Elements and Periodic Table of Elements Chemistry Elements and Periodic Table of Elements

The Basics Element = all the atoms are the same (JC) Element – cannot be broken down chemically into simpler substances (nuclear reactions are a different story!) How do we know what’s an element?

Periodic Table of …… Elements Need to know symbols of elements 1- 36

learn the rest as we go through the course is for Carbon but watch out for ……… Potassium is K Phosphorus is P learn the rest as we go through the course

Be careful Symbol can only have one capital letter Na not NA

History Greeks – 4 elements – were they right? Boyle (2000 ish years later!) better idea of element can’t be broken down into simpler substance

Davy used electricity to break down compounds into their elements (JC – you saw water broken into H and O) he isolated Na, K, Ba, Sr, Ca, Mg

Moseley used x-rays showed that the nucleus had positive charge each element had different positive charge on its nucleus Element ……. all elements have the same atomic number (no. of protons

Same number of electrons in outside shell Periodic Table Same number of electrons in outside shell Vertical Lines are called Groups Horizontal Lines are called Periods Metals on left , non- metals in right division begins at Boron (check with Aluminium Al) Same number of shells

Learning Check Do I know…. (LC) definition of an element? 4 steps in how idea of element developed? Where is a group on PTE? What a group tells you? Where is a period on PTE? What this tells you? Correct way to write the symbols ?

Periodic Table History

Dobereiner He put elements with similar chemical properties together They went into in groups of 3 He noticed these trends in groups of elements such as: Atomic Weight of “middle” element is average of other two – approx. Can you name these elements ?

Dobereiner’s Law of Triads A triad is a group of three elements with similar chemical properties in which the atomic mass of the middle element is approximately equal to the average of the other two. Only worked for very few elements of the 50 or so that were known at the time BUT He was first to make a link between atomic weight and properties

John Newland Arranged the 60 known elements in order of increasing atomic weight His pattern was… Every 8th element was a repeat (i.e. had 7 groups) His Law was called…

Law of Octaves An octave is a group of elements arranged in order of increasing atomic weight, in which the first and the eighth element of each group have similar properties. The properties repeat every 8 as noble gases hadn’t been discovered yet! Only worked for 17 out of 60 elements There were several problems such as iron being grouped with oxygen and sulphur. Laughed at but was basically correct

Mendeleev Arranged the known elements in order of increasing atomic weight His Law was called…

Mendeleev’s Periodic Law: When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically.

Mendeleev: Put elements with the same properties in the same vertical group. Reversed the order of some elements (Te/I) so that their properties matched their group. Left gaps to make the elements fit into the proper column (group). Predicted that elements (eg. Germanium and Gallium) would be discovered to fill these gaps. Predicted their properties correctly.

Mendeleev’s Modern Periodic Table V Periodic Table Gaps left for undiscovered elements Group 0 elements missing Elements discovered since 1869 missing D-block elements arranged as subgroups beside each main group Elements arranged in order of increasing atomic weight in almost all cases. Gaps have been filled Group 0 elements included Elements discovered since 1869 included D-block elements arranged as subgroups in a separate block Elements arranged in order of increasing atomic number

Mendeleev’s table

Moseley – Atomic Number The atomic number of an atom is the number of protons in the nucleus of that atom. Moseley used x-rays to find out how much positive charge each nucleus had In other words the difference between the elements is the number of protons in the nucleus. Once the atomic number was known it was seen that Mendeleev’s table was in order of increasing atomic number – not weight.

Modern Periodic Table In order of increasing atomic number. There were 63 elements in Mendeleev’s table – now 109 No gaps The transition elements are listed separately. Today’s table 1940 – Glenn Seaborg

Do I know it??? Who proposed Law of Triads? Who proposed Law of Octaves? Who proposed Periodic Law? Can I explain each ? Can I name 3 triads? What was Moseley’s contribution to the Periodic Table development? Four differences between Mendeleev’s Table and modern table?

Alkali metals Group 1 Form +1 ions Very reactive Low density Soft-can be cut with a knife Burn in air to form oxides React with water to form hydroxides

4 Groups Periodic Table Group One Group Two Group 7 Alkali metals Group Two Alkaline earth metals Group 7 Halogens Group 8 (O) Noble Gases

Demonstration of the reaction with water of lithium, sodium Alkaline Metals Demonstration of the reaction with water of lithium, sodium and potassium.

Sodium Sodium + Oxygen  Sodium oxide Sodium + Water  Sodium Hydroxide + Hydrogen gas Stored in oil to prevent them from reacting with air or water

Group 2 Alkaline Earths Group 2 Reactive ions with a +2 Mg +2 Harder than group one Burn in air to form oxide React with water to form hydroxides

Beryllium

Barium

calcium

Magnesium

Strontium

Radium

Halogens Group 7 Form -1 ions Cl-1 Reactive Coloured Chlorine, Bromine, Iodine React with hydrogen to form acids

Chlorine Green gas Chlorine + Hydrogen  Hydrogen Chloride gas Hydrogen chloride gas dissolves in water to form Hydrochloric acid. Chlorine reacts with sodium to form Sodium Chloride [Table Salt]

bromine

iodine

Group 18: Noble Gases Group VIII (group 0) of the periodic table Helium and neon used to make lighted signs, refrigerants, and lasers Don’t form ions not reactive - because they have little tendency to gain or lose electrons.