AS chemistry unit one part four

it generally increases going across period 3

• the first ionisation energy drops between magnesium and aluminium before increasing again 
• the first ionisation energy drops between phosphorous and sulphur before increasing

the energy needed to remove 1 mole of electrons from one mole of gaseous atoms to form one mole of gaseous unipositive ions

endothermic

• there are more protons in each nucleus so the nuclear charge in each element increases 
• therefore the force of attraction between the nucleus and the outer electron is increased 
• there is negligible increase in shielding because each successive electron enters the same energy level
• so more energy is needed to remove the outer electron

• look at their electron configuration 
• magnesium : 1s²2s²2p⁶3s² 
• aluminium : 1s²2s²2p⁶3s²3p¹
• the outer electron in aluminium is in the p sub-level . this is higher in energy than the outer electron in magnesium , which is in an s sub level , so less energy is needed to remove it

• look at their electron configurations 
• phosphorous : 1s²2s²2p⁶3s²3p³
• sulphur : 1s²2s²2p⁶3s²3p⁴
• its not immediately obvious what's going on until we look at the arrangements of the electrons 
• the 3p electrons in phosphorous are all unpaired . In sulphur two of the 3p electrons are paired . there is some repulsion between paired electrons in the same sub level . this reduces the force of their attraction to the nucleus , so less energy is needed to remove one of these paired electrons than is needed to remove an unpaired electron from phosphorus

decreases

• the number of protons in the nucleus increases 
• so the nuclear charge increases
• there are more electrons , but the increase in shielding is negligible because extra electron enters the same principal energy level 
• therefore the attraction between the nucleus and the electrons increases 
• so the atomic radius decreases

it increases

relative ability of an atom to attract the bonding electron pair in a covalent bond (to withdraw electron density) . it cannot be measured directly

fluorine is given an electronegativity value of 4

they don't usually form covalent bonds as they are inert

• going across period 3 the nuclear charge increases 
• the atomic radius decreases 
• there are more electrons , but the increase in shielding is negligible because each extra electron enters the same principal energy level
• so electrons are more attracted to the nucleus

with low electro negativities have a tendency to lose electrons and a weaker tendency than others to attract a the bonding pair in a covalent bond

• melting points generally increase going from sodium to silicon , then decrease going to argon (with a "bump" at sulphur)
• boiling points generally increase going from sodium to silicon , then decrease going to argon (with a "bump" at sulphur

• sodium , magnesium and aluminium are all metals . they all have metallic bonding , in which positive metal ions are attracted to de-localised electrons . Going from sodium to aluminium :
• the charge on the metal ions increases from +1 to +2 to +3
• the number of de-localised electrons increases 
•  so the strength of the metallic bonding increases 
• so the melting points and boiling points increase

metalloid (an element with some properties of metals and some of the properties of nonmetals)

giant covalent . it has a giant lattice structure similar to that of diamond , in which each silicon atom is covalently bonded to four other silicon atoms in a tetrahedral arrangement . this extends in 3D to form a giant molecule or macromolecule

• all the silicon atoms are held together by strong covalent bonds 
• which need a very large amount of energy to be broken

• they all have low melting points because : 
• when these four substances melt or boil , it is van der waals forces between the molecules that are broken 
• which are very weak 
• little energy is needed to overcome them 
• sulphur has a higher melting point and boiling point than the other three because : 
• phosphorus exists as P₄ molecules
• sulphur exists as S₈ molecules 
• chlorine exists as Cl₂ molecules
• argon exists as individual Ar atoms 
• the strength of the van der waals forces decreases as the size of the molecule decreases 
• so the melting points and boiling points decrease in the order S₈ > P₄ > Cl₂ > Ar

contain electrons that are free to move . In general metals are good conductors of electricity and non metals are poor conductors of electricty

• sodium , magnesium and aluminium are all metals . they have metallic bonding , in which positive metal ions are attracted to de-localised electrons . the de-localised electrons are free to move going from sodium to aluminium :
• the number of de-localised electrons increases
• there are more electrons which can move and carry charge
• so electrical conductivity increases

• it is a semi conductor because : 
• the four outer electrons in each atom are held strongly in covalent bonds 
• few electrons have enough energy at room temperature to enter the higher energy levels 
• so there are few de localised electrons and silicon is a poor conductor 
• but at higher temperatures more electrons are promoted to higher energy levels 
• so there are many de localised electrons to move

• the outer electrons aren't free to move and carry charge in P , S and Cl because they are held strongly in covalent bonds
• in argon (which exists as single atoms) the outer electrons aren't free to move because they are held strongly and stable in the third energy level

• non metals are on the right 
• metals are on the left