3.2 Periodic trends Flashcards
what are the 6 different physical periodic trends?
- atomic radius
- ionic radius
- melting point
- first ionisation energy
- electronegativity
- electron affinity
explain the period trends in atomic radius across a period
decreases across a period because same shielding effect and higher nuclear charge pulls electrons inwawrds
explain the periodic trend in atomic radius down a group
increases down a group because electrons are added in shells further from the nucleus with the same nuclear charge
are anions or cations larger and why?
anions are larger because you are adding electrons instead of removing them
explain the periodic trend in cationic radius across a period
decreases as cationic charge increases
because there are fewer electrons with a higher nuclear charge which pulls electrons closer
explain the periodic trend in cationic radius down a group
increase down a group because atomic radius increases
explain the periodic trend in anionic radius across a period
increases as anionic charge increases due to more electrons and lower nuclear charge attracting the electrons more weakly
explain the periodic trend in anionic radius down a group
increases downs a group because atomic radius increases
explain the periodic trend in ionisation energy across a period
increases due to the same shielding effect and higher nuclear charge attracting electrons more strongly, requiring more energy to remove an electron
explain the periodic trend in ionisation energy down a group
decreases due to a higher shielding effect with the same nuclear charge attracting electrons less strongly requiring less energy to remove an electron
define periodicity
repeating pattern or physical and chemical properties exhibited because of specific periodic trends
what is an atomic radius?
distance from the nucleus to the valence electrons
what is an ionic radius?
the distance from the nucleus to the outermost electron of a cation or anion
what is electronegativity?
it is the relative measure of the attraction of an atom for the shared par of electrons
define ionisation energy
energy required to remove one mole of electron from one mole of gaseous atoms
define electron affinity
energy released when one mole of electrons is added to one mole of gaseous atoms
explain the periodic trend in electron affinity down a group
decreases down the group because…
- increased shielding effect that outweighs the increase in nuclear charge
- so electrostatic attraction decreases
* note that fluorine does not fit the trend
explain the periodic trend in electron affinity across a period
increases across a period because…
- increases in nuclear charge
- no change in shielding effect
- so the electrostatic attraction increases
* note that phosphorus does not fit the trend
is the first electron affinity negative or positive and why? is this reaction favorable or not?
- it is negative
- as atoms generally want to gain electrons
- this reaction is favorable/ exothermic because its value is negative
is the second electron affinity negative or positive and why? is this reaction favorable or not?
- it is positive
- as the negative ion created from the first electron affinity repels any additional electrons
- this reaction is less favorable/ endothermic because its value is positive
describe the characteristics of the alkali metals
- soft very reactive metal elements
- down the group: reactivity increases and melting point decreases
- low melting and boiling point
- all react with oxygen and water
what does alkali metal form when reacted with oxygen?
metal oxides
what does alkali metal form when reacted with water?
form a metal hydroxide and hydrogen gas
describe the characteristics of halogens
- diatomic non-metal elements
- down the group: reactivity decreases and melting point increases
- very low melting and boiling point
- all halogens reacts with alkali metals and halide solutions
what does halogen form when reacted with alkali metal?
form white/ colourless neutral salts, which are soluble in water
what does halogens form when reacted with halide solutions?
the more reactive halogen will displace the less reactive halogen
how can the presence of halide ions be tested?
through the addition of silver nitrate solution
how do you test for the presence of chloride ions and what are the observations?
- adding silver nitrate solution
- white precipitate will form
how do you test for the presence of bromide ions and what are the observations?
- adding silver nitrate solution
- a cream precipitate will form
how do you test for the presence of iodide ions and what are the observations?
- adding silver nitrate solution
- a yellow precipitate will form
