- Based on physical properties
Eg: Metal & Non-metal
- Based on chemical properties
PERIODIC TABLE
This is the chart of all the known elements.
The chart is divided into:
- 7 periods (horizontal rows)
- 8 groups (vertical columns) – represented by Roman letters (eg: III, VI, V….etc)
Elements are grouped according to their atomic numbers in this chart
- Elements of the same group have similar properties
- Elements at the lower rows (lower periods) have largest atomic numbers (larger weight)
Elements in the same group share similar chemical properties
- because they have the same number of electrons on their outer most orbit
- When the last orbit is ‘complete’ (2, 8, 8,18…..), the element doesn’t react with others (STABLE)
The zig-zag line divides the metals from non-metals
- Metallic elements are arranged on the Right of the periodic table
- Non-metalic elements are arranged on the Left of the periodic table
SIMPLE FORMAT (of the first 20 elements)
Hydrogen:
Atomic number = 1
Protons = electrons = 1
Lightest atom
Helium:
Atomic number = 2
Protons = electrons = 2
METALS & NON-METALS
Metallic elements:
- Eg: Mercury, Aluminium = Below ‘zigzag line’
- They are solid at room temperature (except for mercury, which is liquid at room temperature)
-
Pure metals are usually soft & weak → They can be made harder & stronger by mixing them with other metals or non-metals to form alloys
Non-metallic elements:
- Eg: Iodine, Chlorine, = Above ‘zigzag line’
- There are only 22 non-metallic elements
- only 10 are solid at room temperature
Metalloids:
- Eg: Boron, Silicon = They are just above the ‘zigzag line’
- Have intermediate properties between metals & non metals
- Called ‘semi-metals’
- They are Semi conductors of electricity
General properties of Metals & Non-metals:
USAGE OF METALS & NON-METALS:
Using Metals:
Shiny appearance → used to make jewelery
Doesn’t react with water → used to make water pipes & tanks (to prevent leakage due to corrosion)
Light & resists corrosion → used to make aircraft body
Conducts heat well & has high melting point → used for making cooking pots
Resists corrosion → used for coating food cans which are made of steel (steels is corroded by food – tin protect the steel from being corroded by food)
Reflects light so well → plated onto glass to make mirrors
(Mercury is also used for this purpose)
Using Non-metals:
- for making insecticides
- for making medicinal drugs
-
for hardening rubber (in making car tyres) = Vulcanization of rubber
- Used as rocket fuel
- For making margarine
- For filling weather balloons
- for the formation of plant & animal proteins
- in the manufacture of fertilizers
- cooling agent in its liquid state (refrigerator)
- for the formation of living tissues
- as a fuel
- in pencil leads
- Chlorine kills bacteria (antiseptic)
- Chlorine is added in water purification
- Purplish red solution to wash the wounds has Iodine = Antiseptic (kills bacteria)
- Called antiseptic iodine solution
- for respiration
- for combustion
- in oxy-acetylene flames for welding
When there is more than 1 element → It is called a ‘Molecule’
Molecule can be either:
- Molecule of compound OR
- Molecule of element
COMPOUNDS
Def: This is a substance consisting of two or more elements chemically combined together.
There are thousands of compounds around us
Eg:
N2O, CaCO3, Pure water (H2O), C6H12O6 (glucose)
During the formation of compounds energy (heat and sometimes light) is either:
Similarly, breaking down of a compound into its constituents also involves heating, exposure to light or passing electric current.
Word equation:
Hydrogen + Oxygen ⇨ Water
Hydrogen + Oxygen ⇦ Water
Common properties of compounds:
- Compounds are formed by chemical reactions, which usually involves an exchange of energy
- exchange can be absorption of energy or giving out energy
- exchange of energy can be in the form of heat or light or both
- Properties of a compound is different from the properties of its constituent elements.
- A compound can only be broken down into simpler substances by chemical methods
Can use the following methods:
- Heating (but compounds NOT ALWAYS change to its components when heating)
- exposure to light
- passing electric current through them
- The different elements in a compound are joined together in a fixed proportion by mass.
Formation of compounds:
- Elements + Elements
- Elements + Compounds
- Compounds + Compounds
- Combustion
Some compounds & their names
CuSO4 - Copper sulphate – blue crystals (solid)
Cu (OH)2 - Copper hydroxide – blue precipitate (solid)
CuCO3 - Copper carbonate – green solid
CuCl2 - Copper chloride – green solid
NO - ‘oxide’
NO2 - ‘dioxide’
CHEMICAL REACTIONS
(part 1) (part 1)(part 2) (part 1)(part 2) (part 1)
(part 1)(part 2) (part 1)(part 2) (part 1)(part 2) (part 1)(part 2)
When part 1 & Part 2 combines together → Their valences get exchanged
Eg:
Ca (NO3) 2
Mg (NO3) 2
H2SO4
HNO3
NH4Cl
H2CO3
MIXTURES
A mixture consists of 2 or more substances, which are NOT chemically joined together.
The constituents of the mixture could be ELEMENT, COMPOUNDS or BOTH.
Compounds exist as:
- solid soluble in liquid = SOLUTION
- solid insoluble in liquid = SUSPENSION
- miscible = SOLUTION
- immiscible = SUSPENSION
Some useful mixtures:
- The air we breathe (gas-gas)
This is the mixture of oxygen, nitrogen and the noble gases
- Mineral water we drink (not the pure water)
This is a mixture of the minerals such as calcium, sodium, potassium, magnesium and water
It is a mixture of aluminium, copper, magnesium and manganese.
It is light & strong (metals alone are not that strong)
Used to build aircraft
- Medicine as a suspension (= SHAKE WELL before use)
Common properties of mixtures:
- No chemical reaction takes place during the formation of a mixture
- Thus little or no energy is involved (no heat/light exchange)
- Eg: Air is a mixture of oxygen, nitrogen, carbondioxide, water vapour and
noble gases (without any chemical reactions)
- Mixture has the properties of the of the constituent substances
- Air has the properties all its constituents (eg: helps to burn, because
oxygen is present)
- Constituents of the mixture can be mixed in any proportion by mass
-
Eg: the proportion (by mass) of the different gases in air is not constant →
changes with time & place
- A mixture can be separated into its components by physical means
- Some physical methods of separation are – evaporation, filtration,
Distillation, crystallization, chromatography
- Eg: components of different gases of air can be separated using the
technique ‘fractional distillation’
COMPARISON