Structure of Atom and the Periodic Table



Structure of the atom and the periodic table

In this topic we will discuss the structure of the atom and the periodic table. In Form one an atom was defined as the smallest particle of an element that takes part in a chemical reaction.

An atom is made up of three sub-atomic particles. Electrons, Neutrons and Protons.The central part of an atom is called the nucleus.The nucleus consists of protons and neutrons and the electrons move around the nucleus in energy levels.

Charges of the particles

Protons are positively charged, electrons are negatively charged, while neutrons are neutral.

Electrons surrounding the nucleus occupy regions called energy levels.
For the first twenty elements the first energy level takes a maximum of 2 electrons, second energy level a maximum of 8 electrons,the third energy level takes a maximum of eight electrons. Electrons always occupy the unfilled energy level nearest to the nucleus. When an energy level is full the remaining electrons occupy the next energy level until it is full.

Isotopes are atoms of the same element which have the same atomic number but different mass numbers. The illustration below shows the Isotopes of Lithium atom. Identify the number of protons and neutrons in each isotope.

When an atom Loses or gains electrons it becomes electrically charged.

Charged atoms are called IONS.

Positively charged ions are called CATIONS.

Negatively charged ions are called ANIONS.

During chemical reactions, metals LOSE electrons Non metals GAIN electrons.

Activity: lithium, fluorine, aluminium, magnesium and sulphur have atomic numbers 3,9,13,12 and 16 respectively.

Protons in the nucleus, which are positively charged (+), attract electrons which are negatively charged (-) in the energy levels.For an atom to lose an electron, this force of attraction must be overcome. This is achieved by supplying energy to pull off the electrons. This energy supplied is called IONISATION ENERGY. It is measured in JOULES(J).Ionisation energy is thus defined as the energy required to remove an electron(s) from an atom in gaseous state to produce an ion.

Non- metals gain electrons to become stable since electrons are negatively charged, when an electron attempts to get into the outermost energy level of an atom, it will be repelled by the electrons which are already there. Therefore some force is needed to move the electrons into the energy level.When the electron finally settles in the outermost energy level heat energy is lost. The heat energy lost is more than that used to force the electron into the energy level. The net heat change when a gaseous atom of an element gains an electron is called electron affinity.

When an atom loses or gains electrons it becomes electrically charged. The resultant Charged particles are called ions. Positively charged ions are called cations. Negatively charged ions are called anions.. During chemical reactions, metals lose electrons and therefore form cations. Non-metals gain electrons and therefore form anions.


Coursework e-content also available on CD Discs, Call 0721806317 to Order

Agriculture CDs
Biology CDs
Business Studies CDs
Chemistry CDs
Computer Studies CDs
English CDs
Geography CDs
History CDs
Homescience CDs
Kiswahili CDs
Mathematics CDs
Physics CDs


Our YouTube Videos

Matrices and Transformation

Quadratic Expressions and Equations

Differentiation and Integration

Standard Deviation

Binomial Expansion


Volume Scale Factor

Cubes and Cube Roots

Linear Equations


Natural Numbers

Uniform Circular Motion

Electromagnetic Induction

Quantity of Heat

The Electromagnetic Spectrum

Mains Electricity

Floating and Sinking



Gas Laws



Thin Lenses

Distance and Displacement

Waves I

Refraction of Light


Hooke's Law

Cells and Simple Circuits


Heating effect of Electric Current


Electrostatic I

Particulate Nature of matter

Heat Transfer

Magnetic effect of electric current

The Turning Effect of a Force


Measurement I

Current Electricity II

Introduction to Physics

Measurement II

Equilibrium and centre of Gravity

Newton's Laws of Motion

Sulphuric (VI)acid - contact process

Standard conditions for measuring Enthalpy changes

Oxidation Number and oxidation state

Reaction Rate and Reversible Reactions

Oxides of nitrogen

Oxides of Sulphur

Nitric(V) Acid

Energy Changes in Chemical Reactions

Ammonia preparation and uses

Acid Bases and Salts

Frasch Process of Extraction of Sulphur

Laboratory preparation of chlorine

Hydrogen Chloride and Hydrochloric acid

Separation of Iron filings and sulphur

Reactivity Series of metals

Role of chemistry in the society

Percentage of nitrogen and oxygen in air by volume

Acids,bases and indicators

Allotropes and amorphous carbon

Alkanes,alkenes and alkynes

Salts, Types and Methods of preparation

Akanes, Alkenes and Alkynes - Hydrocarbons

The Mole: Calculations involving mass , volume and moles

The Mole

Hydrocarbons - Alkenes

Effect of electric current on substances

Gas Laws

Volumetric Analysis or titration

Structure of the Atom and the Periodic Table

Structure and Bonding

Sexual Reproduction in Animals

The Cell as the basic unit of Life

monosaccharides, dissacharides, polysaccharides

Classification I - Diversity of Organisms

Gaseous exchange in Mammals

Gaseous exchange in living organisms

Absorption of Water and Minerals Salts


Growth and Development

Classification II

Ecology the study of interrelationships

Reproduction in Plants and Animals

Transport in Animals

Transport in Plants

Osmosis, Diffusion and Active transport

Hottest part of a non-luminous flame

Relative atomic mass

Laboratory apparatus used for heating

Ion Formation

Types of Bunsen Burner Flames

Laboratory safety rules



Oxidation numbers

Ion Formation and charge

Other common laboratory apparatus

Hess' Law of constant heat summation