GROUP 1

GROUP 1

1.       Alkali metals

2.       Exist naturally as compounds

3.       Elements: Lithium, sodium, potassium, rubidium, caesium and francium.

4.       General physical properties of lithium, sodium and potassium:

·         Exist as solid that have silvery and shiny surfaces at room temperature.

·         Low melting points and boiling point compared to other metals

·         Good conductors of heat and electricity

·         Low densities

5.       The Changes In the Physical Properties From Lithium, Sodium to Potassium

a)      Atomic size increases

Reason : Number of shells increases.

b)      Melting point and boiling point decreases

Reason : The increase in atomic size down the group causing the metal bond between atoms become weaker.

c)       Density increases

Reason : Increase in atomic mass more than the increase in atomic radius (volume of atom).

v  Show similar chemical properties (same number of valence electron in its outermost shell) but differ in reactivity.

v  Alkali metals donate one electron from its outermost occupied shell to form an ion with a charge of +1, achieving stable electron arrangement.

Example:

Na → Na⁺  + ē

      2.8.1      2.8

Chemical reaction for alkali metal

1.       Alkali metal + H₂O → Metal hydroxide solution + hydrogen gas

Example: 2Li(s) + 2H₂O(l) → 2 LiOH(aq) + H₂(g)

2.       Alkali metal + oxygen gas → Metal oxide

Example: 4Li(s) + O₂(g) → 2Li₂O(s)

3.       Metal oxide + water → Metal hydroxide solution

Example: Li₂O(s) + H₂O(l) → 2LiOH(aq)

4.       Alkali metal + chlorine gas

Example: 2Na(s) + Cl₂(g) → 2NaCl(s)

5.       Alkali metal + Bromine gas → Metal bromide

Example: 2K(s) + Br₂(g) → 2KBr(s)

** Halogens ( chlorine, bromine are always exist as diatomic molecules, thus the chemical formula are Cl2, Br2 )

GROUP 17

GROUP 17  

Fluorine, Chlorine, Bromine, Iodine, Astatine

1. Group 17 elements are known as halogens.

2. They are exist as  DIATOMIC  MOLECULES with molecular formula of F₂, Cl₂, Br₂, I₂

3. Electronegativity is a measurement of the strength of an atom in a molecule to pull electrons towards its nucleus.

When going down to the Group 17, the electronegativity of halogens decreases.

Explanation:

-          The number of shells occupied with electrons increases.

-          This cause the outermost occupied shells further away from the nucleus.

-          Thus, the strength of nucleus to attract electrons becomes weaker.

5. General physical of halogens:

-       Very low melting points and boiling point. (Weak forces of attraction between MOLECULES )

-       Low density

-       Cannot conduct electricity

When going down the Group 17, The changes in physical properties.
Atomic radius/ atomic size	Melting point and boiling point	Densities  (  )
Increase	Increase	Increase
-       Reason : Number of shells increases	-       Molecular size increases down the group. -        Thus, forces of attraction between molecules become stronger. -       Therefore, more energy is needed to overcome the strong force of attraction.	-       Increase in atomic mass is more than the increase in atomic radius (volume of atom)

Halogens	Physical state	Colour
Fluorine	Gas	Pale yellow
Chlorine	Gas	Greenish-yellow
Bromine	Liquid	Reddish-brown
Iodine	Liquid	Purplish- black

6. All the atoms of the halogens exhibit similar chemical properties because they have same valence electrons.

7. The reactivity of halogens decreases down the Group 17.

Explanation :

-       All halogens have seven valence electrons.

-       Each atom of the halogens will gain one more electron to achieve stable octet electron arrangement and form ion with a charge of negative.

Examples:

F + ē  → F^-

-       When going down to the group 17,  atomic size of halogens increases down the group

-       Thus, outermost occupied shell becomes further away from nucleus.

-       The strength to attract one electron into outermost shell by nucleus becomes weaker.

-       It causes the reactivity to decrease down the group

GROUP 18

Group 18

·         Group 18 elements are called noble gases

·         Elements= Helium, Neon, Argon, Krypton, Xenon, Radon

Physical properties:

·         Colourless gases at room temperature and pressure.

·         Low melting points and boiling points.

·         Low densities

·         Insoluble in water.

·         Do not conduct electricity

·         Poor conductors of heat

·         Exist as monoatomic gases at room condition

The physical properties of group 18 elements change down the group

a)      Atomic radius or atomic size increases.

Reason:

Number of occupied shells in the atom increases

b)      Melting point and boiling point increases.

Reason:

Forces of attraction between atoms become stronger as atomic size of elements increases.

c)       Density of elements increases

Reason:

Atomic mass increases more than the increase of atomic radius (volume of atom).

v  All group 18 elements are inert.

v  Inert means chemically unreactive.

v  Reason : All noble gases have the maximum number of valence electron on

outermost shell, which are two or eight valence electron.

v  Elements that has two valence electrons on the first shell is called duplet electron arrangement.

v  Elements that has eight valence electrons on the outermost shell is called octet electron arrangement.

The Uses of noble gases:

Helium	§  To fill airships and hot air balloons.
Neon	§  To fill neon lamps in signboards.
Argon	§  To fill an electric bulb.
Krypton	§  It is used in lasers to repair the retina of the eye. §  To fill the flash lights of cameras.

2013 FORM 5 TOV 1 PAPER 1 ANSWER

attention!!! 5A and 5B students, please do the corrections and COMPULSORY hand in after school holiday!!!

FORM 5 PAPER 1 (ANSWER)

TOV 1 2013

1	B		21	C		41	C
2	C		22	D		42	C
3	A		23	A		43	B
4	D		24	A		44	C
5	D		25	D		45	D
6	A		26	B		46	C
7	C		27	D		47	A
8	B		28	C		48	C
9	B		29	D		49	C
10	D		30	C		50	C
11	C		31	A
12	A		32	B
13	B		33	C
14	C		34	D
15	B		35	D
16	C		36	A
17	A		37	D
18	C		38	C
19	C		39	A
20	B		40	B