ELEMENTS, COMPOUNDS, AND MIXTURESAccording to the chemical classification of matter there are two main categories: Pure substances Mixtures

Lavoisier, a French chemist on the basis of quantitative studies classified pure substances into elements and compounds. He showed that when we heat mercuric oxide it changes into mercury and oxygen.

Mercuric oxide is a compound because it decomposes into simpler substances, whereas mercury and oxygen cannot be further decomposed into anything simpler as they are elements.ElementIt is defined as a substance that cannot be further reduced to simpler substances by ordinary processes. Elements are made up of particles/atoms of only one kind.For example: Hydrogen and oxygen. There are 114 elements known. Out of these 92 of them occur in nature.Metals and non-metalsElements can be further divided into metals and non-metals.MetalsThey are generally solids with characteristics such as hardness, malleability, ductility high tensile strength, lustre and ability to conduct heat and electricity.For example: Copper, iron, zinc etc.Non-metalsThey are generally non-lustrous, brittle, poor conductors of heat and electricity.For example: Sulphur, phosphorus, nitrogen etc.MetalloidsThese elements have characteristics common to metals and non-metals.For example: Arsenic, tin, bismuth etc.CompoundIt is a pure substance that can be decomposed into simpler substances by some suitable chemical technique. A compound is formed by combination of two or more elements in a definite proportion.For example, water is a compound of hydrogen and oxygen elements present in the ratio of 1: 8.Properties of compounds A compound cannot be separated into its constituents by mechanical or physical means.

For example, if we bring a magnet near a sample of iron sulphide, the iron present in the iron sulphide cannot be separated.

Properties of a compound differ entirely from those of its constituent elements.For example, water is made up of hydrogen and oxygen. However, the properties of hydrogen and oxygen (both gases) are different from water (liquid). Hydrogen is combustible, oxygen is a supporter of combustion whereas water (made up of both hydrogen and oxygen) puts out a flame. Energy changes are involved in the formation of a compound. For example, iron and

sulphur reacts only when heat is supplied. The constituent elements in a compound are in a fixed proportion by weight. In water,

hydrogen and oxygen are present in a fixed ratio of 1:8 by weight. A compound is a homogenous substance. That is it is same throughout in properties and

composition. A compound has a fixed melting point and boiling point. For example, ice melts at 0oC.MixtureA mixture is a material containing two or more elements or compounds that are in close contact and are mixed in any proportion. The components of a mixture can be separated by physical means.For example, air, gun powder, etc.Properties of a mixture A mixture may be homogenous or heterogeneous. A homogenous mixture has a uniform

composition throughout its mass. For example, sugar or salt dissolved in water, alcohol in water, etc. A heterogeneous mixture does not have a uniform composition throughout its mass. There are visible sharp boundaries.

For example: Oil and water, salt and sand, etc. The constituents of a mixture can be separated by physical means like filtration,

evaporation, sublimation and magnetic separation. In the preparation of a mixture, energy is neither evolved nor absorbed. A mixture has no definite melting and boiling point. The constituents of a mixture retain their original set of properties. For example, sulphur

dissolves in carbon disulphide and a magnet attracts iron filings.Types of mixtures Matter  Mixture type  Example Solid  Solid mixture  Iron filings and sulphur

 Solid  Liquid mixture  Common salt and water

 Solid  Gas mixture  Air entrapped in soil Liquid  Gas mixture  Oxygen dissolved in water

 Gas  Gas mixture  Air containing hydrogen, oxygen, nitrogen, carbon dioxide etc.

 Liquid  Liquid mixture  Water and alcohol

Differences between mixtures and compounds Mixtures  Compounds A mixture can be separated into its constituents by physical processes (filtration, evaporation, sublimation, distillation)

 A compound cannot be separated into its constituents by physical processes. It can be separated by chemical means

 A mixture shows the properties of its constituents

 A compound has a new set of properties different from its constituents

 Composition of a mixture varies and the constituents are present in any proportion by weight. It does not have a definite formula

 The composition of a compound is fixed and the constituents are present in fixed proportions by weight. It has a definite formula

 The constituents do not react chemically, thus no energy changes take place

 Chemical reactions take place and energy changes in the form of heat and light are involved

 A mixture does not have a fixed melting point and boiling point Examples: air, sand and salt

 A compound has a fixed melting point and boiling point Examples: H2O (water), FeS (iron sulphide)

 Water is a compound and not a mixture The components hydrogen and oxygen cannot be separated by physical methods such as

filtration, evaporation. Hydrogen and oxygen are present in a fixed proportion of 1: 8. Energy changes accompany the formation of a compound i.e., heat and light are given

out. Properties of water are entirely different from the constituents, hydrogen and oxygen. The boiling point of water is 100oC at 76 cm Hg i.e., one atmospheric pressure.

Let us, look at all these topics deeply.ELEMENT:An element is a substance made of only one atom and cannot be broken down.A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.[1] 

Common examples of elements are hydrogen, nitrogen, and carbon. In total, 117 elements have been observed as of 2007, of which 94, i.e. plutonium and below, occur naturally on Earth. Elements with atomic numbers greater than 82 (i.e,. bismuth and those above), are inherently unstable and undergo radioactive decay. In addition, elements 43 and 61 (technetium and promethium) have no stable isotopes, and also decay. However, the unstable elements up to atomic number 94 with no stable nuclei are found in nature as a result of the natural decay processes of uranium and thorium.[2] 

All chemical matter consists of these elements. New elements are discovered from time to time through artificial nuclear reactions. 

The term 'elements' (stoicheia) was first used by the Greek philosopher Plato in about 360 BC, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a rudimentary treatise on chemistry. Plato assumed that the minute particle of each element had a special geometric shape: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).[3] 

Tetrahedron (fire) Octahedron (air) Icosahedron (water) Cube (earth) 

Adding to the four elements of the Greek philosopher Empedocles, in about 350 BC, Aristotle also used the term "element" and conceived of a fifth element called "quintessence", which formed the heavens. Aristotle defined an element as: 

Element - one of those bodies into which other bodies can be decomposed and which itself is not capable of being divided into other.[4] COMPOUNDS:Compounds are groups of two or more elements that are bonded together. There are two main types of bonds that hold those atoms together, covalent and electrovalent/ionic bonds. Covalent compounds happen when the atoms share the electrons, and ionic compounds happen when electrons are donated from one atom to another. 

We talked about compounds and molecules in the matter tutorials. When we discuss phase changes to matter, physical forces create the changes. When we talk about compounds, bonds are built and broken down by chemical forces. Physical forces (unless you're inside of the Sun or something extreme) cannot break down compounds. Chemical forces are forces caused by other compounds or molecules that act on substances. (A Physical force would crack a solid, but the molecules would remain).

There are millions of different compounds around you. Chances are everything you can see is one type of compound or another. When elements join and become compounds, they lose their individual traits. Sodium alone is very reactive. But when sodium and chlorine combine, they form a non-reactive substance called sodium chloride (Salt, NaCl). The compound has none of the traits or the original elements. The new compound is not as reactive as the original elements. It has a new life of its own. How to distinguish a compound from elements?It is really easy to identify a mixture when it's a formula and if it's to different colored substances. In a formula a Mixture will be joined by a plus sign. When you are actually working with two substances look for the difference between the two, take sulfur and Iron for example, you can see the little yellow speects, so you know right away that it is a mixture. A pure substance you can't just look at it a know it's compound or an element you have to find out if it's homogenous( you can only see one substance) or is it's Heterogenous( you can see more than one) these two you can just look at it and see if it's one or the other. Milk would be an example of homogeneous because you can only see the white nothing else. Sulfur and iron would be an example of heterogeneous because you can see more than one substance(even though Sulfur and Iron together form a mixture). In a elements case you need to look at the Formula it's in like Ne would be an element because it's only one substance. Also if it was Ne2 it still would be one but it's proper name would be a diatomic element but still considered an element. A compound can always be

identified by it's formula it will have to element together without a plus sign in between remember that is a mixture. (Or)An element has only one kind of atom, while compounds have two or more types of atoms. Also, compounds can be broken down further, while elements cannot. (Or) An element, is a pure substance that can not be broken down by chemical means. a compound, is a pure substance that can be broken down by chemical means. by knowing those two things a scientist can distinguish between the two. 

Elements:- 1. carbon  2. aluminum  Compounds:- 1. sodium chloride  2. carbon monoxideMIXTURES:-Mixture BasicsMixtures are absolutely everywhere you look. Mixtures are the form for most things in nature. Rocks, air, or the ocean, they are just about anything you find. They are substances held together by physical forces, not chemical. That statement means the individual molecules enjoy being near each other, but their fundamental chemical structure does not change when they enter the mixture. 

When you see distilled water, it's a pure substance. That fact means that there are just water molecules in the liquid. A mixture would be a glass of water with other things dissolved inside, maybe salt. Each of the substances in that glass of water keeps the original chemical properties. So, if you have some dissolved substances, you can boil off the water and still have those dissolved substances left over. Because it takes very high temperatures to boil salt, the salt is left in the container. 

Mixtures are EverywhereThere are an infinite number of mixtures. Anything you can combine is a mixture. Think of everything you eat. Just think about how many cakes there are. Each of those cakes is made up of a different mixture of ingredients. Even the wood in your pencil is considered a chemical mixture. There is the basic cellulose of the wood, but there are also thousands of other compounds in that pencil. 

Solutions are also mixtures. If you put sand into a glass of water, it is considered to be a mixture. You can always tell a mixture because each of the substances can be separated from the group in different physical ways. You can always get the sand out of the water by filtering the water away. A solution can also be made of two liquids. Even something as

simple as bleach and water is a solution. Problems on Mixtures:In order to solve problems involving mixture, it is necessary to 1) Solve one variable equations involving: one step, two steps, multi-steps

2) Snalyze and understand the problem 3) Srite and solve an equation for the problem Even though there are two different types of mixes, the process for solving them is the same. 1) Dry mixture created from two differently priced components such as two types of candy or two types of nuts. 2) Liquid mixture of a specific strength made from two or more solutions having differing concentrations. Suppose the owner of a candy store mixes two types of candies. She decides to create a 20-pound mixture of raspberry-flavored gumdrops and cherry-flavored jelly beans. The gumdrops sell for $0.95 per pound and the jelly beans sell for $1.20 per pound. She plans to sell the mix for $1.10 per pound. How many pounds of each candy should she use in her mix? First, since two quantities are to be mixed together to produce one mixture, we need to recognize that we will set up an equation that shows the following: Total cost of gumdrops plus total cost of jelly beans equals the total cost of mixture. To arrive at the equation, it is typically helpful to use a table illustrating the problem such as the following: 

Type of Candy Cost of Candy(unit price)

Amount of Candy(in pounds)

Total Cost(in dollars)

gumdrops

jelly beans

mixture The first column shows the types of candy involved, cost is displayed in the second column, amount of each type of candy is listed in the third column, and the fourth column is the product of each cost and each amount for each type of candy. The total cost of the mixture is found by multiplying the cost of each type candy times the amount of each type of candy used in the mixture. The total cost column will be used to write the equation. The candy store owner knows that she wants the total amount of the mixture of candy to be 20 pounds. However, she does not know how many pounds of each type to mix. That is the objective of the problem. So in the “Amount of Candy” column we will use x to represent the amount of gumdrops. Then the “total pounds of candy minus x” will represent the amount of jelly beans: (20 – x). The last column demonstrates that the price of each type candy multiplied times the amount of each type candy represents the total cost of each type candy. The last column is what we use to write the equation. Remember: Total cost of gumdrops plus total cost of jelly beans equals the total cost of mixture. So, using the information in the last column: 

 We are ready to solve the equation to find the amount of each type of candy the store owner should use in her mixture. 

First distribute to remove parenthesesNow multiply the equation by 100Solve for x

pounds 

Since x represents the amount of gumdrops to be used in the mixture the candy store owner will use 8 pounds of gumdrops. From column three of the table, you can see that the amount of jelly beans to be used is (20 - x). Substituting 8 for the x, we see that the store owner needs to use (20 - 8) which is 12 pounds of jelly beans to create the desired mix. We have now learned the candy store owner will mix 8 pounds of raspberry-flavored gumdrops that cost $0.95 per pound and 12 pounds of cherry-flavored jelly beans that cost $1.20 per pound to create a mixture of 20 pounds of candy that sells for $1.10 per pound. Here are 2 questions based on this topic.1. A local grocer has decided to mix 100 pounds of cashews and almonds for a holiday special. Cashews typically cost $8 per pound and almonds cost $3 per pound. How many pounds of each type of nut must he mix to obtain a mixture that will cost his customers $5 per pound?

Solution: We combine the costs of the cashews and almonds and set that equal to the total cost of the mixture.

Type of Nut Cost of Nut(unit price)

Amount of Nuts(in pounds)

Total Cost(in dollars)

cashews

almonds

mixture

  

 pounds 

To find the number of pounds of almonds, substitute 40 for p and simplify. almonds = (100 - p)almonds = (100 - 40) almonds = 60 pounds Summary: 

The answer is that the grocer must mix 40 pounds of cashews that cost $8 per pound and 60 pounds of almonds that cost $3 per pound to create of mixture of cashews and almonds that will be sold for $5 per pound. The following are some common errors you might have made:

A. If you made an error in setting up the equation, by adding p to 100 rather than subtracting it from 100, you would have had the equation   which would give you an answer of p = 18.2 pounds of cashews. You would then have found (100 + p) to be 118.2 pounds of almonds. However, there can only be 100 pounds of mixed nuts, so your solution would be unreasonable. 

B. If you made an error in setting up the table, by placing 100 in the almonds section of the “Amount of Nuts” column and then subtracting p from the 100 in the “Total Cost” column of the table, you would have had thisequation  which would give you an answer of p = 18.2 pounds of cashews. You would then have found that 100 pounds of almonds mixed with 15.4 pounds of cashews equals 84.6 pounds of mixed nuts. The amount of almonds used to mix would be larger than the total amount of nuts in the mix. That would not be reasonable.

2. A chemist needs a 40% solution of alcohol. He plans to mix 3 liters of a 60% solution with a 25% solution. How many liters of the 25%solution must we mix with the 3 liters of the 60% solution to obtain the desired 40% solution of alcohol?

Solution: Set up and solve the equation obtained from the information in the table:

 Step One: Set up a table to gather, organize, and display the information in the problem. We let p represent the number of pounds of cashews to be included in the mixture. 

Type of Nut Cost of Nut(unit price)

Amount of Nuts(in pounds)

Total Cost(in dollars)

cashews

almonds

mixture Step Two: Set up an equation using the information in the table. Step Three: Solve the equation.

  

  

liters Summary: 

The answer is that the chemist must mix 4 liters of a 25% solution with the 3 liters of the 60% solution to obtain the 40% solution desired. (Note: There will be 7 total liters of the 40% solution, but we were not asked to find the amount of the 40% solution.) The following are some common errors you might have made:

A. You might have written the equation  . After solving the equation, you would have found x = 4 liters. However, your answer would state that 4 liters of a 25% solution would be mixed with 1 liter of a 60%solution to obtain a 40% solution. You cannot have a negative number of liters. The answer would have been correct for an incorrect solution. 

B. You might have written the in column two of the table with the 25% solution rather than with the 60% solution. Then you would have the equation  . You would have obtained an answer of x = 2.3 liters. Checking the solution, you would find that the left side of the equation simplifies to 2.13 and the right sideof the equation simplifies to 2.12. Therefore the equation would not be a true statement.

VALENCY:-

Hydrogen is the simplest element. It has one electron. Its outer shell only holds two electrons. Let us use Hydrogen as a standard to see how other atoms combine with it. The table below lists the simplest compound of selected elements with Hydrogen. Valency can be simply defined as the number of Hydrogen atoms that an element can combine with. In the above table, Helium, Neon and Argon have a valency of 0. They do not normally form compounds.Lithium, Sodium and Potasium have a valency of 1 because they combine with one Hydrogen atom. Beryllium, Magnesium and Calcium all have a valency of 2: they combine with two Hydrogen atoms. Note that the valences of all these atoms are equal to the number of outer electrons that these elements have.

Boron and Aluminium combine with three Hydrogen atoms - their valences are 3 - and they have three outer electrons.

Carbon and Silicon combine with four Hydrogen atoms. The valency of these elements is 4. It will come as no surprise that they both have four outer electrons. What about Nitrogen and Phosphorus? They have five outer electrons. But they normally only combine with three Hydrogen atoms. Their valences are 3. Note that 3 is 5 less that 8. These atoms are three electrons short of a full shell. Please note that both Nitrogen and Phosphorus can also have a valency of 5. Some atoms are capable of having more than one valency. That will confuse the issue so I will talk of normal valency.

Now to Oxygen and Sulphur. Both have six outer electrons. Six is two short of a full shell. Their normal valences are 2 and they combine with two atoms of Hydrogen. Water is H2O! Sulphur can also have a valency of 6 (or even 4) in some of its compounds.

Finally, Fluorine and Chlorine - seven outer electrons. This is one short of a full shell. They both combine with a single Hydrogen atom and their normal valences are 1.

As a side note, Chlorine can also have valences of 3, 5 and 7. The reasons are well beyond the scope of this introductory essay.

The rules above can be summarised as follows:

The normal valency of an atom is equal to the number of outer electrons if that number is four or less. Otherwise, the valency is equal to 8 minus the number of outer electrons.

The atoms with full electron shells (Helium, Neon, Argon) are chemically inert forming few compounds. The atoms don't even interact with each other very much. These elements are gases with very low boiling points.

The atoms with a single outer electron or a single missing electron are all highly reactive. Sodium is more reactive than Magnesium. Chlorine is more reactive that Oxygen. Generally speaking, the closer an atom is to having a full electron shell, the more reactive it is. Atoms with one outer electron are more reactive than those with two outer electrons, etc. Atoms that are one electron short of a full shell are more reactive than those that are two short.

The next two sections will discuss exactly how atoms combine together.