Why the sky is blue and the clouds are white?

Ever wondered why the sky is blue?
The sun is a large shiny star that sends light to all surrounding space.
Light can travel in a vacuum, and it travels to earth.
So, if the sun is sending white light, why the sky appear blue!
The light is an electromagnetic spectrum, electromagnetic wave, each wave travels from the sun with a different wavelength and different frequency.
The light coming from the sun contains all types of electromagnetic spectrum, such as; microwaves, infrared light, ultraviolet light, X-rays, gamma-rays, and visible light.
White light is a mixture of wavelengths, of the visible portion, of the electromagnetic spectrum (visible spectrum).
We see all the rainbow colors mixed as white light, but if we passed light through a prism, we will see rainbow colors.
Each color we see comprise a certain amount of energy, has a certain wavelength, and definite frequency.
When white light falls on your red T-shirt, your T-shirt absorbs all colors except for red. Your T-shirt reflects the red color, and you see your T-shirt in red.
A similar thing happens in the sky. When the white color coming from the sun interact with the atmosphere, the air particles absorb all visible colors except for blue.
Air particles scatter the blue color in all directions, this is why we see the sky in blue, and we see the scattered blue color.
But why the clouds appear white?
Clouds are made of water vapor, water vapor consists of large water molecules that scatter all colors.
We see these colors mixed as a white color, and the clouds appear white. Water molecules are transparent, but they are so large that they scatter all visible spectrum and appear white.
So why clouds sometimes appear gray?
The scattered light from the white clouds scatter in all directions, but on a rainy day, the water molecules at the bottom of the cloud become so dense to allow the light to pass, where the top part of the cloud scatter light. The clouds become dark from the bottom, and light from the top, and we see them in gray.
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Matter states and basic unit

The properties of water that depend on polarity: Cohesion and Adhesion of water

Water polarity: cohesion and adhesion of water

Water cycle and properties

What power the surface current?

              • Different temperatures cause different air pressures.

• The warmer the air the higher the pressure.

• Colder areas have low pressure.

• The difference in the pressure causes the wind to form.

• The air will move from high pressure and high temperature to lower pressure and low temperature.

• The air near the equator is hotter than the air near the poles. The air moves from the equator towards the poles creating a wind that pushes the surface of water creating the surface currents.

• So the sun is the main source that powers the surface currents.

What is the difference between mass and weight?

Mass and Weight

Although mass and weight are often mistaken to have the same meaning, mass and weight are different quantities.

Mass is a measure of the amount of matter in an object.

Weight is the force that gravity exerts on an object.
Mass does not depend on the location of the object, but weight does.
The mass of an apple is constant on earth or moon.
On the other hand, the weight is dependent on the location.
The weight of an apple (the force that pulls the apple) differs from a place to another.
The apple would weight only one-sixth on the moon than it does on earth because the gravity of the moon is one-sixth that of the earth.
You can measure the mass of any substance using a balance (the process of measuring mass is called weighing!!). The unit of mass is the kilogram or gram. The balance you use at home measures the mass.
The weight can be measured using a spring scale, and the unit of weight is Newton (kg m/s2)
Weight (W) = mass X gravitational acceleration (g=9.8m/s2).

How to separate mixture components?

Separating mixture components:

       Many different methods can be used to separate the components of a mixture from one another. 

1- Filtration, used to separate a heterogeneous solid-liquid mixture. The mixture is passed through a barrier with fine pores, such as filter paper. Copper sulfate, which is water-soluble, can be separated from sand by shaking with water. On filtration the sand remains on the paper and the copper sulfate solution passes through it.

2- Distillation, used to resolve a homogeneous solid-liquid mixture. The liquid vaporizes, leaving a residue of the solid in the distilling flask. The liquid is obtained by condensing the vapor. Distillation can be used to separate the components of a water solution of copper sulfate.

3- Chromatography, used to separate all kinds of mixtures. This method takes advantage of differences in solubility and/or extent of adsorption on a solid surface.

In gas-liquid chromatography, a mixture of volatile liquids and gases is introduced into one end of a heated glass tube. 

a. Inert solid: The tube is packed with an inert solid whose surface is coated with a viscous liquid. 

b. An non-reactive “carrier gas”: often helium, is passed through the tube. 

The components of the sample gradually separate as they vaporize into the helium or condense into the viscous liquid. Usually the more volatile fractions move faster and emerge first; successive fractions activate a detector and recorder. 

Homogeneous and Heterogeneous mixtures

The mixture:

A mixture contains two or more substances combined in such a way that each substance retains its chemical identity. When you shake copper sulfate with sand, the two substances do not react with one another. In contrast, when sodium is exposed to chlorine gas, a new compound, sodium chloride, is formed.

There are two types of mixtures:

1. Homogeneous or uniform mixtures are ones in which the composition is the same throughout. Another name for a homogeneous mixture is a solution, which is made up of a solvent, usually taken to be the substance present in largest amount, and one or more solutes. Most commonly, the solvent is a liquid, whereas solutes may be solids, liquids, or gases. Soda water is a solution of carbon dioxide (solute) in water (solvent). Seawater is a more complex solution in which there are several solid solutes, including sodium chloride; the solvent is water. It is also possible to have solutions in the solid state. Brass is a solid solution containing the two metals copper (67%– 90%) and zinc (10%–33%).

2. Heterogeneous or nonuniform mixtures are those in which the composition varies throughout. Most rocks fall into this category. In a piece of granite, several components can be distinguished, differing from one another in color.

Heterogeneous can be classified into:

a. Colloid: a mixture in which particles size between size of particles in solution and suspension. Colloids do not settle out if left for long time. Example: Mayonnaise or Ketchup   

b. Suspension: a mixture in which particles are too large that they settle out if left for long time, such as mud in water 

What are the three classification of matter?

Matter and its classifications:

Matter is anything that has mass and occupies space. It can be classified either with respect to its physical phases or with respect to its composition.

The three phases of matter are solid, liquid, and gas. A solid has a fixed shape and volume. A liquid has a fixed volume but is not rigid in shape; it takes the shape of its container. A gas has neither a fixed volume nor a shape. It takes on both the shape and the volume of its container.

Matter can also be classified with respect to its composition:

• pure substances, each of which has a fixed composition and a unique set of properties.

• mixtures, composed of two or more substances.

Pure substances are either elements or compounds, whereas mixtures can be either homogeneous or heterogeneous.

1- Elements

An element is a type of matter that cannot be broken down into two or more pure substances. There are 118 known elements, of which 91 occur naturally.

Many elements are familiar to all of us. The charcoal used in outdoor grills is nearly pure carbon. Electrical wiring, jewellery, and water pipes are often made from copper, a metallic element. Another such element, aluminum, is used in many household utensils.

In chemistry, an element is identified by its symbol. This consists of one or two letters, usually derived from the name of the element. Thus the symbol for carbon is C; that for aluminum is Al. Sometimes the symbol comes from the Latin name of the element or one of its compounds. The two elements copper and mercury, which were known in ancient times, have the symbols Cu (cuprum) and Hg (hydrargyrum).

2- Compounds:

A compound is a pure substance that contains more than one element. Water is a compound of hydrogen and oxygen. The compounds methane, acetylene, and naphthalene all contain the elements carbon and hydrogen, in different proportions.

Compounds have fixed compositions. That is, a given compound always contains the same elements in the same percentages by mass. A sample of pure water contains precisely 11.19% hydrogen and 88.81% oxygen. In contrast, mixtures can vary in composition. For example, a mixture of hydrogen and oxygen might contain 5, 10, 25, or 60% hydrogen, along with 95, 90, 75, or 40% oxygen.

The properties of compounds are usually very different from those of the elements they contain. Ordinary table salt, sodium chloride, is a white, un-reactive solid. As you can guess from its name, it contains the two elements sodium and chlorine. Sodium (Na) is a shiny, extremely reactive metal. Chlorine (Cl) is a poisonous, greenish-yellow gas. Clearly, when these two elements combine to form sodium chloride, a profound change takes place.

Many different methods can be used to resolve compounds into their elements. Sometimes, but not often, heat alone is sufficient. Mercury(II) oxide, a compound of mercury and oxygen, decomposes to its elements when heated to 600°C. Another method of resolving compounds into elements is electrolysis, which involves passing an electric current through a compound, usually in the liquid state. By electrolysis it is possible to separate water into the gaseous elements hydrogen and oxygen.

3-Mixture:

A mixture contains two or more substances combined in such a way that each substance retains its chemical identity. When you shake copper sulfate with sand, the two substances do not react with one another. In contrast, when sodium is exposed to chlorine gas, a new compound, sodium chloride, is formed.

Which has the strongest hydrogen bond?

Which hydrogen bond is stronger the O, N, F hydrogen bond? The effect of the electronegativity on the strength of the hydrogen bond. Reasons behind the fact that hydrogen bond of water is stronger than HF although fluorine has higher electronegativity. The effect of crystal shape of water on the density of ice.

Elements, atom, compound and molecules definition

Elements: the material that is made of the same building block (atoms) . It cannot be broken down into simpler substances by physical or chemical method .

Compound: different atoms joined together

Example: water molecule; it has two hydrogen atoms bonded to one oxygen atom 

The major difference between element and compound is that element are one or a group of similar atoms bonded together for example O2, Fe, and H2.

Compound on the other hand is formed of different type of atoms for example carbon dioxide CO2.

An atom: is the smallest part of matter that can still be recognized as that element.

Example: Carbon atom, oxygen atom, and iron atom.

Molecules: are the smallest units of element or compound that retain the characteristics of the compound.

Molecule contain group of atoms either similar atoms (like in element) or different atoms (like in compound). Examples for molecules: H2, H2O 

What are the classifications of matter?

Matter is a substance that has a mass and occupies a space.
Matter is classified into:

1- Element: contains one type of atoms. Examples: Hydrogen gas, copper element.

2- Compound: made from atoms of different elements bonded together chemically with fixed ratios

chemical and physical properties of compound different from parent elements. Example: Sodium chloride.

3- Mixture: contains more than one compound or element mixed physically without chemical bond with any ratios. Example: Sea water, air and brass alloy.

  

Element	Compound	Mixture
One or more atoms	Two or more atoms	Two or more compounds or elements joined together physically (mixing only)
Same type of atoms	Different type of atoms	Different type of atoms
Iron (Fe) Copper (Cu)  Hydrogen gas H2	Water (H2O)    Carbon dioxide (CO2) Table salt (NaCl)	Sea water   Air (air is a mixture of different gases like oxygen, hydrogen and nitrogen