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Atomic Structure

At the centre of every atom isa nucleus containing protons and neutrons.  Electrons are contained in shells around the nucleus. The total number of electrons is always the same as the number of protons in the nucleus.  In different types of atoms, there are different amounts of protons, neutrons and electrons. i.e in Oxygen, there are 8 protons, 8 neutrons and 8 electrons. in magnesium there are 12 protons, 12 neutrons and 12 electrons. Relative masses Neutron = 1Proton = 0.99862349Electron = 0.00054386734

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Atomic Structure Part 2

Neutrons are neutral, but protons and electrons are electrically charged.   Protons have a relative charge of +1, while electrons have a relative charge of -1. The atomic number is the number of protons in the nucleus of an atom.  The atomic mass is the mass (weight) of all the components of the atom but is dominated by the nucleus composed of protons and neutrons. The atoms of a chemical element can exist in different types. These are called isotopes. They have the same number of protons (and electrons), but different numbers of neutrons.

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Periodic Table, Group 1, and Analysis

There are three main relationships that can be observed when linking element's structure to their position on the periodic table: The group number represents the number of valence electrons in an atom. Example:lithium is in group 1, so it has one valence electron; calcium is in group two, so it has two electrons in its outer shell. The horizontal period on which an atom lies equals the number of electron shells it contains. Example: lithium is in the second period, so it has two shells; calcium is in the fourth period, so it has four electron shells. Generally speaking, as you read left to right along the table, the atomic number goes up by one.

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Properties of Group 1 metals

Alkali metals are known for being some of the most reactive metals. This is due in part to their larger atomic radii and low ionization energies. They tend to donate their electrons in reactions and often have an oxidation state of +1. These metals are characterized as being extremely soft and silvery in color. They also have low boiling and melting points and are less dense than most elements. Li, Na, and K have the ability to float on water because of their low density. All of these characteristics can be attributed to the large atomic radii and weak metallic bonding these elements possess. Group 1 elements have a valence electron configuration is ns1 and are good reducing agents (meaning they are easily oxidized). All of the alkali metals are found naturally in nature, but not in their pure forms. Most combine with oxygen and silica to form minerals in the Earth and are readily mined as they are of relatively low densitys and thus do not sink.

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Reactions of group 1 metals with water

All of these metals react vigorously or even explosively with cold water. In each case, a solution of the metal hydroxide is produced together with hydrogen gas. Lithium's density is only about half that of water so it floats on the surface, gently fizzing and giving off hydrogen. It gradually reacts and disappears, forming a colourless solution of lithium hydroxide. The reaction generates heat too slowly and lithium's melting point is too high for it to melt (see sodium below). Sodium also floats on the surface, but enough heat is given off to melt the sodium (sodium has a lower melting point than lithium and the reaction produces heat faster) and it melts almost at once to form a small silvery ball that dashes around the surface. A white trail of sodium hydroxide is seen in the water under the sodium, but this soon dissolves to give a colourless solution of sodium hydroxide. The sodium moves because it is pushed around by the hydrogen which is given off during the reaction. If the sodium becomes trapped on the side of the container, the hydrogen may catch fire to burn with an orange flame. The colour is due to contamination of the normally blue hydrogen flame with sodium compounds.

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part2

Potassium behaves rather like sodium except that the reaction is faster and enough heat is given off to set light to the hydrogen. This time the normal hydrogen flame is contaminated by potassium compounds and so is coloured lilac (a faintly bluish pink). Rubidium is denser than water and so sinks. It reacts violently and immediately, with everything spitting out of the container again. Rubidium hydroxide solution and hydrogen are formed. Caesium explodes on contact with water, quite possibly shattering the container. Caesium hydroxide and hydrogen are formed

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How to carry out a flame test

Metals change the colour of a flame when they are heated in it. Different metals give different colours to the flame, so flame tests can be used to identify the presence of a particular metal in a sample. This is how you would carry out a typical flame test: dip a clean flame test loop in the sample solution hold the flame test loop at the edge of a bunsen burner flame observe the changed colour of the flame, and decide which metal it indicates clean the loop in acid and rinse with water, then repeat steps 1 to 3 with a new sample

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Flame colours

barium pale green calcium yellow-red copper green-blue lithium red sodium orange potassium lilac

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Electrolysis

Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. For electrolysis to work, the ions must be free to move. Ions are free to move when an ionic substance is dissolved in water or when melted. For example, if electricity is passed through molten lead bromide, the lead bromide is broken down to form lead and bromine.

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Electrolysis Diagram

diagram

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Noble Gases

Why are they unreactive? They already have their maximum number of valence electrons in the outter shells, so they are stable without having to react to gain/lose electrons. Uses Used in balloons and airships. It is much less dense than air, so balloons filled with it float upwards. Used in light bulbs. The very thin metal filament inside the bulb would react with oxygen and burn away if the bulb were filled with air instead of argon. Argon stops the filament burning away because it is unreactive. Used in lasers. Krypton lasers are used by surgeons to treat certain eye problems and to remove birthmarks.

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Properties of Halogens

These reactive nonmetals have seven valence electrons. As a group, halogens exhibit highly variable physical properties. Halogens range from solid (I2) to liquid (Br2) to gaseous (F2 and Cl2) at room temperature. The chemical properties are more uniform. The halogens have very high electronegativities. Fluorine has the highest electronegativity of all elements. The halogens are particularly reactive with the alkali metals and alkaline earths, forming stable ionic crystals.  

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Gases and Acids

Substances with a pH of less than 7 are acids. The more strongly acidic the solution, the lower its pH number. Acidic solutions turn blue litmus paper red. They turn universal indicator paper red if they are strongly acidic, and orange or yellow if they are weakly acidic. Hydrogen:A lighted wooden splint makes a popping sound in a test tube of hydrogen.  Oxygen:A glowing wooden splint relights in a test tube of oxygen. Carbon dioxide: A lighted wooden splint goes out in a test tube of carbon dioxide but this happens with other gases, too. It is better to bubble the test gas through limewater - calcium hydroxide solution. Carbon dioxide turns limewater cloudy white. Ammonia: Ammonia has a characteristic sharp, choking smell. It also makes damp red litmus paper turn blue. Ammonia forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it. Chlorine: Chlorine has a characteristic sharp, choking smell. It also makes damp blue litmus paper turn red, and then bleaches it white. Chlorine makes damp starch-iodide paper turn blue-black.  

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Naming Salts

Naming salts The name of a salt is in two parts: The first part of the name comes from the metal in the metal oxide, hydroxide or carbonate. The second part of the name comes from the acid used to make it. The names of salts made from hydrochloric acid end in chloride, while the names of salts made from sulfuric acid end in sulfate.

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Salts in general

Making an insoluble salt Silver chloride is insoluble - you can see this from the table. You need a soluble silver salt and a soluble chloride salt to make it. Silver nitrate and sodium chloride are both soluble. When you mix their solutions together, you make soluble sodium nitrate and insoluble silver chloride: silver nitrate + sodium chloride → sodium nitrate + silver chloride AgNO3(aq) + NaCl(aq) → NaNO3(aq) +AgCl(s) The silver chloride appears as tiny particles suspended in the reaction mixture - it forms a precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in an oven.

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continued...

Making soluble salts Acids and bases When acids react with bases, a salt and water are made: acid + metal oxide → salt + water acid + metal hydroxide → salt + water Remember that most bases do not dissolve in water. But if a base can dissolve in water, it is also called an alkali. Reactive metals Acids will react with reactive metals, such as magnesium and zinc, to make a salt and hydrogen: acid + metal → salt + hydrogen The hydrogen causes bubbling during the reaction, and can be detected using a lighted splint.

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Rocks

The Earth's atmosphere has remained much the same for the past 200 million years. The pie chart shows the proportions of the main gases in the atmosphere. It is clear that the main gas is nitrogen. Oxygen - the gas that allows animals and plants to respire, and fuels to burn - is the next most abundant gas. These two gases are both elements and account for about 99% of the gases in the atmosphere. The remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions.  

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rocks p2

The composition of air

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Rocks...again!!

Weathering: In physical weathering the rocks are broken down into smaller pieces, but the chemical composition of the rock remains the same. Chemical weathering occurs when rocks are broken down by a chemical change. Biological weathering takes place when rocks are worn away by living organisms.  Erosion: Hydraulic action is when the force of the water erodes the rock and carves into the ground. Attrition is when the rocks and stones in the water bash together which cause bits to break off and this smooths it. Abrasion is when the rocks and stones in the river bash against the sides and bottom of the river channel.  Burial: As layers are piled one upon another, the sediments beneath are buried, sometimes by hundreds of metres of sediment above. The weight of these layers compacts (squashes down) the sediment grains. Minerals deposited from water in the spaces between the sediment grains gradually cements them together. 

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Rocks...again!!

Weathering: In physical weathering the rocks are broken down into smaller pieces, but the chemical composition of the rock remains the same. Chemical weathering occurs when rocks are broken down by a chemical change. Biological weathering takes place when rocks are worn away by living organisms.  Erosion: Hydraulic action is when the force of the water erodes the rock and carves into the ground. Attrition is when the rocks and stones in the water bash together which cause bits to break off and this smooths it. Abrasion is when the rocks and stones in the river bash against the sides and bottom of the river channel.  Burial: As layers are piled one upon another, the sediments beneath are buried, sometimes by hundreds of metres of sediment above. The weight of these layers compacts (squashes down) the sediment grains. Minerals deposited from water in the spaces between the sediment grains gradually cements them together. 

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