TOPIC 3: ATOMIC STRUCTURE

• Atoms contain PROTONS, NEUTRONS, and ELECTRONS.

• Protons have positive charge while neutrons has neutral charge but same mass as protons. 
• Since an atom is electrically neutral, electrons has to carry a negative charge and the amount of electrons is the same as the amount of protons.

• Protons and neutrons are located in nucleus. These make up nucleon number.

• Electrons move around nucleus in an orbit called electron shells. 
• PROTON NUMBER is the number of protons in an atom.
• NUCLEON NUMBER is the number of protons and neutrons in nucleus of an atom. Therefore, to find the number of neutrons, we subtract proton number from nucleon number, i.e.: Nucleon number – Proton number = Neutrons
• ISOTOPES are atoms of the same element with different number of neutrons. Therefore, their nucleon number is different. Example below shows Isotops of Lithium atom.

      

ELECTRONIC CONFIGURATION

 

• Electrons are placed in orbits or called shells or energy levels. First shell contains maximum 2 electrons. 
• Second shell and so and so can occupy 8 electrons. 
• To write electronic configuration we write as n,n,n.... where first n denotes the first shell, second the second shell and so and so for.
  E.g. Sulfur has electronic configuration of 2,8,6.