General Science

This thread contains all info regarding `General Science` and all related facets of science.




Topic # 1





1. MATTER

Everything you can hold, taste, or smell is made of matter. Matter makes up everything you can see, including clothes, water, food, plants, and animals. It even makes up some things you cannot see, such as air or the smell of perfume. You can describe a type of matter by its MATERIAL PROPERTIES such as its colour or how hard it is. Matter is made up of PARTICLES so tiny that only the most powerful microscope can see them.





NON-MATTER
Not everything is made of matter. Non-matter includes the light from a torch, the heat from a fire, and the sound of a police siren. You cannot hold, taste, or smell these things. They are not types of matter, but forms of energy. Everything that exists can be classed as either a type of matter or a form of energy.

MATERIAL PROPERTIES
Different types of matter have different material properties that make them useful for different jobs. A plastic hosepipe is flexible, so it can be pointed in any direction. A perspex visor is transparent, so the wearer can see straight through it. A firefighter’s suit is shiny so it can reflect heat and light. Flexibility, transparency, and shininess are three examples of material properties.

PARTICLES
All matter is made of incredibly tiny particles called atoms. Atoms are far too small to see with our eyes, but scientists have worked out how small they are. There are many kinds of atom. Sand grains are made of two kinds of atom: oxygen and silicon. People are made of about 28 different kinds of atom. Material properties depend on the kinds of atom the material is made from.

SAND PARTICLES
Grains of sand look like pieces of gravel when viewed through a microscope. They have different shapes and sizes. Each grain contains millions of atoms, too small to see with a microscope. A sand grain the size of the full stop at the end of this sentence would contain about 10 million million million atoms.

ATOMS
We cannot really see atoms with microscopes. The best we can do is image them, by bouncing light off the particles. A computer translates the light beams into an image. Scanning tunnelling microscopes (STM) and atomic force microscopes (AFM) do this.

BIOGRAPHY: DEMOCRITUS Greek, 460-c. 370 BC
Democritus was one of the first philosophers (thinkers) to say that everything was made up of particles too small to be seen. He believed these particles could not be destroyed or split. Democritus said that all changes in the world could be explained as changes in the way particles are packed together.








2. SOLIDS

Solids are one of the three states of matter and, unlike liquids or gases, they have a definite shape that is not easy to change. Different solids have particular properties such as stretch, STRENGTH, or hardness that make them useful for different jobs. Most solids are made up of tiny crystals. This is because their particles are arranged in a regular pattern, called a CRYSTALLINE STRUCTURE.






CHANGING SHAPE
Some solids can be hammered or squashed into many different shapes without breaking. They are known as malleable materials. Other solids, such as biscuits or glass, will not bend when hammered or squashed, but will break and split. These materials are brittle.

SHAPE MEMORY METAL
Shape memory metals can remember their shape. When brought to a certain temperature, these metals can be set to a shape that they never forget. They have many uses, including repairing broken bones. Even if the bones move, the metal always returns to its original shape, bringing the bones back to their correct position.

Stretch
Some solids, such as the metal copper, can be pulled and stretched easily into extremely thin wires. They are known as ductile materials. They have this property because their particles are not held in a rigid structure, but are arranged in rows that can slide past one another. Copper can be stretched into a thread half the width of a human hair, and is used in many kinds of wiring, including electrical and telephone wiring.


STRENGTH
Some solids, such as steel or concrete, are difficult to break, even if they are made to carry a heavy weight. This is because their particles are bound together very strongly. Such materials are said to have high strength and are used to construct bridges and buildings. Strength is a different property from hardness. Hard materials cannot be bent or scratched easily.

MOHS HARDNESS SCALE
Hardness is a measure of how easily a material can be scratched. Mohs hardness scale arranges 10 minerals from 1 to 10. The higher the number, the harder the mineral. Each mineral in the scale will scratch all those below it. Other materials can be compared to these minerals. Copper, for example, has a hardness of 2.5.



CRYSTALLINE STRUCTURE
Most solids, such as metals, salt, and sugar, are made up of tiny crystals. Their particles are arranged in regular three-dimensional patterns such as cubes or hexagonal shapes. Not all solids are like this, however. The particles of glass, for example, are not arranged in a regular pattern, and so glass does not have a crystalline structure. Its structure is described as amorphous.








3. LIQUIDS

As water flows along a river, it constantly changes its shape to fit the space available. This is because water is a liquid, and liquids flow and do not have a fixed shape. Instead, they take on the shape of whatever container they are in. If you pour a liquid from a glass onto a plate, the volume of liquid (the space it takes up) stays the same, but its shape changes.






COHESION
Mercury is a liquid metal that is poisonous. When mercury is dropped onto a surface, it rolls off in little balls. This is because the forces between the mercury particles are very strong, so the particles clump together. This force between particles of the same type is called cohesion. Water particles do not have such strong cohesion, so they wet surfaces.

VISCOSITY
A measure of how fast or slowly a liquid can flow is its viscosity. Crude oil, for example, is a liquid that does not flow very easily. It is said to have high viscosity. Heating crude oil lowers its viscosity and enables it to flow more freely through pipes. Other liquids, such as water, flow easily without being heated. Water has low viscosity.

VOLUME
Although they look very different, these two containers contain the same volume of liquid. The volume of a liquid is the amount of space it takes up. Although liquids change their shape when moved from one container to another, their volume always stays the same. For this reason, liquids are usually measured by their volume, in litres or gallons.








4. GASES

Gases are all around us, but although many, such as perfume, can be smelt, most gases are invisible. Like liquids, gases can flow but, unlike solids or liquids, gases will not stay where they are put. They have no set shape or volume, and they expand in every direction to fill completely whatever container they are put into. If the container has no lid, the gas escapes.






EXPANSION
In hot air balloons, a burner heats the air inside. This causes the particles of air to gain more energy and so they move faster and farther apart from one another, pushing at the sides of the balloon. Heat always causes gases to expand. If you left a balloon near a fire, the air inside could expand so much that the balloon would burst.







PRESSURE
Why does a champagne cork explode out of a shaken bottle? The champagne inside the bottle contains lots of tiny bubbles of gas. Shaking the bottle releases the gas, and the high-speed gas particles bang against the cork. This creates an enormous pressure on the cork, and eventually forces the cork out of the bottle.







5. MIXTURES

Almost everything is made of different substances mixed together. Things are only easy to recognize as mixtures if the PARTICLE SIZE of each substance is big enough to see. The flakes, nuts, and raisins in a bowl of cereal are a mixture that is easy to see. A fruit drink, though, doesn’t look like a mixture because the particles of fruit and water are so small. It is a type of mixture called a SOLUTION, made of different, very tiny particles dissolved (evenly spread out) in water.

COMMON PARTICLES
Rock, sand, and seawater are all mixtures of the same substances – such as the minerals feldspar, mica, and quartz – but in different particle sizes. Rock contains these substances in chunks or veins; sand has them as small grains; and seawater contains them as tiny dissolved particles that are invisible to the eye. Rain and rivers dissolve the minerals as they wash over the rock on their way to the sea.

MINERAL MIXTURES
All rocks are mixtures of naturally occurring substances called minerals. Granite is a common rock made of three differently coloured minerals called feldspar, mica, and quartz. The pink grains in granite are feldspar, the black grains are mica, and the light grey, glass-like grains are quartz. Granite is usually about 75% feldspar, 5% mica, and 20% quartz. These proportions can vary and the rock often contains small amounts of other minerals as well.





PARTICLE SIZE
There are many different types of mixtures, which are divided into groups based on how small their particles are. A mixture such as sand has a large particle size. Mud stirred in water is a type of mixture called a suspension; the particles are too small to see when mixed, but they eventually settle out. A mixture such as fog (water and air) is called a colloid; its particles are too small ever to settle out.

COARSE MIXTURES
The particles of some mixtures are large enough to see without a microscope. When you look closely at a handful of sand, for example, you can make out the different coloured grains mixed together. Some sands have smaller grains than others. The smaller the grain size, the softer and more powdery the sand feels.

COLLOID
A colloid is a mixture containing tiny particles of one substance scattered throughout another substance, such as dye particles mixed with glass in a marble. The particles are smaller than those in a suspension, but larger than those in a solution. The particles are so small and light, they do not ever settle out.

EMULSION
Milk is made up of tiny globules of fat scattered throughout water. It is an example of an emulsion, a special type of colloid in which oils or fats are mixed with water to create a creamy liquid or paste. Other examples of emulsions are mayonnaise, emulsion paints, lipsticks, and face creams.

SOLUTIONS
A solution is a mixture in which the different particles are tiny and are mixed completely evenly. Solutions are often made by dissolving a solid, such as sugar, into a liquid, such as water. The sugar is called the solute and the water is called the solvent. Water is the most common solute. Solutions can also be a liquid dissolved in another liquid, for example antiseptic liquid. This is water and alcohol. Or they can be a gas dissolved in another gas, such as oxygen dissolved in nitrogen in the air.

SOLID SOLUTION
Wood’s Metal is found in automatic fire sprinklers. It is an alloy (mixture of metals) containing bismuth, lead, tin, and cadmium. This mix of metals has a low melting point of 71ºC (158ºF). It is used as a sensor in automatic fire sprinklers; if the temperature gets too high, the metal alloy melts and releases the water.




6. ELEMENTS



The enormous variety of matter around you is made from different combinations of substances called elements. Elements are pure substances that cannot be broken down into anything simpler. Some, such as gold and silver, are found on their own. Most elements, however, are combined in twos, threes, and more to make compounds. The NATURAL ELEMENTS are found on Earth. SYNTHETIC ELEMENTS are created in laboratories and are often short-lived.

METEORITE
An element is always the same, wherever it is found. For example, meteorites are large rocks that have landed on Earth from space. Some meteorites contain metal, such as iron, which is a natural element. The iron in a meteorite from space is exactly the same as iron found in rocks on Earth.

ORIGIN OF ELEMENTS
All the elements on Earth were formed in the heart of exploding stars. The early Universe was made of just two elements, hydrogen and helium, which formed into stars. At the fiery core of these stars, the hydrogen and helium were forced together to form new, heavier elements. Even heavier elements were created in the explosions of massive stars, called supernovas.

Table 2. ELEMENTS IN THE EARTH'S CRUST

ELEMENT PERCENTAGE
Oxygen 47
Silicon 28
Aluminium 8
Iron 5
Calcium 3.5
Sodium 3
Potassium 2.5
Magnesium 2
All other elements 1

BIOGRAPHY: JOHN DALTON English, 1766–1844
Chemist John Dalton studied the gases in air. He proposed that everything was made from simple substances called elements. He said that the properties (characteristics) of every particle of one element are identical, and are different to the properties of any other element. This is how elements are defined today.

NATURAL ELEMENTS
There are 90 natural elements, ranging from the lightest, hydrogen, to the heaviest, uranium. Other familiar elements are aluminium, carbon, copper, and oxygen. Every substance on Earth is made up of one or more of these 90 elements. Oxygen is the most common element on Earth. Hydrogen is the most common element in the Universe.

ALUMINIUM
Aluminium is a common element, but it is never found naturally on its own. It has to be extracted from rocks called minerals. This extraction process used to be very difficult and aluminium was once considered a precious metal, more valuable than gold. Nowadays, extraction is much easier, and aluminium is used for many everyday items, such as drinks cans and foil.

SYNTHETIC ELEMENTS
No element heavier than uranium is found naturally. Scientists can, however, collide two smaller elements together at high speeds to form a new, heavier element. Many elements made this way break apart almost immediately, although a few can stay together for a few days or even weeks. Scientists make them to learn more about how elements form and how they change as they get heavier. Synthetic elements include plutonium and einsteinium.

CYCLOTRON
Scientists create synthetic elements in a cyclotron. The cyclotron contains a circular track, into which particles are released. The particles are speeded up to extremely high speeds, before being allowed to collide with a target of another element to form new elements. In the largest cyclotrons, the ring is many kilometres wide and the particles speed at 225,000 kph (13,809 mph).





7. ATOMS



An atom is the smallest part of an element that can exist on its own. Copper, for example, is made from copper atoms, which are different to the oxygen atoms that make up oxygen. Atoms are so tiny that even the full stop at the end of this sentence has a width of around 20 million atoms. Inside each atom are even smaller particles, called subatomic particles. These include a nucleus, which contains protons and neutrons, and electrons that whizz around the nucleus.

FOOTBALL STADIUM
Imagine an atom magnified to the size of a football stadium. The nucleus of the atom would be the size of a pea in the centre of the stadium, and the electrons would be whizzing around the outer stands. Everything in between would be empty space.

NUCLEUS
The nucleus is a tightly bound cluster of protons and neutrons. This carbon atom nucleus has 6 protons and 6 neutrons. Protons have a positive electric charge and neutrons nave no charge. Positively charged protons would normally repel each other, but the nucleus is held together by a powerful force called the strong nuclear force.

ATOMIC NUMBER
Every element has a different atomic number, depending on the number of protons its atoms have in their nuclei. A carbon atom, for example, has 6 protons in its nucleus and so carbon has an atomic number of 6. If the number of protons in the nucleus changes, the atom becomes a completely different element with different properties (characteristics).

ATOMIC MASS
Atoms of different elements vary in mass. Their mass depends on the number of protons and neutrons in their nucleus. A hydrogen atom has one proton and no neutrons, so it has an atomic mass of one. The greater the atomic mass of an atom, the smaller the atom is.

ELECTRIC CHARGES
An atom is usually electrically neutral, which means that it has exactly the same number of positively charged protons as it does negatively charged electrons. In this way, the charges cancel one another out. A carbon atom, for example, always has 6 protons and 6 electrons, and usually has 6 neutrons (although different carbon atoms may contain slightly different numbers of neutrons).

BIOGRAPHY: NIELS BOHR Danish, 1885-1962
In 1913, Bohr published his model of atomic structure in which electrons travelled in orbits around the central nucleus. He also introduced the idea of electron shells, saying that the properties of an atom depended on how its electrons were arranged in the shells. In 1922, Bohr was awarded the Nobel Prize for Physics.