The Periodic Table of Elements
Notes
Download Notes
(Credits to Mustafa Asif)
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
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.
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
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
Reactions of the Alkali metals
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
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
Transition metals
Element
chromium
manganese
iron
nickel
copper
Common ions
Cr2O72- dichromate(VI)
MnO4- manganate(VII)
Fe2+ iron(II)
Fe3+ iron(III)
Ni2+ nickel(II)
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
Uses of transition metals
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.
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:
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