exam 4 - chapter 7 Periodic Properties of Elements

atomic numbers

elements are ordered by their _____

arrangement of electron, specifically valence electrons

patterns of properties and reactivity relate to and are determined by ___

period number represents principal quantum number, n

horizontal rows on periodic table

group number represents # of valence electrons

vertical columns on periodic table

Dmitri Mendeleev and Lothat Meyer (more Mendeleev is remembered for predicting unknown elements)

who helped create the periodic table?

boiling point temperature

what information did Mendeleev use to organize the elements in 1869?

developed the concept of atomic numbers or number of protons

who is Henry Moseley

• observed higher energy emitted X-ray with increasing atomic number

• implies more negative potential energy for n=1

• a more negative PE results from a higher charge in the nucleus from protons

Moseley X-ray experiments summary

more protons in the nucleus will cause higher energy emitted X-ray

what is the conclusion of Moseley’s discovery

Z - S

Effective Nucleu Charge Z_eff=

1. electronic configuration of an atom/valence electrons

2. how strongly the outermost (valence) electrons in the atom are attracted to the nucleus

what two thinks do we depend on when we observe properties

core electrons

shield or screen the valence electrons from the full positive charge of the nucleus

#protons

z =. atomic number =

screening by inner e- (all e- in lower n_

S =

screening constant; the average number of electrons between the nucleus and the valence electron in question (close in value to the number of inner-sehll (core electrons (#e in all lower n level)

S =

1. determine the positive charge of nucleus (Z, number of protons)

2. determine the screening constant, S

• the simplest model to factor S is to count inner core electrons (those with smaller n) as shielding electrons . useful to write the full electron configuration

strategy for determining the Z_eff of an atom/element

more effectively

inner core electrons screen _____ than electrons in the same energy level, n.

Z_eff increases slightly because S, shielding decreases because large diffuse core electron cloud is less effective at screening

trend on periodic table. Down a group.

What is the effective nuclear charge trend

for valence electrons, the effective nuclear charge increases left to right

what is the trend on periodic table for Across a period?

group #

for valence electrons, Z_eff typically =

further

larger n, means electron are on average ___ from nucleus

1) energy of the valence electrons (quantum #,n)

2) attraction of the outer electrons to the nucleus (Zeff)

3) repulsion between electrons in the same n (charge ion)

size of an atom (or an ion) depends on

down bc N increases

size increases as we go _____ a group

L→R bc Zeff increases L→R

size decreases as we go _____ across a period

Z_eff

for transition metals, the gradual decrease in size for d¹-d⁷ is explained by

e^- repulsion

for transition metals, the slight increase at the end of the d block (d⁸-d¹⁰) is explained by ____

smaller than the neutral atom

cations are always ____

decreases as positive charge increases

size of cation ____

always larger than the neutral atom

anions are ___

increases as the negative charge decreases

size of anion ____

a group of atoms/ ions with the same # of e^-

isoelectronic series

increases as nuclear charge/number of protons increases

for isolectronic series, Z_eff ___

pulls shell closer

Increasing nuclear attraction (#protons) for same number of electrons _____

ionization energy

energy required to remove an electron

higher ionization energy

smaller atom size =

going down a group due to size (n)

Ionization energy decrease by ____

L to R across period due to size (Zeff)

Ionization energy increases by ____

• between 2A and 3A (Be vs B)

• between 5A and 6 A (N vs O)

exceptions for ionization energy

the cation is getting smaller

it always gets harder to remove additional elections because

starting to remove inner core electrons =

• this is why chemical reactivity is based on valence electrons only

when is there a jump in ionization energy?

hard

if electron is really close to the nucleus, then it is __ to remove it

easy

if electron is really far from nucleus, then it is ___ to remove it