the chemical earth robin notes

8/4/2019 The Chemical Earth Robin Notes

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Robin Nandy Year 11 Chemistry The Chemical Earth

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The Chemical Earth

Identify the difference between elements, compounds and mixtures in terms

of particle theory

Classification of Matter:

Properties of Matter:

The physical properties of a substance can be observed or measured without changing thecomposition and identity of a substance

Physical properties include colour, density, melting point (MP), boiling point (BP), electricalconductivity and heat conductivity

Chemical properties can only be observed during chemical reactions A chemical reaction is any process in which the identity and composition of at least one

substance is changed Thus they can only be observed when a new substance forms

Solutions:

Any homogenous mixture of two or more substances Solutions consist of the two components; the solvent and the solute (or solutes) The solvent is the component present in the larger amount The solute is the component present in the smaller amount The solvent is the medium in which the solution has dissolved Any solution where the water is the solvent is an aqueous solution

Mixture: Can be separated into two or more

pure substances (which retain their

properties) by physical or mechanical means

Pure Substance: has a constant and definite

composition and cannot be separated into two

or more substances by physical or mechanical

means

Element: a pure

substance which

cannot be

decomposed into

simpler substances

e.g. gold/iodine

Compound: a pure

substance which can

be decomposed into

simpler substances

e.g. water/table salt

Homogenous:

substances with

uniform composition

throughout (can also

be pure substances)

e.g. water/petrol

Heterogeneous:

substances having

non-uniform with

different portions

having different

compositions

e.g. wood/ice water

Matter


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Distinguishing Between Pure Substances and Mixtures:

The melting point is the temperature at which the solid and liquid state are set to be atequilibrium

The boiling point is the minimum temperature at which liquids are converted to vapours byheating i.e. the temperature at which vapour pressure = surrounding pressure

A mixture will have a range of melting points (homogenous in this diagram) A pure substance will have a sharp definite melting point

Identify that the biosphere, lithosphere, hydrosphere and atmosphere

contain examples of mixtures of elements and compounds

Sphere Description Examples

Biosphere The portion of the earth

inhabited and used by living

matter consisting of the other

three spheres. Contains all livingor once living organisms of the

earth.

This refers to animals, plants, algae and

bacteria which are mainly mixtures of

compounds such as carbohydrates,

proteins, fats and vitamins. Most areinsoluble making up the structure

whereas the soluble substances cause

the functioning of the organism

Lithosphere The crust and the top portion of

the mantle including land masses

and the ocean floor

Contains a diverse range of mixtures

including rocks, sand, soil, mineral ores,

coal, oil and carbon. These mixtures are

mainly made up of compounds of Si or O

whereas there are very few un-

combined elements such as Au, Ag, Pt, S

and C

Hydrosphere The water of the earths crustsuch as salt water in oceans, fresh

water in river or lakes and ground

water stored under the earths

surface

Also contains a range of mixtures inwhich the main component is H2O. The

fresh water usually contains small

amounts of compounds from the

elements H, O, Na, Cl, K, Mg and Ca. It

also contains suspended solids and

organisms meaning it is heterogeneous.

Sea water is a mixture of NaCl and H2O

whereas ground water is similar to river

water with more compounds of Cl and S

Atmosphere Layer of gas about 200 to 300 km

thick which surrounds the planet

Mixture of gases i.e. elements such as

O2, N2, Ar and small compounds such asCO2 and CH4


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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 and gases

Properties of mixtures that can be used to separate components include: particle size, particledensity, boiling point, melting point, magnetism, solubility and charge. The term used to describe

the separation of these properties is known as physical separation method.

Solids from solids:

Magnetic separation- Uses magnetic properties of substances- Can be used to separate mixtures where not all substances are magnetic- Is usually used to separate iron ore from other minerals-

Also used to separate valuable minerals such as ilmenite from beach sand Sieving

- Uses the different sizes of substances to separate them- The equipment used (sieve) must contain holes that are between the size of the solids

being separated

- Is often used in kitchens as well as industrial uses including separating fine sand andgravel for concrete and mortar

Undissolved solids from liquids

Sedimentations and decanting- Uses density of substances to separate them- The denser solid will fall to the bottom as sediment- The liquid can then be decanted, thus separating the two- This requires the solid to be insoluble- Can be used to decant sediment from wine

Filtration- Uses different sizes of substances to separate them- If the solid remains suspended in the liquid- Then it can be filtered through filter paper and filter- The liquid will pass through becoming the filtrate- Whereas the solid will remain as the residue- Can be used to separate sand and water

Centrifugation- Uses density and mass of substances to separate them- The spinning force of the centrifuge causes suspended solids to separate- This is due to the increasing rate at which they sick to the bottom- This method can be used to separate different parts of blood


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Dissolved solids from liquids (Solutions)

Evaporation- This uses the different volatilities (ease at which substance changes into gas) of solvent

and solute to separate them

- The more volatile substance(usually the liquid) will evaporate first- This leaves the solute to crystallize into a solid but the solvent disappears- Salt water is separated using this method

Distillation- This uses the dissimilar boiling points of substances- Can be used to separate solids and liquids but more frequently used to separate liquids

Liquids from liquids (miscible)

Distillation and condensation- This uses the dissimilar boiling points of two

miscible liquids i.e. liquids that mix to form a

solution

- The mixture is boiled, the vapours arecollected and then they are condensed

- The liquid with the lower boiling pointvaporises first and then the heating is

stopped

- This vapour is then condensed and collectedas the distillate

Fractional Distillation- This also uses dissimilar boiling points but are for those liquids which

have BPs close together (100 degree range)

- This is similar to normal distillation except for the use of a fractionatingcolumn

- This fractionating column e.g. glass beads provides asurface on which the liquids can cool and condense

- The liquid with the lowest boiling point (highestvolatility) reaches the top of the column and proceeds to

the condenser

- However liquids with higher boiling points condensemore readily and trickle back down to the flask

- Can be used to separate crude oil


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Liquids from liquids (immiscible)

Separating funnel- This uses the density and insolubility of the immiscible liquids

to separate them

- Since these liquids have different densities they form distinctlayers with a junction in between

- The tap is opened to let the denser liquid flow out and closedat the junction to retain the less dense liquid

Gases from gases

Fractional distillation- (same as before) however the gases must be first be liquefied by compressing them

Assess separation techniques for their suitability in separating examples of

earth materials, identifying differences in properties which enable these

separations

The separation of mixtures depends on the differences in the physical properties of thecomponents. The separation technique applied is based on those differences

If the mixture contains several substances, the order in which each is separated must beconsidered to ensure success of later steps

Simplicity and practicality must also be consideredSeparation Technique Properties Used

Magnetic separation Magnetism

Sieving Size

Sedimentation and decanting Density and insolubility

Filtration Size and insolubility

Centrifugation Density and Mass

Evaporation Volatility (Boiling points)

Distillation and condensation Boiling points

Fractional distillation Boiling points

Separating funnel Density and insolubility

Describe situations in which gravimetric analysis supplies useful data for

chemists and other scientists

To decide whether a newly discovered mineral deposit contains a sufficiently highpercentage of the required compound to make its extraction from that deposit economically

viable

To determine composition of soil in a particular location to see if it is suitable for growing acertain crop


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To determine the amounts of particular substances present in water or air to decide howpolluted samples are

To decide whether a particular commercial mixture being sold has the same percentagecomposition as a similar mixture being marketed

Apply systematic naming of inorganic compounds as they are introduced in

the laboratory

In Ionic compounds: Cations come first and remain the same

In Acids:

In molecular compounds: The element with the more positive nature in a compound isnamed first. The second element is named with an -ide ending and prefixes are used to

identify the relative number of atoms in such compounds

Prefix Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca Undeca Dodeca

No. 1 2 3 4 5 6 7 8 9 10 11 12


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Identify IUPAC names for carbon compounds as they are encountered

No. Of C

Atoms

1 2 3 4 5 6 7 8 9 10

Prefix meth eth Prop but pent hex hept oct non dec

Find the longest chain of carbon atoms and the number will give you one of the prefixesabove

If all bonds in this chain are single then it will be an alkane and thus end with the suffix anee.g. butane

If there is a double bond in the chain then it will be an alkene ending with the suffix ene e.g.butane

If there is a triple bond in the chain it will be an alkyne ending with the suffix yne e.g. butyne If there are any alkyls (alkenes with ones less hydrogen atom) attached to these bonds

then there will be a alkyl at the front with a number indicating on which part of the chain it

is bonded e.g. 2-methylbutane

Explain the relationship between the reactivity of an element and the

likelihood of its existing as an uncombined element

Reactive elements are those that readily form other substances by reacting with otherelements

Thus the more reactive an element the more readily it will form compounds Most elements are found naturally occurring in compounds with very few occurring in their

pure state

Group 1, the alkali metals are the most reactive due to their 1 valence electron and thusmakes them more likely to lose this and combine with other elements to achieve full

electron configuration

Group 2, the halogens are also very reactive due to their 7 valence electrons making themmore likely to achieve full electronic configuration by attracting another electron

Group 8, the noble gases are also known as inert gases because they do not react withanything at room temperature due to their stable electronic configuration of 8 outer shellelectrons

The reactivity of most transitionmetals vary however there are a

few such as palladium, platinum

and gold are also unreactive


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Classify elements as metals, non-metals and semi-metals according to their

physical properties

Physical Property Metal Non-Metal

State at room temperature Solid except mercury Solids or Gases except for bromine

Lustre Shiny Dull

Density High Low

Conductivity (heat & electricity) Good Bad except carbon

Strength High tensile strength Brittle

Malleability Can be rolled into sheets Cannot

Ductility Can be drawn into wires cannot

There are several elements which are difficult to classify as they have properties from bothclasses. These are known as semi metals which include B, Si, Ge, As, Sb, Te

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

properties

Metals are usually used for- building materials (strength, low reactivity)- cars, planes, trains (lustre, malleability, strength, densities)- machinery (MP, strength)- electrical wiring (conductivity, ductility, MP, low reactivity)- domestic appliances (conductivity, lustre)- jewellery (lustre, MP, malleability, tensile strength)

Non-metals used in elemental form- Carbon (graphite) in electrodes, dry cells and as a lubricant- Oxygen for medical purposes- Chlorine for bleach, disinfectant and making plastic (PVC)- Argon for filling electric light bulbs- Many compounds of non-metals are used in fuels, fertilisers, synthetic materials, drugs,

cosmetics and detergents

Identify that matter is made of particles that are continuously moving andinteracting

All matter is made of particles In solids these particles are packed closely together in an orderly array with strong forces

holding them together

This causes solids to have definite shapes and be relatively hard However they are not stationary but rather vibrating slightly in their fixed positions In liquids the particles are much more free as forces holding them together are relatively

weak


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Thus liquids do not have definite shapes but rather take the shape of the container they areplaced in as they vibrate as well as make random translational movements

In gases particles have very weak (basically none) forces of attraction and thus move veryrapidly and spread out to fill the whole volume available

Compressing particles refers to pushing them closer together Thus solids and liquids cannot be compressed much since they are already close together

but gases can easily be compressed

Describe qualitatively the energy levels of electrons in atoms

Energy levels also known as shells refer to the orbital path of electrons around the nucleusof an atom

Stating the number of electrons in each consecutive shell as a set of numbers is known asthe electronic configuration

The theoretical maximum number of electrons that can be contained in each energy level isrepresented by the formula 2n^2

8 valence shell electrons is a stable configurationDescribe atoms in terms of mass number and atomic number

These Mass Numbers are the relative masses of atoms... obviously one atom has a verysmall value when measured in grams (1 hydrogen atom 1.7 x 10-27 kg)

Mass numbers are always whole numbers, since there must be whole numbers of protonsand neutrons in each atom, they are not the number on the periodic table but rather the

atomic weight rounded to the nearest whole number

Atomic number represent the number of protons that are present in an atom which is equalto the number of electrons in a neutral atom

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

If an atom has an incomplete outer shell, it may either gain or lose electrons to obtainelectron configuration of its nearest noble gas neighbour, thus becoming charged

Atoms which have lost or gained electrons are charged and known as ions An atom is electrically neutral i.e. p+=e+ When atoms lose electrons it means that p+>e- therefore they have a positive charge and

become cations

When atoms gain electrons it means e->p+ therefore they have a negative charge andbecome anions


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Apply the periodic table to predict the ions formed by atoms gaining or losing

electrons

The periodic table can be used to predict the ions formed by metals and non-metals byobserving their group

Groups 1-3 will form cations with the charges respective to the numbers of the group Groups 5-7 will form anions with charges respective to the numbers of their opposite groups

(1-3)

Group 4 can vary, forming both positive and negative charges of 4 Group 8 does not produce ions as they have stable electronic configuration The transition metals have varying charges but all form cations

Apply Lewis electron dot structures to:

- the formation of ions- the electron sharing in come simple molecules

The lewis dot electron dot diagrams of an atom simply show the symbol of the element andits outer shell electrons (represented by dots) e.g.

To represent a cation, the dots are simply removed as it has lost electrons and the symbolstands alone with brackets and its charge e.g.

To represent an anion, all (8) dots around the symbol will exist as it has gained electrons aswell as brackets and the charge of the ion e.g.

When representing ionic compounds, simply combine the two above e.g. When representing molecular compounds draw the atoms, sharing electrons e.g. The dots for the different atoms should be in different colours Here is an example of a more complex Lewis dot electron for ammonia e.g.

Describe the formation of ionic compounds in terms of the attraction of ions

of opposite charge

When an atom such as that of Na comes near an atom of Cl, the sodium loses its oneelectron to the chlorine and thus has more protons becoming a cation

The chlorine which originally had 7 valence electrons now has a full shell of 8 and thus hasbecome an anion

The opposite charges of these ions cause electrostatic attraction and result in the formationof an ionic compound


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Describe molecules as particles which can move independently of each other

A molecule is the smallest particle of a substance that is capable of separate existence They are like groups of atoms stuck together Thus they have the ability to move independently of each other

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

molecules with more than one atom

The molecules containing just one atom are known as monatomic molecules and are thenoble gases

They contain just one atom because they have a full electronic configuration and aretherefore stable enough to exist alone

However other elements such as oxygen and most other gases exist as diatomic moleculesmeaning they contain 2 atoms

These bonds between molecules in a chemical reaction can be broken during chemicalreactions such as the formation of H2O

Describe the formation of covalent molecules in terms of sharing electrons

Covalent molecules are from covalent bonds that are formed between pairs of atoms by thesharing of electrons

For example two chlorine atoms form a covalent molecule because each chlorine atomneeds one electron to achieve full electronic configuration

Thus they share one electron from each other and form a covalent bond thus becoming acovalent molecule

Construct formulae for compounds formed from:

- Ions- Atoms sharing electrons

For ionic compounds, the formula is empirical and shows the ratio of each ion in thecompound e.g. NaCl has a ratio of 1:1

For atoms sharing electrons (molecules) we use molecular formula which simply shows theamount of atoms of each element in each molecule e.g. water is H2O meaning there are 2

hydrogen atoms and one oxygen atom

Identify the differences between physical and chemical change in terms of

rearrangement of particles

Physical Changes:

Can occur when a substance changes state, size, shape and is dissolved or separated from amixture

No new substances have been created and the particles of the substance remain the same


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Chemical changes:

Can occur when a substance burns, two elements combine to form a compound, a newsubstance forms or disappears

In this type of reaction, new particles are formed but atoms remain the same they have been rearranged into new molecules or ions

Summarise the differences between the boiling and electrolysis of water as

an example of the difference between physical and chemical changes

Boiling of water (Physical Change)

Heat is the energy applied to the liquid water This heat energy causes the intermolecular forces between the various H20 molecules to

break

This results in the formation of H20 gas or water vapour Since the H20 molecules are still present, no new substances have been formed and none

have disappeared

This indicates it is a physical changeElectrolysis of water (Chemical Change)

Electricity is the energy applied to the water This electricity causes the intramolecular forces between the hydrogen and oxygen atoms in

the individual molecules to break

This results in the formation of O2 and H2 molecules The H20 molecules have disappeared and the new substance in the form of oxygen and

hydrogen molecules have formed

This indicates that it is a chemical changeIdentify 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

Decomposing a compound into elements requires a large input of energy because it isnecessary to overcome the strong chemical bonds holding the atoms together in compounds

Synthesis is the formation of a compound and because the high reactivity of most naturalelements, this reaction releases a tremendous amount of energy. Recall that atoms release

energy as they become stable.

Form of Energy Synthesis (released) Decomposition (absorbed)

Heat When copper or steal rusts to

form iron(III)oxide it releases

heat energy

Motor car air bags where sodium azide is

decomposed to sodium and nitrogen gas (by

igniting with a detonating cap)

Light Silver magnesium burns in air to

produce magnesium oxide

Silver chloride is a white solid which turns

purple then black due exposure to the sunlight


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Electricity Lightning causes nitrogen and

oxygen in the air to form NO

(nitric oxide)

Aluminium is extracted commercially by

electrolysing molten aluminium oxide

Explain the amount of energy needed to separate atoms in a compound is anindication of the strength of the attraction, or bond, between them

The stronger the chemical bonding in a compound either due to the electrostatic attractionin ionic compounds or intramolecular forces of molecular compounds the more energy

required to break the compound into elements

Alternatively the stronger the chemical bonding, the more energy released when thecompound is formed from its elements

Identify differences between physical and chemical properties of elements,

compounds and mixtures

Elements and Compounds are all pure substances Each element, and each compound has its own unique properties which are characteristic

and do NOT vary

Compounds have different properties from the elements that it is made of Mixtures are not pure. The properties ofmixtures are usually a blend of the properties of

its parts, and vary according to its exact composition.

An example of the differences in properties can be seen through the comparison ofmagnesium oxide, magnesium and oxygen:

Describe the physical properties used to classify compounds as ionic or

covalent molecular or covalent network

The main physical properties used to distinguish between covalent networks and covalentmolecular are MP, BP and hardness

The MP and BP differ because of the strength of the covalent bonds between the atoms inthe covalent networks cause MP and BP to be very high

Whereas the intermolecular forces of the covalent molecular bonds are weak and thus theyhave low-medium MP and BP

Since the covalent networks are bonded so strongly, they are very hard but brittle at thesame time

Covalent molecular substances (if solid) are usually waxy and soft but can also be hard andbrittle

Properties Magnesium Oxygen Magnesium oxide

State Solid Gas Solid

Colour Silver Colourless White

Reaction with acid H2 gas evolved No reaction No reaction


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Distinguish between metallic, ionic and covalent bonds

Metallic bonding occurs as a three dimensional lattice of positive ions immersed in a sea ofdelocalised electrons

Ionic bonding occurs due to the outright transfer of electrons from one to another causingelectrostatic attraction of ions with opposite charges

Covalent molecular bonds are formed from the sharing of electrons between differentatoms

Covalent networks are lattices in which covalent bonding extends indefinteley throughoutthe whole crystal

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

Metal consists of an orderly three dimensional array of positive ions held together by amobile sea of delocalised electrons

The valence electrons break away from their atoms leaving behind positive ions These free electrons are known as delocalised because they are no longer part of a

particular atoms but move randomly through the lattice

By being shared by several positive ions, they provide the chemical bonding holding thecrystal together

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

ions

There are no separate molecules in ionic compounds Due to the several ions of opposite charge, a crystal lattice forms and all ions of opposite

charge are attracted to each other and thus held tightly

This causes am infinite array of positive and negative ions resulting in the formation of athree-dimensional lattice

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

Due to the fact that ionic compounds occur a indefinite three-dimensional lattices it isimpossible to calculate the exact number of atoms

Thus when writing a formula for a ionic compound the simplest ratio of positive ions tonegative ions is presented known as the empirical formula

Indentify common elements that exist as molecules or as covalent lattices

There are the seven (halogens) diatomic molecules H2, N2, O2, F2, Cl2, Br2, I2 as well as P4 andS8 which all exist as molecules in nature

All other gases exist as monatomic molecules Carbon exists in two different covalent networks including diamond and graphite Often when an element has more than one molecule or lattice they are known as allotropes

and have different physical and chemical properties

Oxygen has O2 and O3


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Phosphorus can also be found in both molecular and lattice forms of P4 Sulphur has crystalline and molecular forms of S8 Tin can also occur in different structures

Explain the relationship between the properties of conductivity and hardness

and the structure of ionic, covalent molecular and covalent network

structures

Ionic Compounds

Solid ionic lattices will NOT conduct because ions cannot move freely because the ions areheld tightly together by electrostatic forces

However, if an ionic compound is melted, the (+ve) and (-ve) ions can move freely andindependently

If a voltage is applied, a current will be carried by the ions migrating in opposite directions Many ionic compounds are soluble in water When they dissolve, the lattice disintegrates and the ions can move freely allowing it to

conduct electricity

Ionic compounds are usually hard due to their electrostatic attraction causing strong bondbetween atoms

However if the ions are shifted, ions of opposite charge come closer together and repel eachother causing the crystal to shatter

Covalent Molecular

Covalent molecular substances do not contain any charged particles which can moveindependently and thus are unable to conduct elecetricity

Because the intermolecular forces holding the molecules together are weak, means that iteasy to distort the substance and therefore it is soft

Covalent network structures

These do not contain any charged ions and there are no free electrons thus are not able toconduct electricity

However they are very hard due to their strong covalent bonds but can be shattered easily

the chemical earth robin notes

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