23. Trends in the Periodic Table

nuclear charge

the charge of all the protons in the nucleus; the attraction between the positively charged protons in the nucleus and the negatively charged electrons in the energy levels

screening effect

in an atom with many energy levels, the electrons in the inner energy levels shield/screen the electrons in the outer energy levels from the effect of the nucleus

effective nuclear charge

how well the electrons can ‘feel’ the positive charge - varies due to number of protons in nucleus and screening effect

atomic radius

half the distance between the nuclei in a single covalent bond of atoms of the same element

electronegativity

the relative force of attraction that an atom in an molecule has for the shared pair of electrons in a covalent bond

first ionisation energy

the minimum energy required to remove the most loosely bound electron from a neutral gaseous atom in its ground state

trends down a group - atomic radius

atomic radius increases - new energy levels occupied, increase in screening effect

trends down a group - electronegativity

electronegativity decreases - increasing atomic radius, increase in screening effect

trends down a group - first ionisation energy

first ionisation energy decreases - increasing atomic radius, increase in screening effect

trends across a period - atomic radius

atomic radius decreases - no increase in screening effect, increase in effective nuclear charge

trends across a period - electronegativity

electronegativity increases - increase in effective nuclear charge, decrease in atomic radius

trends across a period - first ionisation energy

first ionisation energy increases - increase in effective nuclear charge, decrease in atomic radius

exceptions to general trend of ionisation energies

beryillium, nitrogen, magnesium, phosphorous

why are there exceptions to the general trend of first ionisation energies?

sublevels that are exactly half-filled or fully filled are extra stable. extra stability → more difficult to remove an e- → higher first ionisation energy

general trend in successive ionisation energies is that they…

increase as electrons are removed from an atom

why do successive ionisation energies incerase as electrons are removed from an atom?

greater effective nuclear charge, electrons are closer to the nucleus

how do successive ionisation energy graphs provide evidence for the existence of sublevels?

large jumps between electrons removed

what trend is most important for group one - alkali metals?

first ionisation energy values

what trend is most important for group seven - halogens?

electronegativity values