Presentation on theme: "Elements and Periodic Table of Elements"— Presentation transcript:
1 Elements and Periodic Table of Elements ChemistryElements andPeriodic Table of Elements
2 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?
3 Periodic Table of ……ElementsNeed to knowsymbols of elements 1- 36
4 learn the rest as we go through the course is for Carbonbutwatch out for ………Potassium is KPhosphorus is Plearn the rest as we go through the course
5 Be carefulSymbolcan only have one capital letterNanot NA
6 History Greeks – 4 elements – were they right? Boyle (2000 ish years later!)better idea of elementcan’t be broken down into simpler substance
7 Davyused 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
8 Moseley used x-rays showed that the nucleus had positive charge each element had different positive charge on its nucleusElement …….all elements have the same atomic number (no. of protons
9 Same number of electrons in outside shell Periodic TableSame number of electrons in outside shellVertical Lines are calledGroupsHorizontal Lines are calledPeriodsMetals on left , non- metals in rightdivision begins at Boron(check with Aluminium Al)Same number of shells
10 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 ?
12 Dobereiner He put elements with similar chemical properties together They went into in groups of 3He 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 ?
13 Dobereiner’s Law of Triads A triad is a group of three elementswith similar chemical properties in whichthe 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 timeBUTHe was first to make a link between atomic weight and properties
15 John NewlandArranged the 60 known elements in order of increasing atomic weightHis pattern was…Every 8th element was a repeat(i.e. had 7 groups)His Law was called…
16 Law of OctavesAn 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 elementsThere were several problems such as iron being grouped with oxygen and sulphur.Laughed at but was basically correct
17 MendeleevArranged the known elements in order of increasing atomic weightHis Law was called…
18 Mendeleev’s Periodic Law: When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically.
19 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.
20 Mendeleev’s Modern Periodic Table V Periodic Table Gaps left for undiscovered elementsGroup 0 elements missingElements discovered since 1869 missingD-block elements arranged as subgroups beside each main groupElements arranged in order of increasing atomic weight in almost all cases.Gaps have been filledGroup 0 elements includedElements discovered since 1869 includedD-block elements arranged as subgroups in a separate blockElements arranged in order of increasing atomic number
22 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 hadIn 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.
23 Modern Periodic Table In order of increasing atomic number. There were 63 elements in Mendeleev’s table – now 109No gapsThe transition elements are listed separately.Today’s table 1940 – Glenn Seaborg
24 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?
25 Alkali metals Group 1 Form +1 ions Very reactive Low density Soft-can be cut with a knifeBurn in air to form oxidesReact with water to form hydroxides
26 4 Groups Periodic Table Group One Group Two Group 7 Alkali metalsGroup TwoAlkaline earth metalsGroup 7HalogensGroup 8 (O) Noble Gases
27 Demonstration of the reaction with water of lithium, sodium Alkaline MetalsDemonstration of the reaction with water of lithium, sodiumand potassium.
28 Sodium Sodium + Oxygen Sodium oxide Sodium + Water Sodium Hydroxide + Hydrogen gasStored in oil to prevent them from reacting with air or water
29 Group 2 Alkaline Earths Group 2 Reactive ions with a +2 Mg +2 Harder than group oneBurn in air to form oxideReact with water to form hydroxides
40 Group 18: Noble Gases Group VIII (group 0) of the periodic table Helium and neonused to make lighted signs, refrigerants, and lasersDon’t form ionsnot reactive - because they have little tendency to gain or lose electrons.