Jewelweed, a flowering plant, has seed pods that burst open when touched and forcefully eject their seeds. these structures are favorable because they a. can cause genetic changes to occur. b. prevent germination within the seed pod. c. aid in the dispersal of the species. d. attract insects that aid in pollination.

Explanation:

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

2.1: Many-Electron Atoms

2.2: Electron Configurations

2.3: Electron Configurations and the Periodic Table

2.4: Development of the Periodic Table

2.5: Effective Nuclear Charge

The calculation of orbital energies in atoms or ions with more than one electron (multielectron atoms or ions) is complicated by repulsive interaction...

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