periodicity and group 2 Flashcards
what is the trend in atomic radius across a period?
- the atomic radius decreases
- outer eās in same shell
- more proton in the nucleus so greater attraction
- same amount of shielding
- so stronger attraction between nucleus and outer shell electrons
- outer shell electrons are pulled closer to the nucleus
what is the trend in atomic radius down a group
- the atomic radius increases
- more shells/ energy levels
- greater distance between nucleus and outer electron
- increased amount of shielding
-weaker attraction between outer e and nucleus
what is the trend in electronegativity across a period?
electronegativity increases as there are more protons in the nucleus and a smaller atomic radius so there is a stronger attraction between the nucleus and 2 electrons in covalent bond
what is the trend in electronegativity down a group?
- electronegativity decreases down a group due to more shell / shielding leading to a larger atomic radius so there is a weaker attraction between nucleus and 2 electrons in a covalent bond.
what is the trend is ionisation energy down a group?
ā the ionisation energy down a group decreases as there are more shells / energy levels so an an increased amount of shielding which leads to a greater distance between the nucleus and outer e
- so less attraction requires less energy to remove.
what is the general trend in ionisation energy across a period?
- ionisation energy across a group increases as there are more protons and the same shells/shielding. the atoms get smaller therefore stronger attraction from nucleus to e in outer shell.
what are the exceptions in ionisation energy across group 2 and 3?
- in group 2 an electron is lost in the s orbital but group 3 an electron is lost from the p orbital. the p orbital is higher energy than the s orbital so its easier to lose an electron from the p orbital
what are the exceptions in ionisation energy across group 5 and 6?
- group 5 elements loses electrons from an orbital with one electron in it (p3)
- group 6 element loses electrons from orbitals with 2 electrons (p4) extra electron-electron repulsion makes it easier to lose electrons from P4 rather than P3
what is the trend in melting and boing points across a period?
- the mp & bp increase steadily due to strong metallic bonding between molecules, then there is a steep increase in mp and bp due to very strong forces of attraction between giant covalent substances. then there is a steep drop due to weak forces of attraction between simple molecular substances. then an even further drop in monatomic elements. due to weak van der waals forces
Why do the bp and mp of metal increase as the molecule gets smaller?
- a higher charge density between delocalised electrons and positive metal ions creates a strong force of attraction that is hard to break. a smaller ions has more delocalised e-s and a higher charge so its harder to break the bonds between them.
What is the trend in atomic radius in GROUP 2?
- The atomic radius increases because there are more electron shells, so bigger atoms.
What is the trend in ionisation energy in group 2?
- Ionisation energy decreases down the group as the atoms get bigger, so there is more shielding and, therefore, a weaker attraction from the nucleus to the electron in the outer shell.
What is the trend in melting point in group 2?
The melting point decreases as you go down the group, as there is weaker metallic bonding. Metal ions are bigger and have a lower charge density, so they have lower melting points.
What is the general equation for the sulfates of group 2?
- (2 metal) (s) + H2SO4 (aq) -> (2 metal)S04 (aq) + H2 (g)
- Metals lower down in the group have a faster reaction as they are more reactive.
What happens in a displacement reaction in a group 2 metal and another metal sulfate?
- The more reactive group 2 metal will displace the less reactive metal, but if the metal in the metal sulfate is more reactive, no reaction will occur.
- What do barium sulfate and strontium sulfate form in the test tube after a reaction?
- a white precipitate
What is the trend in solubility in the group 2 sulfates down a group?
The solubility decreases down the group
What is the general equation for the hydroxides of group 2?
- (group 2 metal) (aq) + 2OH- (aq) -> (grouo 2 metal (OH)2 (s)
What do the group 2 hydroxides form after the reaction?
- a white precipitate
What is the trend in the solubility of the group 2 hydroxides?
- they increase in solubility down the group
- The first 2 are insoluble; the last two are fully soluble.
- The middle 2 are sparingly soluble.
What is barium sulfate used for?
Barium meals, because they are not soluble they act as a marker for intestines on an x-ray.
What is the use of magnesium hydroxide?
- Milk of magnesia treats constipation and indigestion.
What is the use of calcium hydroxide?
- Ca (OH) slaked lime deneutralises soil.
What is the use of magnesium?
- Mg is used to extract Ti from the ore rutile
- TiO2 + 2C +2CL -> TiCl4 + 2CO
- TiCl4+ 2Mg -> Ti + 2MG Cl2
What is the equation for the use of caO in flue gas desulphurisation?
- Ca0 + SO2 -> CaSo3
