Atoms and Molecules

Atoms and Molecules

1. Atoms

   • Matter is made of atoms
     • Atoms are the smallest unit of an element
   • Represented by small spheres
   • sub-atomic particles
     • protons
       • positive charge (+1)
       • found in nucleus of atom
       • relative mass
         • 1
     • neutrons
       • no charge (0)
       • found in nucleus of atom
       • relative mass
         • 1
     • electrons
       • negative charge (-1)
       • relative mass
         • 0
     • Electronic Structure
       • The e stands for electron
       • The p stands for proton
       • the n stands for neutron
       • The big circle around the neutrons and protons is the electron shell
         • The first electron shell can only have two electrons
           • The rest of the electron shells can have 8 electrons
             • the valence shell is the shell furthest away from the nucleus that is occupied with at least one electron
     • Electronic Configuration
       • Hydrogen atom
         • 1
       • Lithium atom
         • 2.1
       • each electron shell is separated by a dot
         • each no. is the no. of electrons in each electron shell
           • start with the electron shell closest to the nucleus

2. Molecules

   • group of countable atoms
     • cluster of atoms
       • mono-atomic molecules
       • di-atomic molecules
       • tri-atomic molecule

3. Periodic Table

   • Group
     • no. of valence electrons is equal to group no.
     • vertical column of elements
     • Group 0
       • Noble Gases
         • completely filled valence shell
           • most stable elements
             • least reactive of all elements
     • Group 1 & 2
       • Metallic Elements
         • very few valence electrons
           • quite unstable
             • very reactive
   • Period
     • no. of electron shel,ls are equal to period no.
     • horizontal row of elements
   • arranged in increasing atomic no. (proton no.)
   • How to read an element
     • Li is the chemical element symbol
     • the 3 on top of Li is the atomic no.
       • proton no.
         • no. of protons = no. of electrons
     • the 7 under Li is the mass no.
       • no. of protons + no. of neutrons

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