Chap 3: Periodic properties of elements

Question 1

For a hydrogen atom, energy depends on which quantum number ?!

Answer 1

Energy only depends on the principle quantum number, it does not depend on the angular momentum quantum number.

Note: for a given principle quantum number, all orbitals have the same energy in one electron atoms.

Question 2

For a multi electron atom, energy depends on which quantum number ?

Answer 2

Energy depends on both quantum numbers, n and l (but not on ml)

Note: In a multi-electron atom, the orbitals with a given principal quantum number have slightly different energies for different l quantum numbers.

Question 3

Is angular dependence the same in one-electron atoms and multi-electron atoms.

Answer 3

Yes, therefore the quantum numbers, l and ml, can still be used.

Question 4

Pauli’s Exclusion principle

Answer 4

No two electrons can have the same set of four quantum numbers (n, l, ml, ms).

Question 5

aufbau principle.

Answer 5

Electrons enter (i.e., fill) atomic orbitals from lowest energy to highest:

Question 6

Hund’s rule:

Answer 6

When electrons occupy the orbitals of the same energy, the configuration with greatest number of unpaired electrons has lowest energy, which means more stable

Note; that is why in a given orbital we fill in electrons one at a time before pairing.

Question 7

Why is helium not placed into the second column.

Answer 7

It’s bcs helium has a completely filled shell not subshell, unlike, Be with a completely filled ns^2 which is a subshell.

Note: Neon has completely full 2nd shell; Helium has completely full first shell. That is why helium is in 8th column, instead of 2nd column

Question 8

what are closed shells

Answer 8

When electron configuration belonging to noble-gas elements helium (He), neon (Ne), argon (Ar)..) is attained, shells become full

Question 9

Core electrons

Answer 9

The electrons occupying inner shells of an

atom (for example: (C) 1s^2 2s^2 2p^2. 1s^2 are core electrons of carbon

Question 10

paramagentic substances

Answer 10

The elements with unpaired electrons are attracted into magnetic field

Question 11

diamagentic substances.

Answer 11

The elements with all paired electrons are repelled by the magnetic field.

Ex: Alkaline earth Elements (2nd column) and noble gases (8th column) are diamagnetic

Question 12

For neutral atoms at the beginning of the fourth period the electron go into 4s orbital (instead of 3d orbital), because:

Answer 12

(1) . Energy of 4s < Energy of 3d;
(2) . the electron in 4s orbital is attracted to the nucleus much more than the electron in 3d orbital bcs the shape of the 3d orbital is larger than the shape of the 4s orbital.

Note: this is before the d-block.

Question 13

Valency and core electrons for transition elements.

Answer 13

For transition elements count incomplete outermost d- electrons, even though they are not in outermost “n” level

core electrons: for transition metals, also count those in complete d and f sublevels.

Question 14

Diff btn metal and non-metals.

Answer 14

I. OXIDES
Metal oxides: Most oxides are basic and ionic
non-metal oxides: Most oxides are acidic and molecular.

II. IONS

• metals form cations in solution
• non-metals form anions and polyatomic anions.

Question 15

Van der Waals radius, covalent radius, metallic radius, ionic radii, atomic radius

Answer 15

Van der waals radius; The radius of an atom when it is not bonded to another atom

covalent; one-half of internuclear distance btn two atoms bound by a single bond.

Metallic: one-half of the internuclear distance between nearest neighbors in a metallic crystal

Ionic radii: the internuclear distance btn a cation and anion in an ionic crystal gives ionic radii

atomic radius: same as covalent bond, but is the average from the a number of elements or compounds.

Question 16

Bond length.

Answer 16

The sum of atomic radii of atoms that form a chemical bond.

Question 17

Atomic size accross the group and down the period

Answer 17

down the group it increase bcs the number of shells increases occupying more space

accross the group it decreases bcs effective nuclear charge increases.