Download SLE133 – “Chemistry in Our World” Summary Notes Week 1

SLE133 – “Chemistry in Our World” Summary Notes
Week 1

A physical change is a change that does not affect the chemical makeup of a substance or
object. A physical change can be reversed.
Eg:
1. Any statement about a change of state (water evaporating, formation of ice from liquid
water)
2. Dissolving a solute in a solvent ( Dissolving sugar in water)
3. Grinding a substance into a powder or the reverse, making a lump out of small parts
(melting copper pellets to make a large lump of copper)
More examples in ‘exam hints’ section.

A chemical change is a change that affects the chemical makeup of a substance. A reaction
occurs during a chemical change and the reacting compounds are changed into new
compounds. A chemical change cannot be reversed.
Eg:
1. Frying an egg (bonds break and new bonds form, cannot change the fried egg into the
original state)
2. Burning a candle (the wax burns into CO2, H2O, and some other compounds)
More examples in ‘exam hints’ section.

Matter exists in three states;
1. Solid
2. Liquid
3. Gas

Matter
Classification of matter;
A substance which occupies
space and has mass
Pure Substance
Mixture
The substance has a
uniform chemical
composition
The substance consists
of two or more
components
Element
Cannot be further
seperated chemically
Chemical Compound
Homogeneous
Mixture
Can be further seperated
chemically
A uniform Mixture having
the same composition
Heterogeneous
Mixture
A non uniform mixture
having different
compositions at different
regions

All the elements in the periodic table are categorized as Metals (good conductors of heat and
electricity), Nonmetals (poor conductors of heat and electricity), and Metalloids (have both
metallic and non-metallic characteristics).

A physical quantity is a property that can be measured. The unit associated with the physical
quantity is used as a standard of measurement.
Eg:
Physical Quantity
Mass
Length
Time
Unit
Gram (g)
Meter (m)
Second (s)

The difference between mass and weight is that the mass measures the amount of matter in an
object, while the weight measures the gravitational force that the earth, moon or other large
body exerts on an object.

Significant Figures covered at the ‘exam hints’ section.

The difference between energy and temperature is that, energy is the capacity to do work or
supply heat, and temperature is the amount of heat stored in an object.

Heat is a measure of the transfer of thermal energy.

Specific heat capacity of a substance is the amount of heat required to raise the temperature of
1g of that substance by 1OC.

𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑉𝑜𝑙𝑢𝑚𝑒 (𝑚𝐿 𝑜𝑟 𝑐𝑚3 )

𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 =

Specific gravity has no units.
𝑀𝑎𝑠𝑠 (𝑔)
𝑔
)
𝑚𝑙
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑆𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 (
𝑔
)
𝑚𝑙
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑎𝑡 𝑡ℎ𝑒 𝑠𝑎𝑚𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 (
Week 2

An atom is the smallest and the simplest particle of an element

There are three subatomic particles in an atom;

Name
Symbol
Mass (g)
Mass (amu)
Charge
-24
Proton
p
1.673 × 10
1.007276
+1
Neutron
n
1.675 × 10-24
1.008665
0
-28
-4
Electron
e
9.109 × 10
5.485799 × 10
-1
1 Atomic Mass Unit (amu) is equal to 1/12 the mass of a carbon-12 atom

Electrons repel one another, protons repel one another, but electrons and protons attract one
another.

The Atomic Number (Z) of an element is the number of electrons in atoms of that given
element.

The Mass Number (A) of an element is the total number of protons and neutrons in an atom of
that element.

Isotopes are atoms with identical atomic numbers but different mass numbers.
Eg: Isotopes of Hydrogen;
Isotope
Symbol Atomic Number Mass Number
1
Protium
1
1
1H
Deuterium 1H2
1
2
3
Tritium
1
3
1H

Periodic table - group characteristics;
1. Group 1A – Alkali metals
 React violently with water
 Readily lose one electron
 Low melting point
2. Group 2A – Alkaline earth metals
 Less reactive than group 1A metals
 Readily lose two electrons
3. Group 7A – Halogens
 Corrosive nonmetals
 Colorful
 Always found in combination with other elements
 Readily accept one electron
4. Group 8A – Noble gases
 Colorless gases
 Not chemically reactive

Elements in the same group have similar chemical properties.