Section 7.1

Representative Elements:
• Groups 1A through 8A
• Diverse range of physical and chemical properties.
o Metals and nonmetals
o Some are highly reactive and some hardly react at all.
o Solids, liquids, and gases at room temperature
• Elements in the same group on the periodic table have the same amount of valence electrons, therefore, they have similar physical and chemical properties. Representative elements have valence electrons in the s or p orbitals.
• Ionization energy:
o As atomic radius increases, or the atom gets larger, the ionization energy decreases.
o Lower ionization energy makes it easier for element to lose electrons.
o Metals tend to lose electrons, nonmetals gain electrons
o Higher the ionization energy in a nonmetal, the more reactive it is, while in metals, the elements are more reactive with lower ionization energy.
o Thus, for a group of metals, reactivity increases as the atomic number increases, and for a group of nonmetals, reactivity decreases as the atomic number increases.

Diagonal Relationships:
• Some elements in period 2 have more in common with the period 3 elements than the period 3 element in their own group. For example, period 2 element boron has more in common with period 3 element silicon than aluminum has with silicon.

• 1 valence electron
• Placed in group 1A, but is more similar to the nonmetals in group 7A.
• Has both metallic and nonmetallic properties, so it is not considered part of any group because of its one valence electron.
• Was discovered in 1766 by Henry Cavendish.
o Cavendish called it “flammable air” because it burned when ignited in air.
• It was later given the name “hydrogen” in 1783 by Antoine Lavoisier because water is formed when it combines with oxygen.
• It is a gas that is colorless, odorless, and lighter than air.
• The universe contains more than 90% hydrogen by mass
• 3 naturally occurring isotopes
o Protium
 Majority of hydrogen (99.985%)
 No neutrons
o Deuterium
 Makes up 0.015% of hydrogen
 1 neutron
o Tritium
 2 neutrons
 Radioactive
 Produced when cosmic rays bombard water in the atmosphere.
• Physical properties of isotopes differ slightly because of differences in atomic mass.
• When hydrogen acts like a nonmetal, it gains an electron and the stable configuration of helium.
• When reacting with a nonmetal such as oxygen, it becomes more like a metal and loses an electron.
o Forms hydrogen ion H+
 Has a nucleus with only a single proton
• Hydrogen can be produced in a lab when a metal reacts with an acid or when it is separated from oxygen in water with the use of electricity.
• Major industrial use is production of ammonia from nitrogen and hydrogen gases
• Also used to convert liquid vegetable oils into solid fats like shortening.

*Source: Glencoe Science. Chemistry: Matter and Change. 179-180.

Group 1A: Alkali Metals:

Alkali comes from the Arabic term al-qili meaning "ashes of the saltwort plant".
Group 1A metals react with water to form Alkaline solutions.

external image alkalimetals.PNG

Lithium is the lightest Alkaline metal found in water,soil, and rocks. It is also least reactive, and its compounds are less likely to disolve in water.
Lithium and Magnesium are more closely related than the other Alkaline matals.
Lithium's atomic radius is 152 pm and has an ionic radius of 76 pm.
Magnesium's atomic radius is 160 pm and has an ionic radius 72 pm.
Similar physical properties lead to similar chemical properties and that is why lithium and magnesium have a diagonal relationship.

Sodium and Potassium are the most abundant alkali metals. Many biological functions are controlled by sodium and potassium ions, which are found in humans and most vertebrates. Potassium ions are the more common positive ions found within cells. Sodium ions are the more common positive ions found in the fluid that surrounds cells.

A common compound of sodium is: sodium chloride or table salt. The compound of potassium chloride is a salt substitute for those who can't take in a lot of sodium chloride. Potassium compounds are also used in plant fertilizers wich helps with the growth and developement. Postassium nitrate is used as an explosive for large firework displays.

Other Alkali Metals : Rubidium, cesium, and francium are the most reactive alkali metals and have very little commercial use. Rubidium has a melting point of 40°C, melting on a hot and if exposed to air it will burst into flames. Francium is the most reactive alkali metal and is a rare radioactive element. Cesium occurs in lepilodite, pollucte and in other sources.

Group 2A: Alkaline Earth Metals: Old time alchemists classified solids that did not melt in fire as "earths". Elements in Group 2A form compounds with oxygen, called oxides, that qualify as "earths" by this definition, with the exception of berllium oxide, this oxide produces alkaline solutions when it reacts with water.