Preliminary Chemistry Module 1: The Chemical Earth

The living and non-living components of the Earth contain mixtures

1.2 Identify the difference between elements, compounds and mixtures in terms of particle theory:

Element – a pure substance composed of only one type of atom (and cannot be further separated)

Compound – a substance composed of two or more types of atoms bonded together in a fixed ratio (and can be chemically separated into the simpler chemicals)

Mixture – Impure substances which contain a variety of elements and compounds in a variable ratio

1.3 Identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds:

Biosphere – refers to the part of the Earth where living things are found, encompasses the lithosphere, hydrosphere and atmosphere, examples of mixtures include: air (N2, O2, Ar), soil

Lithosphere – is the crust and upper mantle of the Earth that contains rock mixtures, some elements in these mixtures include: O, Si, Al, Fe

Hydrosphere – is the liquid (water) part of the Earth, contains mixtures of water such as: salt water, muddy water, and even dissolved elements such as oxygen

Atmosphere – Gaseous layer that encompasses the Earth, mixtures of air which is a mixture of elements and compounds (such as CO2)

1.4 Identify and describe procedures that can be used to separate naturally occurring mixtures of: solids of different sizes, solids and liquids, dissolved solids in liquids, liquids, gases:

Solids of different sizes – sieving, separating based on solubility Solids and liquids – filtration, sedimentation, decantation Dissolved solids in liquids – evaporating to dryness (like boiling),

evaporation Liquids – distillation, fractional distillation, separating funnel Gases – differences in boiling points (liquefying, then fractional

distillation), differences in solubilities in liquids (dissolving in water), eg. LPG is separated into methane and ethane by a bubbler and 2 U-tubes

1.5 Assess separating techniques for their suitability in separating examples of earth materials, identifying the differences in properties which enable these separations:

1.6 Describe situations in which gravimetric analysis supplies useful data for chemists and other scientists:

Gravimetric analysis is used to determine the mass and/or percentage of different components in a sample (usually a mixture)

Scientists can use gravimetric analysis to determine the percentage of pollutants in air

Chemists can use gravimetric analysis to determine the purity and/or composition of different medicines

Although most elements are found in combinations on Earth, some elements are found uncombined

2.1 Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element:

The more reactive the element, the less likely it is of existing as an uncombined element

This is because more reactive elements need to bond with other elements in order to be stable

Gold (Au), Platinum (Pt) and the noble gases exist as uncombined elements

2.2 Classify elements as metals, non-metals and metalloids according to their physical properties:

Metals Non-Metals MetalloidsUsually high MPs and BPs

Usually low MPs and BPs

Usually high to very high MPs and BPs

Shiny Dull ShinyVery hard or hard Brittle BrittleMalleable Non-malleable Reactivity depends on properties of other elements in

reactionDuctile Non-ductile Unique ‘semi-conductor’ propertiesFine heat conductor Bad heat conductor Act like metals upon reaction with non-metalsFine electricity conductor

Bad electricity conductor

Act like non-metals upon reaction with metals

Solid Solids, Liquids and Gases

Variable chemical properties

Generally higher density

Generally lower density

2.3 Account for the uses of metals and non-metals in terms of their physical properties:

Metals such as copper can be used for electrical wires because they are generally ductile and good conductors of electricity

Helium is a gas that can be used in balloons as it is a gas at room temperature and very light (and is a noble gas – unreactive)

Elements in Earth materials are present mostly as compounds because of interactions at the atomic level

3.1 Identify that matter is made of particles that are continuously moving and interacting:

Matter is made up of particles that are continuously moving and interacting

In solids, the particles are compact and vibrate In liquids, the particles have more space between them and have

translational and vibrational motion (vibrate slightly and fill up what its contained in)

In gases, the particles have a lot of energy, don’t interact with each other as much and have rapid translational motion

3.2 Describe qualitatively the energy levels of electrons in atoms:

There is less energy in electrons further away from the nucleus Energy level: K shell – n=1 – row 1 – 2x12=2 L shell – n=2 – row 2 – 2x22=8 M shell – n=3 – row 3 – 2x32=18 N shell – n=4 – row 4 – 2x42=32

3.3 Describe atoms in terms of mass number and atomic number:

Mass number = protons + neutrons Atomic number = protons = electrons (in neutral element)

3.4 Describe the formation of ions in terms of atoms gaining or losing electrons:

Atoms attempt to fill their outer shells Cation: Element -> Ion + e-

Anion: Element + e- -> Ion

3.5 Apply the Periodic Table to predict the ions formed by atoms of metals and non-metals:

The number of valence electrons an atom has determines whether or not it will form a cation or an anion

Atoms with 3 or less valence electrons (Group 1, 2, 3) are metals form cations

Atoms with 5 or more valence electrons (Group 5, 6, 7) are generally gases and form anions

The transition metals (may have more than one ion and) tend to have a valency of 2 (Cr, Cu, Ag, Au have a valency of 1), forming cations

The valency of an atom is how many electrons an atom needs to gain or lose to fill its outer shell

Noble gases don’t form ions as they have a full outer shell

3.6 Apply Lewis electron dot structures to: the formation of ions and the electron sharing in some simple molecules:

3.7 Describe the formation of ionic compounds in terms of the attraction of ions of opposite charges:

When ionic bonding occurs, the newly formed cation and anion attract each other (due to opposite electrostatic forces) and form an ionic compound (held together by strong ionic bonds)

3.8 Describe molecules as particles that can move independently of each other:

A molecule is the smallest particle of a substance that can have a separate existence and can move independently of other molecules

3.9 Distinguish between molecules containing one atom (the noble gases) and molecules containing more than one atom:

Monatomic molecules (noble gases) – one atom in molecule, eg. Neon Diatomic molecules – two atoms in molecule, eg. Oxygen (O2) Triatomic molecules – three atoms in molecule, eg, Water Tetratomic molecules – four atoms in molecule, eg. Phosphorous (P4)

3.10 Describe the formation of covalent molecules in terms of sharing electrons:

Covalent bonding occurs atoms share one or more pairs of electrons to attain a stable configuration (full outer shell)

Covalent compounds are formed from covalent bonding and are typically formed by non-metals

Covalent bonds are strong but the intermolecular forces between them are weak

3.11 Construct formulae for compounds formed from: ions, atoms sharing electrons:

Some ionic compounds include: Zinc Oxide – ZnO, Silver Nitrate – AgNO3, Ammonium Chloride – NH4Cl, Lead (II) Sulphate – PbSO4, Copper Sulphide – CuS, Aluminium Oxide – Al2O3

Some common covalent compounds include: Water – H2O, Ammonia – NH3, Methane – CH4, Nitric Oxide – NO, Chlorine – Cl2, Hydrogen – H2

Energy is required to extract elements from their naturally occurring sources

4.1 Identify the differences between physical and chemical change in terms of rearrangement of particles:

The difference between a physical and a chemical change is that in a physical change no new substance is formed whereas in a chemical change a new substance is formed

Physical changes include: change of state, change of appearance, dissolving a solid in a liquid, separating mixtures

Signs of a chemical change include: formation of a gas, formation of a solid (precipitate), change in colour, significant change in temperature, disappearance of a solid, an odour is produced

4.2 Summarise the differences between the boiling and electrolysis of water as an example of the difference between a physical change and a chemical change:

Electrolysis is the decomposing of a substance with an electric current using electrodes in a liquid (or solution)

The differences between boiling water and the electrolysis of water are: electrolysis produces two new substances whereas boiling doesn’t, electrolysis is difficult to reverse whereas boiling is easily reversed and electrolysis requires much more energy than boiling

4.3 Identify light, heat and electricity as the common forms of energy that may be released or absorbed during the decomposition or synthesis of substances and identify examples of these changes occurring in everyday life:

Light, heat and electricity are the common forms of energy released or absorbed during a decomposition or synthesis reaction

Endothermic reactions absorb heat and exothermic reactions release heat

Example of decomposition reaction in everyday life: when heat is added to bicarbonate soda in baking, it is decomposed into sodium carbonate, water and carbon dioxide. The carbon dioxide causes the dough to rise. 2NaHCO3 → Na2CO3 + H2O + CO2

Example of synthesis reaction in everyday life: the synthesis of limestone from lime and carbon dioxide. Limestone is also known as carbon carbonate and lime is also known as carbon oxide. CaO + CO2 → CaCO3

4.4 Explain that the amount of energy needed to separate atoms in a compound is an indication of the strength of the attraction, or bond, between them:

The stronger the chemical bonding in a compound, the more energy that is required to break the compound into atoms

The stronger the chemical bonding in a compound, the more energy that is released when a compound is formed from its atoms

Therefore the amount of energy needed to separate atoms in a compound indicates the strength of the bonds between the atoms

The properties of elements and compounds are determined by their bonding and structure

5.1 Identify differences between physical and chemical properties of elements, compounds and mixtures:

Some physical properties include: lustre, hardness, ductility, conductivity, malleability, etc

Some chemical properties include: reactivity, valency, etc

5.2 Describe the physical properties used to classify compounds as ionic or covalent molecular or covalent network:

5.3 Distinguish between metallic, ionic and covalent bonds:

Metallic bonding is where a ‘sea’ of delocalised electrons hold the metal cations in a 3D array in the solid

Covalent bonding is where electrons are shared between atoms Ionic bonding is where atoms give up electrons to each other to form ions

which bond with each other

5.4 Describe metals as 3D lattices of ions in a sea of electrons:

Metals bond by releasing their outer shell electrons to move freely around the lattice structure of positive cations as a sea of delocalised electrons

This bonding makes metals solids (except Hg), with high melting and boiling points, malleable and ductile, generally good conductors of electricity and heat (as liquids and solids) and typically hard.

5.5 Describe ionic compounds in terms of repeating 3D lattices of ions:

Ionic bonding forms crystals with the electrostatic attraction extending throughout the entre lattice

This strong attraction makes ionic compounds hard but brittle (as if two opposite charges are forced together they repel – shattering)

This also makes ionic compounds unable to conduct electricity as the ions are not free to move

When dissolved in water, the ions are broken up, allowing the ions to move towards an electrode and hence conducting electricity

5.6 Explain why the formula for an ionic compound is an empirical formula:

In ionic compounds the formulae specify the rations in which the ions are present, not the composition of discrete molecules

This means that by definition the formulae for ionic compounds are empirical formulae (because there are no molecules, so they tell the ratio by atoms of elements)

5.7 Identify common elements that exist as molecules or as covalent lattices:

Some elements that exist as molecules: H2, O2, N2, Br2 (liquid), I2 (solid), P4, S8

Some elements that exist as covalent lattices: C (diamond or graphite), the semi-metals B, Si, Ge, As, Sb and Te form what is basically consider to be a covalent lattice though their bonding electrons are not as firmly localised as in diamond

5.8 Explain the relationship between the properties of conductivity and hardness and the structure of ionic, covalent molecular and covalent network structures:

Structural feature in Ionic Lattice Physical property determined by structure in Ionic Lattice

Strong ionic bonds throughout the crystal. A lot of energy is needed to break these bonds.

High melting and boiling points. Hard.Crystalline

Heating makes the ions vibrate. This breaks the bonds and the ions are then free to move and carry the current.

Good electrical conductors when molten

Water moves between the ions, pushing them apart and breaking the ionic bonds. The ions are then free to move and carry the electric charge.

Good electrical conductors when in solution

Ions are held in fixed positions by strong ionic bonds that extend throughout the lattice. The ions can only vibrate, they are not free to move and carry out the charge.

Poor electrical conductors when in solid.

Structure features in Covalent Molecular Physical property determined by structure in Covalent Molecular

No free electrons, no free ions present Poor conductors of electricity in all statesWeak dispersion forces between molecules result in low boiling points so usually gases at room temperature

Not hard

Structural feature in Covalent Network Physical property determined by structure in Covalent Network

No free electrons, no ions present Poor conductors electricity in all statesStrong covalent bonds that extend throughout the lattice Hardness

Structural feature in Metallic Lattice Physical property determined by structure in Metallic Lattice

Outer shell electrons are delocalised (not held in place by an atom) and thus they are mobile and free to carry charge

Good conductor of electricity

Strong metallic bonds between the positive metal ions and the sea of negatively charged delocalised electrons. A lot of energy is needed to break these metallic bonds

High melting and boiling points. Hard

The mobile, delocalised outer shell electrons can carry heat

Good conductor of heat

The rows of metallic ions in the lattice can slide over each other without coming apart or disrupting the bonds

Malleable and ductile

The sea of delocalised electrons reflect light Shiny lustre