chem mod 2⚛️ Flashcards
what is a salt
H+ ion in an acid is replaced by a metal ion
why does first ionisation energy decrease down group
- bigger atomic radius
- more shielding
- nuclear attraction decreases
what is first ionisation energy
-energy required to remove one electron from each atom in one mole of gaseous atoms
why is second ionisation energy greater than first
- ion is smaller
- less electron repulsion
- same number of protons attracting less electrons
explain trend of ionisation energy across period
- generally increases
- number of protons increases
- atomic radius decreases
- so greater nuclear attraction
- from group 2 to 3 there is a decrease
- as group 3 elements have outer electron in p shell which has a higher energy level
- from group 5 to 6 there is a decrease
- in group 5 the outer electrons are on their own in the orbital (eg nitrogen 2p3)
- in group 6 one pair of the outer electrons have to share an orbital so there is greater repulsion (eg oxygen 2p4)
shape and angle for 4 bonding pairs around central atom
tetrahedral
109.5
what is a mole
- amount of substance that has the same number of particles as there are atoms in 12 g of carbon 12
- avogadros number
- 6.02x 10^23
when reacting calcium with hcl, why does more calcium react than expected
ca + h2o -> ca(oh)2 + h2
-calcium reacts with water
shape and angle for two bonding pairs around central atom
- linear
- 180
shape and angle for 3 bonding pairs around central atom
- trigonal planar
- 120
angle and shape for 3 bonding pairs 1 lone pair around central atom and why
- pyramidal
- 107
- lone pairs repel more than bonded pairs
shape and angle 2 bonding pairs 2 lone pairs (water)
- bent
- 104.5
5 bonding pairs shape
trigonal bipyramid
6 bonding pairs shape
octahedral
sulfide compounds contain what
formula for ammonium sulfide
contain S
(NH4)2S
are silver compounds solid or aq
most are solid except like nitrates etc
what is uncertainty
half of smallest division
how to calculate percentage error
uncertainty/reading x100
if 2 readings eg titrations then double
how to reduce percentage error
- more precise equipment (more dp)
- use larger amounts eg volume or mass
how to ensure all water of crystillation is removed
heat to constant mass
ionic equation for displacement of bromine by chlorine
Cl2 + 2Br- —> 2Cl- +Br2
problem with combustion of chlorohydrocarbon
formation of HCl
IE trend down group
- decreases
- larger atomic radius
- more shielding
- weaker nuclear attraction
- easier to remove electron
why does IE decrease from mg to al
Mg electron removed from 3(s)
Al electron removed from 3(p)
Al electron has higher energy level
what is a weak acid
partially dissociates
test for sulfates
BaCl2
forms white precipitate
0 degrees celsius in kelvin
273K
what shape would a molecule with 3 bonding pairs have and why
trigonal planar
because electron pairs repel
why are carbon and oxygen p block elements
highest energy electron is in p orbital
explain in terms of electrons whether magnesium is oxidised or reduced
oxidised because loses 2 electrons
how to get solid from solution after reaction
filter to obtain solid
dry solid
relative isotopic mass
-mass of an isotope compared to 1/12th of the mass of an atom of carbon 12
relative atomic mass
weighted mean mass of an atom of an element relative to 1/12th of the mass of carbon 12
dm3 to m3
divide by 1000
why is yield not 100%
- purification may result in some loss
- reaction ma not have gone to completion
what is a strong acid
completely dissociates in water
what is an alkali
releases OH- ions into solution
what id an isotope
atom of an element with different neutrone number
ehat is electronegativity
ability of an atom to attract electrons in a covalent bond
