Unit 2 : The Periodic Table

 

 Course Book pg number

 

1. Describe the Periodic Table as a method of classifying elements and its use to predict properties of elements.

 

The Periodic Table can be used to classify elements and predict properties of elements by the way that they are arranged in the table…

* Elements are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups.

*  Elements in the same periodic group have the same amount of electrons in their outer shell, which gives them similar chemical properties.

* We can deduce the electronic configurations of elements from their positions in the Periodic Table

Ø Group 1 has 1 electron in its outer shell, group 2 has 2 etc…

Ø Period 1 has 1 shell, period 2 has 2 shells etc…

 

Practice :

Write the number of group, period to which the element belong:

a) Oxygen :  Group-      , Period -

b) Sodium :

c) Chlorine :

 

2. Describe the change from metallic to non-metallic character across a period.

 

● From left to right elements change from metallic to non-metallic character

 ● Metallic character/properties:

Ø Shiny

Ø Conductive

Ø Dense

Ø Malleable

● On either side of the red line, you have some elements known as “metalloids” that have both metallic and nonmetallic properties, such as silicon (which forms silicon dioxide…)

  

3. Explain the relationship between Group number, number of outer shell electrons and metallic/nonmetallic Character

 

v Group number- shows the number of electrons in the outer shell.

 

 ● Metallic /nonmetallic- metals form positive ions by losing electrons and nonmetals form negative ions by gaining electrons.

 

Ø All of group 1 and 2 are metals.

Ø All of group 7 and 8 (0) are nonmetals.

Ø In groups 3,4,5,6 there is a transition between metals and nonmetals.

 

2. Group properties:

 

1. Properties of elements in Group I:

 

Characteristics of Group 1 elements or Alkali Metals

·         They are very Soft, have lower density than other metals, also lower melting and boiling points

·         They all are highly reactive

·         Most of the reactive ones must be stored under oil, to prevent them from reacting with air(oxygen in the air) or with water vapor.

·         Reactivity of group one metal increases down the group

·         They form +1 charged ions when forms compounds

·         All of the group 1 compounds are white, they all dissolve to form a colorless solution

 

Group 1 elements show similar chemical properties due to the fact that they have the same number of outer shell electrons

a) Melting point : Low melting points compared to most other metals

▪ As you go down the group, melting points decrease

b) Density : Low densities – they will float on water

▪ As you go down the group, densities increase

c) Reaction with water :

Ø All react vigorously with water to create an alkaline solution and hydrogen

Ø More bubbles with reaction with water = more vigorous reaction = more reactive alkali metal (Group I metal)

Ø Reactivity increases down the group (so reaction becomes more vigorous)

 

How Group 1 metals react with water

All of the group 1 metals react vigorously with water, they all react with water to produce metal hydroxide and hydrogen gas.

How sodium reacts with water:  Sodium reacts vigorously with water, it floats on the surface of the water, as its density is less than water. There is vigorous effervescence of hydrogen gas, hydrogen gas is released rapidly which causes sodium to dart on the surface of the water. The reaction is highly exothermic, releases tons of heat

                                    2Na(s) + 2H₂O(l)→ 2NaOH(aq) + H₂(g)

How Lithium reacts with water  Lithium reacts similarly sodium reacts with water, but reacts a little bit slower than sodium, as its reactivity is less than sodium.

How potassium reacts with water similar observation as in the case of potassium, but reacts much more vigorously, the potassium metal even catches fire and burns with a lilac flame.

Rubidium and Caesium with water these metals react so vigorously with water, that it is dangerous to carry out their reaction with water and they are hardly used.

 

Practice:

 

1. Describe the trend of group 1 elements down the group.

a. Density : G 1 elements density increases down the group ( Lithium is less densed than Francium)

b. Reactivity : Their reactivity increases down the group (Lithium is least reactive, Francium is most reactive)

c. Melting and boiling point : Their melting and boiling point decreases down the group.

 

a. Write the word equation for the reaction of Lithium with water.

Lithium + water                                           Lithium hydroxide + Hydrogen gas

 b. Sodium with water.

 c. Potassium with water.

 

4. Li, Na and K are kept under same group in the periodic table. Why?

Lithium, Sodium and Potassium have 1 electron at their outermost shell. So they are kept under Group 1. They show similar chemical and physical properties.

 

5. Group 1 elements are stored under oil. Why?

Ans: Group 1 elements are very reactive. They will react with oxygen in the air if they kept open. So they are stored under oil.

 

Group 7 Elements – The halogens  

Date :

Properties of halogens

1. They all are not metals.

2. They have low melting and boiling point.

3. They have 7 electrons at their outermost shell. So they belong to Group 7.

4. They all show similar chemical properties .so they are kept under same group.

5. They react with group 1 metals and form metal halides.

 Practice:

1. Describe the trend in density, colour, reactivity and melting point of halogens down the group.

Ans :a) Density : Density increases down the group.

b) Colour: Colour get darkens down the group.

 

c)Reactivity: Reactivity decreases down the group.

d) Melting point : Melting point increases down the group.

  

2. Name the most reactive halogen.

Ans: Flourine

 

Reactivity of halogens:

1. Halogens react with metals and form metal halides.

EX : Chlorine react with sodium and form sodium chloride.

2. More reactive halogen displaces less reactive halogen from metal compound.

Ex :

Potassium iodide + ChlorinePotassium chloride + iodine.

In this reaction chlorine displaces iodine from potassium iodide. Because chlorine is more reactive than iodine.

 

3. Write the equation for the reaction of sodium with chlorine.

Ans : Sodium + Chlorine                                                 Sodium chloride

4. Reaction of potassium with[s1]  Bromine.

 

Transition elements :

Distinctive properties of transition elements

1. They can form colored compounds.

2. They can used as catalysts.

EX: Iron and vanadium oxide.

3. They can show different oxidation states.

Oxidation state = The number of electrons lost by the atom / its charge.

4. They have high melting and boiling point.

5. They are strong, tough and highly densed.

 

 

Noble gases                        18/11/2021

Properties of noble gases:

1. They all are colourless, odorless, unreactive gases.

2. They have low melting and boiling points.

3. They all are nonmetals belongs to group 8/ 0

4. They have low density.

5. They have full outer shell electrons. So they are unreactive.

6. They are monatomic (Element made of one atom)

 

Trend in Group 8 :

a. Atomic size  increases down the group ( helium is the smallest noble gas)

b. Melting point and boiling point decreases down the group

c. Density increases down the group  (Helium is the least densed)

Practice:

Give reason:

1. Helium is used to fill balloons.

Ans: Because helium is less densed than air.

2. Argon is used in electric bulbs

Ans: Because Argon is unreactive gas.

3. Helium is used in airships.

Because helium is unreactive gas, it does not burn.

4. Noble gases are unreactive.

Ans: Because they have full outer shell electrons

 5.Write the names of noble gases and state their symbol.