Chemistry Notes Term 1 – The Chemical Earth

1) Construct word and balanced formulae as they are encountered

Types of Chemical ReactionsSynthesis:

One new chemical being formed e.g. 2Mg(s)+O2(s) -> 2MgO(s)

A + B -> A:B

Decomposition:One chemical broken down into 2 or more

e.g.MgCO3(s) -> MgO(s)+CO2(g)

A:B -> A + B

Displacement Reaction: One chemical takes the place of another

e.g.CuSO4(aq) + Mg(g) -> MgSO4(aq) + CU(s)

A:B + C -> A:C + B

Double Displacement ReactionTwo chemicals takes the place of two others

e.g. Pb(NO3)2 + 2NaCl(aq) -> PbCl2 +2NaNo3(aq)

A:B + C:D -> A:C + B:DCommon ReactionsCombustion:

a) Element + Oxygen → Element Oxide

b) Hydrocarbon + Oxygen → Carbon dioxide + Water

Metal + Acid = Metal Salt + Hydrogen

Metal + Water = Metal Hydroxide + Hydrogen

Metal + Oxygen = Metal Oxide

2) Identify the difference between elements, compounds and mixtures in terms of particle theory.

All matter is made of continually moving matter Elements:

Simplest pure substances consisting of only one types of atom. They cannot be decomposed. They are homogenous.

Compounds: Pure substances composed of two or more elements that are chemically bonded

together. Have fixed amounts of atoms of each component bonded together and can be decomposed into elements or simpler compounds. Homogenous.

Mixtures: 2 or more elements or compounds that aren’t chemically bonded and are easily

separated by physical processes. Can be heterogeneous or homogenous.

Properties: There will be a combination of properties of the constituent chemicals. E.G. An Iron-Sulphur mixture would be a dirty yellow colour having blended the yellow of the sulphur with the grey of the iron.

3) Identify biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds The Earth and it’s spheres:

Biosphere: Where living things are found. Most living things are composed of cells. Cells contain large amounts of water,

hence, oxygen and hydrogen are abundant in the biosphere. Lithosphere:

Crust and top part of mantle Contains many different types of minerals that are combined in different

proportions to form sedimentary, igneous and metamorphic rocks. Hydrosphere:

Discontinuous layer on Earth Contains all soluble substances Water is abundant compound in the hydrosphere.

Atmosphere: Gaseous layer around the Earth

4) Identify and describe procedures that can be used to spate naturally occurring mixtures of: Solids of different sizes, Solids and Liquids, Dissolved solids in liquids, Liquids, Gases. Solids of different sizes

Sieving Used in:

(a) Cooking, bar screens and sewage filtration Solids and Liquids

Sedimentation and Decantation Solids of different mass either float or sink. By tipping the liquid and floating

substances, the sunken substances are left(a) Uses:

(i) Water Treatment Filtration

The less dense through(a) Uses:

(i) Sewage (ii) Swimming pool

Froth floatation Uses:

(a) Treatment of metal ore Dissolved solids and liquids

Fractional Distillation The apparatus contains a fractionating column which consists of hundreds of

glass beads. This arrangement allows for repeated condensations and evaporations, thus the solution is distilled 10-100 times. Liquid with the lowest b.p comes off first(a) Uses:

(i) Fractional Distillation of crude oil Evaporation

Different boiling points of liquids(a) Uses:

(i) Production of Salt Liquids

Centrifugation Liquids of different density

(a) Uses(i) Separation of colloids of milk, hence skim milk(ii) Separation of blood

Chromatography A medium (paper), then run the solvent up the medium which separates

mixture based solubility. The higher up it runs, the more soluble it is.(a) Uses:

(i) DNA profiling Separating Funnel

2 immiscible liquids(a) Uses

(i) Separating oil from water(ii) Extract perfume from mixture

Gases Fractional Distillation. Gases are condensed to liquid state then distil Differences in solubility. Gases are run through a series of “u” shaped tubes each

containing a substance that will dissolve a particular gas, thus leaving only the desired gases at the end.

Solids (Magnetic) Magnetic Separation

Uses(a) Rubbish recycler

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

6) Describe situations in which gravimetric analysis supplies useful data for chemists and Analysis of the composition of a substance by its mass or weight may be undertaken

to determine: The percentage of a required mineral Soil composition e.g. Sulfate content Extent of toxicity of a body of water Quality control Pollution control

% w/w = Percentage weight for weight E.g. Students analysed a 6.13g sample of fertiliser and determined that it

contained 2.13g of magnesium sulphate. What is the % w/w composition of MgSO4 in the sample? 2.13/6.13 = 33.8 % w/w

%w/v = Percentage weight for volume E.g. Water is 1g/cm3

7) ?8) ?9) Explain the relationship between the reactivity of an element and the likelihood of its

existing as an uncombined element Unreactive

Can exist freely because they do not require losing or gaining electrons, hence they do not react. This means they are able to exist by themselves.

Cannot exist freely because they are too reactive to be stable, hence by forming a stable shell, by combining with other elements or themselves, they can stabilise, hence exist as a compound.

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

10)Refer to notes11)Identify that matter is made of particles that are continuously moving and interacting

In particle theory, all matter is made up of constantly moving particles Metals

Particles are in order Vibrate

Liquids Particles are in less order Translational and vibrational

Gas Particles are well away from each other Rapid translational movement

12)Describe qualitatively the energy levels of electrons in atoms Valence electrons found in most outermost shell, therefore have highest energy The number of electrons indicates how reactive the element is

13)Describe atoms in terms of mass number and atomic number Mass number = Neutrons + Protons Atomic number = Proton number = Electron number

14)Describe the formation of ions in terms of atoms gaining or losing electrons Metals form cations (positive) when they are ions. This is because they are on the left

side of the periodic table, hence their valencies are 1+,2+ and 3+. It is much easier to lose electron than to gain.

Non-metals form anions(negative) when they are ions. This is because they are on the right side of the periodic table, hence their valencies are 3-,2-,1-. For them , it would much easier to gain electrons than to loose them.

If the element has a valency of 4, it either lose or gain. Hydrogen can also lose or gain an electron as it only has one electron, hence it is easy

for it both ways.15) See above16)Describe the formation of ionic compounds in terms of the attraction of ions of opposite

charge Ionic bonding is when Metals and Non-metals bond through electrostatic means

attraction. The Cation (Metal) gives the Anion(Non-metal) it’s valence electrons, hence forming a bond.

This bond is strong due to it’s lattice structure.17)Describe molecules as particles which can move independently of each other

Molecules are made up of several atoms joined together by intramolecular forces. Molecules are particles that may move independently of each other. The forces that

hold the molecules together are known as intermolecular forces. If these forces break (caused by energy such as hammer to shatter or boiling) the molecules break free from the intermolecular forces and roam free.

Intramolecular forces are broken down to start chemical reactions. Methods such as electrolysis can break intramolecular bonds, which allow atoms/ions to roam freely to make stable bonds. This energy is known as activation energy

18) Distinguish between molecules containing one atom (the noble gases) and molecules with more than one atom Mono-atomic molecules (Noble gases) Di-atomic molecules( H2,O2,N2 etc)

Only non-metals 19)Describe the formation of covalent molecules in terms of sharing of electrons

Covalent bonds form when non-metals share their electrons to reach a stable status. There are 3 types of covalent bonds

Single, Double and Triple bonds Covalent bonds can be polar, meaning the more electronegative element will attract

electrons more strongly There are 2 types of structures

Covalent Network Where molecules are held together by INTRAmolecular bonds Lattice structure

Covalent Molecular Where molecules are held together by INTERmolercular bonds

20)See workbook21)Identify the differences between physical and chemical change in terms of

rearrangement of particles

Chemical Change is when the intramolecular forces are broken, hence a new substance is produced Chemical Change Indicators

Colour change Precipitate forms -> New insoluble product Gas forms (bubbles) Energy Change

(a) Light(b) Heat(c) Sound(d) Electricity

Physical Change is when the intermolecular forces are broken, hence no new substances are formed, rather the substance just changes state. E.g. Ice into Water.

22)Difference between the boiling and electrolysis of water as an example of the difference between physical and chemical change

23)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 EXOTHERMIC -> gives off heat

Additional energy released as new bonds form e.g. light, sound and heat ENDOTHERMIC -> takes in heat

More energy taken in then given out therefore mixture usually cools down

Decomposition is the breaking of a compound

Synthesis is the formation of new compounds which is mostly initiated by heat but also by light and electrical energies.

24)Explain 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 amount of energy needed to decompose chemical compounds and mixtures is

indicative of the strength of the bonds. The easier the intermolecular bond is to break, the more reactive the element is. For example, Sulphate requires less energy to break its bonds as it is more reactive say, Magnesium Oxide.

Similarly in intramolecular bonds, the reason why some compounds can be broken by boiling while others can be broken by electrolysis indicates how strong the attraction is.

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

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

Ionic Covalent Network Covalent Molecular

Solid Solid Solids, Liquid

High mpt bpt High mpt bpt

Does not conduct electricity or thermal

Does not conduct electricity or thermal

Do not conduct electricity or thermal

Good conductor when molten

Brittle because distortion breaks covalent bonds

Does not conduct electricity unless reacted with water to form ions

Lattice Structure Lattices held by intramolecular forces

Held by weaker intermolecular forces

27)Distinguish between metallic, ionic and covalent bonds

Metallic bonding forms between metals. The structure is cations surrounded by a sea of delocalised anions Highly conductive electricity and thermal Malleable Solids besides Mercury Ductile The higher the group, the more electrons per atom, hence stronger bonds

Ionic bonding is between a metal and non metal – where the metal gives electrons while non metals take electrons May carry electrons in aqueous state

Covalent bonding is between non metals – where the non-metals share their electrons 2 types

Molecular Network

28)Describe metals as 3D lattice of ions in a sea of electrons Metallic bonding is cations in a sea of anions made up of 3D lattice

29)Describe ionic compounds in terms of repeating 3D lattices of ions Ionic compounds form 3D crystal lattices, causing them to be very strong and not able

to conduct electricity/thermal. The cations and anions bond infinitely, hence it repeats

30)Explain why the formula for an ionic compound is empirical Because ionic compounds can form infinitely, it would be impractical to record the

exact amount of anions and cations, instead, we find the ratio – which is the empirical formula was use.

31)Identify common elements that exist as molecules or as covalent lattices Covalent Molecules

All diatomic gases Nitrogen, Oxygen, Iodine, Fluorine Phosphorous exists as P4

Sulfur exists as S8

Covalent Lattices Carbon exists as diamond 3D lattice and graphite 2D lattice

32)Explain the relationship between the properties of conductivity and hardness and the structure of ionic, covalent and network structures Ionic

Hard (Lattice) Non conductive (No free electrons however there are in aqueous)

Covalent Network Hard Non conductive

Covalent Molecular Weaker bonds