s3.1 periodicity Flashcards
what are the names of the groups in the periodic table?
group 1 -> alkali metals
group 2 -> alkaline earth metals
groups 3-12 -> transition metals
group 17 -> halogens
group 18 -> noble gases
La-Lu -> lathanides
Ac-Lr -> actinides
how can you deduce the electron configuration of an element based on it’s position on the periodic table?
1s¹ 2s¹
- s block element
- group 1 (number of valence electrons)
- period 2 (highest occupied main energy level)
what is periodicity?
trends in properties of elements across a period or down a group.
what is electron shielding?
electron shielding occurs when the inner electrons shield the outer electrons from the full attraction of the nucleus.
electron shielding remains constant across a period because the number of shielding electrons is the same across a period.
electron shielding increases down a group because the number of shielding electrons increases down a group.
what is effective nuclear charge?
effective nuclear charge is the net positive charge experienced by outer valence shell electrons from the force of attraction between protons in the nucleus and the force of repulsion between inner core electrons.
effective nuclear charge increases across a period.
the effective nuclear charge can be approximated by the following equation, where Z is the atomic number and S is the number of shielding electrons:
Zeff = Z - S
what is atomic radius?
the atomic radius is measured as half the distance between neighbouring nuclei.
what is the trend in atomic radius across a period?
atomic radii DECREASES across a period:
nuclear charge increases across a period.
electrons are added to the same main energy level - electron shielding remains constant across a period.
the effective nuclear charge increases, so electrons are pulled closer to the nucleus.
what is the trend in atomic radius down a group?
atomic radii INCREASES down a group:
- the number of occupied energy levels increases.
- this results in a weaker attraction between the nucleus and the valence electrons (less effective nuclear charge).
what are the trends in ionic radius?
ionic radius INCREASES DOWN A GROUP because of the increasing number of occupied energy levels.
ionic radius DECREASES ACROSS A PERIOD for the positive ions, INCREASES for the negative ions, and then DECREASES again.
what is the trend in ionic radius across a period?
positive ions:
- smaller in size than their parent atom
- loss of electrons from outermost energy level
- increased attraction between nucleus and valence shell electrons
- decrease in cation radii across a period due to increased effective nuclear charge
negative ions:
- larger in size than their parent atom
- gain of electrons into outermost energy level increases repulsion between electrons
- decreased attraction between nucleus and valence shell electrons
- decrease in anion across a period due to increased effective nuclear charge.
what is the trend in ionic radius in isoelectronic species?
the number of protons increases but the number of electrons remains the same.
the attraction between the nucleus and electrons increases, which causes the ionic radius to decrease.
what is the trend in ionisation energy down a group?
first IE decreases down a group:
- although the nuclear charge increases, the distance between the nucleus and the valence electron increases
- the shielding by inner shell electrons increases
- the effective nuclear charge is decreasing
what is the trend in ionisation energy across a period?
first IE increases across a period:
- nuclear charge increases
- atomic radii slightly decreases
- shielding by inner shell electrons remains the same
- the electrostatic attraction between the nucleus and valence electrons increases
what are the exceptions to the trend in ionisation energy across a period?
- aluminium first IE is lower than that of magnesium because of the shielding effect of the newly filled 3s orbital
- sulphur first IE is lower than that of phosphorus due to spin-pair repulsion between the newly paired up electrons in one of the p orbitals.
- there is a rapid decrease in IE between the last element in one period and the first element in the next caused by:
- increased distance between the nucleus and outer shell electrons
- increased shielding by inner electrons
- these factors outweigh the increased nuclear charge
what is the trend in electronegativity across a period?
electronegativity values increase across a period:
- nuclear charge increases but electron shielding remains constant. atomic radius decreases across a period
- stronger attraction between the nucleus and the bonding pair of electrons
what is the trend in electronegativity down a group?
electronegativity values decrease down a group:
- atomic radius and electron shielding increases
- weaker attraction between the nucleus and the bonding pair of electrons
what is the trend in electron affinity across a period?
first electron affinity generally increases across a period:
- nuclear charge increases and electron shielding remains constant
- elements across the period have a higher effective nuclear charge
- stronger attraction between the added electron and the nucleus
what is the trend in electron affinity down a group?
first electron affinity decreases down a group:
- less exothermic
- elements further down have a larger atomic radius, with outer valence shells further away from the nucleus plus increased shielding
- weaker effective nuclear charge between the added electron and the nucleus
what is the trend in melting point across a period?
a general increase then a decrease
what is melting point like in metals Na - Al?
melting point increases due to the increasing strength of metallic bonding caused by the larger number of delocalised electrons contributing to the ‘electron cloud’ - larger charge and smaller size of ions gives rise to a larger charge density
what is melting point like in non-metals Si - Ar?
much lower melting points as they are simple covalent molecules. melting point depends on the weak intermolecular london forces. the larger the molecule the greater the london forces.
sulphur - melting point rises slightly as the molecule is bigger so has slightly stronger london forces
chlorine - melting point falls slightly as the molecule is smaller
what is metallic character?
metallic character is the tendency of an element to lose electrons and form positive ions. metals tend to lose their outer electrons to form positive ions and non-metals tend to gain electrons to form negative ions.
metallic character decreases from left to right across a period and increases down a group in the periodic table
what is non-metallic character?
non-metallic character is the tendency of an element to accept electrons and form negative ions. non-metallic character increases from left to right across a period and decreases down a group in the periodic table
