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The Periodic Table of Elements

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Periodic Table


The Periodic Table

  • Elements are arranged in order of proton numbers
  • Vertical columns of elements are called groups
  • Horizontal rows of elements are called periods
  • Across the period, the elements change from metals to non-metals
  • Elements close to the staircase line, like silicon or germanium, can have some properties of the metals and of the non-metals --> metalloids
  • Group number: indicates number of electrons in the outermost shell of an atom
  • Period number: indicates the number of electron shells in an atom
  • Metals always from positive ions while non-metals always form negative ions

Source: http://aphschem.blogspot.com/2009/09/92209-metal-or-non-metal.html

 Properties
Group I and II metals
  • Group I : alkali metals
  • Group II: alkaline earth metals
  • reactive
  • reactivity increases down the group
Metalloids- elements close to the staircase line
  •  have properties of both metals and non-metals
  • metalloids beneath the staircase line are called Poor Metals (eg tin and lead)
Non-metals
  • often gases (except Br, P, S, C, B, Se)
  • low melting points
  • poor conductors of heat and electricity (except graphite)
  • form mainly covalent compounds
Transition metals
  • typical metals
  • strong and hard
  • good conductors of heat and electricity
  • high melting points
  • many of these metals have variable oxidation state eg Copper(I) and Copper(II), Iron(II) and Iron(III)
  • not very reactive
  • compounds formed often have characteristic colours. Examples:
    • Copper(II) compounds are blue
    • Iron(II) compounds are green
    • Iron(III) compounds are yellow and green
    • Manganate(VII) compounds are purple
    • Dichromate compounds are orange
  • transition metals and their compounds are used as catalysts to speed up industrial reactions. Examples:
    • iron in Haber Process to manufacture ammonia
    • Nickel used in manufacture of margarine from vegetable oils
    • Platinum or vanadium(V) oxide in the Contact Process to manufacture sulphuric acid

Periodic Law

  • Elements in same group has the same number of valence shell electrons which the amount is the same as the group number.
    • e.g. Group II has elements with valency of 2 electrons.
  • The charges relates to the group number and number of valence electrons.
    • Elements on left side periodic table lose ions to form cation.
    • Elements on right side periodic table gain ions to form anion
    • Elements in Group IV can lose or gain electrons depending on reacting element.
    • Transition metals may form variable cation of 2+ or 3+
  • Elements in same group form same type and number of bonds due to the same number of valence electrons.
    • e.g. Sodium in Group I forms NaCl, so other elements in Group I does the same. (RbCl, KCl, LiCl, CsCl)
  • From left to right, elements gradually change from metal to non-metal
  • Elements close to dividing line in periodic table in back part of the note (in bold) are called metalloids having properties of metals and non-metals.

 PropertiesTrend down a group
 Trend across a period (Left to Right)
 Atomic size
 the size of the atom increases
 the size of atom decreases
 Ionization energy*
 decreases down a group
 increases across a period
 Electron affinity*
 decreases down a group        
 increases across a period
 Electronegativity* decreases down a group
 increases across a period
 Electropositivity* increases down a group
 decreases across a period

  • Ionization energy is the minimum amount of energy required to completely remove an electron from a gaseous atom
  • The Electron affinity of a molecule or atom is the energy change when an electron is added to the neutral atom to form a negative ion. (in simple terms, it refers to how much an element loves an electron)
  • Electronegativity is the tendency for an atom to attract electrons to itself
  • Electropositivity is the tendency for an atom to lose an electron

Changes in Group

  • Proton number increase going down the group
  • On each sides of periodic table, the change of the proton number small & gradual
  • In transition metals, the gradual change is larger

Using the Periodic Table

Predicting Properties

1) Formula and Structures
  • Given chlorine, iodine and bromine of Group VII forms molecules of Cl2, I2 and Br2 respectively, predict the molecular formula of Fluorine. eg. F2
  • From example, we know elements in same group form same formula.
2) Properties of Elements
  • Properties of element changes down the group.
  • i.e. given list of Group 7 elements, predict the properties of astatine.

Octet rule

Cations

- Metals form cations (position ions)
- Cations are smaller than their atoms

Anions

- Non-metals form anions (negative ions)
- Anions are larger than their atoms

Isotopes

- Have the same atomic number (number of protons) but different mass number or different number of neutrons

Differences between metals and non-metals

Metals
 Non-metals
Usually solids at room temperature except mercury
Often gases except:
Bromine: liquid
Sulphur: solid
Phosphorus: solid
Iodine: solid
Carbon: solid
Boron: solid
Silicon: solid
High melting and boiling points
(except Group I)
Low melting and boiling points
(except B, C, Si)
Good conductors of heat and electricity
Poor conductors of heat and electricity
(except carbon/graphite)
Often shiny, ductile, malleable, and possess great tensile strength
Normally dull, soft, cannot be drawn out into wires or made into flat sheets
Most compounds are ionic
Most compounds are covalent
Oxides are usually basic or amphoteric
Oxides are usually neutral or acidic
Often form hydrogen gas with dilute acids
Never form hydrogen gas from acids
Always form position ions (cations)
Always form negative ions (anions)

Group I metals

  • called Alkali metals - the metals react with water to form alkaline solutions: the solutions turn red litmus paper blue
  • have one outer shell electrons
  • shiny, silvery solids
  • soft, easily cut with scalpel
  • low densities and melting points - these increases down the group
  • good conductors of heat and electricity
  • reacts easily in air so they're kept in oil
  • chemically reactive - reactivity increases down the group (Caesium most reactive of all metals
    • This is because the atoms become larger as we go down the group.
    • It becomes easier for the outermost, single valence electron to escape to form an ion as the attractive force of the nucleus is further away and weaker
  • have 1 valence electron
  • loses one outermost electron to form an ion of +1 charge eg. Li+, Na+, K+
  • react violently with air or oxygen, catching fire, and burning with characteristic flame colors to form white oxides. To avoid this, the metals are stored under oil
    • eg. 4K (s) + O2 (g) ----> 2K2O (s)
  • They also react vigorously with water, forming the alkaline hydroxide and releasing hydrogen gas
    • eg. 2Na (s) + 2H2O (l) ---> 2NaOH (aq) + H2 (g)
  • Because alkali metals are such reactive metals, they combine directly with reactive non-metals such as the halogens to form salts
    • eg. 2Na (s) + Cl2 (g) ----> 2NaCl (s)

Flame colour

 Alkali metal
Flame color
 Li red
 Na yellow
 K lilac
 Rb -

Reactions of the Alkali metals

 Alkali metal  
Reaction with air (oxygen)
Reaction with water
Reaction with chlorine
 lithiumburns with a red flame to give lithium oxide (white solid)
4Li + O2 ---> 2Li2O
floats on water and reacts quickly to produce lithium hydroxide and hydrogen gas
2Li + 2H2O ---> 2LiOH + H2
burns with a bright flame to give a white solid of lithium chloride
2Li + Cl2 ---> 2LiCl
 sodiumburns with a bright yellow flame to produce white sodium oxide
4Na + O2 ---> 2Na2O
floats on water and reacts very quickly to produce sodium hydroxide and hydrogen gas
2Na + 2H2O ---> 2NaOH + H2
burns with a bright flame to give a white solid of sodium chloride
2Na + Cl2 ---> 2NaCl
 potassiumburns violently with a lilac colored flame to produce white potassium oxide
4K + O2 ---> 2K2O
floats on water and reacts violently to produce potassium hydroxide and hydrogen gas
2K + 2H2O ---> 2KOH + H2
burns vigorously in chlorine with a bright flame to give a white solid of potassium chloride
2K + Cl2 ---> 2KCl

Group VII (Halogens)

  • reactive non-metals
  • have seven outer shell electrons
  • poisonous
  • low melting and boiling points - increases down the group
  • elements become darker and solidify down the group
  • reactivity decreases down the group
    • because of their atomic size, which increases down the group
    • therefore it becomes more difficult for the nucleus to attract an electron to form an ion
  • most reactive is fluorine; least reactive is iodine
  • all halogens form ions with single negative charge eg F-, Cl-, Br-
  • Exists as diatomic molecules eg F2, Cl2, Br2, I2
  • reacts vigorously with metals to form ionic salts
  • halogens become less reactive down the group

Halogen
Colour
State
 Fluorine pale yellow
 gas
 Chlorine yellowish green
 gas
 Bromine red brown
 liquid
 Iodine shiny black
 solid

  • Any halogen above another in the group will displace it from a solution of its salt ----> displacement reactions
  • This means that the more reactive halogen can take the place of the less reactive halogen of its salt.
    • eg. Cl2 + 2KBr -----> 2KCl + Br2
  • When chlorine gas is bubbled through a colorless solution of potassium bromide, reddish brown color of bromine is seen.
    • eg. Cl2 + 2KI ----> 2KCl + I2
  • When chlorine gas is bubbled through a colorless solution of potassium iodide, it turns brown and finally a black precipitate of iodine is formed.

Group O (Noble/Inert Gases)



  • Exist as monatomic (single atom)
  • least reactive elements in the gaseous state; do not form bonds
  • low melting and boiling points
  • have stable electronic configuration with full electrons on their shells
  • chemically inert
    • because the outermost shell of the element is full.
    • It does not tend to combine with other elements, either covalently or ionically, and there is chemically inactive

 Name Uses
 Helium
 in air ships, weather balloons
 Neon in advertising lights
 Argon an inert gas for electric bulbs, welding and making steel
 Kryton gas-filled electronic devices and lasers
 Xenon electronic flash guns
 Radon natural radioactive gas

Transition metals

 Element Common ions
chromium
 Cr2O72-     dichromate(VI)
 manganese MnO4      manganate(VII)
 iron Fe2+           iron(II)
 Fe3+           iron(III)
 nickel
 Ni2+           nickel(II)
 copper Cu+             copper(I)
 Cu2+          copper(II)

  • often form colored compounds
  • can have variable oxidation states ---> no fixed number of valence electrons
  • form complex ions eg MnO4- (manganate(VII) ions)
  • high melting and boiling points
  • high densities
  • can have catalytic properties

 Industrial process Description
Contact Process
uses vanadium(V) oxide to help in the conversion to sulphur trioxide
Haber Process
uses an iron catalyst with iron oxide promoters to make ammonia gas
Margarine manufacture
uses nickel catalyst in the hydrogenation of alkene

Uses of transition metals

Transition metal
Uses
 Tungstenused in filaments of electric light bulbs as it is ductile and has a melting point over 3000oC
 Chromiumhard, unreactive (has protective oxide coating) and attractive. So used for chromium-plating and in making stainless steel
 Titaniumtitanium and its alloys are light but as strong as steel so used in aircraft construction
 Manganesehard brittle metal used to harden steel
 Nickela strong metal that resists corrosion. Used in stainless steel and in coinage metals like cupronickel which has an attractive silvery appearance
 Zinc        a grey metal with a blue tinge. Main use is to galvanise iron to prevent it from rusting
 Copperunreactive metal and malleable. So used for making water-pipes

Advantages
  • Since transition elements speed up chemical processes in industries, they saves time in manufacture
  • Less energy is needed for manufacture in industries, hence lower cost
  • Since less energy is needed, more energy resources can be conserved, e.g. oil to generate electricity in producing iron.

MCQ

1. Which property decides the order of the elements in the Periodic Table?
a. masses of their atoms
b. number of electrons in the outer shell
c. number of neutrons in the nucleus
d. number of protons in the nucleus

2. The element with a proton number 12 has similar chemical properties to the element with the proton number
a. 2
b. 11
c. 13
d. 20

3. Which element is in Group IV, Period 5 of the Periodic Table?
a. antimony
b. arsenic
c. lead
d. tin

4. Which statement about a new element, which has seven outer electrons in its atoms, is correct?
a. it is monatomic
b. it forms a covalent compound with hydrogen
c. it forms a positive ion
d. it forms covalent compounds with Group I elements

5. Which list contains 3 elements that all exist as diatomic molecules at room temperature?
a. hydrogen, fluorine, neon
b. nitrogen, chlorine, neon
c nitrogen, oxygen, fluorine
d. oxygen, chlorine, helium

6. Which statement shows that iron is a transition metal?
a. Iron(II) sulphate crystals are green
b. Iron(III) oxide is basic
c. Iron rusts in moist air
d. Iron reacts with dilute hydrochloric acid

7. A metal X forms oxides with the formulae XO and X2O3
Where is X in the Periodic Table?

a. Group II
b. Group III
c. second Period
d. transition elements

8. Which of the following is a property of aqueous potassium iodide?
a. it does not conduct electricity
b. it is decolorised by chlorine
c. it reacts with aqueous bromine to form iodine
d. it reacts with aqueous lead(II) nitrate to form a white precipitate

9. Many properties of an element can its compounds can be predicted from the position of the element in the Periodic Table. What property could not be predicted in this way?
a. acidic or basic nature of its oxide
b. formula of its oxide
c. number of isotopes it has
d. its metallic or non-metallic properties

10. The element with a proton number 12 has similar chemical properties to the element with the proton number
a. 2
b. 11
c. 13
d. 20

11. The proton number of Indium, In, is 49. What is the most likely formula for the oxide of Indium?
a. In2O
b. In2O3
c. InO
d. InO2

12. The element with proton number 12 has similar chemical properties to the element with the proton number 
a. 2
b. 11
c. 13
d. 20

13. Which statement about groups in the Periodic Table is correct?
a. All groups contain both metals and non-metals.
b. Atoms of elements in the same group have the same total number of electrons.
c. In Group I, reactivity decreases with increasing proton number.
d. In Group VII, the melting point of the elements increases with proton number.

14. Which property decides the order of elements in the Periodic Table?
a. masses of their atoms
b. number of electrons in the outer shell
c. number of neutrons in the nucleus
d. number of protons in the nucleus

15. An element X, necessary for plant growth, can be added to the soil only in the form of compounds which contain the ion X. What is X?
a. hydrogen
b. nitrogen
c. phosphorus
d. potassium

16. The element Cs is in the same group of the Periodic Table as sodium and potassium. Which of the following is likely to be a property of caesium?
a. It does not conduct electricity.
b. It reacts vigorously with water to give off hydrogen.
c. It forms the ionic chloride with formula CsCl2
d. It forms an acidic oxide.

17. Which statement is most likely to be true about the elements in Group I of the Periodic Table?
a. They occur uncombined in nature.
b. They are equally reactive chemically.
c. They form chlorides of similr fornulae.
d. They become less metallic as the proton number increases.

18. Astatine (At) is in Group VII of the Periodic Table. Which of the following is a property of astatine?
a. It forms a basic oxide.
b. It is a good conductor of electricity.
c. It is displaced by chlorine from aqueous potassium astatide.
d. It displaces iodine from aqueous potassium iodide.

19. Which statement about a new element, which has seven outermost electrons in its atoms, is correct?
a. It is monatomic.
b. It forms a covalent compound with hydrogen.
c. It forms a positive ion.
d. It forms covalent compounds with Group I elements.

20. Fluorine is the first element in Group VII of the Periodic Table. Which statement will not be true of fluorine?
a. Fluorine exists in diatomic molecules.
b. Fluorine forms negative ions.
c. Fluorine is less reactive than chlorine.
d. Silver fluoride will be sensitive to light.

Answers

1. d
2. d
3. d
4. b
5. c
6. a
7. d
8. c
9. c
10. d
11. b
12. d (Mg and Ca are in the same group in the Periodic Table)
13. d
14. d
15. d (Group I metals donate 1 outermost electrons to form X+ ions)
16. b
17. c
18. c (Chlorine, being more reactive than At, displaces At from its aqueous salt)
19. b
20. c

Worked Solutions

1. The elements below are all in Group I of the periodic Table.
 elementsymbol
electronic structure
 lithium Li 2, 1
 sodium Na 2, 8, 1
 potassium K 2, 8, 8, 1
 rubidium Rb 2, 8, 18, 8, 1
 caesium Cs 2, 8, 18, 18, 8, 1

a. Which element reacts most vigorously with cold water?

b. Write the formula of a caesium ion

c. How many protons are there in a rubidium ion?

d. Group I elements are very good conductors of electricity. Use a simple model of the structure and bonding of the metal to explain this.

Solutions

a. Caesium

b. Cs+

c. 37

d. Metal consists of a lattice of cations in a sea of delocalised electrons. When a potential difference is applied across the metal, the electrons flow towards the positive potential, thereby conducting electricity.

2. This question is concerned with the following list of substances.

potassium
zinc oxide
lead(II) bromide
hydrogen
oxygen
carbon

Each substance can be used once, more than once, or not at all.

Name a substance from the list above which

a. reacts violently with water

b. conducts electricity when molten but not when solid

c. is amphoteric

d. has a formula of the type XY2

e. has an allotrope with a structure similar to that of silica

f. has a low melting point

g. is produced at the cathode during electrolysis of dilute sulphuric acid

Solutions

a. potassium

b. lead(II) bromide

c. zinc oxide

d. lead(II) bromide

e. carbon

f. oxygen

g. hydrogen

3. Chlorine, bromine, and iodine are elements in Group VII of the Periodic Table. 
a. Describe how you would carry out a series of experiments to show the trend in reactivity of these three elements, using the reagents below.

aqueous chlorine
aqueous bromine
aqueous iodine
aqueous potassium chloride
aqueous potassium bromide
aqueous potassium iodide

Your answer should include details of:
- which of the reagents you would use in each experiment
- a table showing the observations you would expect to see
- the equations for any reactions

b. Chlorine reacts with water to make a solution that can be used as a bleach. The equation is show below
Cl2 + H2O ---> HCl + ClOH

Use oxidation numbers to show that chlorine is both oxidised and reduced in this reaction.

Solution

3a. A more reactive halogen would displace a less reactive halogen from its salt solution. Displacement reactions are carried out to investigate the trend of reactivity of the halogens.

Add a few drops of chlorine water into a test tube containing 2cm3 of potassium chloride solution. Record changes observed. The experiment is repeated with potassium bromide and potassium iodide solution.

To find out the order of reactivity of the halogens, a second set of experiments is conducted with bromine water added to test tubes containing 2cm3 of each of the salt solution provided and a third set of experiments conducted with iodine solution added to 2cm3 of each of the salt solution.

The results are shown below:

 Halogen added KCl    KBrKI 
 Cl2 (aq) -
Colourless solution turned brown. Br2 formed Colourless solution turned reddish brown. I2 formed 
 Br2 (aq)No displacement reactionColourless solution turned reddish brown. I2 formed 
 I2 (aq)No displacement reactionNo displacement reaction-

Equations:

Cl2 + 2KBr ---> 2KCl + Br2

Cl2 + 2KI ---> 2KCl + I2

Br2 + 2KI ---> 2KBr + I2

3b. Chlorine is oxidised to ClOH and reduced to HCl at the same time. In the oxidation process, oxidation number of chlorine increased from 0 in Cl2 to +1 in ClOH.

In the reduction process, oxidation number of chlorine decreased from 0 in Cl2 to -1 in HCl.

4a. The reaction of aluminium chloride with water is as follows:
2AlCl3 + 6H2O ---> 2Al(OH)3 + 6HCl
Each of the following compounds
  • aluminium bromide (AlBr3)
  • aluminium nitride (AlN)
  • aluminium carbide (Al4Cl3)
reacts with water in a similar way. Predict the formula of the compound produced, other than aluminium hydroxide in each case.

b. NaNO3     NH3     CuSO4     MgCO3     Al2O3
Choose from the above list of compounds one which contains:
i. an element found in Group II of the periodic table
ii. a metallic element showing an oxidation number of +3
iii. a non-metallic element showing an oxidation number of -3
iv. a non-metallic element showing an oxidation number of +5

Solution

4a. 
aluminium bromide: HBr produced
aluminium nitride: NH3 produced
aluminium carbide: CH4 produced

4bi. MgCO3
4bii. Al2O3
4biii. NH3
4biv. NaNO3

5. The Periodic Table is arranged in groups. 
a. Rubidium (Rb) is in Group I of the Periodic Table. It reacts with water according to the equation below
2Rb (s) + 2H2O (l) --> 2RbOH (aq) + H2 (g)
Predict what you would see when a small piece of rubidium is added to cold water.
b. Chlorine is in Group VII of the Periodic Table. Chlorine, Cl2, reacts with aqueous sodium bromide. 
i. Predict what you would see in this reaction.
ii. Write a balanced equation for this reaction.

Solution

5a. Rubidium will react violently with cold water. It melts into a silvery ball, effervesces and releases a lot of heat and light energy.
5bi. The colourless solution of sodium bromide will react with the yellowish green chlorine gas to form a solution that is reddish brown in colour.
5bii. Cl2 + 2Br- --> 2Cl- + Br2

6. Chlorine, bromine and iodine are elements in Group VII of the Periodic Table.
a. Describe the trend in colour and physical state at room temperature and pressure as the atomic number increases.
b. Aqueous chlorine is an oxiding agent.
i. Name the products formed and write the ionic equation for the reaction between aqueous chlorine and aqueous potassium bromide.
ii. Name the product formed when aqueous chlorine reacts with aqueous iron(II) chloride.

Solution

6a. As atomic number increases down the group, the physical states change from gas (fluorine and chlorine) to liquid (bromine) and then to solid (iodine, astatine). The colour intensity also increases from pale yellow (fluorine) to yellowish green (chlorine) and then to red-brown (bromine) and finally to black (iodine and astatine).

6bi. Chloride and bromine.
2Br- + Cl2 --> 2Cl- + Br2

6bii. iron(III) chloride
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