Chemical Families:
Reference: Chapter 13, p. 367
Metals:
They make up the mojority of elements in the periodic table. Most are reactive and rarely exist in its elemental form. They are elements that tends to lose electrons easily in the presence of other substances. So, by definition, alkali and alkali earth elements are the most metallic.
1. Properties of metals:
a. The properties of metals are due to the metallic bond. The electrons in metals have a lot of freedom of movement within the different energy levels. This availability of electrons and close spaced energy levels of metals allow for easy movement of electrons. The electrons are spread throughout the crystal structure of the metal. These electrons are involved in the chemical bond and they can slide past each other and still remain bonded. The electrons are said ot be non-locallized in the metal.
b. The sliding of atomic layers gives metals malleability, the ability to be shaped without breaking, and ductility, the ability to be drawn into a wire. The movement of the outermost electrons is responsible for the good electrical and thermal conductivity of metals.
2. Examples of metals:
a) Alkali metals:
1. They are not found in nature in their elemental form because of their high reactivity. They are usually silvery, shiny, conduct electricity.
2. They form mostly ionic compounds, that will dissolve in water.
eg. Sodium reacts w/ water to form sodium hydroxide
eg. Sodium and potassium are important in the body in the nerve transmission.
In the body, there is a constant concentrtion within the body. The reason why someone who is exerting extreme physical activity gets cramps is because there is an imbalance of electrolytes. Balance of electrolytes is used for commercial products such as Gatorade.
b) Alkaline metal:
1. They are denser, harder and have higher melting point and boiling point than alkali metals.
2. They are less reactive than alkali metals.
3. Magnesium and calcium are the most common of the alkali earth metals. Magnesium alloys are common in sports equipment which requires light weight such as in bikes, backpack frames, and rackets. Magnesium burns to produce magnesium oxide. It is often used in fireworks. Magnesium hydroxide in water is known as milk of magnesia, an excellent antacid, and acts as a mild laxative.
Calcium carbonate is the main ingredient of limestone. It is only slightly soluble, but under the presence of carbon dioxide, it forms calcium hydrogen carbonate, which is a bit more soluble. In rainwater, there is a small amount of carbon dioxide dissolved in the water, it filters through the limestone and the rock is dissolved away. Calcium carbonate may be deposited as stalagtites and stalagmites. Ground water often contains dissolved calcium hydrogen carbonate and magnesium hydrogen carbonate. This is referred to as hardwater.
c) Aluminum:
1. This is the third most abundant element on earh
2. It is reactive, and it reacts with oxygen usually forming an oxide.
3. The process of purifying is usually costly. That is the reason why there is a strong push towards recycling aluminum.
4. It has low density, good conductivity, it forms a protective coating that will protect it .
5. Its alloy are strong, lightweight, workable, avaible for construction, and have numerous uses.
Transition Metals:
They are not as reactive as alkali metals. They are good conductors of heat and electricity. Except for zinc, the melting temperature for transition metals are quite high. Many aqueous solutions of transition metal compounds are colored. For exception of iron and titanium, the transition metals are not very abundant in Earth’s crust.
So, transition metals have the following properties: strength, high melting point, malleability, durability, and form colorful compounds.
Transition metals are harder than alkali metals since they have more electrons available for metallic bonding.
1. Copper:
Not reactive, and abundant in supply. Copper reacts with sulfuric acid to form copper sulfate, a blue solution characteristic of Cu2+ ions.
2. Silver:
Uses in the photographic industry. Photographic films contain gelatinous silver halides. Silver crystals form when exposed to light. The amount of crystal that forms depends on the amount of light being exposed to the film.
The Metalloids:
1. The Properties:
1. intermediate of metals and nonmetals
2. may form ionic or covalent compounds
3. under certain conditions, metalloids may conduct electricity, but do so very poorly. They are termed semiconductors.
2. Examples:
1. boron: boron carbide form crystals with structure similar to that of diamonds and are used for grinding, polishing. Boric acid is used as an antiseptic in eyewashes.
2. Arsenic: member of the “heavy metal poisons” family such as
lead, mercury,and cadmium, which have a strong affinity for sulfur.
Sulfur is present in enzymes present in cells. The reaction of
heavy metals and the sulfur in the enzyme severely alters the
reactions in cells.
3. Silicon: Most abundant element on earth in the form of silicon
dioxide.
The Non-Metals:
These are elements that have a strong tendency to accept electrons in the presence of other elements. When two non-metals form a compound, they tend to share the electrons in a covalent bond.
1. Nitrogen Family:
a) nitrogen: nitrogen gas is held together by a triple bond which is strong and very difficult to break. Therefore nitrogen gas is very unreactive. Nitrogen is widely used commercially as fertilizers.
b) Phosphorus: has many allotropic forms.
2. Oxygen Family:
a) Oxygen: vital for life in the process of cellular respiration.
b) sulfur: exists in many allotropic forms.
3. Halogens:
They are very rective. Each have a distinct color and will gain one electron to complete their outer energy level. All halogens form diatomic molecules. Fluorine is the most reactive of all elements.
4. Noble gases:
They are unreactive. Argon was the first noble gas to be discovered.
In 1962, Neil Bartlett was working with a extremely reactive compound platinum (VI) fluoride, and tried using it to react with xenon. The first compound formed with a noble gas was XePtF6
Reactivity trends in the periodic table
1. Reactivity of metals:
- metals usually lose electrons during a chemical reaction
REASONS FOR REACTIVITY TREND:
1. there is an decrease in ionization energy when move towards the left
and towards the bottom. This is related to an increase in atomic radii.
eg. Calcium vs. Potassium ( more reactive)
eg. Potassium ( more reactive) vs. Sodium
2. Reactivity of non-metals:
- Non-metals usually gain electrons in a chemical reaction.
- As you move right of periodic table, reactivity increases ( except for the noble gases )
REASONS FOR REACTIVITY TREND:
1. The reason is partially due to the atomic radius of the atoms. As we move towards the right, there is a decrease in atomic radius.
a) Electrons are attracted to the nucleus due to the attraction between the electrons and protons.
b) This attraction is referred as the nuclear charge of the atom.
c) The nuclear charge tends to increase as we go to the right since there is an increase in the number of protons, which causes a decrease in atomic radius.
2. All of this will create a slightly larger “attraction” between the electron gained and nucleus.
3. As we go down a column, the reactivity of non-metals decreases.
a) The reason is because there is an increase in atomic radius which makes attraction between the nucleus and the GAINED electron smaller compared to an atom with small radius.
Note: Fluorine has the smallest radius, therefore it has the largest nuclear attraction towards other electrons. It is, therefore, very reactive.