ELEMENTS, COMPOUNDS AND

MIXTURES

• YEAR 9, WEEK 3
 TOPIC: ATOMIC STRUCTURE
• CONTENT
• Meaning of Atom; Concept of Electrons,
Protons and Neutrons
• Simple atomic model; Properties of atoms
• Concept of Elements, Molecules, Compounds
and Mixtures
 SUB TOPIC 1: Meaning of Atom; Concept
of Electrons, Protons and Neutrons
• MEANING OF ATOM
• Matter (solid, liquid or gas) is made up of tiny particles
called atoms.
• An atom is the smallest particle of matter which can
take part in a chemical reaction.
• An English Chemist called John Dalton (1766 - 1844)
put forward some statements about the atom in1803
and 1808 which are referred to as Dalton’s atomic
theory. These helped to explain some observations
about the structure and behavior of atoms
Structure of Matter
Modern physics has revealed successively deeper layers of
structure in ordinary matter. Matter is composed, on a tiny scale,
of particles called atoms. Atoms are in turn made up of
minuscule nuclei surrounded by a cloud of particles called
electrons. Nuclei are composed of particles called protons and
neutrons, which are themselves made up of even smaller
particles called quarks. Quarks are believed to be fundamental,
meaning that they cannot be broken up into smaller particle.
• However with advancement in
science and the contribution of more
scientists like J.J Thomson in 1897,
Robert Millikan in1909-1916 and
Earnest Rutherford in 1911, the
theory has been modified.
 ATOMIC THEORY
Presently, scientists agree that:
1. An atom is made up of a number of small particles namely, the
electron, the proton and the neutron. None of these can exist on
its own naturally.
2. An atom is the smallest particle of matter that can take part in a
chemical reaction.
3. In nuclear reactions atoms can be created or destroyed.
4. Some atoms of the same element have different masses for
example in those elements that have isotopes.
5. Most inorganic compounds are formed by the joining of atoms of
two or more elements in a definite whole number ratio, but for
large organic molecules such as proteins, fats and starches which
involve the joining of thousands of atoms, this theory does not
hold.
 CONCEPT OF ELECTRONS, PROTONS AND
NEUTRONS
An atom is made up of three fundamental
particles; the electrons, protons and neutrons.
Structurally, an atom consists of a small dense,
centrally placed nucleus which is surrounded by
electrons. The nucleus is made up of the protons
and the neutrons. The protons and neutrons are
collectively called the nucleons. Most of the
atom is empty space. Most of the mass is
concentrated in the nucleus.
 ELECTRONS
These are tiny particles situated at a
comparatively great distance from the centre of
the atom. They travel rapidly and continuously
in orbits around the nucleus. An electron has a
negative charge and a very negligible mass of
about 9.1 × 10-28g, this is about 1800 times
lighter than the hydrogen atom.
 PROTONS
• These are tiny, positively charged particles
found in the nucleus of an atom. The positive
charge is equal in magnitude to the negative
charge on the electron. Thus, an atom with
the same number of electrons and protons is
electrically neutral. The mass of the proton is
1 × 10-24g, which is about 1800 times larger
than that of the electron.
 NEUTRONS
• These are tiny particles found in the nucleus of
an atom. They have no electric charge i.e. they
are neutral. Neutrons have about the same
mass as a proton.
Sub- atomic Unit of electric Relative mass
Particle charge

Proton +1 1.00

Electron -1 1/1840

Neutron none 1.00

 EVALUATION

• What is an atom?
• Name the fundamental particles of an atom
• State the charges on these particles and their
relative masses.
• Who was the first chemist to propound
theories about atoms?
 Sub-Topic 2: SIMPLE ATOMIC MODEL

• Ernest Rutherford in 1909 proposed a model

of the atom. His model showed a small dense,
positively charged nucleus surrounded by
relatively empty space and electrons
continuously orbiting the nucleus at a great
distance from it. However in the light of
further experimental results, other models of
the atom have been proposed.
• The electrons occupy different orbits or shells
called K,L,M,N, shells or 1,2,3,4, shells round
the nucleus. These shells may also have sub
shells designated s, p, d, subshells.
HYDROGEN

SODIUM
 PROPERTIES OF ATOMS
• Atoms have several properties that help
distinguish one type of atom from another
and determine how atoms change under
certain conditions. These properties include;
 PROPERTIES OF ATOMS
• The Atomic number: The number of protons in the
nucleus of an atom is called its atomic number (Z). All
atoms of the same element have the same number of
protons and so have the same atomic number. Atoms are
normally electrically neutral so the atomic number also
shows how many electrons an atom has. However, an
atom may lose or gain an electron to become a charged
particle called an ion. When an atom loses an electron it
forms a positively charged ion called a cation. When an
atom gains an electron it forms a negatively charged ion
called an anion. The number of electrons thus determines
many of the chemical and physical properties of an atom.
 PROPERTIES OF ATOMS
• The Mass number: The sum of the protons
and neutrons in the nucleus of an atom is
called the mass number of the atom (A). The
number of neutrons is denoted by N.

• The relationship between the number of

neutrons and protons is given by; A=Z - N
 PROPERTIES OF ATOMS
• The Atomic Mass and Weight: Scientists use a device
called a mass spectrometer to measure atomic mass. The
mass of an atom is measured in terms of a unit called the
atomic mass unit (amu). An amu is defined as exactly
1/12 the mass of an atom of carbon with six protons and
six electrons.
• An element’s atomic weight represents the mass of one
mole of its atoms. A mole is the mass of a very large
number of atoms. A mole of atoms of any element
contains 6.02 × 1023 atoms. This is also called the molar
mass.
 PROPERTIES OF ATOMS
• Isotopes: Atoms of the same element that
differ in mass number (A) are called isotopes.
They have the same atomic number (Z). These
elements have the same number of protons in
their nucleus but different numbers of
neutrons. For example, hydrogen has three
isotopes 1H; 2H; 3H called Protium, Deuterium
and Tritium respectively
HYDROGEN ISOTOPES
 EVALUATION
• Draw a simple atomic model of Helium atom
with two electrons, two protons and two
neutrons.
• Briefly describe the three types of hydrogen
atoms that exist.
• Write the (a) mass number (b) atomic
number of Sodium atom.
 Sub-Topic 3: Concept of Elements,
Molecules, Compounds and Mixtures
• ELEMENT: A substance that is made up of only
one type of atoms is called an element. An
element cannot be broken down into anything
else. Examples are magnesium, copper, zinc,
gold, iron, oxygen, carbon, chlorine, etc.
 Concept of Elements, Molecules,
Compounds and Mixtures
• MOLECULE: The smallest unit of a substance
which can exist on its own and retain the
properties of the substance is called a
molecule. A molecule may be made up of one
atom only e.g. Argon (Ar) or a combination of
atoms e.g. Oxygen (O2).
 Concept of Elements, Molecules,
Compounds and Mixtures
• COMPOUND: A substance formed by the
chemical combination of the atoms of
different elements is a compound. Examples
are Sodium chloride (salt), water, kaolin,
carbon (iv), oxide, sand, etc.
 Concept of Elements, Molecules,
Compounds and Mixtures
• MIXTURE: A substance formed when elements
or compounds are mixed without any
chemical reaction occurring is called a
mixture. Examples are crude oil, soil, cup of
tea, air, palm oil, solution of salt and water,
etc. The components of a mixture can be
separated by physical means like evaporation,
magnetization, filtration, Sublimation, etc.
 Differences between compounds and
mixtures
MIXTURES COMPOUNDS

1. Mixtures can be separated easily 1. Compounds can not be separated

2. Mixture have the properties of 2. Compounds do not have the

the substances present in it properties of the elements

3. No chemical change takes place 3. A compound is always formed due

when a mixture is made to a chemical reaction

4. There is no heat taken in or 4. Heat is either taken in or given out

given out when a mixture is when a compound is made
Made
5. A compound always contains the
5. A mixture can contain elements elements in fixed proportions, e.g.
in any proportion FeS contains 7g of iron to 4g of
sulphur
 PROPERTIES OF ELEMENTS,
COMPOUNDS AND MIXTURES
 ELEMENTS
(a) Chemical Properties:
1. Some elements are very reactive e.g. Sodium, Potassium, Chlorine,
Oxygen, etc. Sodium metal readily gets ignited on exposure to air.
2. Some elements are moderately reactive e.g. when iron is exposed
to moist air it gradually begins to rust.
3. Some elements are virtually unreactive e.g. Gold does not rust
when exposed to moisture.

(b) Physical Properties

4. Some elements have light density e.g. Hydrogen gas while some
are heavy e.g. Gold, Lead, etc.
5. Some elements are colourless e.g. Oxygen, Hydrogen and Nitrogen
while some are coloured e.g. Chlorine, Bromine, etc.
6. Solid, non-metallic elements are brittle and have a dull surface e.g.
Phosphorus and Sulphur while the metallic elements are malleable
and have a shiny surface e.g. Iron and Aluminium
7. All metals exist as solids at room temperature except Mercury
which is a liquid.
 COMPOUNDS
(a) Physical Properties:
1. Most compounds formed from the chemical combination
of metals and non-metals are soluble in water but not in
organic solvents like kerosene.
2. Compounds formed from the chemical combination of
non-metals are soluble in organic solvents like kerosene
and petrol.
3. Compounds have definite melting and boiling points.
(b) Chemical Properties
4. Some chemicals react chemically with acids to form a new
compound e.g. sodium hydroxide and hydrochloric acid
react chemically to form sodium chloride and water.
5. Some compounds decompose on heating e.g. calcium
trioxocarbonate (iv) on heating produces calcium oxide and
carbon (iv) oxide.
 MIXTURES
Physical Properties:
1. Mixtures can be separated by physical
means.
2. Mixtures do not have definite boiling or
melting points.
3. The colour of individual constituents is
visible.
 USES OF SOME ELEMENTS,
COMPOUNDS AND MIXTURES
 USES OF ELEMENTS
• (a) Gold is used in making jewelry and coins. It
is also used in art work and dentistry.
Radioisotopes of gold are used in biological
research and in treatment of cancer.
• (b) Iron is used for production of galvanized
sheet metal and electromagnets. Iron
compounds are used for medicinal purposes in
the treatment of anemia and also in tonics
 USES OF COMPOUNDS
• (a) Kaolin is used in the manufacture of fine
porcelain and china ware; pottery, stoneware and
bricks; as a filler for pigments and manufacture of
paper.
• (b) Salt is used as a seasoning; as preservative for
meats; in dyeing and in manufacture of soap and
glass. Table salt is combined with small quantities of
iodide to prevent occurrence of goiter. Industrially
salt is a source of chlorine and sodium. Chlorine is
used in manufacture of hydrochloric acid, chloroform
and bleaching powder. Sodium is used for sodium
carbonate, baking soda and sodium hydroxide.
 USES OF MIXTURES
• (a) Crude oil is used as fuel (petrol, kerosene,
diesel, gas, etc.) and raw material in the chemical
industry. Derivatives are used in manufacture of
medicine, fertilizers, plastics, paints, building
materials and for generating electricity.
• (b) Coal is used as fuel. It is used by electric
power plants to produce electricity. Industrially it
can be converted to coke and mixed with iron
ore and limestone to produce iron. The coal
gases given off during the process of coke
formation are used to manufacture solvents,
fertilizers, medicine, pesticides, etc.
 EVALUATION
• Define the following terms and give two
examples of each (a) element (b) molecule (c)
compound (d) mixture
• Mention two things each example can be used
for.
• Enumerate three differences between
elements, compounds and mixtures
 HOMEWORK
1. Complete the missing information below
Element Atomic Atomic Number Number Number
Number Mass of of of
Electrons protons neutrons
Hydrogen          

Carbon          

Oxygen          

Chlorine          

Sodium          

2. Air is a mixture of gases, mention three of the gases and state two uses of each.