The Chemical Earth Notes 1s6954

The Chemical Earth

200 Reshad Azizi 8

1. The living and non-living components of the Earth contain mixtures •

Construct word equations from observations and written descriptions of a range of chemical equations

Acid + Base -> Salt + Water Acid + Metal -> Hydrogen + Salt Acid + Carbonate -> Salt + Water + Carbon Dioxide •

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

The particle theory states that all matter consists of particles which are constantly moving. Element: An element is a pure substance made up of one type of atom. It cannot be decomposed into simpler substances Compounds: Compounds are pure substances made up of two or more elements. It can be decomposed into simpler substances. Mixtures: Mixtures are substances made of parts in which the parts keep their own properties. They are either made of compounds mixed together, elements mixed together or both. They do not have a definite composition Homogenous (Uniform composition throughout) e.g. salt water, petrol Heterogenous (Non-uniform composition throughout) e.g. granite, sand •

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

The spheres of the Earth Biosphere Lithosphere Hydrosphere Atmosphere

Description All living things The rocks and crusts of the Earth The waters of the Earth The gases of the Earth

Examples Blood, Cell sap in plants Soil Salt Water Air

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Identify and describe procedures that can be used to separate naturally occurring mixtures of:

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Solids of different sizes – Sieving

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The Chemical Earth

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Solids and liquids – Filtration (Substance remaining – residue) (Substance ing through the filter paper – filtrate)

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Dissolved solids in liquids – Evaporation or crystallisation

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Liquids – Distillation, fractional distillation or decantation

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Gases – Fractional Distillation

The process of distillation: The separation technique of distillation can be used to separate liquids of different boiling points by heating the mixture with a Bunsen burner. The liquid with the lowest boiling point evaporates first, and then is condensed (water vapour becoming a liquid) into a condenser to form a liquid which can be collected. The liquid with the higher boiling point is left behind in a round bottom flask. The process of fractional distillation: •

Assess separation techniques for their suitability in separating examples of Earth materials, identifying the differences in properties which enable these separations

Mixture separated

Method of separation

Solids of different sizes Solids and liquids Dissolved solids in liquids

Sieving Filtration Crystallisation

Liquids

Distillation/Fractional

Gases

Fractional Distillation

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Property used in separation Particles of different sizes Particles of different sizes Liquid has a lower boiling point than solid Large/Small difference in boiling points Small difference in boiling points

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

Gravimetric analysis is quantitative analysis by weight or mass. Examples of gravimetric analysis include: 1. Mining company – wants to know the composition of an ore sample to see if it is financially viable to mine the ore 2. Health authority – wants to know the composition of air near an industrial area to see if the air is polluted 3. Pharmacies – can use the process in mixing various chemicals to manufacture the drugs.

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200 Reshad Azizi 8

Apply systematic naming of inorganic compounds as they are introduced in the laboratory

Naming binary compounds – Binary compounds are those that consists of two elements only (Note: Metallic is not a binary compound) Ionic • Metal and non-metal form a composition • Metal is written first •

Non-metal modified with ‘ide’ E.g. NaCl – Sodium Chloride MgO – Magnesium Chloride

Covalent • Non-metal and non-metal form a composition • The non-metal furthest to the left in the periodic table is written first in the name • Because non-metals have differing valencies, the prefixes mono, di, tri, tetra etc are used to show the numbers of atoms of the non-metal in the molecule e.g. CO Carbon Monoxide CO2 Carbon Dioxide

Covalent Prefixes: Di-, tri-, tetra, penta, hexa-, hepta-, oct-, non- and decThey are used to indicate HOW MANY atoms there are for that element

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The Chemical Earth

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

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

The higher the reactivity, the less likely it is to exist as an uncombined element. Less reactive elements include the noble gases (stable outer shell – no reaction). Highly reactive elements include the alkali metals (Group 1) •

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Classify elements as metals, non-metals and semi-metals according to their physical properties Metals Are solids at room temperature except mercury (liquid) High electrical conductivity Shiny lustre Malleable (hammered) Ductile (drawn into wires) High range melting and boiling point

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Non-Metals Poor electrical conductivity Dull lustre Brittle (break when trying to break them) Non-ductile Low density, melting and boiling point

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Semi-Metals Poor conductors Properties of metals and nonmetals (also known as metalloids e.g. Boron, Silicon) Low density and malleability High lustre e.g. Silicon is shiny Medium range melting and boiling point

for the uses of metals and non-metals in of their physical properties

Metals 1. Mercury - Used in thermometers – liquid state expands when heated 2. Iron – used in building construction and car-making – high tensile strength and hardness 3. Copper – Good conductors for domestic appliances

Non-metals 1. Carbon – Good conductors used in batteries 2. Oxygen - for medical purposes to help with breathing 3. Argon - gas for filling light bulbs

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

Identify that matter is made of particles that are continuously moving and interacting. 4

The Chemical Earth

200 Reshad Azizi 8

Matter is made of particles which are constantly moving and interacting. The movement of the particles occurs in: Solids – Particles are compactly packed, they vibrate within the space available (vibrational movement) Liquids – In liquids, the particles are all over each other. They move about freely. Gases – Particles are well separated in space and more freely •

Describe atoms in of mass number and atomic number

Mass number – the number of protons plus neutrons in the atom Atomic number – the number of protons in the atom •

Describe qualitatively the energy levels of electrons in atoms

The electron is an extremely small negatively charged particle 1/1836 the mass of a proton. Electrons in an atom move very rapidly and randomly, but not in fixed positions. Electron configuration: the arrangement of electrons around the nucleus They are arranged in different shells or energy levels. The more valence shells an atom has, the more PROTONS, NEUTRONS AND ELECTRONS it contains. Therefore, there is more energy. •

Describe the formation of ions in of atoms gaining or losing electrons

Ions are charged atoms or charged groups of atoms (review chemistry formulae sheets!) Monatomic Ions E.g. Na+, Ca2+, K+, Cl•

Ions Polyatomic Ions - Radicals NH4+, CO32-, SO42

Apply the periodic table to predict the ions formed by atoms of metals and non-metals

1. Cations (Positively charged ions) lose electrons 2. Anions (Negatively charged ions) gain electrons for an octet (stable shell) of electrons

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Apply Lewis electron dot structures to: 5

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the formation of ions

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the electron sharing in some simple molecules

Lewis symbols are also known as electron dot symbols. It consists of the symbols of the element and the dots representing the valence electrons. Note: Practice Lewis dot diagrams •

Describe the formation of ionic compounds in of the attraction of ions of opposite charge

Ionic compounds form from a metal (+ve cation) with a non metal (-ve anion) e.g. NaCl. The ionic bonds are the strong electrostatic attraction between positive and negative ions. The formula of an ionic compound gives the ratio in which ions are present (empirical formula) Note: Practice drawing models •

Describe molecules as particles which can move independently of each other

Molecules form when two or more atoms bond by sharing electrons (covalent bonds). Molecules can exist as elements e.g. 02, N2, Cl2 and compounds e.g. H2O, CO2, CH4, SO2 etc. Within molecule forces – Intramolecular forces (electrolysis) Forces between the molecules – Intermolecular forces (boiling) •

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

Molecules Monatomic Gases Diatomic Gases E.g. Noble Gases E.g. O2, H2, Cl2 It contains full outer shell and they don’t Two atoms bonded covalently combine with other atoms. Exists as single atoms. •

Describe the formation of covalent molecules in of sharing of electrons

Bonding: The forces that hold an atom together is known as bonding. Bonding is of different types: 1. Ionic Bonding

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The Chemical Earth

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2. Metallic Bonding 3. Covalent Bonding. Ionic bonding – the attractions between the positive and negative ions due to electrostatic attraction Metallic bonding – attractions between the positive ions and the sea of delocalised electrons Covalent Bonding – The sharing of electrons between non-metal atoms (negative ions, cations) 4. Energy is required to extract elements from their naturally occurring sources •

Identify the difference between physical and chemical change in of the rearrangement of particles

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Physical change is a change of state, with no new product made. It can be easily reversed, and less energy changes are involved. The particles in a physical change are not rearranged.

Indications of physical changes include 1. Melting lead 2. Boiling water 3. Solid dissolving in a liquid.

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Chemical change is the formation of a new substance, with a new product made. It is difficult to reverse, and high energy changes are involved. The particles in a chemical change are rearranged to form new substances.

Indications of chemical changes include: 1. New gas formed 2. Precipitate (solid formed) 3. Colour change 4. Significant change in temperature 5. Disappearance of a precipitate

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The Chemical Earth

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6. Odour is produced

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

1. 2. 3. 4.

Boiling Does not produce any new substances, just a conversion of a liquid to gas Easily reversed by cooling the vapour Requires less energy Does not alter the actual particles, it just separates them from one another

1. 2. 3. 4. 5.

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Electrolysis Electrolysis is the process by which an electric current produces a chemical change Produces two new substances, hydrogen and oxygen gases i.e. H2 and O2 Difficult to reverse Requires much more energy for the two gases to be decomposed Breaks the particles up into H2 and O2

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

1. Light given off often in oxidization 2. Heat given off in all exothermic reactions 3. Electricity given off in reactions occurring within a battery Decomposition (breaking of a chemical substance into simpler substances) occurring in everyday life: 1. Sodium Azide decomposes to sodium and N gas, air bag 2. Limestone, calcium carbonate, is decomposed to CO2 and CaO to make glass, cement etc Synthesis (formation of a compound from simpler compounds or elements) in everyday life: 1. Rust Fe  FeO 2. Burning coal, C  CO2 •

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 8

The Chemical Earth

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The stronger the chemical bonding in a compound, the more energy that is required to break the compound into atoms. Alternatively, the stronger the chemical bonding in a compound, the more energy that is released when the compound is formed from its atoms. 5. The properties of elements and compounds are determined by their bonding structure •

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

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Physical properties are those related to changes of state and physical changes, including lustre, hardness, ductility, conductivity etc.

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Chemical properties include relating to chemical changes, including reactivity and valency, which bonds will work and which won’t etc.

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

Melting and boiling points Conduct electricity?

Molecular solids Covalent molecular Low

Metallic Variable

No

Yes

Hardness and/or workability

Soft

Forces holding particles together in the solid

Intermolecular (between molecules)

Variable hardness; malleable and ductile Delocalized electrons (metallic bonding)

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Lattice Solids Ionic Covalent network High Very high As solid: no Molten: yes Dissolved: Yes Hard and brittle

No

Electrostati c

Covalent bonding throughout the crystal

Hard and brittle

The Chemical Earth

200 Reshad Azizi 8

• Distinguish between metallic, ionic and covalent bonds Metallic bonds are held together by a sea of delocalized electrons, with positive ions (cations) Ionic bonds are held together by the electrostatic attraction of positive and negative ions Covalent bonds are held together between anions (negatively charged ions) with weak intermolecular forces

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Describe metals as three-dimensional lattices of ions in a sea of electrons

Metallic bonding results in an orderly 3D array of positive ions held together by a ‘sea’ of delocalised electrons (valence electrons only). These electrons move freely throughout the lattice, holding it together and causing the metal to be a conductor of electricity. These delocalised electrons also hold the metal together when distorted – thus making metals malleable and ductile. The lattice formation makes metals hard. •

Describe ionic compounds in of repeating three-dimensional lattices of ions

Ionic bonding forms crystals; the electrostatic attraction between the opposite charges extends throughout the entire lattice. This strong attraction makes ionic substances hard, but also brittle; distorting the crystal bring opposite charges together – they repel each other – causing the crystal to shatter. This orderly array 10

The Chemical Earth

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means that in solid form, ionic substances do not conduct electricity; the ions are not free to move towards a charged electrode. However, when melted or dissolved in water, the arrangement of ions is broken up, allowing the ions to move towards an electrode, hence conducting electricity. •

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

Empirical Formula is the lowest ratio formula. It does not tell you the number of atoms present For example, NaCl means that for every 1 Na there is 1 Cl (not the exact amount of each element) ¬

The empirical formula is used for ionic compounds because the size of the lattice is unknown therefore a ratio must be used

Another example is glucose C6H12O6 is its molecular formula, whereas its empirical formula (lowest ratio) is CH2O Molecular Formula does tell you the number of atoms present. •

Identify common elements that exist as molecules or as covalent lattices

Covalent Molecules: -

Noble gases (monatomic)

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H2, O2, F2, N2 and Cl2 (diatomic gases)

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Br2 (liquid) and I2 (solid)

Covalent Lattices: -

Carbon; diamond (3D) and graphite (2D)

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

Ionic Lattices: the strong electrostatic attraction between the ions makes ionic substances hard, and they are brittle because any distortion of the crystal brings opposite charges into , and they repel each other. As solids, they do not conduct electricity as their ‘orderly array’ does not allow the ions to migrate 11

The Chemical Earth

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towards a charged electrode. When melted or dissolved in an aqueous solution, the orderly arrangement is broken up, allowing for the movement of ions towards the oppositely charged electrode. Covalent molecules: covalent molecular substances are soft, because their intermolecular forces (forces between pairs of molecules) are weak. These weak intermolecular forces also mean that covalent molecular have low melting and boiling points. Because covalent molecules are a neutral species, they do not conduct electricity as a pure substance or in a solution – however, some covalent substances react with water when mixed, and form ions capable of conducting electricity. Eg hydrogen peroxide → hydrochloric acid. Covalent network solids: covalent lattices are very hard and brittle (e.g. diamond, quartz), due to the covalent bonds that extend throughout the entire lattice. Apart from graphite, covalent lattices do not conduct electricity, as they do not contain any ions, and all the electrons are tied up in covalent bonds.

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