Metals, Metalloids, and Nonmetals

1A 2A 3A 4A 5A 6A 7A 8A(1) (2) (13) (14) (15) (16) (17) (18)

3B 4B 5B 6B 7B — 8B — 1B 2B(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)

1 H He

2 Li Be B C N O F Ne

3 Na Mg Al Si P S Cl Ar

4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

7 Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Uub — Uuq — — — —

6 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

7 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

  

Key: metal metalloid nonmetal

 

The elements can be classified as metals, nonmetals, or metalloids.  Metals are good conductors of heat and electricity, and are malleable (made into sheets) and ductile (made into wire).  Most of the metals are solids at room temperature, with a characteristic silvery shine (except for mercury, which is a liquid).  Nonmetals are (usually) poor conductors of heat and electricity, and are not malleable or ductile. Many of the elemental nonmetals are gases at room temperature, while others are liquids and others are solids.  The metalloids are intermediate in their properties. Some of these semiconductors are extremely important in computers and other electronic devices. A solid black line [stair-step] can also indicate the separation of the metals from the nonmetals.  The metals are to the left of the line (except for hydrogen, which is a nonmetal), the nonmetals are to the right of the line, and the elements immediately adjacent to the line are the metalloids.

Valence Electrons, Octet Rule and Bonds

Valence electrons are the other shell electrons and the only electrons associated with the formation of bonds. These electrons are in the highest occupied energy level, farthest from the nucleus, therefore the easiest to remove. They determine the chemical properties of an element. Valence electrons are important for following the Octet Rule .

An atom is considered stable if its outermost shell has the noble gas configuration. The Octet Rule states when atoms bond, they lose, gain, or share electrons to attain a filled outer level of eight electrons. Exception is made for Hydrogen and Helium in energy level one with only two electrons to fill their outer shell. We can represent valence electrons with the Lewis Dot Structure. This is drawn as the element symbol surrounded by dots corresponding to the number of valence electrons. Lewis Structures are not used for complex compounds or molecules due to the complexity of bonds and interactions.

When elements combine to form compounds, there are three types of bonding that can result.  C ovalent bonds result when atoms share electrons to produce neutral molecules.  In general, metal and nonmetals combine to form ionic compounds. Nonmetals combine with other nonmetals to form covalent compounds (molecules). Ionic bonds form when there is a transfer of electrons from one species to another, producing charged ions which attract each other very strongly by electrostatic interactions. Metals that bond with each other form metallic bonds where the electrons move within an “electron sea.” The figure below shows the three main types of chemical bonds [pg 280 textbook]

Covalent Compounds

When nonmetals combine with other nonmetals, they tend to share electrons in covalent bonds resulting in the formation of neutral molecules. Covalent compounds have an electronegativity differences between 0.0 to 1.7. [See Electronegativity and Periodic Trends Chart Reference]

Ionic Compounds - Cations

Following the periodic trends, metals are further to the left on the periodic table and have low ionization energies and low electron affinities. Metals lose their valence electrons relatively easily and gain valence electrons with difficulty.  They also have fewer valence electrons, and can form ions (and thereby satisfy the octet rule) more easily by losing their valence electrons to form positively charged cations. Cations are smaller than the neutral atom due to losing electrons [See figure below].

Ionic compounds are held together in a regular array called a crystal lattice by the attractive forces between the oppositely charged cations and anions.  These attractive forces are very strong, and most ionic compounds therefore have very high melting points.  Ionic compounds can conduct electricity when they are dissolved in water. [sodium chloride, NaCl melts at 801°C and aluminum oxide, Al2O3 melts at 2054°C].  

The main-group metals usually form charges that are the same as their group number.

Group 1A metals such as sodium and potassium form 1+ charges Group 2A metals such as magnesium and calcium form 2+ charges Group 3A metals such as aluminum form 3+ charges Group 4A elements form 4+ Exceptions: Tin and lead in Group 4A can form either 4+ or 2+ charges, Exceptions: Bismuth in Group 5A can form either a 5+ or a 3+ charge.

The transition metals can form 2+, 3+ or 4+ ions. The different charges are determined by the elements they form bonds with and vary among the transition metals. We also may represent charges in transition elements with a Roman Numeral after the symbol.

The transition metals can form 2+ charges by losing their valence s electrons. [Except silver and gold]. The transition metals can also form 3+ charges by losing electrons from their d orbitals. [Except Cu 2+,

Zn 2+, Ag +, Cd 2+, and Hg 2+] Exceptions: Ag +, Zn 2+ and Cd 2+ form only ONE charge. Exceptions: Sn 2+, 4+ and Pb 2+, 4+

Ionic Compounds - Anions

Following the periodic trends, nonmetals are further to the right on the periodic table and have high ionization energies and high electron affinities, so they gain valence electrons relatively easily, and lose valence electrons with difficulty. They have a larger number of valence electrons, and are closer to having a complete octet of eight electrons. The Group 5 and higher elements form negatively charged anions according to their group number [8 minus Group Number] by gaining electrons. Anions are larger than the neutral atoms since they gain valence electrons. [See figure below]. Ionic compounds have an electronegativity differences from 1.8. [See Electronegativity and Periodic Trends Chart Reference]

Group 5A metals form 3- charges [8 – 3 = 5] Group 6A nonmetals form 2- charges [8 – 2 = 6] Group 7A nonmetals form 1- charges [8 – 1 = 7] Group 8A elements have a full valence shell and do not readily form ionic or molecular compounds.

Neutral atoms and cations Neutral atoms and anions

Metallic Compounds

When metals combine with each other, the bonding is usually described as metallic bonding. In this model, each metal atom donates one or more of its valence electrons to make an electron sea that surrounds all of the atoms, holding the substance together by the attraction between the metal cations and the negatively charged electrons.  Electronegativity differences are rarely considered for metals due to this principle. Different metals can be combined very easily to make alloys, which can have much different physical properties from their constituent metals. 

Steel is an alloy of iron [Fe] and carbon [C], which is much harder than iron itself. Chromium, vanadium, nickel, and other metals are also often added to iron to make steels of various types. 

Brass is an alloy of copper [Cu] and zinc [Zn] which is used in plumbing fixtures, electrical parts, and musical instruments. 

Bronze is an alloy of copper [Cu] and tin [Sn], which is much harder than copper; when bronze was discovered by ancient civilizations, it marked a significant step forward from the use of less durable stone tools.

Summary The figure below displays the arrangement of electrons within the three types of bonds. Hydrogen bonds are displayed here but will be discussed in a subsequent lesson. https://www.youtube.com/watch?v=OTgpN62ou24

https://www.angelo.edu/faculty/kboudrea/periodic/physical_metals.htm

Greater than 1.8...Polar Covalent0.5 - 1.79Covalent

Differences

Chart

3.2 3.13.0 2.92.8 2.7 2.6 2.52.4 2.3 2.2 2.1 2.0 1.9 1.81.7 1.61.5 1.41.3 1.2 1.1 1.0 0.90.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Electronegativity Difference

.3 2 3.1 3.02.9 2.82 .7 2.62.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5.4 11.3 1.2 1.1 1.0 0.9 0.80.7 0.6 0.5 0.4 0.3 0.2 0.1

Ionic

0.0 - 0.49