Quiz

Group 0(Noble Gas)

1.The noble gases are all unreactive gases because they have full outer shells of electrons.

2.They are all monatomic gases(each molecule consists of a single atom)

3.Some important uses of noble gases:

-Helium is used in balloons because it has a low density.

-Argon and neon are used in light bulbs because they are unreactive and so protect the white-hot filament from reaction with air.

-Argon is used in the extraction and welding of some metals because it is unreactive and so protects the hot metal from reaction from oxygen in the air.

Helium,Atomic number:2
Electronic Configuration:2

Neon,Atomic number:10
Electronic Configuration:2,8

Argon,Atomic number:18
Electronic Configuration:2,8,8

Krypton,Atomic number:36
Electronic Configuration:2,8,18,8

Xenon,Atomic number:54
Electronic Configuration:2,8,18,18,8

Radon,Atomic number:86
Electronic Configuration:2,8,18,32,18,8

-They are all colourless.The forces between the atoms are very weak and so are all gases.

-Going down the group,from helium to radon, the density increases and the melting and boiling point increases.This is because the atoms become heavier and require more energy to melt or boil.

Group V||(Chlorine,Bromine and Iodine)

1.They are all diatomic covalently bonded molecules called halogens. Diatomic means that each molecule contains two atoms. The formulae are (Cl2,Br2 and I2).

2.They all either gain one electron from a metal to form an ionic bond or share one electron with a non-metal to form a covalent bond.

3.The halogens exist in solid,liquid and gaseous states at room temperature(onli group of the periodic table).

-Chlorine is a yellow-green gas.

-Bromine is a red-brown liquid.

-Iodine is a dark violet(almost black) solid.When iodine is heated,it sublimes to become a gas with a purple vapour.

-Their reactivity decreases from chlorine to bromine to iodine.

-Metal halides are compounds formed from a metal and a halogen.These are ionic salts which form a giant structure.The halogens will react with transition metals.

aluminium + chlorine -> aluminium chloride
2Al(s) + 3Cl2(g) -> 2AlCl3(s)

-The relative reactivity of the halogens,as described in properties of group V elements,can be shown by displacement reactions(a place of another less reactive halogen from a compound).

-Bromine bubbled through a solution of potassium iodide in water will displace the less reactive iodine,forming iodine and potassium bromide.

bromine + potassium iodide -> potassium bromide + iodine
Br2(g) + 2Kl(aq) ->2KBr(aq) + I2(aq)

-Similarly,chlorine will displace less reactive halogens. Chlorine will displace both bromine and iodine from the halide salt.

chlorine + sodium bromide -> sodium chloride + bromine
Cl2(g) + 2NaBr(aq) ->2NaCl(aq) + Br2(aq)

chlorine + potassium iodide -> potassium chloride + iodine
Cl2(g) + 2KI(aq) ->2KCl(aq) + I2(aq)

Group ||(Magnesium and Calcium)

-Going downwards in group (akaline earth metals),elements are softer,with lower density and higher melting and boiling points.This is because the atoms become heavier(bigger) and require more energy to melt or boil.

-The reactivity increases downward from top,hence calcium is more reactive than magnesium.They are both silvery white metals,covered with a thin layer of oxide.

Reaction With Water

Magnesium(Mg)

-Does not react with cold water.It reacts with gaseous water(steam) to form magnesium oxide and hydrogen.

magnesium + steam-> magnesium oxide + hydrogen.
Mg(s) + H2O(g) -> MgO(s) + H2(g)

-Magnesium oxide will not dissolve in water.

Calcium(Ca)

-Calcium(and the heavier group metals) will react with cold water. They will sink as they react,unlike the group metals which float.

calcium + water-> calcium hydroxide + hydrogen
Ca(s) + H2O(l) -> Ca(OH)2(s) + H2(g)

-Calcium hydroxide is called slaked lime and will dissolve a little in water to form lime water.

Group |(Akali Metals)

The group elements have the following properties:
1.They are soft and silvery solids.
2.The elements have low densities and low melting points.
3.They react vigorously with cold water to form an akaline solution of the metal hydroxide and hydrogen gas.
4.The elements burn brightly when heated in chlorine gas.The product is a white solid of metal chloride (e.g. NaCl, KCl)

Lithium
Observation for (3): Fast reaction
Equation for reaction(3): 2Li + 2H2O -> 2LiOH + H2

Observation for (4): Burns with bright flame;white solid produced.
Equation for reaction(4): 2Li + Cl2 ->2LiCl (white solid)


Sodium
Observation for (3): Very fast reaction;sometimes an explosion
Equation for reaction(3): 2Na + 2H2O ->2NaOH + H2

Observation for (4): Burns with bright flame;white solid produced;reaction more vigorous than lithium
Equation for reaction(4): 2Na + Cl2 ->2NaCl (white solid)

Potassium
Observation for (3): Immediate explosion
Equation for reaction(3): 2K + 2H2O ->2KOH + H2

Observation for (4): Burns with bright flame;white solid produced;reaction more vigorous than sodiumEquation for reaction(4): 2K + Cl2 ->2KCl (white solid)

5.Atoms of group elements have one electron in their outer shells.
6.Atoms of the elements lose one electron to form ions with a charge of +1 im compounds.
For Example:
Electronic Configuration of Sodium atom: 2.8.1
Electronic Configuration of Sodium ion,Na+: 2.8

The following changes take place down the group:
1.The melting points of the elements decrease.
2.The elements become more reactive.They react more vigorously with water and chlorine.

Properties of other elements can be predicted from:
-known properties of lithium,sodium and potassium
-the changes down the group

For example, predict how you would expect rubidium(Rb) to react with water, and write an equation for the reaction. Rubidium is below potassium in group .

-Rubidium would be expected to react with water to produce hydrogen gas and a solution of rubidium hydroxide,like the other elements in the group.
So the equation would be: 2Rb + 2H2O -> 2RbOH + H2
-The trend in group is for the elements to become more reactive down the group.So rubidium would be expected to be more reactive than potassium.Hence it would explode with water.

Periodic Trends

Definition: Periodic Table is a table of elements arranged in order of increasing proton number to show the similarities of chemical elements with related electronic configurations.

-The elements are arranged in increasing order of their proton(atomic) number in seven horizontal rows called 'periods'.

-Chemically similar elements are arranged in eighteen vertical columns called 'groups'.

-Group number indicates the number of electrons in the outermost principal quantam shell of an atom.

-Period number indicates the number of electron shells in an atom.

-A dividing(staircase-shaped) line seperates the metals and non-metals(metals lie to the left of the line and non-metals to the right)

-Hydrogen(H) is an exception as it is a non-metal and is placed in the top left-hand corner of the table.

-Semi-metals or metalloids are elements with both metallic and non-metallic characteristics and therefore fall along the staircase line.

Postition of an element in periodic table

-The position of an element depends on its proton(atomic) number and hence on its electronic configuration.

-The number of outermost orbital(n) of an atom indicates the period number.

-The total number of electrons in that outermost orbital indicates the group number of an element.

(Going downward from left to right,each new period means addition to another electron shell)
(From one group to another from top down,electrons are added in the same shell gradually filling up the shell.)

-For a given proton number which is equal to the number of electrons,the arrangement of electrons can be derived(using 2n^2).

(The number of shells will determine the element's period number.)
(And the number of electrons in the outermost shell will determine the group number.)

-Thus,position of an element can be derived from the proton number or electronic arrangement.

Relationship between group number and ionic charge

-The group number of an element depends on the total number of electrons present in the outermost shell or valence shell.

-Ionic charge of an element depends on the total number of electrons in that shell.

-If number of electrons in the valence shell is less than 5,then the ionic charge or valence will be same as the number of electrons in that shell.

-If it is equal to or greater than 5,then ionic charges will be 8 minus the number of electrons.

Similarities between elements in the same group

-The elements in the same group have same number of valence electrons.

-Due to the similarity in the number of valence electrons,elements in the same group have similar chemical properties.

-Each element has 2 electrons in the outermost shell which they tend to lose to attain a stable,noble gas configuration.

-Hence,they are very reactive and are not found free in nature.

-Because they tend to lose 2 electrons,they all form ions with a +2 charge i.e become bivalent and hence undergo similar chemical reactions.

-Thus, the similarity in their electron configurations causes them to share the same properties.

Metallic and non-metallic character of elements

-An element's position in the periodic table indicates how metallic or non-metallic,an element is relative to other elements.

-The general trend in metallic/non-metallic properties in the periodic table is as follows:
(Metallic character increases from top to bottom within a group.)
(Metallic character decreases from left to right across a period.)

-For example,Caesium(Cs) is one of the most metallic elements. If we exclude noble gas, Fluorine is the most non-metallic element.

Relationship between group number,number of valence electrons and metallic/non-metallic character

-An atom is said to be metal if it loses one or more electrons when supplied with energy.

-Similarly, an atom is said to be non-metal if it gains one or more electrons supplied with energy.

-Number of valence electrons in outer shell increases progressively by one per group across a period with increasing non-metallic character.

-Valence of an element(increases from c1 to 4, from group to V and then)(decreases from group V to V down to zero for noble gases)

-Elements of group ,, are metallic, while groups V,V,V,V are non-metallic.

Dimitri Mendeleev and the History of the Periodic Table

Dimitri Mendeleev was born on February 7th 1834 in Tobolsk, a Town in Siberia.
In 1869 at the age of 35 the famous Russian Scientist perceived a totally new classification Method "the periodic table", he included all the 65 elements known in his time by their atomic weights and chemical valency.
Mendeleev then went even further, using the remaining gaps and spaces in his periodic table, he correctly concluded that a further group of yet unknown elements must exist in order to fill in the gaps in his Periodic Table, this group we now know as the lanthanides, and is Group six of our modern Standardised Periodic Table.


The Modern Periodic Table

Fifty years after Dimitri Mendeleev created the Periodic cable, the British scientist Henry Moseley discovered that the number of protons in the nucleus of a particular type of atom was always the same.
When atoms are arranged via their atomic number, the few remaining problems with Mendeleev's original periodic table disappeared.
Due to Moseley's work, the modern periodic table is based on the atomic numbers of the elements rather than atomic mass.
Dimitri Mendeleev's work on the Periodic Table recognised.
Dimitri Mendeleev has clearly left his mark on modern science, indeed all modern Scientists are familiar with Standardised version of his Periodic table.
Mendeleyev's homeland, Russia, has recognised the significance of his work by naming the "Mendeleyev University of Chemical Technology" in Moscow in his honour.