Understanding Chemical Element Families in the Periodic Table

1. How can chemical elements be grouped into families? How can the similarities between elements in the same group be explained ? (Trends in reactivity) BRINGS YOU BACK HERE Periodic Table Group 1 Reactivity trends in Group 1 Group 7, the Halogens Reactivity trends in Group 7 Group 0, the Noble Gases.

2. Argon (Ar) has more mass than potassium (K), yet they are put in the opposite order, using their increasing atomic numbers. This is so they can be in correct group, with elements of similar properties. THE PERIODIC TABLE H He Li Be Ne C N O Na Mg Ar Cl Al Ca K Cr Fe Cu Zn Ni The chemical elements used to be arranged in order of their increasing relative atomic masses in horizontal rows. -- watch them arrive in order of increasing mass This list is best arranged so that elements with similar chemical properties come in vertical columns. These are GROUPS. To do this, we arrange elements in order of ATOMIC NUMBER This is how the modern Periodic Table is arranged

3. These are the METALS H He Li Be Ne B F C N O Na Mg Ar Cl Al Si P S Ca Sc Ti Br Kr K V Se Cr Fe Cu Zn As Mn Co Ni Ge Ga THE PERIODIC TABLE, continued. In the modern periodic table, elements are arranged using their increasing ATOMIC NUMBER These are the NON-METALS The atomic number is the number of protons in the nucleus of the atom of the element. The COLUMNS are called GROUPS. They tell us HOW MANY OUTER-SHELL ELECTRONS the element has This is Hydrogen – it is not in a group Group 7 – the Halogens These are the Transition Metals – they are not in a group Group 2 The ROWS are called PERIODS. They tell us HOW MANY SHELLS OF ELECTRONS the element has Group 5 Group 1 – the Alkali Metals The elements in each group have SIMILAR CHEMICAL PROPERTIES This is because they have the same number of electrons in their outer shell. The number of outer electrons determines chemical behaviour, because they are the only ones involved in bonding. Group 8 (or 0) – the Noble Gases Group 4 Group 3 Group 6 Eg: the elements in group 2 (Be, Mg, Ca…) have 2 electrons in their outer shell Eg: the elements in the third period (Na, Mg, Al…) have 3 shells of electrons

4. THE ATOMIC (PROTON) NUMBER IS ABOVE EACH SYMBOL 2 He 1 H THE ELECTRONIC STRUCTURE IS BELOW EACH SYMBOL 1 2 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne PERIODIC TABLE WITH THE FIRST 20 ELEMENTS. 2 : 1 2 : 2 2 : 3 2 : 4 2 : 5 2 : 6 2 : 7 2 :8 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 2:8:1 2:8:2 2:8:3 2:8:4 2:8:5 2:8:6 2:8:7 2:8:8 19 K 20 Ca The halogens in group 7 all have seven electrons in their outermost shells. The other two halogens that come below fluorine & chlorine are bromine and iodine. The noble gases in group 0 all have full outer electron shells. This gives them stability & explains why they don’t react. The metals in group 1 all have one electron in their outermost shells Here, across the second period, the second energy level is gradually filling with electrons Here, across the third period, the third energy level is gradually filling with electrons 2:8:8:1 2:8:8:2

5. H He Li Be Ne B F C N O  Na Mg Ar Cl Al Si P S Ca Sc Ti Br Kr K V Se Cr Fe Cu Zn As Mn Co Ni Ge Ga balanced Group 1 – the Alkali Metals REACTIVITY INCREASES DOWN THE GROUP Called the alkali metals because they react with water to give ALKALIS and hydrogen: The alkali metals also react with: Sodium is more reactive than lithium Potassium is more reactive than sodium Chlorine, to make chlorides: Na + Cl2 NaCl sodium + water  sodium hydroxide + hydrogen 2 2 Na + H2O  NaOH + H2 2 2 2 Sodium moves around and melts when added to water Potassium moves around faster and bursts into flame And similarly with the other halogens, bromine & iodine, to make bromides & iodides NOT balanced • In this reaction the metal: • FLOATS (they have low density) • MELTS (they have low melting points) • MOVES around the surface • May catch FIRE Oxygen, to make oxides: K + O2 K2O The MELTING and BOILING POINTS decrease down the group Sodium has a lower melting point than lithium Potassium has a lower melting point than sodium 4 2 The reaction with ACIDS is too VIOLENT to carry out…. All Group 1 compounds are IONIC The metals lose one electron to form +1 ions

6. WHY DOES REACTIVITY INCREASE DOWN GROUP 1? Li X X Na K X X X X X X X X X X X X X X X X X X X X X X X X X X X K Na Li Li Li Li X X X X X X X X X X X X As we go down the group, each element has an extra shell of electrons All Group 1 react by losing their single outer electron to make a 1+ ion X X X X X X X X X X X X X X X X X The more easily it loses the electron, the more reactive the element is So the outer electron gets further from the nucleus The further away the outer electron is, the smaller the force attracting it to the nucleus So going down the group, it gets easier to lose the outer electron. So the elements get more reactive.

7. H He Li Be Ne B F C N O Na Mg Ar Cl Al Si P S Ca Sc Ti Br Kr K V Se Cr Fe Cu Zn As Mn Co Ni Ge Ga I x x o o x x o x x x x x o o x x x x x x o o Cl Cl o x x H o x x x x Na Na Group 7 – the Halogens The halogens are typical non-metals: The halogens exist as covalent, DIATOMIC MOLECULES • They have LOW BOILING POINTS • Fluorine and chlorine are gases • Bromine is a volatile liquid • Iodine is a solid that sublimes readily F2 Cl2 Br2 I2 When solid, they are brittle and crumbly They react with METALS to form IONIC COMPOUNDS The ions are formed by gaining one electron. They always have charge -1 Halogens also bond with NON-METALSCOVALENTLY They are poorconductors of heat & electricity • The halogens are all brightly coloured: • Chlorine is greenish-yellow • Bromine is brown • Iodine is a bluey-black solid, but purple as a gas o o o o o o o o These compounds have low melting and boiling points and exist as simple molecules. chloride ion Cl- sodium ion Na+

8. H He Li Be Ne B F C N O Na Mg Ar Cl Al Si P S Ca Sc Ti Br Kr K V Se Cr Fe Cu Zn As Mn Co Ni Ge Ga I sodium chloride solution sodium bromide solution Chlorine +  bromine + Group 7 – the Halogens REACTIVITY DECREASES DOWN THE GROUP Chlorine is more reactive than bromine Bromine is more reactive than iodine A more reactive halogen can displace a less reactive one from its compound: Cl2 + NaBr  Br2 + NaCl 2 2 The MELTING and BOILING POINTS increase down the group chlorine has a lower melting point than bromine bromine has a lower melting point than iodine

9. WHY DOES REACTIVITY DECREASE DOWN GROUP 7? H He Li Be Ne B F C N O X X Na Mg Ar Cl Al Si P S X Ca Sc Ti Br Kr K V Se Cr Fe Cu Zn As Mn Co Ni Ge Ga I X X X X All Group 7 react by gaining one electron to make a 1- ion O The more easily it gains & keeps the electron, the more reactive the element is As we go down the group, each element has an extra shell of electrons So the outer electrons get further from the nucleus The further away the outer electrons are, the smaller the force attracting them to the nucleus So going down the group, it gets harder to gain an extra electron. So the elements get less reactive.

10. H He Li Be Ne B F C N O Na Mg Ar Cl Al Si P S Ca Sc Ti Br Kr K V Se Cr Fe Cu Zn As Mn Co Ni Ge Ga X X X X X X X Ne X X X Group 0 (or 8) – the Noble Gases The Noble Gases have these non-metal properties: WHY ARE THE NOBLE GASES SO UNREACTIVE? • Very low boiling points (they are all gases) • Poor conductors of heat and electricity The Noble Gases are all very unreactive – they do not form compounds All of them have 8 electrons in their outer shell Unlike other gases, they exist as individual atoms - they don’t form bonds with each other either! THE END • Going down the group: • Density increases • Boiling point increases This means they have no tendency to gain, lose or share electrons USES Neon and argon in filament lamps and electric discharge tubes - they provide an inert atmosphere – so the metal in the filament won’t react. Helium in balloons - it is lighter than air - and unlike hydrogen, it isn’t dangerous if there’s fire