Answer:
An element is the simplest form of matter that cannot be split into simpler substances or built from simpler substances by any ordinary chemical or physical method. There are 110 elements known to us, out of which 92 are naturally occurring, while the rest have been prepared artificially. Elements are further classified into metals, non-metals, and metalloids.
Table 2.11.1: Characteristic properties of metallic and non-metallic elements:
Distinguishing luster (shine)
Non-lustrous, various colors
Nonmetals
Elements that tend to gain electrons to form anions during chemical reactions are called non-metals. These are electronegative elements. They are non-lustrous, brittle and poor conductors of heat and electricity (except graphite). Non-metals can be gaseous, liquids or solids.
Physical Properties of nonmetals:
Physical State: Most of the non-metals exist in two of the three states of matter at room temperature: gases (oxygen) and solids (carbon).
Non-Malleable and Ductile: Non-metals are very brittle, and cannot be rolled into wires or pounded into sheets.
Conduction: They are poor conductors of heat and electricity.
Luster: These have no metallic luster and do not reflect light
Conductivity: Poor conductors of heat and electricity
Melting and Boiling Points: The melting points of non-metals are generally lower than metals
Seven non-metals exist under standard conditions as diatomic molecules:
H2(g)
N2(g)
O2(g)
F2(g)
Cl2(g)
Br2(l)
I2(l) (volatile liquid - evaporates readily)
Chemical Properties of Nonmetals
Non-metals have a tendency to gain or share electrons with other atoms. They are electronegative in character.
Nonmetals, when reacting with metals, tend to gain electrons (typically attaining noble gas electron configuration) and become anions:
Nonmetal + Metal -> Salt
3Br2(l)+2Al(s)→2AlBr3(s)(2.11.4)
Compounds composed entirely of nonmetals are molecular substances (not ionic).
They generally form acidic or neutral oxides with oxygen that that dissolve in water react to form acids:
Physical Properties of Metalloids
State: They are all solid at room temperature.
Conduction: Some metalloids, such as silicon and germanium, can act as electrical conductors under the right conditions, thus they are called semi-conductors.
Luster: Silicon for example appears lustrous, but is not malleable or ductile (it is brittle - a characteristic of some nonmetals). It is a much poorer conductor of heat and electricity than the metals.
Solid Solutions: They can form alloys with other metals.
Chemical Properties of Metalloids
Their physical properties tend to be metallic, but their chemical properties tend to be non-metallic.
The oxidation number of an element in this group can range from +3 to -2, depending on the group in which it is located.
Trends in Metallic and Nonmetallic Character
Metallic character is strongest for the elements in the leftmost part of the periodic table, and tends to decrease as we move to the right in any period (nonmetallic character increases with increasing ionization values). Within any group of elements (columns), the metallic character increases from top to bottom (the ionization values generally decrease as we move down a group). This general trend is not necessarily observed with the transition metals.
2.10: Electron Affinities 2.12: Electronegativity
Recommended articles
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2.2: Electron Configurations
2.3: Electron Configurations and the Periodic Table
2.4: Development of the Periodic Table
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