The Periodic Table

Metals, Nonmetals, & Metalloids, Families,

Periodic Trends

• Modern periodic table arranged in order of increasing atomic number.

Periodic Properties of the Elements

• 1869: Dmitri Mendeleev and Lothar Meyer publish identical tables. Mendeleev gets the credit and becomes “Father of Periodic Table”.

• 1913: Henry Moseley develops concept of atomic numbers.

Characteristics of Metals

• Most elements are metals Have a shiny luster; most are silvery

• All solids at room temperature except Hg

• Are malleable (thin sheets) and ductile (wires)

• Many have a very high melting point (1900°C for chromium)

• Good conductors of heat and electricity

• Form cations

• Metal + nonmetal = ionic cmpd

Characteristics of Nonmetals

• Do not have luster; various colors• Poor conductors of heat and electricity• Melting points are generally lower than those of

metals• May be solids, liquids, or gases at room temp• Have high electron affinity; form anions• Compounds of nonmetals with metals are ionic• Compounds with only nonmetals are molecular

Characteristics of Metalloids

• Include the elements B, Si, Ge, As, Sb, Te, At• Form the division line between metals and

nonmetals on the periodic table

• Have intermediate properties. • Si and Ge are used in integrated circuits and computer chips.

Parts of Periodic Table

• Representative elements: Group A elements

• Transition elements: Group B elements (d-block)

• Inner Transition (Rare Earth) elements (f-block)

• Group 1A: Alkali metals; Group 2A: Alkaline Earth metals; Group 6A: Chalcogens; Group 7A: Halogens; Group 8A: Noble Gases

Hydrogen

• Does not belong to any group

• Diatomic gas at RT

• Metallic at extreme pressures

• Usually forms covalent bonds

• Hydrogen ion (1+ charge) or hydride ion (1- charge)

What is Electron Shielding?

• Core e-’s shield or screen outer e-’s from the full charge of the nucleus.

• Electrons in the same shell repulse each other.

• Electrons in any orbital will partially shield an e- in any other orbital.

What Determines Effective Nuclear Charge (Zeff)?

• The Zeff felt by outer electrons is determined by: Zeff = proton # - core electron #

• Effective nuclear charge increases as nuclear charge increases.

• Effective nuclear charge decreases as the e- moves farther from the nucleus.

Periodic Trend 1: Atomic Radius

Atomic radius decreases

up a family (bottom to top

of periodic table).

WHY? Lower-numbered

energy levels are closer to the nucleus.

Atomic radius decreases

across period from left to right.

WHY? Shielding stays

constant across a period so Zeff increases. Electrons move closer to the nucleus

Periodic Trend 2: Ionic Radius

CATIONS Radius of a cation is

smaller than its parent atom.

WHY?a. Outermost electrons

leave to form a cation.b. New outermost

electrons are in a lower energy level, closer to the nucleus.

ANIONSRadius of an anion is larger

than its parent atom.

WHY? a. Electrons are added to

outer shell to form an anion.

b. More electron-electron repulsion.

Ionic Radius Trend Up a

Family

Cation radii decreaseup a family (bottom to

top).

WHY?Atomic radii decrease up

a family, and cations are smaller than their parent atoms.

Follows same pattern as atomic radius!

Anion radii decreaseup a family (bottom to

top).

WHY?Atomic radii decrease

up a family, and anions are larger than their parent atoms.

Follows same pattern as atomic radius!

Ionic Radius Trend Across

a Period• The ionic radius trend changes across a

period as we move from metals to nonmetals.

• The radii of metallic ions decrease while the radii of nonmetallic ions increase across a period.

• This causes a wave-like pattern on the table.

Ionization Energy

• Ionization Energy is the minimum amount of energy needed to remove an electron from the ground state of an isolated gaseous atom or ion. Formation of cations!First Ionization Energy (I1) removes the first electron from a neutral atom:

Na(g) Na+(g) + 1e-

Second Ionization Energy (I2) removes the second electron from an ion:Na+(g) Na2+(g) + 1e-

*** The greater the ionization energy,the more difficult it is to remove an

electron.

Variations in Successive Ionization Energies

• Ranking of ionization energy:

• Every element shows a large increase in ionization energy when electrons are removed from its noble gas core.

I1 < I2 < I3

Periodic Trend 3: Ionization Energy

Ionization energy increases as we go up a family (bottom to top).

Ionization energy increases as we go from left to right across a period.

WHY? As atom gets

smaller, it is harder to remove electrons because they are more attracted to the nucleus.

WHY? As Zeff increases

and the atom gets smaller, it is harder to remove electrons.

Periodic Trend 4: Electronegativity

• Electronegativity: the ability of atoms in a molecule to attract electrons to itself. Greater electronegativity = greater ability to attract electrons.Values from 0.7 for Cs to 4.0 for F.Metals are least electronegative, halogens most electronegative.