Lecture 4 Physical and Chemical Properties

of Substances II

Human Biology and Organic Chemistry I HS 37-006-31 (41)

Dr. Thomas Lui (thomas81hk@gmail.com)

1. Chemical equation

2. Chemical properties of elements in different group of the periodic table

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Chemical Property

A property or characteristic of a substance that is observed during a reaction in which the chemical composition or identity of the substance is changed e.g. Combustion Toxicity Oxidation Flammability

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Chemical Equation

Symbolic representation of a chemical reaction

Reactants → Products

Reactants • Starting materials in a chemical reaction • Altered or incorporated into another substance in a chemical reaction

Products

• Substances that are formed as the result of a chemical reaction

e.g.

2H2(g) + O2(g) → 2H2O(l)

Reactants Product

Gas Liquid

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Chemical Properties of Group 1 elements (ns1)

Group 1 elements : alkali metals • Soft, extremely reactive metals, explode while exposure to water • Ductile and malleable • Formation of +1 ions

Reaction with water

2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)

• Reactivity increases down the group

Li : gently Na : violently K : explosive

e.g. 2Na + 2H2O → 2NaOH + H2

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Chemical Properties of Group 1 elements (ns1)

Reaction with oxygen

4M(s) + O2(g) → 2M2O(s) Metal oxide

2M(s) + O2(g) → M2O2(s) Metal peroxide

M(s) + O2(g) → MO2(s) Metal superoxide

Group 1 element

Type of oxide

Oxide (O2-) Peroxide (O22-) Superoxide (O2

-)

Li ++

Na + ++

K + ++

Rb + ++

Cs + ++

++ Major product + Minor product

* Type of oxide formed depends on the stability of the product 5

Chemical Properties of Group 1 elements (ns1)

Storage of Group 1 metal • In pure oil, or even in vacuum-sealed tube • Prevent from reacting with water and oxygen

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Chemical Properties of Group 2 elements (ns2)

Group 2 elements : alkaline earth metals • Soft, reactive metals, all found in Earth’s crust • Less reactive than Group 1 metals • Formation of +2 ions

Reaction with water

M(s) + 2H2O(l) → M(OH)2(aq) + H2(g) (Except Be)

e.g. Mg + 2H2O → Mg(OH)2 + H2

Reaction with oxygen

2M(s) + O2 (g) → 2MO(s)

• Sr and Ba : form peroxide • BeO : amphoteric in nature, thin protective layer

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Flame Test

Identify the presence of certain elements

Upon heating, electrons in the elements are able to move from their ground state to higher energy levels

As they return to their ground state, energy is released in the form of electromagnetic wave

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Flame Test

Color flame is produced when the wavelength of the emitted electromagnetic wave falls within the vision light region

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Flame Test

Group 1 element

Flame color Group 2 element

Flame color

Li Crimson Be -

Na Golden yellow Mg Dazzling white

K Lilac Ca Brick red

Rb Violet Sr Blood red

Cs Violet Ba Apple green

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Chemical Properties of Group 13 elements (ns2p1)

Metals, except B (metalloid)

Reaction with water

2M(s) + 6H2O(l) → 2M(OH)3(s) + 3H2(g) (Except B)

• Al does not react with cold water because of the protective layer; however, it reacts with steam

Reaction with oxygen

4M(s) + 3O2 (g) → 2M2O3(s)

• B2O3 : colvent, acidic • Al2O3 : thin protective layer • Metal oxide : alkali (except Al2O3 and Ga2O3 : amphoteric)

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Chemical Properties of Group 14 elements (ns2p2)

C : nonmetal; Si and Ge : metalloid; remaining : metal

Carbon (C) • Able to form both organic and inorganic compounds

e.g. CH4 (organic) vs. CO2 (inorganic) • Able to form single bond, double bond and triple bond

Silicon (Si)

• Reaction with oxygen and chlorine on heating

Si(s) + O2(g) → SiO2(s) (Giant covalent structure)

Si(s) + 2Cl2(g) → SiCl4(l)

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Chemical Properties of Group 15 elements (ns2p3)

N, P : nonmetal; As and Sb : metalloid; remaining : metal

Nitrogen (N) • Reaction with reactive metal – Form metal nitride

N2(g) + 6Li(s) → 2Li3N(s)

N2(g) + 3Mg(s) → Mg3N2(s)

• Reaction with oxygen to give a variety of oxides

e.g. N2O, NO, NO2, N2O3, N2O5

• Reaction with hydrogen

N2(g) + 3H2(g) 2NH3(g) (Weak base, reducing agent ) Fe, 500oC, 200 atm

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Chemical Properties of Group 15 elements (ns2p3)

Phosphorus (P) • Involves several allotropes : white (the most common), red, violet

and black phosphorus

• Reaction with oxygen

P4(s) + 3O2(g) → P4O6(s) (limited oxygen)

P4(s) + 5O2(g) → P4O10(s) (excess oxygen)

• Reaction with chlorine

P4(s) + 6Cl2(g) → 4PCl3(s) (limited chlorine)

P4(s) + 10Cl2(g) → 4PCl5(s) (excess chlorine)

! White phosphorus is extremely dangerous. It ignites under all but the most delicate conditions with a lot of flame and can be explosive

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Chemical Properties of Group 15 elements (ns2p3)

Phosphorus (P) • Phosphorus is an essential part of our life. It is the building block of

many biological molecules, such as ATP, ADP and DNA

As, Sb and Bi have extensive 3-dimension structures with different properties

ATP ADP

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Chemical Properties of Group 16 elements (ns2p4)

O, S and Se : nonmetal; Te and Po : metalloid

Sulphur (S) • Consists of 8 S atoms covalently bounded together in a crown-

shaped S8 ring

• Reaction with oxygen

S(s) + O2(g) → SO2(g)

! Highly irritating. Cause damage to respiratory system

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Chemical Properties of Group 16 elements (ns2p4)

Sulphur (S) • Reaction with halogen (except I2)

S + 3F2 → SF6

2S + Cl2 → S2Cl2

O2, S8 and Se8 : Simple molecular structure; Te and Po : Giant 3-

dimension structure

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Chemical Properties of Group 17 elements (ns2p5)

Group 17 elements : halogens • Poisonous and extremely reactive nonmetals • Exist in all 3 states of matter at room temperature

Iodine (solid); bromine (liquid); chlorine and fluorine (gas) • Formation of -1 ions

Function as oxidizing agent, oxidizing power decrease down the

group • React with both metal and nonmetal

2Na + X2 → 2NaX

2P + 3X2 → 2PX3 (X=Br2 or I2)

2P + 5X2 → 2PX5 (X=F2 or Cl2)

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Chemical Properties of Group 17 elements (ns2p5)

Reaction with water (except I2)

• F: 2F2 + 2H2O → 4HF + O2

• Cl: Cl2 + H2O → HCl + HOCl (HOCl is used as bleach)

• Br: Br2 + H2O → HBr + HOBr

Reaction with hydrogen

H2(g) + X2(g) → 2HX(g)

• F2 : reacts explosively by radical chain reaction • Cl2 : explodes when exposure to light • Br2 and I2 : react much more slowly

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Chemical Properties of Group 18 elements (ns2p6)

Group 18 elements : noble gases • Inert gases • Monoatomic

Full-filled outer ns and np orbitals (octet electron configuration)

• Extremely low tendency of gain or loss electron • Very stable

Stability decreases down the group

e.g. Xe can form compound with F2

Xe(s) + F2(g) → XeF2(s), XeF4(s), XeF6(s)

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Reference

1. Bettelheim FA, Brown WH, Campbell MK & Farrell SO (2010). Introduction to general, organic & biochemistry, 9th edition: Thomson Brooks/Cole.

2. McMurry J, Castellion ME, Ballantine DS, Hoeger CA & Peterson VE (2010). Fundamentals of general, organic & biological chemistry, 6th edition: Pearson Prentice Hall.

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