atomic number

Background on the Periodic Table

Dmitri Mendeleev: given creditfor Periodic Table (~1870)

--

--

organized Table byincreasing atomic mass left spaces and predictedproperties of undiscoveredelements

Henry Moseley: put elements inorder of increasing____________.

Mendeleev

Moseley

Describing the Periodic Table

periodic law: the properties of elements repeat every so often

period:

group (family):

horizontal row; there are 7

vertical column; there are 18 18

1716151413

129 101187654

1

3

21234

67

5

computer chips

metalloids (semimetals): “stair” between metalsand nonmetals

properties: in-between those of metalsand nonmetals; “semiconductors”

Regions of the Table (cont.)

(B, Si, Ge, As, Sb, Te, Po)

Si and Ge

computer chips

metals

nonmetals

Same number of valence e– =

Li Na

In any group, the element BELOW has one moreoccupied energy level than does the element ABOVE.

Li Na

similar properties

1s2 2s1 1s2 2s2 2p6 3s1

The period that an element is in is the same as theenergy level that its valence electrons are in.

Li Na

v.e– in 2nd E.L. v.e– in 3rd E.L.

in 3rd periodin 2nd period

alkali metals:

alkaline earth metals:

halogens:

noble gases:

contain f orbitals

lanthanides:

coinage metals:

transition elements:

main block (representative) elements:

group 1 (except H); 1+ charge;very reactive

group 2; 2+ charge;less reactive than

alkalisgroup 17; 1– charge; very reactive

group 18; no charge; unreactive

elements 58–71

actinides: elements 90–103

group 11

groups 3–12; variable charges

groups 1, 2, 13–18

alkaline earth metals

halogensnoble gaseslanthanides

alkali metals actinidescoinage metalstransition elements

main block elementsmetalloids

hydrogenmore nonmetals

more metals

Periodic Trends

We will be studying four trends across the Periodic Table.

Atomic radii: the distance from the nucleus to the farthest e-.

Ionic radii: the distance from the nucleus to the farthest e- in that element’s ion.

Electronegativity: the propensity for an element to attract e- from another atom. It’s ability to bond.

Ionization energy:: the amount of energy required to pull one e- away from an element; to remove one electron.

Trends

Atomic radius

Ionization energy

Electronegativity

Periodic Trend

Electron shielding: the inner e- block some of the pull from the nucleus so the valence e- don’t feel as much.

- --

-

--

-++++

+++

Feels the force of 7 p+

Feels the force of 5 p+

Effective nuclear charge is how many p+ are pulling on that e-

shielding effect: kernel e– “shield” valence e–

from attractive force of the nucleus

Li v.e–

K v.e–

-- caused by kernel and valence e–

repelling each other

As we go , shielding effect increases...

tougher to remove

easierto

remove

Shielding Effect

Kernel electrons block the attractive force of the nucleus from the valence electrons

+nucleus

Valence

Electrons--

-

-

Electron Shield“kernel”electrons

Periodicity

there are trends in properties of elements

-- left-right AND up-down trends

atomic radius: the size of a neutral atom

add a new energylevel each time

WHY?

…increases as we go

…decreases as we go

WHY?

coulombic attraction: attraction between (+) and (–)

it has to do with…

Coulombic attraction depends on…

2– 2+

2+ 2– 1–

2–

1+

2+

amount of charge distance between charges

+ + – –

H

He

+ –

+ – + –

As we go , more Coulombic

attraction, No new energy level, more

pull = smaller size

Decreasing Atomic Size Across a Period

As the attraction between the (+) nucleus and the (–) valence electrons , the atomic size .

From left to right, size decreases because there is an increase in nuclear charge and Effective Nuclear Charge (# protons – # core electrons).

Each valence electron is pulled by the full Effective Nuclear Charge.

Li Be B1s22s1 1s22s2 1s22s22p1

Li Be B

Atomic Radii

Li

Na

K

Rb

Cs

ClSPSiAl

BrSeAsGeGa

ITeSbSnIn

Tl Pb Bi

Mg

Ca

Sr

Ba

Be FONCB

1.52 1.11

1.86 1.60

2.31 1.97

2.44 2.15

2.62 2.17

0.88 0.77 0.70 0.66 0.64

1.43 1.17 1.10 1.04 0.99

1.22 1.22 1.21 1.17 1.14

1.62 1.40 1.41 1.37 1.33

1.71 1.75 1.46

IA IIA IIIA IVA VA VIA VIIA

=1 Angstrom

Relative Size of Atoms

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 350

ionic radius:

cations anions

Ca atom Ca2+ ion Cl atom Cl1– ion

the size of an ion

20 p+

20 e–

20 p+

18 e–

17 p+

17 e–

17 p+

18 e–

Ca Ca2+ Cl Cl1–

cations are smaller anions are larger

Formation of Cation - Cation is Smaller than Parent.

11p+

sodium atomNa

e-

loss of one valence

electron

e-

e-

e-

e-e-

e-

e-

e- e-

e-

sodium ionNa+

11p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-e-

Formation of Anion - Anion is Bigger than Parent Atom

17p+

chlorine atomCl

e-

e-

e-

e-

e-e-

e-

e-

e- e-

e-

e-

e-

e-

e-

e-

e-

e-

gain of one valence

electron

chloride ionCl1-

17p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Sizes of ions: electron repulsion

Valence electrons repel each other.

9

+

• When an atom becomes an anion (adds an electron to its valence shell) the repulsion between valence electrons increases without changing effective nuclear charge.

• Thus, F– is larger than F

Fluorine atomF

1s22s22p5

9+-

--

-

--

--

-

F1-

1s22s22p6

+1e+1e-- 9+-

--

-

--

--

-

-

Fluorine ionFluoride ion

Trends in Atomic and Ionic Size

152

186

227

Li

Na

K

60

Li+

95

Na+

133

K+

e

e

eF-

136

Cl-

181

Br-

195

F

Cl

Br

64

99

114

e

e

e

Metals NonmetalsGroup 1

Al

143

50

eee

Group 13 Group 17

Cations are smaller than parent atomsAnions are larger than parent atoms

Al3+

IA IIA IIIA IVA VA VIA VIIA

0.60 0.31

0.95 0.65

1.33 0.99

1.48 1.13

1.69 1.35

1.71 1.40 1.36

0.50 1.84 1.81

0.62 1.98 1.85

0.81 2.21 2.16

0.95

Li1+ Be2+

Na1+ Mg2+

Cl1-

N3- O2- F1-

S2-

Se2- Br1-

Te2- I1-

Al3+

Ga3+

In3+

Tl3+

Ca2+K1+

Sr2+Rb1+

Cs1+ Ba2+

Li

Na

K

Rb

Cs

ClSPSiAl

BrSeAsGeGa

ITeSbSnIn

Tl Pb Bi

Mg

Ca

Sr

Ba

1.52 1.11

1.86 1.60

2.31 1.97

2.44 2.15

2.62 2.17

0.88 0.77 0.70 0.66 0.64

1.43 1.17 1.10 1.04 0.99

1.22 1.22 1.21 1.17 1.14

1.62 1.40 1.41 1.37 1.33

1.71 1.75 1.46

Be B C N O F

= 1 Angstrom

AtomicRadii

IonicRadii

Cations: smaller than parent atoms

Anions: LARGERthan parent atoms

Ionization Energies

• Energy is required to remove an electron from an atom to form a cation.

• Ionization energy () is the amount of energy needed to remove an electron from the gaseous atom E in its ground state:

• Larger values of mean that the electron is more tightly bound to the atom and is harder to remove.

• Units for ionization energies are kilojoules/mole (kJ/mol) or electron volts (eV) - 1 eV = 96.49 kJ/mol.

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Electronegativity

The ability of anatom in a compound to attract sharedelectrons to itself.

Linus Pauling1901 - 1994

Electronegativity:

It is a measure of the ability of an atom to attract additional electron to it.

Group: Electronegativity decreases down a group because the outer energy level is further away from the nucleus which results in a weaker nuclear charge available to attract additional electrons or less ability for an atom to attract electrons to it.

Electronegativity (Cont.):

Period: Electronegativity increases moving across a period from left to right because the atoms in the same period have the same number of energy levels but the number of protons increase as you go from atom to atom across a period increasing the attraction between the nucleus and the outer energy level resulting in a greater ability for atoms to attract electrons to it.

electronegativity:

Linus Pauling quantifiedthe electronegativity scale.

the tendency fora bonded atom toattract e– to itself

As we go , electronegativity…

As we go , electronegativity…

decreases.

increases.

electronegativity increases