The Periodic Table
The stucture of the Periodic Table
- 1808: John Dalton -> arranged all known elements in order of their masses.
- 1863: John Newlands -> law of octaves.
- 1869: Dimitri Mendeleev -> arranged all known elements in order of mass and properties, and he left gaps for the undiscovered alements.
Protons and Neutrons dicovered!
- 1900+: Modern Periodic Table -> all elements arranged according to atomic number (number of protons)
The Modern Periodic Table
Elements are arranged in order of atomic number (number of protons) and NOT according to mass.
e.g 40 39
Ar is placed before K in the periodic table, despite it being heavier than K.
e.g 128 127
Te is before I
Te has one proton less than I, but must have 2 more neutrons than I, and this is why it's heavier.
The Structure of the Periodic Table
Groups = columns
= group number = number of electrons in the outer shell
= elements in the same group have similar properties (chemical and physical)
= some groups have names
Group 1 = alkali metals Periods = rows
2 = alkaline earth metals = period number = number of shells
7 = halogens altogether
0/8 = noble gases = elements change properties from stronglty metallic -> metalloids -> non-metals (periodicity)
The Structure of the Periodic Table (continued)
no. of protons + neutrons
mass number 23
atomic number 11
number of protons
Group 1: Alkali metals
Physical properties: Chemical properties:
- soft (can be cut with a knife) Metal Obvservations Reactivity (1-most
- low density (floats on water) 2-least)
- relatively low melting point Lithium (Li) - fizzing. 3
- shiny when freshly cut - moving about the
surface of the water.
- Quick reaction.
Sodium (Na) - more fizzing 2
- moves about faster
- quicker reaction
Group 1: Alkali metals (continued)
Metal Observations Reactivity (1-most 3-least)
Potassium (K) - violent fizzing 1
- catches fire
- very quick reaction
another observation: solution left after reaction turns universal indicator blue/purple
This reaction forms two products:
1) flammable gas -> hydrogen, H2
2) alkaline solution -> metal hydroxide e.g LiOH, NaOH, KOH
Group 1: Alkali metals (continued 2)
metal + water -> metal hydroxide + hydrogen
2Li(s) + 2H2(l) -> 2LiOH(aq) + H2(g)
2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)
2K(s) + 2H2O(l) -> 2KOH(aq) + H2(g)