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Uses of Static Electricity

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 19:50:59 +0300

Uses of Static Electricity

The Electrostatic Precipitator

Electrostatic precipitators are used in industry for environmental protection. In factories, power plants and chemical plants smoke and other exhaust have to be treated to remove dust particles and other particulates before it is released into the atmosphere.

Highly positively charged wires are stretched across the centre of the chimney or exhaust vent to form a grid. The wires are charged to a positive charge of about 50,000V. As the smoke passes over the wires the particles carried in the smoke become positively charged. These particles are then attracted towards negatively charged collecting plates where they stick. Thus, the dust particles are separated from the smoke which then carries on up the chimney and into the atmosphere. The negatively charged collecting plates are periodically struck with a mechanical hammer to remove the dust particles which then drop into a collecting bin.

Remember, the principle would also be true if the wires were negatively charged and the collecting plates positively charged. As the process relies on the principle that opposite charges attract.

Paint Spraying/Crop Spraying

The principles of electrostatics are used are used by industry in the process of paint spraying for e.g. the automotive industry when spraying cars. The nozzle of the spray gun is given a charge. The paint droplets exiting the nozzle gain this charge. As the droplets all hold the same charge they repel each other so that they spread out into a fine mist. The object to be painted is grounded or earthed. The charged droplets are attracted to the grounded object, even the back of it due to the electrostatic attraction (remember charged objects are attracted to uncharged objects). This process requires less paint and gives a uniform finish.

The same principle is used to benefit farmers in crop spraying. If the fertilizer/pesticide is given the same charge the droplets repel to form a larger cloud thereby increasing the coverage. These are then attracted to the uncharged crops.

The Photocopier

Photocopiers consist of a drum or belt covered with a layer of photoconductive material. A photoconductive material conducts electricity when struck by light (photo meaning light and
conductive referring to conducting electrons).

When a photocopier is started a high voltage wire distributes a positive charge evenly on the surface of the belt or drum. An intense beam of light moves across the sheet of paper to be copied placed on the glass surface. The dark areas on the paper absorb the light and the white areas reflect the light back onto the drum/belt below. The reflected light strikes the positively charged photoconductive material on the metal neutralising it (by producing electrons). The dark areas on the paper for e.g. the text or picture that do not reflect the light leave regions of positive charges on the surface of the belt/drum (like a shadow).

Negatively charged, dry black pigment particles known as toner are then spread over the drum/belt. These negatively charged particles are attracted to the positively charged regions on the drum/belt (remember opposite charges attract). A blank sheet of paper is passed over the charged wire making it positive and then passed over the drum/belt. The positively charged paper attracts the toner off the drum/belt. The paper plus toner is then heated and passed through rollers to melt and fuse the toner to the paper.

Conductors and Insulators

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 19:35:37 +0300

Conductors & Insulators

Conductors are materials which allow the electrons to move freely inside them. All metals are good conductors because they contain a large number of free electrons inside them that can move easily from atom to atom.

Insulators do not allow electrons to pass through them. They do not contain free electrons inside them.

Conductors
Insulators

All metals e.g. copper, silver, etc.
Glass
Water
Plastics
Skin
Air
Rubber

Static Electricity and Lightening Hazards

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 18:53:45 +0300

Static Hazards

Sparks

Sparks can cause explosions. When flammable liquids like gasoline (petrol) are transferred from tankers to aircrafts static electricity poses a very serious hazard. Gasoline is an insulator. When it transferred from a tanker to an aircraft it rubs against the inside of the hose and builds up a lot of charge. This large amount of charge can form sparks and cause an explosion.

To prevent this from happening tankers/aircrafts use grounding or earthing devices. These are copper wires on the hose and the aircraft that draw the electrical charge away from the gasoline and into the ground/earth (hence the name grounding or earthing).

Lightning

In storm clouds water droplets collide with dust particles, ionising radiations and each other. These collisions cause electrons to be knocked of the particles and accumulate in the cloud. The negative charges collect at the bottom of cloud and induce positive charges to accumulate on the ground. Eventually, the potential difference between the cloud and the ground become so great that the negative charges from the cloud are attracted towards the positive charges from the ground. When the two charges meet a flash of lightning is produced. Lightning bolts can heat up the air to temperatures hotter than the sun this causes the air around the bolt to expand explosively producing the sound we hear as thunder. As light travels a million times faster than sound we see the lightning before we hear the thunder.

Lightning Hazards

Lightning strikes are hazardous to buildings especially tall ones like tower blocks and chimney stacks. The energy in a bolt of lightning can severely damage and burn buildings. Lightning conductors provide protection for building by providing the path of least resistance for the lightning into the earth.

Lightning conductors are a sharp pointed metal rod placed on the top of a building. As charged storm clouds induce positive charge the point of the lightning conductor becomes positively charged. If lightning strikes it will be hit the conductor (due to it being the tallest object with the positive charge), it will the travel down the rod and into earth where it will be dissipated safely.

Attraction and Repulsion

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 18:20:04 +0300

Attraction & Repulsion

Rubbing a polythene strip on wool causes some of the outer electrons in the wool to move over to the polythene strip. As the polythene gains electrons it becomes negatively charged. The wool looses electrons and is left with a net positive charge (more protons to electrons).

Only the negative electrons move. The positive protons remained fixed in the atoms nucleus.
Rubbing materials to generate charge only works for insulated objects. Conductors direct the charge flow to earth.

When two electrically charged bodies are brought together they exert a force on each other. Electrically charged objects may attract or repel each other or attract small uncharged objects place near them.

Opposite charges attract. Like charges Repel.

Example

Balloon

A balloon can be made to stick to a wall by using the principles of electrostatics.

When a balloon is rubbed against clothes the negative electrons from the clothes get transferred to the balloon making the balloon negatively charged. When the balloon is placed near a wall or ceiling (a neutral object) it stays there and doesn�t fall. This is because the negative charge of the balloon repels some of the electrons in the wall or ceiling away from the surface. This results in an overall positively charged surface causing the negatively charged balloon to be attracted (remember opposite charges attract).

The separated charges in the wall or ceiling are called INDUCED charges.

Optimum Conditions for Enzymes

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 16:20:59 +0300

Optimum conditions for enzymes

Enzymes are sensitive and work best under specific conditions. Enzyme activity is affected by several things and each type of enzyme has its own specific optimum conditions under which it works best.

1. Substrate concentration

Enzymes work best when there is a
high enough substrate concentration for the reaction they catalyse. If too little substrate is available the rate of the reaction is slowed and cannot increase any further.

Sometimes, if there is too much product accumulating, the reaction can also be slowed down. Therefore it is important that the product is removed regularly.

2. Temperature

Enzymes are affected a great deal by temperature. If the temperature is too cold the enzymes move around too slowly to meet the substrate and for a reaction to occur. As the temperature increases though, so does the rate of reaction. This is because heat energy causes more collisions between the enzyme and the substrate. However as you will remember all enzymes are proteins and at too high temperatures the proteins break down. The active site of the enzyme becomes distorted and so the substrate no longer fits and hence the reaction does not occur. We say that the enzyme has been denatured.

3. pH

The pH must be correct for each enzyme to work at its best. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on its site of action. For example, enzymes in the stomach have an optimum pH of about 2 because the stomach is acidic, but intestinal enzymes have an optimum pH of about 7.5. If conditions are too alkaline or acidic for that particular enzyme then its activity is affected. This occurs because the enzyme�s shape, especially the active site, is changed so can no longer bind to the substrate molecule. We say that the enzyme is denatured.

How Enzymes Work

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 16:13:59 +0300

How Enzymes work

Enzymes work by intervening in chemical reactions by locking onto the substrate at their active site and speeding up the reaction. Enzymes can work in different ways, some enzymes help to break down large molecules into smaller ones, others build up large molecules from smaller ones whilst there are some that help change one molecule into another.

One of the fastest enzymes known is catalase. Catalase is found in many living cells and breaks down hydrogen peroxide into water and oxygen. Hydrogen peroxide is often formed as a product of reactions in cells, and can be poisonous if it builds up it is the job of catalase to remove the harmful hydrogen peroxide.

The substrate (hydrogen peroxide) and the enzyme (catalase) are continuously on the move. Every so often they collide so that the substrate molecule fits into the enzyme�s active site. Once in the active site the reaction takes place between the substrate and enzyme, the substrate is broken down into the two products (water and oxygen). When the required product has been produced, the enzyme releases itself and moves on. The enzyme is not used up in the reaction and so is ready to work again! No matter what job an enzyme does it will work in this similar way.

Enzymes

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 02:35:49 +0300

What are Enzymes?

Enzymes are proteins made up of long chains of amino acids. They control chemical reactions that take place in all living things such as digestion, respiration and photosynthesis. They are knows as
Biological catalysts as they speed up chemical reactions allowing them to occur at a faster rate. During this process, however the enzymes themselves do not get used up and so can continue catalysing the reaction.

Each enzyme has its own specific 3-dimensional structure and is folded into a unique shape which allows other molecules to fit into it. The area where these molecules fit into is known as the enzyme�s active site. The molecules which fit into the active site are knows as the substrate. The enzyme and the substrate fit together using a lock and key mechanism.

Active Transport in Cells

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 02:04:51 +0300

Active Transport

Sometimes organisms require certain substances and therefore need to move dissolved substances from a region of low concentration to a region where they are at a higher concentration. This process is of course the opposite to the direction in which particles would normally move in diffusion. This is active transport. In active transport particles move against a concentration gradient and therefore require energy which must be supplied by the cell. Carrier proteins that are found in the cell membrane of cells use energy to transport molecules or ions across the membrane, against the concentration gradient. When organisms utilise active transport the energy for the process comes from respiration. Due to this the cells capable of active transport usually have more mitochondria, in which respiration takes place than other cells.

We can say thus say the definition of active transport is as follows:

The movement of particles from an area of low concentration to an area of high, against a concentration gradient.

Active Transport in Plant Cells

Plants require mineral salts such as nitrates for growth. The concentration of nitrates is higher on plant root cell than it is in the soil solution surrounding it. The plant cannot rely on diffusion as the nitrates would diffuse out of root cell into the soil. Hence the cells utilise energy to actively transport nitrates across the cell membrane into the root cell, against the concentration gradient.

Active Transport in Animals

The process of active transport takes place in humans during digestion of food in the ileum (small intestine). Once food has been absorbed by the villi after some time the concentration of food molecules inside the villi increases at this point no more food can diffuse in. As more food is still required simple sugars, amino acids, vitamins and minerals are actively transported into the villi form an area of low concentration to an area of high concentration, against the concentration gradient.

Osmosis in Plant Cells

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 01:53:25 +0300

Osmosis in plant cells

Osmosis is the way in which plants take up water. This is how. Root hairs of the plant take in water from the soil by osmosis. The cell membrane of the root hair cell acts a partially permeable membrane (the cell wall is fully permeable) and because the cell sap inside the vacuole is a strong solution (low water concentration) water passes from the soil (high water concentration) into the root hair cell by osmosis. The concentration of the sap in the vacuole is now weaker as there is a high concentration of water. Water will now pass from this area of high concentration to the next cell which has a low water concentration by osmosis. In this way water continues to move along the cells of the root up the xylem to the leaf. all the time water is moving to areas of lower water concentration

As water enters plant cells it makes the cell swell up. The water moves into the plant cell vacuole and pushes against the cell wall. Eventually the cell contains as much water as it can hold. The strong cell wall stops the cell bursting. We say that cell is turgid. Turgid cells are useful implants as the give the plant support as they keep the stems of plants upright.

When plants are placed into a strong sugar or salts solution water will pass out of the cells by osmosis. As water passes out, the sap vacuole starts to shrink. These cells are no longer firm they are limp. We say that they are flaccid and the plant will wilt.

If a lot of water leaves the cells then the cytoplasm starts to peel away from the cell wall. We say that the cell has undergone plasmolysis.

Osmosis in Animal Cells

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 01:45:09 +0300

Osmosis in animal cells

As you will remember animal cells have partially permeable cell membrane. This means that if they are placed in pure water because their cytoplasm is a stronger solution than the pure water, water will pass into the cells by osmosis. The cells will therefore swell up. However animal cells have no cell wall to stop them swelling too much so they keep swelling until they burst. We call this haemolysis.

Osmosis in Cells

mybb@mybb.ru (De Brave) — Tue, 29 Jan 2019 01:24:18 +0300

Osmosis

Now we have established the general features of both animal and plant cells we must also remember that many cells do look different and this is because they have their own special jobs to do. These cells display specialised features that make them suited to carry out their specific function.
As we know each cell is surrounded by a cell membrane. This membrane has tiny holes in it which allow small molecules to pass through but not large ones. Due to this nature the cell membrane is described as being partially (or selectively) permeable.

Osmosis is a special kind of diffusion involving water molecules. It occurs when two solutions are separated by a partially permeable membrane.

The definition of osmosis is as follows:

Osmosis is the movement of water molecules from an area of high water concentration (weak/dilute solution) to an area of low water concentration (strong/concentrated solution) through a partially permeable membrane.

Water is actually moving both ways to try to even up the concentration, however more water molecules are moving from the pure water towards the sugar solution because there is a higher concentration of water molecules in the pure water solution than the sugar solution. The result is a net transfer of molecules down a concentration gradient from the water to the sugar solution. Eventually the level of water on the lower water concentration side rises while that on the more concentrated side falls. When the concentration of water is the same on both sides the movement of water will be the same in both directions at this point the net exchange of water is zero and the system is in equilibrium.

Example of Diffusion in Animal Cell

mybb@mybb.ru (De Brave) — Mon, 28 Jan 2019 11:36:54 +0300

Example of diffusion in an animal cell

The cells in our body need glucose and oxygen for respiration. Both these are carried in the blood. When blood reaches the cells the molecules of glucose and oxygen diffuse out of the blood and into the cells.

As cells use up the glucose and oxygen they produce waste chemicals and carbon dioxide. If these were to build up in the cells they would poison them, therefore they diffuse out of the cells into the blood.

Another example of diffusion in animal cells is the exchange of carbon dioxide and oxygen between the alveoli in the lungs and the blood. See gaseous exchange .

Example of Diffusion in Plants

mybb@mybb.ru (De Brave) — Mon, 28 Jan 2019 09:43:35 +0300

Example of diffusion in plant cells

In order to carry out photosynthesis a plant requires carbon dioxide. On the underside of leaves there are small holes known as stomata, carbon dioxide diffuse into the leaves via these. Leaves produce oxygen and water vapour and these in turn diffuse out via the stomata.

In and Out of the Cell: Diffusion

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 23:58:04 +0300

In and Out of Cells

Water is the main component of all cells. We find water in the cytoplasm and in cell sap. This water contains many dissolved substances and these substances plus the water enter and leave the cells through the cell membrane. The cell membrane allows certain particles through it but it blocks the passage of others. Because of this nature it is described as a partially (or selectively) permeable membrane. Particles enter and leave cells by three processes:

1. Diffusion
2. Osmosis
3. Active transport

Diffusion

Particles in liquids and gases have kinetic energy, therefore they move about at speed in all directions. These particles move in a random motion. Where there is an area of high concentration some of these particles collide into one another, lose energy and slow down. Others will escape from the area of high concentration to an area of low concentration elsewhere. Very few particles travel the opposite way. The result is a concentration gradient with particles diffusing from an area of high concentration to an area of low concentration. Diffusion occurs in gases and with any substance in a solution.

Therefore we can say that the definition of diffusion is as follows:

Diffusion: The movement of particles from an area of high concentration to an area of low concentration until they spread out evenly.

There are two important rules to remember.

1. The larger the particles the slower the rate of diffusion.

2. The greater the difference in concentration the greater the rate of diffusion.This difference is known as the concentration gradient.

Example of diffusion in plant cells

Example of diffusion in animal cells

Cells, Tissues and Organs

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 22:31:18 +0300

Cells, Tissues and Organs

As we mentioned before, cells are the building blocks of life.

When we have a group of similar cells working together this is called a tissue, for example muscle tissue is made up of lots of muscle cells. All the cells in a tissue look the same and perform the same job.

A group of different tissue working together to do a specific job is known as an organ, our heart, stomach, lungs are all organs.

Different organs working together form an organ system, our heart and blood vessels work together as part of our circulatory system.

All of our organ systems put together make up a living organism and that is you!

Cellular and Multicellular Organisms

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 22:19:00 +0300

Unicellular Organisms

Some living organisms are made up of once cell only, these are called unicellular. These organisms have a large surface area to volume ratio and rely on simple diffusion to meet their needs. An example of a unicellular animal is Amoeba.

All seven life processes take place inside this one cell. Amoebas are found in ponds and ditches. They move by changing their shape, they push out pseudopodia in the direction they want to move and the rest of the cell flows after them. Amoeba feed on smaller organisms such as bacteria. The pseudopodia flow around the food engulfing it, the food is then taken into the cytoplasm in a food vacuole. Enzymes further break down the food.

Useful substances that the amoeba requires like Oxygen pass into to the amoeba from the water around by diffusion and waste substances such as carbon dioxide pass out into the water also via diffusion.

Multicellular Organisms

Multicellular organisms are those which are made up of many cells. Humans are multicellular. Multicellular organisms can be much larger and more complex. This is because the cells of the organism have specialised into many different types of cells such as nerve cells, blood cells, muscle cells all performing different functions.

Static Electricity

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 04:50:28 +0300

What is Static Electricity?

Static electricity is caused by the transfer of charge.

Atoms are made up of protons, neutrons and electrons each with their own properties.

Protons have a Positive (+) charge.
Electrons have a Negative (-) charge.
Neutrons are Neutral (no charge).

The positive charges (protons) are held in the nucleus of the atom.
The negative charges (electrons) are spread in orbits around the nucleus.

The protons and neutrons are held very tightly in the nucleus. But some of the electrons are held very loosely and can move from one atom to another. If an atom looses an electron the number of protons (positive charges) exceeds the number of electrons (negative charges) and the atom is positively charged.

If an atom gains an electron the number of protons (positive charges) is lesser than the number of electrons (negative charges) and the atom is negatively charged.

One method in which electrons can be moved or transferred is by rubbing two insulators together Rubbing causes friction between the two surfaces increasing the surface contact and allowing more electrons to be transferred. The object which looses electrons becomes positively charged and the one that gains the electrons becomes negatively charged.

Therefore,

Static Electricity is the imbalance of Positive and Negative Charge

Cell Specialisation

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 04:21:07 +0300

Cell Specialisation

Cell Specialisation � Animals

Red Blood Cell

Specific Function:

Contain haemoglobin which transports oxygen to other cells and around the body.

Specialised Feature:

Have biconcave shape for maximum surface area to allow more oxygen to be absorbed efficiently.

Biconcave shape also allows for a flexible framework which means cells can squeeze through the thinnest of capillaries.

Cells have a thin outer membrane allowing oxygen to diffuse through easily.

Have no nucleus so there is more room for oxygen to be carried in the cell and hence around the body.

Sperm Cell

Specific Function:

To fertilise the ovum (female egg cell).

Specialised Feature:

The tail of the sperm cell enables it to swim to the ovum and fertilise it.

The head is streamlined also to aid swimming

The head contains genetic information and a nucleus and has an enzyme to help penetrate the egg cell membrane to allow fertilisation.

The middle section immediately behind the head is packed with mitochondria to provide energy.

Nerve Cell

[Motor Nerve Cell]

Specific Function:

Transmit electrical nerve impulses and so carry information from one part of the body to another ie from receptor to an effector.

Specialised Feature:

Dendrites extend from the cell body to make connections with other neurones.

Have a long axon (nerve fibre) to carry the impulse to the target organ.

End plate forms a synapse with an effector (a muscle or a gland).

Cell Specialisation � Plants

Xylem Cell

Specific Function:

Small tubes that carry water from the roots to the leaves.

Specialised Feature

Long and tube-like hollow vessels to carry the water.

Cells have no end walls between them so they form a 'pipeline' to carry the water.

Spirals and rings of lignin in the cell walls strengthen them to withstand pressure of water.

Root Hair Cell

Specific Function:

Absorb water and mineral ions from the soil.

Specialised Feature

Located in the root epidermis and in direct contact with the soil

Thin walls make up-take of water easier.

Wall nearest the soil has a long 'finger-like' projection with very thin walls into the soil. This projection increases the surface area for more efficient uptake of water and ions.

Leaf Palisade Cell

Specific Function:

Carries out photosynthesis.

Specialised Feature

Packed with chloroplasts which contain the light absorbing pigment chlorophyll.

Regular shaped closely packed cells forming a continuous layer for efficient and maximum absorption of sunlight.

Cells

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 02:24:12 +0300

What are Cells?

Cells are what make up all living things. They are the building blocks of life. Plant and animal are built up of cells that are stuck together.

Structure of Animal and Plant Cells

It is important that you know the structure of animal and plant cells and are able to label the different parts. It is a favourite with examiners to have diagrams of cells requiring labelling in exams

A Plant Cell
An Animal Cell

There are many similarities and differences between animal and plant cells.
Make sure you know these.

Similarities
Differences

1. Have a nucleus
1. Plant cells have a cellulose cell wall
2. Have a cytoplasm
2. Plant cells have a vacuole containing cell sap
3. Have a cell membrane
3. Plant cells have chloroplast
4. Contain mitochondria
4. Many plant cells have a box-like shape whilst animal cell shape varies
5. Contain ribosomes
5. Plant cells have the nucleus to the side of the cell, animal cells have a nucleus in the middle

Life Processes

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 01:59:13 +0300

Life Processes

Biology is the study of living things . All living things are called organisms, both plants and animals are living organisms. But how we decide whether something is living or non-living depends on 7 life processes. If something is living it will carry out the 7 life processes below.

The acronym MRS GERN may help you to remember the seven important life processes common to plants and animals.

1. Movement

Both animals and plants have the ability to move. Plants are rooted and move slowly as they grow. Their roots move down into the soil and their stems move up towards the light. Animals on the other hand move quickly and can move their entire bodies. They can move in search of food, shelter or to avoid danger.

2. Respiration

Respiration is the process of extracting energy out of the food we eat. All living things respire because they need energy to grow, to replace worn out parts and to move. Respiration takes place in the mitochondria of the cell. There are two types of respiration, with and without oxygen. Aerobic respiration uses oxygen and releases a large amount of energy. Anaerobic respiration does not require oxygen and releases a smaller amount of energy.

3. Sensitivity

All living organisms are sensitive, this means that they have an awareness of changes in their environment. Animals respond quickly to stimuli such as heat, light, sound, touch and chemicals which have taste and smell. On the other hand plants generally appear less sensitive and their response is slower. Plants respond to light by moving their leaves towards it, the flowers of some plants open in the morning and close at night when it is dark. Some plants, however, do respond quickly such as the Venus flytrap response to touch.

4. Growth

All living organisms grow. Plants continue growing throughout their lives. Animals stop growing once they reach adulthood. Even when growth stops, materials within an animal�s body are still being replaced from its food.

5. Excretion

All living things make waste products these can be useless or harmful to it and therefore need to be got rid of. Excretion is the process of getting rid of metabolic waste. Plants store waste substances in their leaves, the waste is removed when their leaves fall off. Animals breathe out waste carbon dioxide, other waste substances leave the body in urine and sweat. Note: Getting rid of faeces or undigested food is not excretion but egestion.

6. Reproduction

All living things must produce offspring like themselves in order for their species to survive. This is the process known as reproduction. Plants produce seeds that give rise to new plants of the same species. Animals lay eggs or have babies. Reproduction can be of two types, Sexual which involves two parents and the union of two gametes and Asexual where one parent can reproduce itself.

7. Nutrition

Nutrition is needed for energy and growth, both plants and animals need food. Plants are able to make their own food by photosynthesis. They use sunlight to turn simple molecules like carbon dioxide and water into more complex carbohydrate molecules. Animals are unable to make their own food so rely on other plants and other animals for their nutrition. Animals take in complex substances and break them down into small, simple, soluble molecules which can be used for energy and growth.

Elements: Relative Atomic Mass

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 01:08:42 +0300

Relative Atomic mass

Different types of atoms have different masses. This mass is too small to measure using a conventional scale, therefore we compare their masses to each other. A carbon atom having a mass number 12, i.e. (12C) is taken as standard for this comparison and its relative atomic mass is 12.

The relative atomic mass of an element compares the mass of atoms of the element with the 12C isotope.

It is written as Ar or R.A.M.

Some of the elements exist in nature as a mixture of their isotopes in specific proportions.

The R.A.M of such elements is the average mass of the different proportions of each isotope in the mixture.

R.A.M. of some elements:

hydrogen
1
oxygen
16
copper
63.5
iron
55.8

It�s important to note that atomic number and mass number are always whole numbers because they are based on the number of sub-atomic particles, while the R.A.M. can have fractions because it is the average mass of different isotopes.

Example

A sample of chlorine gas is a mixture of 2 isotopes, chlorine-35 and chlorine-37. These isotopes occur in specific proportions in the sample i.e. 75% chlorine-35 and 25% chlorine-37. Calculate the R.A.M. of chlorine in the sample.

Solution

The average mass, or R.A.M. of chlorine can be calculated using the following equation:

R.A.M.
=
(mass of isotope-A x % of isotope-A) + (mass of isotope-B x % of isotope-B)
100
=
(35 x 75) + (37 x 25)
100
=
3550
100
R.A.M.
=
35.5

Elements: Isotopes

mybb@mybb.ru (De Brave) — Sun, 27 Jan 2019 00:48:32 +0300

Isotopes

All the atoms of a particular element have the same number of protons. This proton number or atomic number determines the chemical properties of an atom. However, the number of neutrons may vary within the atoms of an element.

Atoms of the same element that have the same number of protons but different number of neutrons are called isotopes of that element.

Or in other words,

Atoms of the same element with the same atomic number but different atomic masses are called isotopes of that element.

Example

The atomic number of carbon is 6. All carbon atoms have the same atomic number, but their mass number might differ because of different number of neutrons.
Most of the carbon atoms contain 6 protons and 6 neutrons, and has a mass number 12. However, some carbon atoms also exist with 6 protons and 8 neutrons, which gives it a mass number 14.
12C and 14C are isotopes of carbon.

Comparison of two isotopes of carbon

Electrons
6
6
Same
Protons
6
6
Same
Neutrons
6
8
Different
Atomic number
6
6
Same
Mass number
12
14
Different

Calculating sub-atomic particles from atomic number and mass number

mybb@mybb.ru (De Brave) — Sat, 26 Jan 2019 23:42:08 +0300

Calculating sub-atomic particles from atomic number and mass number

We can calculate the number of sub-atomic particles (i.e. electrons, protons, neutrons) if the atomic mass or atomic number is provided for an element. Similarly, the atomic number and mass number can be calculated for any element if the number of subatomic particles is known.

From the definitions of Atomic number and Atomic mass, we know:

Atomic number = the number of protons

Mass number = the number of protons + the number of neutrons

From these, we can deduct:

Number of neutrons = Mass number � Atomic number

Atom has no overall charge, which means the there are equal number of negatively charged electrons and positively charged protons. If we know the number of protons (or atomic number) of an atom, this will be equal to the number of electrons of that atom.

Number of electrons = Number of protons

Example Question:

Calculate the sub-atomic particles for

Solution:

From the provided data, we know:

Mass number: 23
Atomic number: 11

As we know:
Number of protons = Atomic number

Therefore,
Number of protons = 11

Since, Number of electrons = Number of protons

Therefore, Number of electrons = 11

As we know:
Mass number = number of protons + neutrons
and, Atomic number = number of protons

Therefore,
Number of neutrons = Mass number � Atomic number
= 23 � 11
Number of neutrons = 12

Elements: Atomic Mass

mybb@mybb.ru (De Brave) — Sat, 26 Jan 2019 21:58:55 +0300

Atomic Mass

As we already know that nucleus of an atom contains protons and neutrons.

The number of protons and neutrons in an atom of an element is called Atomic mass, or Mass number

Protons and neutrons have the same mass of 1 unit, while electrons are very light and their mass can be ignored and taken as zero.

Atomic Mass = number of protons + number of neutrons
= 6 + 6 = 12
Therefore, the mass number of carbon is 12.

Elements: Atomic Number

mybb@mybb.ru (De Brave) — Sat, 26 Jan 2019 18:38:16 +0300

Atomic Number
Each atom of a specific element contains the same number of protons. For example, all the atoms of carbon contain 6 protons in their nucleus.

The number of protons in an atom of an element is called Atomic number.

Each element has a unique atomic number, which is also used to arrange the elements in the Periodic Table.

Atomic Number = Number of protons
= 6
Carbon has 6 protons; therefore the atomic number of carbon is 6.