Chapter 7 Periodicity Flashcards
How did Mendeleev arrange the periodic table
In order of atomic mass
And lined the elements in groups of with similar properties
If the groups properties did not fit Mendeleev swapped around elements and left gaps
How is the periodic table arranged
Form left to right the element are arranged in order of increasing atomic number
In the groups each element has the same number of outer shell electrons and similar properties
Horizontally they are arranged in periods the number of the period gives the highest energy electron shell in an elements atoms
What is periodicity
Across a period there is a repeating trend in properties of the elements
Examples are
electron configuration
Ionisation energy
Structure
Melting points
Periodicity - electron configuration
For each period the s and p sub shells are filled the same way - periodicity
Define first ionisation energy
How easily an atom loses electrons to form positive ions
- the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ions
Na(g)= Na+(g) + e-
Factors affeting ionisation energy
Atomic radius - the greater the didtance between the the nucleus and the outer electron the less the nuclear attraction
Nuclear charge - the more protons there are in the nucleus of an atomthe greater the attraction between the nucleus and the uter electrons
Electron sheilding - inner shell electrons repel outer shell electrons ghis repulsion is the shielding effect and reduces the attraction between the nucleus and outer electrons
Why is the secod ionistation enrgy higher than the first
after the first electron is lost , the electrons are pulled closer to the nucleus ,nuclear attraction on the remaining lectrons increase and more ionisation energy will be needed to remove the next electron
definition of the second ionisattion energy
the energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ions
trend in first ionisation energies down a group
atomic radius increases
shielding increases as there are more inner shell
increase in. nuclear charge is not felt
nuclear attraction on outer elevtrons decreases
first ionisation energy decreases
trend in first ionisation energy across a period
- nuclesr charge increases
- same shell same shielding
- nuclear attraction increases
- atomic radius decreases
- first ionisation energy increases.
subshell trends in first ionisation energy beryllium vs boron
FIE decreases from berillium to born (across a period )
the 2p subshell in. boron has a higher energy than the 2s subshell in beryllium
therefore the 2 p electron is easier to remove than one of th 2s electrons in berryllium
so the first ionisation enrgy in boron is less than the first ioniattion energy of beryllium
first ionisation energy nitrogen vs oxygen
although theyre across a period the first ionisation energy drops between nitrogen and oxygen
oxygen marks the start of electron pairing in the p orbitals of the 2p subshell
in both elements the highest enrgy electrons are in a 2p subshell
in oxygen the paired electrons in one of the 2p orbitals repel eachother making it easier to remove an electron from an oxygen atom than a nitrogen atom
