Unit 2 - Atoms, Elements and Compounds

Inside an atom:

• The center of an atom is the nucleus

  • has protons and neutrons

  • protons + neutrons = nucleons/mass number

  • proton number = atomic number

• subatomic particles

  • proton, p, +1 charge

  • neutron, n, no charge

  • electron, e, -1 charge

Isotopes:

• number of neutrons = nucleon number - proton number

• same proton number but different nucleon number are called isotopes

• Isotopes can be used to increase or decrease reactivity

Electronic Structure:

• Orbits called shells

  • First shell —> 2 electrons

  • Second shell —> 8 electrons

  • Third shell —> 8 electrons

  • Fourth shell —> 18 electrons

• Electronic configuration

  • Sodium 2,8,1

  • Periodic Table

    • Horizontal lines called periods

    • Vertical lines called groups

  • groups have a similar configuration

  • periods have a consecutive configuration

  • number of electrons in the outer shell are called valency electrons

  • Noble gas configuration

    • full outer shells

    • perfect configuration

    • eg: Neon 2,8

End of Chapter