Physical vs.

Chemical Properties
Physical Properties: The properties those are associated with the physical state of the substance are
called physical properties like colour, smell, taste, hardness, shape of crystal, solubility, melting or
boiling points, etc. For example, when ice is heated, it melts to form water. When water is further heated,
it boils to give steam. In this entire process only the physical states of water change whereas its chemical
composition remains the same.
Examples:
Melting Point: The temperature at which a solid becomes a liquid.
Boiling Point: The temperature at which a liquid changes to a gas.
Density: The mass of a substance per unit volume.
Color: The visual appearance or color of the substance.
State of Matter: Whether the substance is a solid, liquid, or gas at a given temperature and pressure.
Solubility: The ability of a substance to dissolve in a solvent (like salt in water).
Conductivity: The ability of a substance to conduct heat or electricity.
Chemical Properties:
The chemical properties depend upon the composition of the substance. When a substance undergoes a
chemical change, its composition changes and a new substances are formed. For example, decomposition
of water is a chemical change as it produces hydrogen and oxygen gases.
Examples:
Reactivity: How a substance reacts with other substances, such as acids, bases, or oxygen.
Flammability: The ability of a substance to burn or ignite, causing combustion.
Toxicity: How harmful a substance is to living organisms.
Oxidation States: The ability of a substance to gain or lose electrons, often in reactions with oxygen
(like rusting of iron).
Acidity or Basicity: Whether a substance acts as an acid or base when dissolved in water (pH level).
Corrosiveness: The tendency of a substance to corrode or degrade materials (such as metals) through
chemical reactions.
Physical vs. Chemical Changes
Physical Changes: Changes that only affect the physical properties of a substance without altering its
chemical structure. Examples include melting ice into water or dissolving sugar in water.
Chemical Changes: Involve a transformation where the substance’s chemical structure changes, resulting
in the formation of a new substance. Examples include burning wood or rusting iron.
Atom & Ion. Element, Compound & Mixture:
Atom:

Definition: An atom is the “smallest unit of matter” that retains the chemical properties of an element. It
consists of a nucleus made of protons (positively charged) and neutrons (neutral), with electrons
(negatively charged) orbiting around the nucleus. atom, the basic building block of all matter and
chemistry. Atoms can combine with other atoms to form molecules but cannot be divided into smaller
parts by ordinary chemical processes.

Most of the atom is empty space. The rest consists of three basic types of subatomic particles: protons,
neutrons, and electrons. The protons and neutrons form the atom’s central nucleus.

Protons: Positively charged particles in the nucleus.

Neutrons: Neutral particles in the nucleus.

Electrons: Negatively charged particles that orbit the nucleus in electron shells.

The nucleus is small and dense compared with the electrons, which are the lightest charged particles in
nature. The electrons circle the nucleus in orbital paths called shells, each of which holds only a certain
number of electrons.

An ordinary, neutral atom has an equal number of protons (in the nucleus) and electrons (surrounding
the nucleus). Thus the positive and negative charges are balanced.

Example: A hydrogen atom consists of one proton in the nucleus and one electron orbiting it.

Ions:
An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or
gained one or more electrons. ion, any atom or group of atoms that bears one or more positive or negative
electrical charges. Positively charged ions are called cations; negatively charged ions, anions. Ions are
formed by the addition of electrons to, or the removal of electrons from, neutral atoms or molecules or
other ions; by combination of ions with other particles; or by rupture of a covalent bond between two
atoms in such a way that both of the electrons of the bond are left in association with one of the formerly
bonded atoms.
For example, Na+, K+ are cations. The following equations show the formation of cations from atoms.
For example, Cl- and O-2

Na ( aq ) → Na+ ( aq ) + e-

Elements

In the early ages, only nine elements (carbon, gold, silver, tin, mercury, lead, copper, iron and sulphur)
were known. At that time, it was considered that elements were the substances that could not be
broken down into simpler units by ordinary chemical processes. Until the end of nineteenth century,
sixty-three elements had been discovered. Now 118 elements have been discovered, out of which 92
are naturally occurring elements. Modern definition of “element is that it is a substance made up of
same type of atoms, having same atomic number and cannot be decomposed into simple substances by
ordinary chemical means.” It means that each element is made up of unique type of atoms that have
very specific properties. Elements occur in nature in free or combined form. All the naturally occurring
elements found in the world have different percentages in the earth's crust, oceans and atmosphere.

Elements are represented by symbols, which are abbreviations for the name of elements. A symbol is
taken from the name of that element in English, Latin, Greek or German. If it is one letter, it will be
capital as H for Hydrogen, N for Nitrogen and C for Carbon etc. In case of two letters symbol, only first
letter is capital e.g. Ca for Calcium, Na for Sodium and Cl for Chlorine.

The unique property of an element is valency. It is combining capacity of an element with other
elements. It depends upon the number of electrons in the outermost shell.in simple covalent
compounds, valency is the number of hydrogen atoms which combine with one atom of that element or
the number of bonds formed by one atom of that element e.g. in the following compounds.

The valency of chlorine, oxygen, nitrogen and carbon is 1, 2, 3 and 4, respectively. Some elements show
more than one valency, i.e. they have variable valency. For example, in ferrous sulphate (FeSO4 ) the
valency of iron is 2. In ferric sulphate (Fe2 (SO4 )3 ), the valency of iron is 3. Generally, the Latin or Greek
name for the element (e.g., Ferrum) is modified to end in 'ous' for the lower valency (e.g. Ferrous) and
to end in 'ic' for the higher valency (e.g. Ferric).

Atomic Number and Mass Number

The atomic number of an element is equal to the number of protons present in the nucleus of its atoms.
It is represented by symbol ‘Z’ . As all atoms of an element have the same number of protons in their
nuclei, they have the same atomic number.. For example, all hydrogen atoms have 1 proton, their
atomic number is Z=l. All atoms in carbon have 6 protons, their atomic number is Z=6. Similarly, in
oxygen all atoms have 8 protons having atomic number Z=8 and sulphur having 16 protons shows
atomic number Z = 16.

The mass number is the sum of number of protons and neutrons present in the nucleus of an atom. It is
represented by symbol 'A'. It is calculated as A=Z+n where n is the number of neutrons. Each proton and
neutron has lamu mass. For example, hydrogen atom has one proton and no neutron in its nucleus, its
mass number A=l+0 =1. Carbon atom has 6 protons and 6 neutrons, hence its mass number A=12.

Compound

Compound is a substance made up of two or more elements chemically combined together in a fixed
ratio by mass. As a result of this combination, elements lose their own properties and produce new
substances (compounds) that have entirely different properties. Compounds can't be broken down into
its constituent elements by simple physical methods. For example, carbon dioxide is formed when
elements of carbon and oxygen combine chemically in a fixed ratio of 12:32 or 3:8 by mass. Similarly,
water is a compound formed by a chemical combination between hydrogen and oxygen in a fixed ratio
of 1:8 by mass.

Compounds can be classified as ionic or covalent. Ionic compounds do not exist in independent
molecular form. They form a three dimensional crystal lattice, in which each ion is surrounded by
oppositely charged ions. These oppositely charged ions attract each other very strongly, as a result ionic
compounds have high melting and boiling points. These compounds are represented by formula units
e.g. NaCl, KBr. The covalent compounds mostly exist in molecular form. A molecule is a true
representative of the covalent compound and its formula is called molecular formula e.g. H 2O, HCl,
H2SO4.

Mixture

When two or more elements or compounds mix up physically without any fixed ratio, they form a
mixture. On mixing up, the component substances retain their own chemical identities and properties.
The mixture can be separated into parent components by physical methods such as distillation,
filtration, evaporation, crystallisation or magnetization. Mixtures that have uniform composition
throughout are called homogeneous mixtures e.g. air, gasoline, ice cream. Whereas, heterogeneous
mixtures are those in which composition is not uniform throughout e.g. soil, rock and wood.

Difference between compounds and mixture