Atoms & Periodic Table

Atoms & Periodic Table

1. Definitions

   • Atoms: the smallest particle of any chemical
   • Elements: Pure substance made of one atom
   • Compound: Two or more atoms chemically joined together
   • Mixture: Two or more elements mixed together

2. History of the Atom

   • 1803
     • -John Dalton's atomic theory was first introduced. -"Atoms cannot be divided into anything smaller." -No nucleus
   • 1897
     • -J.J. Thomson's atomic theory took over Dalton's after the discovery of electrons.  -The electrons proved Dalton's theory wrong as Dalton thought that atoms couldn't be broken down into anything simpler. Thomson's theory showed that the atom contained smaller pieces. -Plum Pudding Model
   • 1913
     • -Niels Bohr's idea of a planetary model evolved around the same time as he introduced 'a quantum of energy.' -His experimental evidence supported his theory that electrons occupy orbits or shells around the nucleus of each atom.
   • 1909
     • -Ernest Rutherford came up with the idea of the nucleus (the nuclear model). -This supported Thomson's idea. -His assistants, Geiger and Marsdon, carried out a gold foil experiment which demonstrated that the atom has a nucleus.  -The experiment used the alpha particles emitted by a radioactive element as a further insight to the atomic structure.
   • Today
     • -Today we use a mixture of Bohr's model and the Quantum Mechanical Model which is slightly more difficult to understand and is based on mathematics. 

3. Subatomic Particles

   • Proton
     • -Relative mass of 1 (1.67 x 10[to the power of -27]kg) -Electrical charge of +1, positive
   • Electron
     • -Relative mass of 0, too small for record (1.8 x 10[to the power of -32]kg) -Electrical charge of -1, negative
   • Neutron
     • -Relative mass of 1 (1.67 x 10[to the power of -27]kg) -Electrical charge of 0/ neutral/no charge
   • The overall charge of an atom is neutral
     • Every atom has the same amount of protons as it does electrons and this therefore cancels out the overall positive and negative charges
   • Finding the amount of protons, electrons and neutrons in an atom
     • Protons = Atomic Number
     • Electrons = Atomic Number
     • Neutron = Mass number - Atomic Number
     • e.g. Boron (11,5) P:5, E:5, N:6

4. Electronic Structure

   • -Count the number of electrons using the element's atomic number -The first shell takes a maximum of 2 electrons -The next two shells contain 8 electrons, and then 18.  -[keep filling the shells until you run out of electrons]
   • Elements in the same group react similarly because they have the same amount of electrons in the outer shell

5. Ions

   • -A charged particle -Can be positive or negative -Made from atoms gaining or losing electrons
   • Loss of an electron
     • -Positive Charge
   • Gain of an electron
     • -Negative Charge

6. Isotopes

   • An atom of an element with more neutrons, but the same amount of protons

7. Properties Of Metals and Non Metals

   • Metals
     • -Lustrous (shiny) -Strong -Solid -High Density -Good Conductor of Heat -Good Conductor of Electricity -Malleable -Sonorous
   • Non Metals
     • -Weak -Brittle -Low Density -Makes a Dull Sound -Dull Appearance -Poor Conductor of Heat -Poor Conductor of Electricity -Can be Solid, Liquid or Gas

8. Arranging the Periodic Table

   • Arranged in order of increasing atomic number
     • The atomic number tells you how many protons or electrons are in an atom
       • Electrons are found in the shells around the nucleus. The number of electrons in the outer shell is the same as the group number
         • The number of shells is the same as the period number
           • Metals are found on the left of the periodic table

9. Alkali Metals (Group 1)

   • Properties
     • -Soft -Shiny when cut (but react with air quickly so they tarnish) -Low melting point -Low density (float on water)
   • Reactions With Water
     • -Lithium fizzes slowly -Sodium reacts faster than Lithium and melts into a ball  -Potassium reacts the fastest with a lilac flame and explodes
   • Reactivity
     • -The reactivity of the alkali metals increases as you go down the group -This is because the outer electron is further from the nucleus so it is less tightly held -There is a greater distance so there is less attraction and increased shielding/repulsion from other shells of electrons

10. Noble Gases (Group 0)

11. Halogens (Group 7)

12. Mendeleev and Newlands