously. (Reactive compounds can havestrong bonds)

✘ recall a range of common compounds using their commonnames and chemical formulae

these should be used continuously through the module(s)


✘ recall that a new compound is formed by rearranging atomsrather than creating matter

the energy involved in chemical reactions is not of themagnitude of nuclear energy

5. The properties of Earth’s natural resources aredetermined by their bonding and structure

✘ identify differences between physical and chemical properties ofelements, compounds and mixtures

A broad range of physical properties can be developed bysimple observations of the world around us.Chemical properties is less obvious - range of chemicalreactions studied is limited. Stage 5 (5.7.2e) covers a range of reactions.These will be needed as resources as the amount of experimental in the

Chemical Earth is somewhat limited.

✘ compare some physical and chemical properties of a range ofcommon ores including bauxite and an iron ore mined inAustralia with those of the elements from which they are formed

Data book very useful here, as will be the Metals module.Conversion of ores to their elements is very energy intensive.


✘ identify and describe some uses of the ores or materials from the ores

✘ describe the physical properties used to classify compounds as ionic orcovalent

melting point, boiling point, conductivity, hardness, malleable,ductile, lustre, nature of aqueous solutions formed - it is implied that the students need to know what the variationsin each of these properties is as it relates to ionic and covalentsubstances


✘ distinguish between metallic, ionic and covalent bonds

Can use ideas of localised/mobile electrons.These are extreme models and they have limitations - the mostimmediate being how to describe SiO2 and graphite/diamond

✘ describe metals as three-dimensional lattices of ions in a sea ofelectrons

explains many of the properties of metals


✘ describe ionic compounds in terms of repeating three-dimensionallattices of ions

The level of sophistication of the lattice description here is not clear.To fully describe the lattice and the stoichiometry the idea of the fillingof holes in a lattice is needed. The syllabus probably does not expectthat level of detail. Choose simple examples eg NaCl

✘ describe covalent compounds as molecules or as covalent lattices

A covalent lattice is necessary because, ie some covalently bondedsystems have some of the properties of ionic substances. It may bepossible here to relate the idea of covalent lattices to gem stones.Idea of intermolecular forces will also be necessary here to explainwhy many covalent systems exist as solids.


✘ identify common elements that exist as molecules or as covalent lattices

The data book is useful here - students will need to know aboutallotropes eg Phosphorus can be both a molecular solid and covalentlattice

✘ explain the relationship between the properties of conductivity andhardness and the structure of ionic, covalent molecular and covalentnetwork structures

Care: most examples are clear cut. Ionic substances do not have mobile,charge carrying species in the solid but do in the melt. Ionic substancesare not hard but are brittle despite the strong electrostatic interactions.Graphite conducts (poorly)!!

New versus Old

✘ Of all the modules, The Chemical Earth appears to have themost in common with the old 2U Chemistry syllabus.

✘ The Chemical Earth draws from both the old Preliminary courseas well as the HSC course.

✘ Preliminary Core 1 Atoms and ElementsPreliminary Core 2 CompoundsPreliminary Core 3 Atomic structureHSC Core 8 Structure and Bonding

are the most relevant sections - some being able to be liftedalmost directly into the new syllabus

✘ Note that some of the suggested experiences of the old syllabusare now part of the core of the new syllabus, eg the relativeabundances if elements in the various spheres.

Resources for the Chemical Earth

✘ Any recent edition of a level 1 University text.CHEMISTRY “The Molecular Nature of matter and Change.”Silberberg, 2nd Ed, McGraw HillGeneral Chemistry. Ebbing and Gammon, 6th Ed, Houghton MifflinGeneral Chemistry. Atkins and Jones, 3rd Ed, FreemanOthers include the books by Zumdahl and also Chang.

✘ SI Data Book - Aylward and Findlay It now has useful safety dataon many common chemicals included.

✘ WWW

✘ Australian Companies - Comalco, BHP etc

✘ Reference Encyclopedia such as Britannica.

the chemical earth - unsw chemistry

Documents