7. Trends In The Periodic Table Flashcards
Atomic radius def.
The atomic radius of an atom is defined as half the distance between two nuclei of atoms of the same element that are joined together by a single covalent bond.
Atomic radius increase and decrease
Decrease across a period
Increase down groups
Exception to atomic radius
Noble gases; they don’t form covalent bonds
2 reasons why atomic radius increases down groups
- new energy level
- screening effect of inner electrons
2 reasons why atomic radius decreases across periods
- increase effective nuclear charge
- no increase in screening effect
Increase in effective nuclear charge: atomic radius
- no. of protons increases
- increased pos. pull on outer electrons
- draws closer to nucleus
No increase in screening effect
- extra electrons SAME energy level
- no new energy level to add to screening effect
- and shield outer electrons from pos.charge
First ionization energy
First ionization energy of an atom is the minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state.
Formulas for ionization energies
X(g) —> X+(g) + e-
X+(g) —> X2+(g) + e-
X2+ (g) ——> X3+(g) + e-
Second ionization energy
Second ionization energy is the energy required to remove an electron from an ion with one positive charge in the gaseous state.
Ionization increase and decrease
Increase across periods
Decrease down groups
2 reasons ionization increase across:
- Increase effective nuclear charge
- decreasing atomic radius
Increase effective nuclear charge : ionization
-no.of protons increasing
-increased pos.attraction
-electrons held more firmly
I.e more energy required to remove them
Decreasing atomic radius : ionization
-outermost electrons getting closer
-increased attraction between nucleus and electron
,, more energy required for removal
Increase screening effect : ionization decrease
-although nuclear charge increases, pos.force canceled out by corresponding screening effect
-outermost electrons shielded from pos pull.
,, easier, less energy to remove
Why is there exceptions to ionization trend?
Any sublevel that is completely filled or half filled has extra stability.
More energy required to break into these stable levels- jump in graph.
4 exceptions to ionization
Be, N, Mg, P
bean magpie ;
Evidence for energy levels from ionization
- second e always harder to remove as it’s taken from a K+ ion
- sudden large jumps imply we’re breaking into a new energy level w extra stability, closer to nucleus
2 reasons why ionization values increase
-Pos. Charge on ions increases for each e removed : greater pos. Attraction on remaining electrons
- pos ions becoming smaller as e removed.
e closer to nucleus; increased attraction.
Electronegativity increase &decrease
Same as ionization.
Increase across,
Decrease down.
2 reasons electronegativity increase across
- increase effective nuclear charge
- decreasing atomic radius
Increase effective nuclear charge: electronegativity increase
- no.of protons increase
- greater pos.attraction on outermost electrons involved in bonding
2 reasons for electronegativity decrease
- Increase atomic radius
2. Increase screening effect
Alkali metals what sort of compounds & why
Ionic compounds
- low ionization energy
- low electronegativity
reason alkali reactivity increases down group
- atomic radius increases
- screening effect too
- causes ioniz.energy to decrease
- outermost electrons more easily lost
Alkali metals oxygen reaction notes
- form oxides
- stored under oil
- lose shiny colour when exposed to air
Alkali metals oxygen reaction formula
2K + 1/2 O2 —-> K2O
Alkali metal + water.what do they form
Hydroxide +hydrogen gas
Alkali metal + water formula
Na +H2O —-> NaOH + 1/2H2
Halogens notes
- very reactive: need 1 electron
- oxidizing agents (take electrons)
- not free in nature
- most electronegative
Halogens reactivity increas/decrees
Increases UP the group
Reason halogen reactivity increase up the group
- most electronegative @top
- bc electronegativity decreases down
- greater pull on electrons
- easier to react to draw in other e & fill outer level
Halogens experiment
Cl (g) bubbled through bromide ions solution
- cl takes e ; more electronegative
- turns bromide into bromine
- colorless solution turns red
Halogens experiment formula
Cl2 + 2Br- —-> 2Cl- + Br2
The same can be seen as in the experiment w halogens in..
Bromine + iodide ions —-> iodine
Sentence summing up halogen experiment
The more reactive halogen displaced the less reactive halogen from a solution of its ions.
Boilin points halogens : increase or decrease
Increase down the group
Reason why boiling point increases down group of halogens
- atomic radius increases
- electron clouds bigger
- greater chance to form temporary dipoles
- stronger van der Waals forces
Examples of halogens showing the boiling point :
Fl, Cl: gas
Br: liquid
Iodine : solid. At room temp
