English Resume: Compare The Element

Compare the Element

Objective:

·         Exploring element and compounds

·         Comparing element on the periodic table

Vocabulary:

·         Element

·         Compound

·         Matter

·         Periodic table

·         Compare

·         Contrast

Background:

All known substances can be classified as solids, liquids, gases, or plasma. In addition, a fifth state of matter, the Bose-Einstein condensate has been discovered recently. However, it is not stable at normal earth conditions. Likewise, although plasma is the most abundant state of matter in the Universe, it is not common on the Earth under normal conditions, except for lightning. Most matter that students are familiar with will therefore be in a solid, liquid, or gaseous state.

An element is a pure substance that cannot be decomposed into simpler substances by normal chemical means. There are 109 different elements. Ninety of these are naturally occurring; the rest have been created in laboratories. Elements 110 and 118 are still being researched on. There will be more elements as technology can identify them. A symbol is used to represent the full name of an element. For example, H represents hydrogen; O represents oxygen, and Al represents aluminum. Sometimes the Latin name for an element is used as the basis for its symbol, for instance K represents potassium (kalium in Latin).

Three subatomic particles compose elements: protons, neutrons, and electrons. Protons, which have an electrical charge of +1, and neutrons, which have a neutral charge, make up the nucleus of an element. This nucleus is surrounded by a "cloud" of electrons, each of which as a charge of -1. The electrons spin around the nucleus in what are called orbits or shells. Each of the orbits can contain a set number of electrons. For instance, the first orbital from the nucleus has 2 electrons, the second has 8, the third has 8, the 4th has 16 and the fifth has 32, and so on. Each shell may not be full, depending on the number of electrons in the element, and the inner shells fill before the outer shells fill. Sodium, for example, has 11 electrons, which are located in the first, second, and third shells (2+8+1.)

An element has a uniform composition. Different elements may join together; these combinations are called compounds. A compound can be separated into its component elements by chemical means. For example, common table salt is a compound made of two elements: sodium and chlorine. Table salt can be broken down into sodium and chlorine by mixing it with water. However, sodium and chlorine cannot be easily broken down into any simpler forms.

Five Reaction Chemistry Paradigms

Each of the five reaction chemistries can be considered to be a paradigm, where a paradigm is a particular theoretical framework or way of thinking. The result is that it can be difficult to think in terms of more than one of the five reaction chemistries at the same time.

Consider the hydride ion, H^–. The hydride ion is a Lewis base and as such the the hydride ion can be qualitatively compared with other nucleophilic and proton abstracting Lewis bases:

We can ask questions such as "is the hydride ion a good proton abstractor, is it a good nucleophile and does it ever act as a spectator ion?" When asking questions like these we can compare the hydride ion with other Lewis bases such as ammonia, dialkyl ethers, fluoride ion and hydroxide ion. (Note that the hydride ion is not congeneric with these other Lewis bases.)

The hydride ion, H^–, is also a reducing agent and it can be compared with other reducing agents such as the electron, electron donating metals and electron donating metal ions:

But, the set of all Lewis bases cannot be compared with the set of all reducing agents as illustrated by a Venn diagram:

Of the species above, only the hydride ion is both a Lewis base and a reducing agent. While it is possible to compare and contrast Lewis bases with other Lewis bases, and it is possible to compare and contrast reducing agents with each other, it is not possible to compare and contrast the set of Lewis bases and the set of reducing agents at the same time.

Likewise,

• The proton, H⁺, is a Lewis acid and an oxidising agent.

• Dioxygen, O2, is a diradical and an oxidising agent.

• Photochemical methods can convert triplet diradicals into singlet diradicals.

• The benzene radical cation, [C6H6]^+•, is both a radical and a Lewis acid.

• Photochemical and redox methods can be used to produce radicals.

There are many examples like this in reaction chemistry space.