3.1 Flashcards
brief periodic table history
döbereiner: groups of three elements (triads) ordered by atomic weight had similar properties
newlands: arranged in atomic weight and suggested law of octaves every eighth had similar properties
mendeleev: still in atomic weight but left gaps for undiscovered elements and predicted their properties also switched elements if the atomic weight order didn’t match the properties
moseley: arranged by atomic number not weight
what is periodicity
the trend in properties that is repeated across each period
what are the three things to mention when explaining a trend in periodicity
electron shielding
atomic radius
nuclear charge
what is the first ionisation energy
the energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions
write the first ionisation equation for chlorine
Cl (g) —> Cl+(g) + e-
what are the rules when creating a first ionisation equation
must be gaseous
only 1+ because it’s the first electron
never diatomic
never minus because an electron is being removed
what are successive ionisation energies
a measure of the amount of energy required to remove each electron in turn
what happens to electron attraction when an electron is removed
there is less repulsion between the remaining electrons and each shell is drawn in slightly closer to the nucleus
what’s the trend in ionisation energy across a period
increases across the period (because smaller atomic radi and higher nuclear charger) but decreases between group 2 and 3 because it goes from s subshell to p subshell (p orbital have higher energy than s orbitals) also a decrease from group 5 to 6 (p3 to p4) because teh orbital pairs up causing a repulsion which destabilises the atom and makes it easier to lose an electron
what happens to ionisation energy down a group
decreases
what is second ionisation energy
the energy required to remove one electron from each 1+ ion in 1 mole of the gaseous element to form 1 mole of 2+ ions
structure of metallic bonding
positive ions in a fixed giant lattice
outer shell electrons are delocalised in a sea of delocalised electrons that is spread throughout the structure and can move within. the metal is held together by the attraction between all the positive ions and all the negative electrons
why do metals have a high melting and boiling point
the attraction between the positive ions and negative atoms is very strong
high energy is needed to dislodge the ions from their rigid positions in the lattice
what does metallic bonding strength rely upon
number of outer electrons donated to the electron cloud (from group number) and the size of the metal ion
metallic bonding strength trends across the period and down the group
increases across period (more electron delocalised)
decreases down group (lower electron density)
why can metals conduct electricity
they have mobile delocalised electrons that can flow through the structure electrons attracted to the positive end are replaced by those entering from the negative end
why are metals ductile and malleable
because the layers can slide over eachother due to the delocalised electrons
melting point trends across a period
increasing from group 1-3 metals, then at group 4 (or three aswell in boron’s case) increases further because of giant covalent then dramatically decreases because from group 5 onwards they are simple molecularly bonded (just depends on number of electrons cos london forces)
what’s the reactivity trend down group 2
increases down the grouo