main group chemistry Flashcards
what are second and third period behaviours and why
2nd period elements are often anomalous in their behaviours, whereas the 3rd period elements are more representative of their group (can extrapolate the behaviour of heavier elements w/i a group by looking @ 3rd period element)
what can the anomalous behaviour be traced to (3)
1) small size and high electronegativity (ion sizes, acid-base behaviour, electron-deficient compounds, and strength of acids
2) maximum of four covalent bonds (no d orbital)
3) more common occurrence of multiple bonding (good π overlap of 2p orbitals) - more likely between pair of 2p on smaller atoms that can be in proximity, than between a pair of diffuse 3p orbitals on larger atoms that are widely separate
metallic behaviour increases proceeding down a group, therefore
positive oxidation states are prevalent proceeding down a group
true or false: all halogens can form only one oxidation state (-1)
false, only fluorine forms the -1 oxidation state because of its high EN. however, the other halogens can assume different oxidation states (including the oxidation states when combined w/ more EN elements, ex. HOCl)
explain why expanded octets and corresponding hybridization sp3d and sp3d2 are not observed in 2nd row elements
for an expanded octet, there must be valence d-orbitals available. in the 2nd row, the only allowed subshells are s and p, so 2d orbitals do no exist, therefore there can be no expanded
explain why it is more common to see multiple bonding in 2nd row elements that in 3rd row and beyond.
the small size of the 2nd row elements allows for effective overlap between p orbitals and adjacent atoms. in larger elements, the separation between adjacent atoms is larger and the p-orbitals are larger and more diffuse so that there is no effective overlap for p-p π bonding to occur to as great of an extent as in 2nd row elements
where does hydrogen fit on the periodic table (3 spots)
hydrogen has no perfectly suitable position in the periodic table due to its unique behaviour.
- fits group 1 because of the ns1 electron configuration and a common +1 oxidation state. unlike group 1, hydrogen shares it’s electrons w/ nonmetals rather than transferring it
- like group 14 elements, hydrogen has a half filled valence level, also has similar IE, EA, and EN
- like group 17 elements, hydrogen occurs as diatomic molecules and fills its outer level either by electron starting or gaining an electron to form an anion. unlike the anions of group 17 elements (which are common and stable), the H- (hydride) ion are rare and reactive (has a lower EN than halogens)
-elemental hydrogen is very reactive and combines with nearly every other element, it forms three types of hydrides (ionic, covalent, and metallic)
what are ionic hydrides
with very reactive metals, hydrogen forms saltlike hydrides, group 1 and larger group 2 elements (Ca, Sr, Ba). In water, H- is a strong base.
The hydride ion, H- is also a powerful reducing agent: it is used to reduce transition metal ions such as Ti(IV) to the free metal
what are covalent hydrides
H reacts w nonmetals to form covalent hydrides (most are gases)
- Haber-Bosch Process to form NH3
what are metallic hydrides
metallic hydrides, such as TiH1.7, typically do not have a specific stoichiometric formula because the metal can incorporate variable amounts of hydrogen, depending on the pressure and temperature
what are alkali metal properties
-unusually “soft” metals
- have the lower melting/boiling points and densities compared to other metals
- the strange properties can be attributed to their relatively large atomic sized (in their respective periods) and to the 4s’ electron configuration
- the single valence electron is not held tightly and the metallic bonding is weak (in the solid) -> crystal structure can be easily deformed
- extremely reactive and powerful reducing agents
what are some reactions that alkali metals perform
reduce halogens to form ionic solids in highly exothermic reactions
- 2 M(s) + X2 -> 2MX(s)
react vigorously w/ H2O to give
- 2 M(s) + H2O(l) -> 2 M+(aq) + 2 OH-(aq) + H2(g)
reduce H2 to form ionic hydrides
- 2 M(s) + H2 (g) -> 2 MH(s)
reduce O2 in the air, and tarnish rapidly
what are alkaline earth metal properties
these are harder and higher melting than the alkali metals, and are somewhat less reactive. occur naturall as ionic compounds of M2+
what are some of the uses of alkaline earth compounds
- CaCo3 (heat)-> CaO (lime) which is a important industrial compound for steelmaking, glassmaking, whitening paper, neutralizing acidic soil, …
- alkaline earth metals form ionic compounds
- alkaline eath metals are strong (only Ca, Sr, and Ba reduce water)
why is Be different
- it is unreactive in air and water
- BeO is an amphoteric oxide
- Be compounds have strong covalent character and coduct electricity poorly in the molten state
BeCl2 - each Cl “bridge” two Be atoms
- each Be is sp3 hybridized and has a complete octet
