ch 2 atomic structure

extent of deflection depends on

|charge| / mass ratio of the particle

atomic number

number of protons in the nucleus of an atom

nucleon number

total number of protons and neutrons in the nucleus of an atom

isotopes

atoms of the same element having the same atomic number but different nucleon number

atomic orbital (contains 2 electrons)

region of space around the nucleus where there is a high probability of finding an electron at any moment in time

s orbital shape

spherical

p orbital shape

dumb-bell

d orbital shape

butterfly

type of d orbitals

subshell (contains spdf orbitals)

group of orbitals with the same energy level and shape but different orientation in space

principal quantum shell

a group of subshells that are about equal distance from the nucleus

first principal quantum shell is closest to the nucleus and has the

lowest energy

as distance between orbital and nucleus increases, size of orbital

increases

electronic configuration of Cu

[Ar] 3d5 4s1 as half filled subshell is more stable than 3d4 4s2

electronic configuration of Cr

[Ar]3d10 4s1 as more symmetrical 3d electron cloud that shields the nucleus more effectively

first ionisation energy

of an element is the amount of energy needed to remove one mole of electrons from one mole of gaseous atoms to form one mole of singly-charged gaseous cations

second ionisation energy

of an element is the amount of energy needed to remove one mole of electrons from a singly-charged gaseous cations to form one mole of doubly-charged gaseous cations

factors influencing ionisation energy

1) nuclear charge

2) shielding effect

ionisation energy ……… across a period

generally increases

IE trend across period explanation

• no. of protons increase, nuclear charge increase

• successive electrons are added to the same outermost shell, shielding effect remains approximately the same

• effective nuclear charge increases

• attraction between nucleus and outermost electron increases

• more energy needed to remove outermost electron

exceptions for IE increase over period

• ns2 and ns2np1

• ns2np3 and ns2np4

reason for exception across period

2s2(Be) and 2s2 2p1(B)

• less energy needed to remove 2p electron in B as it is removed from higher energy subshell, and filled 2s subshell in Be provide shielding, less energy needed to remove outermost electron in 2p1

2s2 2p3 (N) and 2s2 2p4 (O)

• less energy required to remove the paired 2px electron in O as it experiences inter-electronic repulsion

1st ionisation energy ……… down the group

deceases

reason for trend down the group

• no. of protons increase, nuclear charge increase

• number of principal quantum shell increases, shielding effect increases significantly

• outermost electron is further away form nucleus, attraction between nucleus and outermost electron decreases

• less energy required to remove outermost electron

1st IE between periods ……

decreases significantly

reason for trend between periods

• nuclear charge increases

• one/two more principal quantum shell, shielding effect increases significantly

• outermost electron is further away form nucleus, attraction between nucleus and outermost electron decreases

• less energy required to remove outermost electron

successive IE always…… and why?

increases, because each electron is removed from an ion becoming more positively charged, harder to remove the negatively charged electron from a positively charged ion due to electrostatic attraction

atomic radius

half the shortest inter-nuclear distance found in the structure of an element

atomic and ionic radii……. down the group

increases

reason for atomic/ionic radii trend down the group

• no. of protons increases, nuclear charge increases

• no. of principal quantum shells increases, shielding effect increases significantly

• outermost electron is further away form nucleus, attraction between nucleus and outermost electron decreases

• less energy required to remove outermost electron

atomic radius ….. across a period

decrease

reason for atomic radii trend across a period

• atoms have same number of principal quantum shells

• as no. of protons increase, nuclear charge increases

• as successive electrons are added to the same outermost shell, shielding effect remains approximately the same

• effective nuclear charge increases

• outermost electron is attracted more closely to the nucleus

ionic radius ……. across a period for ions with same isoelectronic configuration

decreases

reason for trend of ionic radius across a period for ions with same isoelectronic configuration

• as no. of protons increase, nuclear charge increases

• as the species are isoelectronic(same no. of electrons), shielding effect remains (approximately) the same

• effective nuclear charge increases

• outermost electron is attracted more closely to the nucleus

within the same period, anions are ……. than cations

larger because anions have one shell more of electrons

cations have …… radii than their respective atoms

smaller, as there is one shell less of electrons

anions have …… radii than their respective atoms

larger, as there more more electrons than protons, net attractive force for ve by nucleus decreases

electronegativity

of an atom is a measure of its ability to attract the shared pair of electrons in a covalent bond (or electron density) towards itself

electronegativity …… across the period and why?

increases, as effective nuclear charge increases

electronegativity…… down the group and why?

decreases, as attraction between the outermost electron and nucleus decreases