Chapter 7

1st developed by Dmitri Mendeleev (Russia) & Lothar Meyer (Germany) on the basis of the similarity in chemical and physical properties

Mendeleev …◦ started by organizing elements by increasing mass.◦ Recognized a repetition of pattern. ◦ Placed elements by same column same properties ◦ Predicted correctly about the existence of new elements

Henry Moseley ◦ established that each element has a unique atomic

number, which added more order to the periodic table◦ Identified the atomic number with the # of protons in

the nucleus of the atom & the # of electrons in the atom.

Atoms aren’t hard spheres with well-defined shells of electrons

The edges of atoms are a bit “fuzzy” The quantum mechanical model of the atom

supports the notion of electron shells: certain distances from the nucleus at which there is a higher likelihood of finding an electron

The size of an atom can be gauged by its bonding atomic radius, based on measurements of the distances separating atoms in their chemical combinations with other atoms

Measure the atomic radius from the center of the nucleus to the outermost electron.

1) Atom size increases going down a group. 2) Atomic size decreases going left to right across the period.

Ionization energy – the minimum energy required to remove an electron from the ground state of the isolated gaseous atom or ion

1st ionization energy (I1) – The energy needed to remove the first electron from a neutral atom, forming a cation

2nd ionization energy (I2) – the energy needed to remove the second electron

The greater the ionization energy, the harder it is to remove an electron

HIGH ionization energy means the atom holds onto the electron tightly and a lot of energy is need to pull it off

LOW ionization energy means the atom holds onto the electron loosely so breaking it apart doesn’t require much energy

Periodic Trends in Ionization Energies Ionization energy decreases as you move down a

group. Ionization energy increases as you move from left

to right on the periodic table. Representative elements show a larger range of

values of I1 than do the transition metal elements

Electron affinity – the energy change that occurs when an electron is added to a gaseous atom

A negative electron affinity means the anion is stable

A positive electron affinity means the anion is higher in energy than are the separated atom and electron. The anion is not stable and will not form

If the electron affinity is negative, the atom releases energy.

Normally, non-metals have a more negative electron affinity than metals. The exception is the noble gases.

Election affinities become more negative as we proceed from left to right

Halogens have the most negative electron affinities

The electron affinities of the noble gases are all positive since the added electron would have to occupy a new, higher-energy subshell

Electron affinity doesn’t change greatly as we move down a group. Electron affinity should become more positive (less energy released).

MetalsMetals Non-MetalsNon-MetalsHave a shiny luster; various Have a shiny luster; various colors, although most are colors, although most are silverysilvery

Do not have a luster; Do not have a luster; various colorsvarious colors

Solids are malleable and Solids are malleable and ductileductile

Solids are usually brittle; Solids are usually brittle; some are hard, and some some are hard, and some are softare soft

Good conductors of heat Good conductors of heat and electricityand electricity

Poor conductors of heat Poor conductors of heat and electricityand electricity

Most metal oxides are Most metal oxides are ionic solids that are basicionic solids that are basic

Most non-metallic oxides Most non-metallic oxides are molecular substances are molecular substances that form acidic solutionsthat form acidic solutions

Tend for form cations in Tend for form cations in aqueous solutionsaqueous solutions

Tend to form anions or Tend to form anions or oxyanions in aqueous oxyanions in aqueous solutionsolution

Pg. 239 --Table 7.3 Characteristic Properties of Metals and Nonmetals

Metallic Character - The tendency of an element to exhibit properties of metals

Metallic character generally increases going down a column and decreases going from left to right across a period

Metals conduct heat & electricity They are malleable & ductile Solids at room temp. except mercury(Hg)

(it’s liquid) Melt at very high temps Have low ionization energies & are

consequently oxidized (lose electrons) when they undergo chemical reaction.

Many transition metals have the ability to form more than one positive ion.

metal oxide + water metal hydroxide

◦ Most metal oxides are known as basic oxides◦ Ex: Na2O (s) + H2O(l) 2NaOH (aq)

metal oxide + acid salt + water

◦ Ex: MgO (s) + 2HCl (aq) MgCl2 (aq) + H20 (l)

Not lustrous & generally are poor conductors of heat and electricity

Non-metals commonly gain enough electrons to fill their outer p sub-shell completely, giving a noble gas electron configuration.

Molecular substances - Compounds composed entirely of nonmetals ◦ Ex: oxides, halides, and hydrides

Melting points are generally lower than those of metals

Nonmetal oxide + water → acid

◦ Most nonmetal oxides are acidic oxides◦ CO2 (g) + H2O (l) H2CO3 (aq)

Nonmetal oxide + base salt + water

◦ CO2 (g) + 2NaOH (aq) Na2CO3 (aq) + H2O (l)

Have properties that are intermediate between those of metals and nonmetals

Group 1A: The Alkali Metals

Characteristics◦ Soft metallic solids◦ Silvery◦ metallic luster ◦ high thermal and electrical conductivities◦ Low densities and melting points◦ Most active metals◦ Exist in nature only as compounds

Group 2A: Alkaline Earth Metals Solids with typical metallic properties Harder, more dense, and melt at higher

temperatures when compared to alkali metals Very reactive towards nonmetals, but not as

reactive as alkali metals

Both alkali and alkaline earth metals react with hydrogen to form ionic substances that contain the hydride ion, H-

Hydrogen Hydrogen is a nonmetal with properties that

are distinct from any of the groups of the periodic table

It forms molecular compounds with other nonmetals, such as oxygen and the halogens

Group 6A: The Oxygen Group Most important element in group 6A Exists in several allotropic forms (different

forms of the same element in the same state) Oxygen is encountered in two molecular forms,

O2 (common form) and O3 (aka ozone) Oxygen has a strong tendency to gain electrons

from other elements, thus oxidizing them In combination with metals, oxygen is usually

found as the oxide ion, O2-, although salts of the peroxide ion, O2

2-, and superoxide ion, O2-, are

sometimes formed

Sulfur!! 2nd more important element in group 6A Also exists in several allotropic forms Elemental sulfur is more commonly found

as S8 molecules In combination with metals, it is more often

found as the sulfide ion, S2-

Nonmetals that exist as diatomic molecules

There melting and boiling points increase as you go down the column

Have the most negative electron affinities of the elements

Their chemistry is dominated by a tendency to form 1- ions, especially in reactions with metals

Group 8A: The Noble Gases aka inert gases Nonmetals that exist as monoatomic gases Very unreactive since they have completely filled

s and p subshells. Have the complete octet Have large 1st ionization energies Only the heaviest noble gases are known to form

compounds, and they do so only with very active nonmetals, like fluorine