Substance and mixture

Examples of pure chemical substances. From left to right: the elements tin (Sn) andsulfur (S), diamond (an allotrope of carbon),sucrose (pure sugar), and sodium chloride(salt) and sodium bicarbonate (baking soda), which are both ionic compounds.

A chemical substance is a kind of matter with a definite composition and set ofproperties.^[48] A collection of substances is called a mixture. Examples of mixtures are air and alloys.^{[citation needed]}

Chemistry, a branch of physical science, is the study of the composition, properties and behavior of the matter. As it is a fundamental component of matter, the atom is the basic unit of chemistry. Chemistry is concerned with atoms and their interactions with other atoms, with particular focus on the properties of the chemical bonds formed between species. Chemistry is also concerned with the interactions between atoms or molecules and various forms of energy (e.g. photochemical reactions, oxidation-reduction reactions, changes in phases of matter, separation of mixtures, properties of polymers, etc.).
Chemistry is sometimes called "the central science" because it bridges other natural sciences like physics, geology and biology with each other. Chemistry is a branch of physical science but distinct from physics.
The etymology of the word chemistry has been much disputed. The genesis of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several millennia in various parts of the world, particularly the Middle East.

Characteristics of Atom

All matter consists of particles called atoms. This is a list of the basic characteristics of atoms:

• Atoms cannot be divided using chemicals. They do consist of parts, which include protons, neutrons, and electrons, but an atom is a basic chemical building block of matter.

• Each electron has a negative electrical charge.

• Each proton has a positive electrical charge. The charge of a proton and an electron are equal in magnitude, yet opposite in sign. Electrons and protons are electrically attracted to each other.

• Each neutron is electrically neutral. In other words, neutrons do not have a charge and are not electrically attracted to either electrons or protons.

• Protons and neutrons are about the same size as each other and are much larger than electrons. The mass of a proton is essentially the same as that of a neutron. The mass of a proton is 1840 times greater than the mass of an electron.

• The nucleus of an atom contains protons and neutrons. The nucleus carries a positive electrical charge.

• Electrons move around outside the nucleus.

• Almost all of the mass of an atom is in its nucleus; almost all of the volume of an atom is occupied by electrons.

• The number of protons (also known as its atomic number) determines the element. Varying the number of neutrons results in isotopes. Varying the number of electrons results in ions. Isotopes and ions of an atom with a constant number of protons are all variations of a single element.

• The particles within an atom are bound together by powerful forces. In general, electrons are easier to add or remove from an atom than a proton or neutron. Chemical reactions largely involve atoms or groups of atoms and the interactions between their electrons.

Chemistry of fireworks colour

Creating firework colors is a complex endeavor, requiring considerable art and application of physical science. Excluding propellants or special effects, the points of light ejected from fireworks, termed 'stars', generally require an oxygen-producer, fuel, binder (to keep everything where it needs to be), and color producer. There are two main mechanisms of color production in fireworks, incandescence and luminescence.

Incandescence

Incandescence is light produced from heat. Heat causes a substance to become hot and glow, initially emitting infrared, then red, orange, yellow, and white light as it becomes increasingly hotter. When the temperature of a firework is controlled, the glow of components, such as charcoal, can be manipulated to be the desired color (temperature) at the proper time. Metals, such as aluminium, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework.

Luminescence

Luminescence is light produced using energy sources other than heat. Sometimes luminescence is called 'cold light', because it can occur at room temperature and cooler temperatures. To produce luminescence, energy is absorbed by an electron of an atom or molecule, causing it to become excited, but unstable. When the electron returns to a lower energy state the energy is released in the form of a photon (light). The energy of the photon determines its wavelength or color.

Sometimes the salts needed to produce the desired color are unstable. Barium chloride (green) is unstable at room temperatures, so barium must be combined with a more stable compound (e.g., chlorinated rubber). In this case, the chlorine is released in the heat of the burning of the pyrotechnic composition, to then form barium chloride and produce the green color.Copper chloride (blue), on the other hand, is unstable at high temperatures, so the firework cannot get too hot, yet must be bright enough to be seen.

Quality

Pure colors require pure ingredients. Even trace amounts of sodium impurities (yellow-orange) are sufficient to overpower or alter other colors. Careful formulation is required so that too much smoke or residue doesn't mask the color. With fireworks, as with other things, cost often relates to quality. Skill of the manufacturer and date the firework was produced greatly affect the final display (or lack thereof).

Firework Colorants

Color	Compound
Red	strontium salts, lithium salts  lithium carbonate, Li2CO3 = red  strontium carbonate, SrCO3 = bright red
Orange	calcium salts  calcium chloride, CaCl2  calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5
Gold	incandescence of iron (with carbon), charcoal, or lampblack
Yellow	sodium compounds  sodium nitrate, NaNO3  cryolite, Na3AlF6
Electric White	white-hot metal, such as magnesium or aluminum  barium oxide, BaO
Green	barium compounds + chlorine producer  barium chloride, BaCl+ = bright green
Blue	copper compounds + chlorine producer  copper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blue  copper (I) chloride, CuCl = turquoise blue
Purple	mixture of strontium (red) and copper (blue) compounds
Silver	burning aluminum, titanium, or magnesium powder or flakes

Balancing chemical equations

A chemical equation describes what happens in a chemical reaction. The equation identifies the reactants (starting materials) and products(resulting substance), the formulas of the participants, the phases of the participants (solid, liquid, gas), and the amount of each substance. Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products. The quantities are expressed as grams or moles.

It takes practice to be able to write balanced equations. There are essentially three steps to the process:

1. Write the unbalanced equation.
   • Chemical formulas of reactants are listed on the lefthand side of the equation.
   • Products are listed on the righthand side of the equation.
   • Reactants and products are separated by putting an arrow between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions.

2. Balance the equation.
   • Apply the Law of conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only onereactant and product.
   • Once one element is balanced, proceed to balance another, and another, until all elements are balanced.
   • Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

3. Indicate the states of matter of the reactants and products.
   • Use (g) for gaseous substances.
   • Use (s) for solids.
   • Use (l) for liquids.
   • Use (aq) for species in solution in water.
   • Write the state of matter immediately following the formula of the substance it describes.

Worked Example Problem

Tin oxide is heated with hydrogen gas to form tin metal and water vapor. Write the balanced equation that describes this reaction.

1. Write the unbalanced equation.

   SnO₂ + H₂ → Sn + H₂O

2. Balance the equation.

   Look at the equation and see which elements are not balanced. In this case, there are two oxygen atoms on the lefthand side of the equation and only one on the righthand side. Correct this by putting a coefficient of 2 in front of water:

   SnO₂ + H₂ → Sn + 2 H₂O

   This puts the hydrogen atoms out of balance. Now there are two hydrogen atoms on the left and four hydrogen atoms on the right. To get four hydrogen atoms on the right, add a coefficient of 2 for the hydrogen gas. Remember, coefficients are multipliers, so if we write 2 H₂O it denotes 2x2=4 hydrogen atoms and 2x1=2 oxygen atoms.

   SnO₂ + 2 H₂ → Sn + 2 H₂O

   The equation is now balanced. Be sure to double-check your math! Each side of the equation has 1 atom of Sn, 2 atoms of O, and 4 atoms of H.

3. Indicate the physical states of the reactants and products.

   To do this, you need to be familiar with the properties of various compounds or you need to be told what the phases are for the chemicals in the reaction. Oxides are solids, hydrogen forms a diatomic gas, tin is a solid, and the term 'water vapor' indicates that water is in the gas phase:

   SnO₂(s) + 2 H₂(g) → Sn(s) + 2 H₂O(g)

   This is the balanced equation for the reaction. 

Alphabetical list of elements

Here's a list of the chemical elements, arranged alphabetically according to IUPAC name:

Actinium

Aluminum 

Americium 

Antimony 

Argon

Arsenic 

Astatine 

Barium 

Berkelium 

Beryllium 

Bismuth 

Bohrium 

Boron 

Bromine 

Cadmium 

Calcium 

Californium

Carbon 

Cerium 

Cesium

Chlorine

Chromium 

Cobalt 

Copernicium 

Copper 

Curium 

Darmstadtium 

Dubnium 

Dysprosium

Einsteinium 

Erbium

Europium 

Fermium 

Flerovium

Fluorine 

Francium 

Gadolinium 

Gallium 

Germanium 

Gold 

Hafnium 

Hassium 

Helium 

Holmium 

Hydrogen

Indium 

Iodine

Iridium 

Iron

Krypton 

Lanthanum 

Lawrencium 

Lead 

Lithium 

Livermorium

Lutetium 

Magnesium 

Manganese

Meitnerium 

Mendelevium 

Mercury 

Molybdenum 

Neodymium 

Neon 

Neptunium 

Nickel 

Niobium 

Nitrogen 

Nobelium 

Osmium 

Oxygen

Palladium 

Phosphorus 

Platinum 

Plutonium 

Polonium 

Potassium 

Praseodymium

Promethium 

Protactinium 

Radium 

Radon 

Rhenium 

Rhodium 

Roentgenium 

Rubidium 

Ruthenium 

Rutherfordium 

Samarium 

Scandium 

Seaborgium 

Selenium 

Silicon 

Silver 

Sodium

Strontium 

Sulfur 

Tantalum 

Technetium 

Tellurium 

Terbium 

Thallium 

Thorium 

Thulium 

Tin

Titanium 

Tungsten 

Ununoctium

Ununpentium

Ununseptium

Ununtrium

Uranium 

Vanadium 

Xenon 

Ytterbium 

Yttrium 

Zinc 

Zirconium

States of matter

Matter occurs in four states: solids, liquids, gases, and plasma. Often the state of matter of a substance may be changed by adding or removing heat energy from it. For example, the addition of heat can melt ice into liquid water and turn water into steam.

Solids

• A solid has a definite shape and volume.
• Examples of solids include ice (solid water), a bar of steel, and dry ice (solid carbon dioxide).

Liquids

• A liquid has a definite volume, but takes the shape of its container.
• Examples of liquids include water and oil.

Gases

• A gas has neither a definite volume nor a definite shape.
• Examples of gases are air, oxygen, and helium.

Some introductory chemistry texts name solids, liquids, and gases as the three states of matter, but higher level texts recognize plasma as a fourth state of matter.

Plasma

• Plasma has neither a definite volume nor a definite shape.
• Plasma often is seen in ionized gases. Plasma is distinct from a gas because it possesses unique properties. Free electrical charges (not bound to atoms or ions) cause plasma to be electrically conductive. Plasma may be formed by heating and ionizing a gas.
• Stars are made of plasma. Lightning is plasma. You can find plasma inside fluorescent lights and neon signs.

Facts of Chemistry

1. Chemistry is the study of matter and energy and the interactions between them. It is a physical science that is closely related to physics, which often shares the same definition.

2. Chemistry traces its roots back to the ancient study of alchemy. Chemistry and alchemy are separate now, though alchemy still is practiced today.

3. All matter is made up of the chemical elements, which are distinguished from each other by the numbers of protons they possess.

4. The chemical elements are organized in order of increasing atomic number into the periodic table.The first element in the periodic table is  hydrogen

5. Each element in the periodic table has a one or two letter symbol. The only letter in the English alphabet not used on the periodic table is J. The letter q only appears in the symbol for the placeholder name for element 114, ununquadium, which has the symbol Uuq. When element 114 is officially discovered, it will be given a new name.

6. At room temperature, there are only two liquid elements. These are bromine and mercury.

7. The IUPAC name for water, H₂O, is dihydrogen monoxide.

8. Most elements are metals and most metals are silver-colored or gray. The only non-silver metals are gold and copper.

9. The discoverer of an element may give it a name. There are elements named for people (Mendelevium, Einsteinium), places (Californium, Americium) and other things.

10. Although you may consider gold to be rare, there is enough gold in the Earth's crust to cover the land surface of the planet knee-deep.

Quotes About Chemistry

The meeting of two personalities is like the contact of two chemical substances: if there is any reaction, both are transformed.

No, this trick won't work... How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?

Scientist believe in things, not in person.