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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.

 

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