ib chem topic 3 periodicity

Mendeleev's Periodic Law

When elements were arranged in order of increasing atomic weight, properties of the elements repeated in a pattern

the color of transition metal complexes

• color is from electrons absorbing light to get promoted - so the complex shows the complementary (cuz it was not absorbed)

• NOT THE SAME AS HYDROGEN EMISSION SPECTRUM WHICH EMITS PHOTONS

transition metals as catalysts (4)

• The ability of transition metals to form more than one stable oxidation state means that they can accept and lose electrons easily

• This enables them to catalyse certain redox reactions

  • They can be readily oxidised and reduced again, or reduced and then oxidised again

• A heterogeneous catalyst is in a different physical state (phase) from the reactants

• A homogeneous catalyst is in the same physical state (phase) as the reactants

explain variable oxidation state using ionization energy

• Using titanium and vanadium as examples, the graph below shows that the first few ionisation energies are relatively small and relatively close together

  • This means that the energy difference associated with removing a small number of electrons enables transition metals to vary their oxidation state with ease

groups/families

elements share similar chemical and physical properties

Metals

- solid at room temp (except Hg)
- have lustre, malleable, ductile
- good conductors of electricity
- subcategories: alkali metals, alkaline earth, transition

alkali metals (group 1)

- most reactive metals - lowest ionization E
- Reactivity increases down group cause more electrons + further away
- react with water to make hydroxides (bases)
- react w/ O to form ionic oxides (also basic)

Alkaline Earth Metals (Group 2)

react with water to form metal hydroxides

Transition Metals (Groups 3-12)

All the d block groups on the periodic table (but not all d blocks are transition metals)
- complex bonding mechanisms due to d orbital availability
- when ionized, have incomplete d orbitals

metalloids

Elements that have properties of both metals and nonmetals.
- have lesser metallic characteristics despite appearing metallic

Nonmetals

gases/brittle solids
- poor conductors of heat and electric current
- nonmetal oxides form acidic solutions with water

Halogens (Group 17)

readily form compounds with metals cause wanna accept electrons
- reactivity decreases down group
- gas to solid down group

what do halogens form precipitates with

Pb 2+, Ag +, Cu +

Halogen displacement reactions

A more reactive halogen can displace a less reactive halogen from a salt solution. ONLY WORKS WHEN HALOGEN ATOM (DIATOMIC) IS MORE REACTIVE THAN THE HALIDE

Noble Gases (Group 18)

colorless and extremely unreactive (inert) because of their full valence shell (ns2 np6)
- very low melting and boiling points = gas

metallic character

a measure of how easily an element loses a valence electron

Oxides become more _____ down a group and more _____ across a period.

more ionic down a group (wanna get rid of e) and less ionic from left to right

Aluminum Oxide is special cause:

amphoteric - acts both as acid and base

oxides want to dissolve in water:

ionic oxides - basic solutions cause OH ions
non-metal oxides - acidic

electrostatic force

attraction or repulsion of particles or objects because of their electric charge.

how to tell electrostatic force

1. greater gap between ionic charges = stronger electrostatic forces
2. greater distance between particles = weaker

Modern Periodic Law - Moseley

When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically

atomic radius trend

increases down each group because of shielding effect, decreases across each period because of increase in effective nuclear charge. electrostatic attractive force between p/e increases left to right

effective nuclear charge

the positive charge that an electron experiences from the nucleus, equal to the nuclear charge but reduced by any shielding or screening from any intervening electron distribution.

Zeff = # of p - # core e

cations are _____ than their parent atoms

smaller, the outermost electron is removed and repulsions between electrons are reduced

anions are ____ than their parent atoms

larger, electrons are added and repulsions between electrons are increased

ionization energy relation to atomic radius

inversely proportional, IE proportional to 1/atomic radius

electron affinity

the minimum energy change in that occurs when a mole of electrons is added to a mole of gaseous atoms.
- more negative (exothermic) across a period
- group 17 have highest electron affinities in terms of negative values (highest amount of energy released)

oxidation state

the real or apparent charge of an atom when all bonds are assumed to be ionic
- refers to how the electrons are distributed

reduction

causes a decreased oxidation state from:
removing oxygen
atom gaining electron
adding hydrogen

complex molecule/ion

any central ion (transition metal) surrounded by a definite number of chemical species (ligands)