Periodic Table And Energy Flashcards
Periodic table then
Mendeleev arranged elements in order of atomic mass
-also lined up elements with similar properties
-left gaps assuming some were yet to be discovered
Trends across a period
same number of shells
- different number of electrons in outer shell
Trends down a group
Same number of electrons in outer shell
-number of shells increase (shielding)
-atomic radius increases
Ionisation energy
how easily an atom loses electrons to form positive ions
-atomic radius increases i energy decreases
-nuclear charge increases I energy increases
-electron shielding increases i energy decreases
Successive ionisation energies
He(g) —> He+(g) + e-
He+(g) —> He2+(g) + e-
Second ionisation energy
energy required to remove one electron from each ion in 1 mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
1st ionisation trends
across period- (increases)
nuclear charge increases⬆️
nuclear attraction increases⬆️
atomic radius decreases🔻
Down group- (decreases)
atomic radius increases
shielding ⬆️
nuclear attraction🔻
giant covalent structures
-insoluble in most solvents
-do not conduct electricity
(except graphene & graphite)
-high melting & boiling points
trends in melting point (period 2)
-Li –> C increases (giant structures)
-decreases dramatically to N as they are simple molecules so easier to overcome bonds
trends in melting point (period 3)
Na –> Si increases as they are giant structures and atomic charge increases
-decreases dramatically to P as it is now simple molecules
group 7 halogens
electronegativity decreases as you move down
-number shells increases
-weaker attraction
-BP increases as you move down
-more electrons and more induced dipoles (harder to break)
halogen colours
fluorine-pale yellow gas
chlorine- yellow green gas
bromine - dark red/brown liquid
iodine - grey black solid
astatine- very rare & radioactive solid
qualitative analysis of halide ions
-add nitric acid to get ride of carbonate ions
-then add silver nitrate
fluoride- no precipitate
chloride-white precipitate (dissolves in dilute NH3)
bromide-cream precipitate (dissolves in conc NH3)
iodide-pale yellow precipitate ( does not dissolve in either)
Qualitative analysis of sulphate ions
Sulfate ions
- dilute nitric acid (remove carbonate ions) + barium nitrate
white preciptate BaSO4 formed
qualitative analysis of carbonate ions
carbonate ions
-add dilute nitric acid; if bubbles form product could be carbonate
-check if CO2 bubble thru limewater (cloudy)
Enthalpy H
measurement of the heat energy in a chemical system
ethalpy change = H(products) - H(reactants)
endothermic reaction
heat into system from surroundings
system gains temp
-surroundings temp decreases
-bond breaking energy required
exothermic reaction
-bond making
heat transferred to surroundings from system
loses heat (temp drops)
-temp of surroundings increases
standard enthalpy change conditions
pressure= 100kpa
temp= 25 c
conc= 1moldm3
state=physical state normally
standard enthalpy change of reaction
enthalpy change that accompanies a reaction in the molar quantities shown in chemical equation under standard conditions
standard enthalpy of formation
enthalpy change that takes place when 1 mole of a compound is formed from its elements under standard conditions
1/2 O2 to make the product 1 mole only
standard enthalpy of combustion
the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions
standard enthalpy change of neutralisation
the enthalpy change that accompanies the reaction of an acid and a base to form one mole of water under standard conditions
q=mc^T
q= energy change of surroundings
m= mass of surroundings
c= specific heat capacity (4.18kjg-1k-1)
^T= change in temp
if - = endothermic
if + = exothermic
q/n to see per mole of the reactant
opposite to answer +/- as now talking about reactant heat loss or gain
HESS law
states that reaction can take place by 2 routes and the total enthalpy change is the same for either route
triangle
A-B = ^H1
A-C-B = ^H2 + H3
elements - arrows go away
products - either
combustion - arrows go towards
rate of reaction
measures how fast a reactant is being used up or how fast a product is formed
change in conc / time
increasing gas pressure effect on rate
when gas is pressed into smaller volume the pressure of a gas is increased and the rate of reaction increases
catalysts
a substance that changes the rate of a chemical reaction without undergoing any permanent change itself
- catalyst not used up in reaction
- always regenerated
homogenous catalyst
catalyst that is the same physical state as the reactants
heterogenous catalyst
catalyst that is in a different physical state to the reactants
Boltzmann distribution (temp)
as temperature increases a higher proportion of molecules can overcome the activation energy
-more successful collisions
boltzmann distribution ( catalyst)
when a catalyst added, greater proportion of molecules exceed the new lower activation energy
lower activation energy
Dynamic equilibrium
the rate of the forward reaction is the same as the rate of the backwards reaction
- concentration of products does not change
le chateliers principle
states that when a system in equilibrium is subjected to an external change the system readjusts itself to minimize the affect of the change
