Atomic structure

Isotopes

Atoms of the same element with the same number of protons but different numbers of electrons. Since they have different number of neutrons, they have different masses and different physical properties

S orbital is ___ in shape and ___ (direction?)

Spherical, non-directional.

As n increases, the s orbital becomes more ___

Diffuse

P orbitals have a ___ shape and are ___ (direction?)

Dumbell, directional

The 3 p orbitals in the same subshell are degenerate.

Yes

Aufbaf Principle

Electrons fill orbitals according to this sequence

Hund’s Rule

Orbitals of a subshell must be occupied singly by electrons of parallel spins before pairing can occur

The Pauli Exclusion Principle

If there are 2 electrons in the same orbital, they must be of opposite spins

Excited state of an atom

When an electron temporarily occupies an energy state greater than its ground state

Where are electrons added to in anions?

The next available orbital

Where are electrons removed from cations?

Orbitals with the highest energy (ie. outermost)

Electrons are more easily removed from orbitals with ___ energy level

higher

Isoelectronic species

Same total number of electrons

What is the outermost electronic configuration of d-block elements?

(n-1)d^x ns^y, where n is the group number

How do the number of electron shells affect electrostatic attraction between nucleus and outermost electrons?

As the number of electron shells increase, n increases and the number of inner shell electrons increase. The EAnoe decreases

What is the electronic configuration of Cr? (24e)

1s2 2s2 2p6 3s2 3p6 3d5 4d1

What is the electronic configuration of Cu? (29e)

1s2 2s2 2p6 3s2 3p6 3d10 4s1

To form anions, electrons are added to the ___ ___ ___

Next available orbital

To form cations, electrons are removed from orbitals with the ___ ___

Highest energy

Isoelectronic species

Species with same total number of electrons

3 factors that affect strength of electrostatic attraction between nucleus and electrons

1. No. Of electron shells

2. Nuclear charge

3. Shielding effect

Shielding effect contributed by inner-shell electrons are ___ significant compared to outermost electrons.

More

Which factors are considered when discussing the trend of atomic properties

1. Across a period

2. Down a group

1. Nuclear charge, shielding effect

2. Number of electron shells, nuclear charge, shielding effect

Explain the trend in atomic radii across a period

Atomic radii decrease across a period.

Across a period,

• number of electron shells remain the same

• Number of proteins increases → NC increases

• Number of electrons also increase but e are added to same outermost electron shells → SE remains approximately constant

• EAnve increases → e cloud size decr

Explain the trend in atomic radii down a group

Atomic radii increase down a group

Down a group,

• number of electron shells remain increase

• shielding experienced by VE increases significantly as there are more inner shell electrons

• Despite increasing nuclear charge, EAnve decreases → electron cloud size decr

Explain why the radius of a cation is always ___ than that of the parent atom.

Smaller

• Both cation and parent atom have the same number of protons → same NC

• However, cation has one less e shell than parent atom and outermost electrons are shielded to a smaller extent as there are less inner-shell electrons Despite increasing

• EAnoe stronger in cation → smaller e cloud → smaller radius

Explain why the radius of an anion is always ___ than that of the parent atom.

Greater

• Both anion and parent atom have the same number of protons → same NC

• However, anion has more electrons than parent atom → shielding incr

• EAnoe weaker in anion → larger e cloud → greater radius

Explain the trend of ionic radii of isoelectronic species across the period

Decrease

• Na+, Mg2+, Al3+ are isoeletronic species across→ outermost electrons experience same SE

• However, NC increases from Na+ to Al3+

• EAnoe increases from Na+ to Al3+ → electron cloud size decr

• Ionic radii decr

(Same explanation for period 3 anions)

Why is there a sharp increase in ionic radius from Al3+ to P3-?

Ionic radius of P3- is bigger than that of Al3+.

From Al3+ to P3-,

• Number of electron shells increase

• Shielding experienced by outermost electrons increases significantly as there are more inner shell electrons

Despite increasing NC,

• EAnoe decreases → size of electron cloud incr

First ionisation energy

The energy required to remove 1 mole of electrons from 1 mole of gaseous M atoms to form 1 mole of gaseous M+ ions.

Explain the trend in first IEs across a period

First IE generally creases across a period

• Number of electron shells remain the same

• Number of protons increase → NC increases

• Number of electrons also increases but electrons are added to the same outermost e shell → SE remains approximately constant

• EAnve incr → incr in energy required to remove VE from atom

Why is the ionisation energy of Al lower than that of Mg? [IE irregularity 1: Grp 2 and 13)

• The 3p electron to be removed from Al is at a higher energy level than the 3s electron to be removed from Mg

• Less energy required to remove 3p electron in Al as it is less attracted to the nucleus than 3s electron in Mg

• First IE of Al lower than that of Mg

More energy is required to remove an electron at a higher energy level. T/F?

F. Less energy is required as the electron at higher energy level is less attracted to the nucleus.

Why is the IE of S lower than that of P? [IE irregularity 2: Grp 15 and 16)

• The 3p electron to be removed from S is a paired electron while that to be removed from P is an unpaired electron.

• Due to greater electron-electron repulsion between paired electrons in the same orbital, less energy is required to remove the paired 3p electron from S.

• 1st IE of S lower than that of P

Explain the trend in first IE down a group

First IE of elements generally decrease down a group.

Down a group,

• Number of electron shells increases

• Shielding experienced by VE increase significantly as there are more inner-shell electrons

• Despite increasing NC, EAnve decreases → decr in energy required to remove a ve

• First IE decr down group

Why is the first IE of grp 1 element lower than that of preceding grp 18 element?

• Group 1 element has 1 more e shell than preceding grp 18 element

• Shielding experienced by VE is greater in grp 1 element

• Despite increasing NC, EAnve decreases → decr in energy required to remove 1 ve

• First IE of grp 1 element lower than preceding grp 18 element

Explain the trend in successive IEs of an element

Increase

• Number of protons same → NC remains the same

• Number of electrons decr → SE experienced by remaining outermost shells decreases

• EAn remaining electrons incr → incr in energy required to remove subsequent electrons

Deduce group number from large jump in IE (Eg. Between 5th and 6th IE)

Group 15

• Large jump in 5th and 6th IE

• Significantly more energy is required to remove the 6th electron as it is located in an inner electron shell that experiences less shielding

• 5 electrons in valence shell → group 15

Electronegativity

The electronegatively of an atom in a molecule is a relative measure of its ability to attract bonding electrons

Explain the Trend in electronegativity across a period

Increases across period

• Number of electron shells remain the same

• Number of proteins increases → NC increases

• Number of electrons also increases but are added to same outermost electron shell → SE remains approximately constant

• EAn bonding electrons increase

Explain the trend in electronegativity down a group

Decreases

• No, of e shells increases Number

• Shielding experienced by bonding electrons increases significantly as there are more inner-shell electrons

• Despite increasing NC, EAnbe decreases