PERIODIC TABLE

The elements in the periodic table are arranging according to INCREASING PROTON NUMBERS.

The vertical columns are known as Groups while the horizontal rows are known as Periods.

Elements of the same group have the same number of valence electrons ( outershell electrons)

Eg:
All ements of group 1 have 1 valence electrons;
All elements of group 2 have 2 valence electrons.

Elements of the same period have the same number of electron shells.

Eg:
All elements of period 1 ( Hydrogen and Helium ) have 1 electron shell.
All elements of period 2 (Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Sulphur, Fluorine, Neon ) have 2 electron shells.

There exist a group of elements without any grouping.

These are the transition metals.

Transition metals are characterized by their variable ( more than 1 ) valencies.

Eg:
iron ion exist as iron (II) ion and iron (III) ion;
copper ion exist as copper(I) ion and copper(II) ion.

STRUCTURE OF ATOMS

(Typical MCQ Question!!)

Location of Particles

Protons, neutrons are found in nucleus
Electrons orbit in electron shells

Mass of Particles

Proton = 1
Neutron = 1
Electron = 1/1840 ~ 0

Charges of Particles

Proton = +1
Neutron = 0
Electron = -1

Isotopes (Typical Structure Question!! )

Isotopes are atoms of the same element with different nucleon numbers but same proton number.
Eg: Carbon-12, Carbon-13, Carbon-14

CHEMICAL BONDS

Ionic Compounds

Ionic compounds are formed by metal (gp 1-3) and non-metal (gp 4-7)

Properties
-High melting point and boiling point ( considered as one point in exam ).

-Soluble in water.

-Conduct electricity in molten (hot liquid ) and in aqueous states
Note: does not conduct electricity in solid states!!!

Metal conduct electricity in molten and in solid states.

Covalent Compounds

Covalent compounds are formed only by non-metal elements.

Properties
-Low melting and boiling points

-Soluble in organic solvents

-Poor conductor of electricity

EXCEPTION: HCl is a good conductor of electricity.
Reason: When HCl dissolves in water, it dissociates to produce H+ and Cl-. It is the free mobile ions that conduct electricity! (Typical MCQ Question! )

(Typical Structure Question)

Question: Both sodium chloride and chlorine gas are compounds of chlorine; sodium chloride exist as a solid while chlorine exist as a gas. Explain why.

Answer:
Sodium chloride is an ionic compound [ 1mark ]. A large amount of energy is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions [ 1mark] . Hence high melting point. This is why it exist as a solid at room
temperature.

Chlorine gas is a covalent substance [ 1mark]. A small amount of energy is needed to overcome the weak intermolecular force of attraction between the molecules [ 1mark]. Hence low melting point. This is why it exist as a gas at room temperature.

Note: Although 'Hence high melting point. This is why it exist as a solid at room temperature.' has no mark allocation, this phrase has to be included for the completeness of answer!

STATES SYMBOLS

STATES SYMBOLS

(s) represents solid states
(l) represents liquid states
(g) represents gaseous states
(aq) represents aqueous states - means dissolved in water.

Question 1: 'Is water in aqueous state?'
Answer: No!! Simply because water cannot dissolve in water!!!

Question2: ' Is there any difference between gases vs gaseous?'
Answer: gases are particles that can move freely, while gaseous is to describe the state of the particles.

ELEMENTS, MIXTURES & COMPOUNDS

Element

An element is a substance that cannot be broken down into simpler substances by chemical means.
Eg: oxygen (O2), carbon (C), sulphur (S)
Note: Elements can be found in the Periodic Table.

Do not be confused:
1) An element can exist as molecules.Eg: hydrogen (H2), nitrogen (N2)
Molecule simply means more than 1 atom.
So, you can have the same type of atoms ( O2, N2, H2 , S8 ) or different types of atoms (CO2, CH4, H2O)

Compound

When it is made up by different types of atoms joined together chemically, it becomes a compound.
In this case, CO2 and CH4 are compounds.

A compound is a substance made up by more than 1 elements joined chemically together.

Eg: Calcium carbonate (CaCO3) ~contains 3 elements namely calcium(Ca), carbon (C) and oxygen (O)
Number of atoms in CaCO3 = 1+1+ 3(1) = 5 atoms

MIXTURE

Made up by at least 2 substances not joined together chemically.

Mixture can be catagorised by three types:

1) Element + Element
Eg: Iron(Fe) + Carbon(C)

2) Element + Compound
Eg: Copper (Cu)+ Water (H2O)

3) Compound + Compound
Eg: sodium chloride (NaCl) + water (H2O)

Common mistake made by students:

'A mixture can ONLY be separated by physical means'. (WRONG!!)

* EXPLANATION *
A mixture can also be separated by chemical means!!Compound is a substance that cannot be separated by physical means.

FORMULAS

All ions formed from:

group 1 ,(H+), (NH4+) have charges (+1)

group 2, Pb2+, Cu2+,Fe2+ have charges (+2)

group 3, have charges (+3)

group 6, (CO32-), (SO42- ) have charges (-2)

group 7, (OH-), (NO3-) have charges (-1)


* certain ions have various valency:
(Fe2+, Fe3+) , (Pb2+,Pb4+)

PURIFICATION

1) FILTRATION

Eg: sand from sand + water mixture



2) CRYSTALLISATION

Eg: copper(II)sulphate from impure copper(II)sulphate mixture

* Crystallisation is usually carried out with filtration.


3) DISTILLATION

Defn: to obtain pure liquid from a solution of solute
Eg: water from sea water


4) FRACTIONAL DISTILLATION

Defn: to separate liquids with different boiling points
Eg:

(i) ethanol from ethanol(78'C) + water(100'C)

(ii) crude oil into petrol, kerosene, lubicating oil etc

(iii) air into nitrogen, oxygen, carbon dioxide etc

5) CHROMATOGRAPHY

Defn: a method to separate and identify mixtures


Eg: separates dyes or colour from food/ ink/ pigments,check amounts of pesticides in vegetables, check if medicine contains banned drugs etc

(6) SUBLIMATION

Defn: a process in which substances changes from solid states to gaseous states through heating.

Eg: Ammonium chlorides ( NH4Cl ), dry ice ( solid CO2) ,naphthalene ( mothballs ), iodine



To test if a substance is pure / impure ( typical MCQ question!! )

CHECK IF IT HAS A FIXED BOILING / MELTING POINT------> IF IT IS PURE, IT WILL HAVE A FIXED MP/BP



Disclaimer: Picture are obtained from these websites-
GCSE Chemistry noteswww.wpbschoolhouse.btinternet.co.uk/page01/ElCpdMix/EleCmdMix.htm

EXPERIMENTAL DESIGN

BURETTE
- for measuring volumes of liquids up to 1 decimal place
eg: 27.5 cm3, 36.2 cm3

PIPETTE
- for measuring fixed volumes of liquids
eg: 20.0 cm3, 25.0 cm3, 50.0 cm3
Cannot measure odd volumes.
eg: 28 cm3, 38.5 cm3

MEASURING CYLINDER
-for measuring volumes of liquids to nearest 1 cm3
eg: 23 cm3, 36 cm3

BEAKER
-for boiling liquids / containing liquids
Never use it to measure volumes!

COLLECTION OF GASES

-FOR HEAVY GASES : downward delivery

-FOR LIGHT GASES : upward delivery

-FOR INSOLUBLE GASES: displacement of water