Mixtures, elements, solutions and compounds

Wan Wei Ren

What are elements? The most fundamental substances from which

all material things are constructed. The smallest particle that retains the

properties of an element is an atomAn atom is a basic unit of matter consisting of a

dense, central nucleus surrounded by a cloud of negatively charged electrons.

The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.

What are elements?

There are 117 elements that we are aware of till date.

Most of those elements are rather rare. Only about 10 elements make up 99% of

everything in the Earth’s crust. Elements can be classified into the periodic

table.

Periodic table

What is a periodic table?

The most important chemistry reference there is. 

Elements are arranged left to right and top to bottom in order of increasing atomic number.  Order generally coincides with increasing atomic mass

The different rows of elements are called periods and elements that lie in the same column on the periodic table are called a group

Period

In the periodic table of the elements, elements are arranged in a series of rows so that those with similar properties appear in vertical columns.

Elements of the same period have the same number of electron shells; with each group across a period, the elements have one more proton and electron and become less metallic. This arrangement reflects the periodic recurrence of similar properties as the atomic number increases.

Period

Seven periods of elements occur naturally on Earth. There is a period 8, which includes elements which may be synthesized after 2010

The first period contains fewer elements than any other, with only two, hydrogen and helium. They therefore do not follow the octet rule.

Period 2 elements involve the 2s and 2p orbitals. They include the biologically most essential elements besides hydrogen: carbon, nitrogen, and oxygen

All period three elements occur in nature and have at least one stable isotope. All but the noble gas argon are all essential to basic geology and biology

Period

Period 4 includes the biologically essential elements potassium and calcium, and is the first period in the d-block with the lighter transition metals. These include iron, the heaviest element forged in main-sequence stars and a principal component of the earth, as well as other important metals such as cobalt, nickel, copper, and zinc. Almost all have biological roles.

Period 5 includes the important metals silver and tin and the biologically important element iodine.

Period 6 is the first period to include the F block, with the lanthanides (rare earth elements), and includes the heaviest stable elements. Many of these heavy metals are toxic and some are radioactive, but platinum and gold are largely inert.

Period and Row

All elements of period 7 are radioactive. This period contains the heaviest element which occurs naturally on earth, uranium. Most of the subsequent elements in the period have been synthesized artificially. Whilst some of these (e.g. plutonium) are now available in tonne quantities, most are extremely rare, having only been prepared in microgram amounts or less. Some of the later elements have only ever been identified in laboratories in quantities of a few atoms at a time.

Elements in a group have similar configurations of the outermost electron shells of their atoms: as most chemical properties are dominated by the orbital location of the outermost electron. There are three conventional ways of numbering: One using Arabic numerals, and two using Roman numerals.

Compounds

Pure substances that are made of two or more kinds of elements, combined together in fixed proportions.

Properties of compounds are different from those of an individual elements involved.

A particular compound always has a specific atom ratio and a specific percentage by mass of each element in the compound.

Compounds

Compounds can be separated into simpler substances by chemical reactions.

Water can be broken down into hydrogen and oxygen by passing an electric current through it (Electrolysis) . Electrolysis is a method of using an electric current

to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic cell.

Some common compounds

Name of compound

Composition Comparison of properties

Table salt Sodium and Chlorine

Sodium is a metal while Chlorine is a poisonous gas

Ammonia Nitrogen and Hydrogen

The elements are harmless, but Ammonia has a pungent smell

Some common compounds

Name of compound

Composition Comparison of properties

Ethyl alcohol Carbon, Hydrogen, Oxygen

Hydrogen and Oxygen are gases while Carbon is a black solid

Hydrogen Sulfide Hydrogen and Sulfur

Hydrogen is an odourless gas while Sulfur is a pale yellow solid

Mixtures

Any sample of matter can be classified as either a pure substance can be either a pure substance and a mixture.

The composition of a mixture may vary. A mixture still retains the properties of its components. The components of a mixture are not chemically

combined together. A mixture can be separated into its components

through physical means There are two types of mixtures ~homogeneous or

heterogeneous.

Homogeneous mixture

A homogenous mixture is the same throughout. A solution is a homogenous mixture; it has

uniform composition and appearance throughout.

Solids such as sugar and salt dissolve in water to make solutions.

Almost all metal alloys, such as bronze, brass and steel, are really solutions of one solid dissolved in another solid; therefore they are homgenous.

Heterogeneous mixture

A heterogeneous mixture does not have uniform properties throughout.

The composition of one part (or phase) differs from the composition of another part (or phase).

An oil-and-water mixture is an example of a heterogeneous mixture.

What is a solution?

An intimate homogeneous mixture of two or more substances.

The substances can be in the form of atoms (such as copper and zinc in brass), ions (such as sodium chloride dissolved in water), or molecules (such as table sugar dissolved in water).

Components of a solution

The substance being dissolved (or the substance with the lessser amount) is called the solute.

The component whose physical state is retained (or the substance present in greater amount) is called the solvent.

Solutions formed are not always liquid, for example air, which is a gaseous solution of oxygen, argon, water vapour and other gases in nitrogen

Sources

http://ion.elte.hu/~akos/orak/atfsz/atom/rutherford_atom11.pdf

http://www.wadsworthmedia.com/marketing/sample_chapters/156253629X_ch08.pdf

http://cococubed.asu.edu/papers/wallerstein97.pdf

http://www.nrel.gov/hydrogen/pdfs/40605.pdf