lecture 4 - periodic trends

what is a proton?

a subatomic particle with a positive electric charge

what is a neutron?

a subatomic particle with no electric charge

what is an electron?

a subatomic particle with a negative electric charge

what determines an atom’s atomic number?

the number of protons

what determines an atom’s identity?

the number of protons

what is the mass number of an atom?

the total number of protons and neutrons

what is an element?

a substance whose atoms all have the same atomic number

what is a metal?

an element that is conductive, malleable, ductile, and tends to lose electrons

what is a nonmetal?

an element that is not conductive, not malleable, and tends to gain electrons

what is a metalloid?

an element that shares properties of both metals and nonmetals

what happens to the number of protons across a period?

it increases by one for each element

what happens to the number of electron shells down a group?

one shell is added each row

what is shielding?

the reduction in attraction between the nucleus and valence electrons due to inner electrons

what causes shielding?

core (inner) electrons blocking nuclear charge

what is effective nuclear charge (Zₑff)?

the net positive charge experienced by valence electrons

what equation approximates effective nuclear charge?

Zₑff = Z - S

what does Z represent in Zₑff = Z- S?

atomic number

what does S represent in Zₑff = Z- S?

shielding from inner electrons

as the number of core electrons increases, what happens to shielding?

shielding increases

as shielding increases, what happens to attraction between nucleus and valence electrons?

attraction decreases

how does effective nuclear charge (ENC) change across a period?

it increases

how does effective nuclear charge (ENC) change down a group?

it decreases

which electrons experience the strongest effective nuclear charge?

electrons closest to the nucleus

which shell experiences the least shielding?

the 1s shell

what is atomic radius

the distance from the nucleus to the outermost electron

how does atomic radius change across a period?

it decreases

how does atomic radius change down a group?

it increases

why does atomic radius decrease across a period?

increasing effective nuclear charge pulls electrons closer

why does atomic radius increase down a group?

additional electron shells and increased shielding

which element has the largest atomic radius in a group?

the element lowest in the group

which elements have the smallest atomic radius in a period?

noble gases

what is ionic radius?

the distance from the nucleus to the outer edge of an ion’s electron cloud

are cations larger or smaller than their neutral atoms?

smaller

why are cations smaller than neutral atoms?

loss of electrons reduces repulsion and increases effective nuclear charge per electron

are anions larger or smaller than their neutral atoms?

larger

why are anions larger than neutral atoms?

added electrons increase electron-electron repulsion

for ions with the same number of electrons, what determines size?

number of protons

among isoelectric ions, which is smallest?

the ion with the greatest nuclear charge

what is ionization energy?

the energy required to remove the outermost electron from a neutral atom in the gas phase

how does ionization energy change across a period?

it increases

how does ionization energy change down a group?

it decreases

why does ionization energy increase across a period?

increasing effective nuclear charge

why does ionization energy decrease down a group?

increased atomic size and shielding

which element generally has the highest first ionization energy in a period?

noble gases

which group has the lowest first ionization energy?

alkali metals

what is the p³ vs p⁴ ionization energy exception?

removing an electron from a paired p orbital is easier due to electron repulsion

which has higher ionization energy: oxygen or nitrogen?

nitrogen

why does nitrogen have a higher ionization energy than oxygen?

nitrogen has a half-filled p subshell

what happens to ionization energy when a noble gas configuration is reached?

the next ionization energy increases dramatically

why is the second ionization energy of alkali metals very large?

the first electron removal creates a noble gas configuration

why is the third ionization energy of alkaline earth metals very large?

removing two electrons creates a noble gas configuration

what is electronegativity?

a measure of an atom’s ability to attract electrons in a bond

how does electronegativity change across a period?

it increases

how does electronegativity change down a group?

it decreases

which element has the highest electronegativity?

Fluorine

why are noble gases not assigned electronegatvity values?

they generally do not form bonds

what is ΔEN?

the difference in electronegativity between two bonded atoms

what type of bond forms when ΔEN < 0.5?

nonpolar covalent

what type of bond forms when 0.5 < ΔEN < 1.7?

polar covalent

what type of bond forms when ΔEN > 1.7?

ionic

in a polar covalent bond, which atom has a partial negative charge?

the more electronegative atom

which bond has the highest ΔEN: C-H, C-N, C-O, C-F?

C-F

which hydrogen halide has the greatest ΔEN?

H-F