Year 10 Advanced Science – Chemistry Notes by Mr. E Hung @2010 May – revised 2013

1. Differences between Element, compound and mixture

Element = a pure substance consists of only one kind of atom that can’t be separated into simpler parts. Eg. Gold, Sodium, Oxygen, Mercury

Compound = a pure substance consists of two or more kinds of atoms (elements) chemically bind together that can’t be separated by physical means.Eg. carbon dioxide, sodium chloride, copper sulphate

Mixture is a substance consists of 2 or more substances that can be elements or compounds. A mixture can be separated into its components by physical methods.Eg. Air, Mineral water, milk, cake mix

A homogeneous mixture has the same uniform appearance and composition throughout. Eg. sugar solution, mineral water, colloid

A heterogeneous mixture consists of visibly different substances or phases. Eg. A suspension, emulsion

2. What is a molecule?Molecule = the simplest structural unit of an element or compound. Some elements can exit as a single atom, eg. Na, Ne, Au but others can’t. Eg Oxygen as O2, Nitrogen as N2, Chlorine as Cl2. Each is the smallest molecule or structure of an element. A compound consists of more than one kind of atom chemically combined together, eg. Carbon dioxide as CO2, Copper sulphate, CuSO4.

3. Symbols for First 20 and 20 other common elements:H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K CaHorrible Heary Little Begger Boys Catch Newts On Friday Near Naples, Magnificent Albert Sits Planning Some Clever Arrangement Keeping Calm.

Fe Ag Au Zn Pb Cu Ti U Br I Hg Ni W Ba Sr Cr Co Sn Cs Fr

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4. Electronic Configuration of the First 20 ElementsGp 1AlkaliMetals

Gp 2Alkaline

Earth Metals

Gp 3 Gp 4 Gp 5 Gp 6 Gp 7Halogens

Gp 8Noble Gases

Period 1 H(1)

He(2)

Period 2 Li(2, 1)

Be(2, 2)

B(2, 3)

C(2, 4)

N(2, 5)

O(2, 6)

F(2, 7)

Ne(2, 8)

Period 3 Na(2, 8, 1)

Mg(2, 8, 2)

Al(2, 8, 3)

Si(2, 8, 4)

P(2, 8, 5)

S(2, 8, 6)

Cl(2, 8, 7)

Ar(2, 8, 8)

Period 4 K(2, 8, 8, 1)

Ca(2, 8, 8, 2)

Br

Sr I

Ba NinaPascoe

Out-Standing

5. Atomic Structure – showing the Protons, Neutrons and Electrons (electronic configuration)PEA (Proton number = Electron number = Atomic number)Atomic Mass = Protons + Neutrons (Neutrons = Mass – Protons)

Magnesium (Mg) (2,8,2) Carbon (C) (2,4) Sodium (Na) (2,8,1) Argon (Ar) (2,8,8)P=E=A=12Nucleus:12P + 12NMass = P+N= 24

PEA = 6Nucleus: 6P + 6NMass = 6+6 = 12

PEA = 11Nucleus: 11P + 12 NMass = 11+12 = 23

PEA = 18Nucleus: 18P + 22NMass = 18+22 = 40

6. What are Isotopes? Isotopes are different types of atoms of the same chemical element, each having a

different number of neutrons. They differ in mass number but not in atomic number. The number of protons (the atomic number) is the same because that is what

characterizes a chemical element. Eg. carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with

mass numbers 12, 13 and 14, respectively. The atomic number of carbon is 6, so the neutron numbers in these isotopes of carbon

are therefore 12−6 = 6, 13−6 = 7, and 14–6 = 8, respectively. The mass number of an atom is not a whole number because of the presence of

isotopes. Eg. Chlorine has a mass number of 35.5 (Proton = 17, Neutron = 18 or 20)

Chlorine consists of atoms of isotopic masses 35 (75%) and 37 (25%)Average Mass =( 35 x 0.75 ) + ( 37 x 0.25 ) = 35.5

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1 2

3 754 6 8 9 10

11 12 13 14 15 16 17 18

19 20

2

7. Electron Dot or Lewis Diagram: Scientists have devised a simple way to illustrate these outer shell electrons using

simple diagram. These electrons also called valence electrons. It is these valence electrons that make similar property of the elements within the

group.

8. Formation of Ionic Compounds

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[Mg]2+ [ O ]2-OMg

One Magnesium atom donates 2 electrons, being accepted by one atom of oxygen.(Two hands to two holes) MgO

3

9. Formation of Covalent Compounds – Covalent Bonding

simply O=O

simply O=C=O

simply

10. Differences between Ionic and Covalent CompoundsIonic Compounds Covalent Compounds

Elements involved Between Metal and Non-metal Non-metals onlyElectrons Donating and Receiving Electrons Sharing ElectronsExist as Ions in water or solid lattice Neutral moleculesBonding Weaker forces between ions

But strong forces in solid stateStrong forces between atomsBut weak forces between molecules

Melting and boiling points Very high Very lowConducting electricity Conducts electricity in molten or aqueous

form due to the presence on ionsCan’t conduct electricity – no ions – neutral molecules only

Examples Solid like Sodium chloride Solid like glucose, liquid like water and gas like carbon dioxide

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Each Na+ ion in NaCl is surrounded by six Cl- ions, and vice versa. Removing an ion from this compound therefore involves breaking at

least six bonds. Some of these bonds would have to be broken to melt NaCl, and

they would all have to be broken to boil this compound. As a result, ionic compounds such as NaCl tend to have high

melting points and boiling points. Ionic compounds are therefore solids at

room temperature. Cl2 consists of molecules in which one

atom is tightly bound to another, as shown in the figure above. The covalent bonds within these molecules are at least as strong as an

ionic bond, but we don't have to break these covalent bonds to separate one Cl2 molecule from another.

As a result, it is much easier to melt Cl2 to form a liquid or boil it to form a gas, and Cl2 is a gas at room temperature.

11. What are metallic bonds? In the metallic bond, an atom achieves a more stable

configuration by sharing the electrons in its outer shell with many other atoms.

The valence electrons are not closely associated with individual atoms, but instead move around amongst the atoms within the crystal.  

Therefore, the individual atoms can "slip" over one another yet remain firmly held together by the electrostatic forces exerted by the electrons.  

This is why most metals can be hammered into thin sheets (malleable) or drawn into thin wires (ductile).  

When an electrical potential difference is applied, the electrons move freely between atoms, and a current flows.

12. Writing Chemical Formula for Ionic Compounds: M=Metal; N=Non-metalCation Anion/ Radical Chemical Formula Examples

M 1+ N 1- MN NaCl, LiF, KI, NaOH, KNO3, NH4Cl

M 2+ N 2- MN MgO, CaS, MgSO4

M 3+ N 3- MN AlPO4

M 3+ N 2- M2N3 Al2O3

M 2+ N 3- M3N2 Ca3(PO4)2

M 2+ N - MN2 BaBr2, MgCl2

M 1+ N 2- M2N Li2O, (NH4)2SO4

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13. Giant Covalent Bonds: eg. Diamond, Graphite and Silicon Dioxide (glass/sand).

very high melting points because all atoms are held firmly in place by strong covalent bonds. In graphite each carbon atom is held in place by three strong covalent bonds which gives

graphite a high melting point. In diamond 4 strong covalent bonds holds each atom in place. This also gives diamond a very

high melting point.  The four bonds make diamond very hard. Graphite has weak bonds between layers so the layers slip over each other making graphite

soft. Silicon dioxide has a high melting point - around 1700°C. Very strong silicon-oxygen covalent

bonds have to be broken throughout the structure before melting occurs.

14. Physical Properties of Metals: They are good conductors of heat and electricity. They are malleable and ductile in their solid state. They show metallic luster. They are opaque. They have high density (except lithium and sodium) They are solids (except mercury) They have crystal structure in which each atom is surrounded by eight to twelve near neighbors

15. Chemical Properties of Metals: They have one to four valence electrons. They readily lose electrons to form Cations – forming ionic compounds. Metals can be easily oxidized. Oxidation is informally known as the process of

corrosion. Iron + Oxygen + Water Iron oxide (hydrated) = RUSTFe(s) + O2(g) + H2O(I) Fe2O3 . x H2O(s)

Metals can react with acid in a single displacement reaction to make hydrogen gas and an aqueous solution of a salt.Magnesium + Hydrochloric acid Magnesium chloride + Hydrogen gasMg + HCl ---------> MgCl2 + H2

Some reactive metals, like sodium or calcium will react with water to make a base.

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Diamond Silicon dioxide

6

16. What are Transition Methods?

A group of hard, tough metal elements, which conduct electricity. Includes well known metals such as gold, silver, iron, copper and platinum. There are 38 of them with 1 to 4 valence electrons, Many have variable valence electrons:

Copper (I) & Copper (II), Iron (II) & Iron (III) Very hard and strong Higher densities High melting points High boiling points High electrical conductivity Malleable and Ductile Not as reactive as Group 1 and Group 2 elements (metals) Compounds with colours

From left to right, aqueous solutions of: Co(NO3)2 (red); K2Cr2O7 (orange); K2CrO4 (yellow); NiCl2 (turquoise); CuSO4 (blue); KMnO4 (purple).

17. There are 7 evidences of chemical reactions:(1) A change in colour

(2) Heat may be given out as you can feel the warmth of the test tube – exothermic (3) Heat may be absorbed from the surrounding, giving you the feeling of cold - endothermic(4) A Precipitate is formed from mixing 2 solutions

(5) Fizzing or bubbling implies a gas is formed.(6) Sound may be given out.(7) Light may be given out.

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18. Different types of Chemical Reactions:

Reaction type What happens? One Example

CombinationOr Synthesis

2 simple chemicals react together to produce a more complicated chemical. A+ B ----- > C

Combustion(Burning)

The combination of a substance with oxygen. The products are carbon dioxide, water

CH4(g) + O2(g) CO2(g) + H2O (l)

C2H5OH(g) + 2O2(g) CO2(g) + 3 H2O (l)

Decomposition A larger molecule is broken down into smaller or simpler chemicals.D ------ > E + F

Calcium Carbonate Calcium Oxide+ Carbon dioxide

2CaCO3 2CaO + 2CO2

Hydrogen peroxide2H2O2 2H2O + O2

SingleDisplacement

An element replaces the metal part of a compounds and the metal in this compound is deposited as free metal. (related to Metal Reactivity Series)M1 + M2N -------- > M1N + M2

Zinc + Copper Sulphate Zinc Sulphate + Copper

(The blue colour of the Copper sulphate solution disappeared)

No reaction if it is:Copper + Zinc sulphate (as copper is a weaker metal than Zinc)

Double Displacement(Replacement)

Two solutions with ions are mixing up with the formation of new products. Both cations and anions are swapping around.M1N1+ M2N2 -------- > M1N2 + M2N1

NB: Neutralisation Reaction &Precipitation Reaction are Double Displacement reaction

PrecipitationReaction

A precipitate (a solid) is formed from mixing 2 solutions together.NB: Precipitation Reactions are Double Displacement reaction

Lead Nitrate + Potassium Iodide Lead Iodide + Potassium Nitrate(Lead Iodide is a yellow precipitate)

Neutralisation(Acid and Base)

An acid reacts with an alkali to form a salt and waterThe hydrogen ion and hydroxyl ion combine to form waterNB: Neutralisation Reactions are Double Displacement reaction

Hydrochloric acid + Sodium hydroxide Sodium chloride + water

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19. Reactivity Series: By studying replacement reactions we can arrange the metals in decreasing order of

reactivity.

K Na Ca Mg Al Zn Fe Pb Cu Ag Au

Most Reactive ---------------------------------------------------------------------- Least Reactive aluminum will replace zinc in an aqueous solution of a zinc compound. Silver will not

replace tin. (Single Replacement Reaction)

Summary of the Reactivity of metals with water and acid:Metals Remarks

Stored in Oil K, Na Extremely reactive; reacts vigorously with oxygen (air))

Reacting with water K, Na, Ca Highly reactive metals

Reacting with acid K, Na, CaMg, Al, Zn, Fe, Pb

Reactive metals

No Reaction Gold Au Unreactive – not reacting with oxygen

20. What are Alloys?

A mixture of two or more metals, or a metal and a non-metal. For example, brass is an alloy of copper and zinc, and steel is an alloy of iron and carbon.

An alloy is created for its desirable properties that can’t be obtained from the pure metal. Some common Alloys used in our daily life:

21. Methods of preventing Corrosion of Metals:

1. Painting - to prevent contact between the metal and oxygen2. Coating with Plastic, Oil, Grease or Tar - to prevent oxygen contact with the metal3. Coating with Metal - Galvanising iron with zinc4. Sacrificial Protection - enclosing a metal to be protected with a more reactive metal

which will corrode first22.

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