S1 Building Blocks Summary Notes

Transcription

1 S1 Building Blocks Summary Notes Atoms & Molecules 1 We are developing our understanding of atoms and molecules. Atoms are the simplest building blocks of every substance in the universe. There are just over 100 different types of atoms. Elements are made up of only one type of atom and can be found in the Periodic Table. The element Oxygen has the chemical symbol O 2 which means there are two oxygen atoms bonded together. When atoms join together they form molecules. Chemists list all the elements on the Periodic Table where each element has a name e.g. Magnesium a symbol e.g. Mg an atomic number e.g. 12 When writing the symbols the first letter is a CAPITAL followed by a small letter. In this example we can see the name of the element Carbon along with its symbol C (notice this symbol only has one letter which must be a capital).

2 Using the Periodic Table 2 We are developing our knowledge of the periodic table. Studying the periodic table like the one above we can see that it can be split into two main sections Metals and Non-metals. Metals conduct electrical current but non-metals do not conduct. Metalloids are elements that have characteristics of both metals and non-metals. We can also see that each element has a number, which indicates the position of the element on the periodic table. The number also tells us how many protons each element has in its nucleus. This number is known as the atomic number. Hydrogen has the atomic number 1 which means it has only one proton in its nucleus. It can never have any other atomic number! If it had two protons it would no longer be Hydrogen but instead it would be Helium.

3 Groups and Periods 3 We are developing our knowledge of the periodic table. Elements in the same column have very similar chemical properties. The columns in the periodic table are called GROUPS. The rows in the periodic table are called PERIODS. Some of the groups have special names: Group 1 Alkali Metals reactive metals, must be stored under oil Group 7 Halogens reactive nonmetals Group 8 Noble Gases very unreactive non-metals e.g. sodium e.g. chlorine e.g. helium

4 Solids, Liquids and Gases 4 We are developing our knowledge of the periodic table. Solid elements have a melting point above room temperature* Gas elements have boiling points below room temperature* Liquid elements have: a melting point below room temperature* a boiling point above room temperature* *Room temperature is approximately 25 o C Examples: Water Melting point = 0 o C Boiling point = 100 o C As room temperature is greater than its melting point it cannot be a solid. Room temperature is less than its boiling point so it cannot be a gas. Therefore it must be a liquid. Gold Melting point = 1064 o C Boiling point = 2856 o C As room temperature is less than its boiling point it cannot be a gas. Room temperature is also less than its melting point so it cannot be a liquid and so must be a solid.

5 Oxygen Melting point = o C Boiling point = o C As room temperature is greater than its melting point it cannot be a solid. Room temperature is also greater than its boiling point so it cannot be a liquid. Therefore it must be a gas. Elements & Compounds 5 We are investigating the properties of elements. The periodic table consists of many elements with various characteristics and properties. This makes each element useful for some applications but not for others. e.g. Aluminium is a soft, light metal which makes it useful for aeroplane parts and window frames but not for construction parts like girders that need to be strong and solid. The different properties of each element can also be useful if we need to separate mixtures of elements. e.g. If Iron and sulphur are added together they can be easily separated using a magnet. This is because iron has magnetic properties and sulphur does not. The same iron and sulphur mixture when heated together creates a new substance that cannot be separated using a magnet. This is because the heat has caused the iron and sulphur to chemically join (bond) together, creating a new compound called iron sulphide which does not have magnetic properties. sulphur iron iron sulphide

6 This chemical reaction can be written as a word equation: Sulphur + Iron = Iron Sulphide Other chemical reactions can also be written as a word equation. e.g. Magnesium + Oxygen = Magnesium Oxide As compounds are chemically joined together (bonded) much more energy is needed to split them up. Whereas mixtures of elements are not bonded together so are relatively easy to split up. Naming Compounds 6 We are learning how compounds are named. The name of a compound can tell you the names of the elements that it is made from. If the compound is sodium chloride (salt) then the elements are sodium and chlorine. The first element in the compound does not change its name and it s usually the furthest left in the periodic table or, if in the same group, the furthest up the table. e.g. a compound of sulphur and chlorine is called sulphur chloride and not chlorine sulphide. Oxygen is always the second element in an oxide compound. e.g. you get sulphur oxide, not oxygen sulphide!

7 Element furthest left comes first when naming the compound Element furthest to the right comes second in the compound name Sodium + Chlorine = Sodium Chloride Examples of how compounds are named: Elements magnesium, oxygen sodium, phosphorus calcium, iodine potassium, carbon lead, sulphur copper, nitrogen carbon, oxygen sulphur, copper Compound magnesium oxide sodium phosphide calcium iodide potassium carbide lead sulphide copper nitride Carbon oxide copper sulphide

8 Chemical Reactions in Air 7 We are investigating the reactions of elements and air. Copper is an element which reacts with oxygen to form a different coloured compound called copper oxide. The new compound is greater in mass than the original copper as oxygen has bonded to it. The Statue of Liberty is an example of this process. The statue is made from copper, but even before it was partly assembled in Paris it had started to become dull - the copper was reacting with the oxygen in the air. The statue was reassembled in New York in 1886 but within a few years it had turned black since copper oxide had formed. Over many years the black copper oxide reacted with the small amounts of carbon dioxide in the air. The Statue of Liberty eventually turned green. The surface was now coated with copper carbonate. Investigating Chemical Reactions 8 We are investigating the signs of a chemical reaction During a chemical reaction a new substance is always formed. We can tell that a chemical reaction has taken place by looking for one or more of the following changes 1. A colour change 2. An energy change 3. Heat is given out or taken in (and therefore the temperature changes) 4. Light or sound is produced. 5. A new substance is formed (gas or precipitate)

9 The Reactivity Series 9 We are learning to investigate the extraction of useful substances from natural materials. Some metals are more reactive than others. Sodium will react when placed in water, but gold will not be affected by the water at all. The reactivity of a metal determines how easy it is to extract from rocks in the ground (known as metal ores). The Reactivity Series is a list of metals shown in their order of reactivity. Potassium (K) Most Reactive Sodium (Na) Lithium (Li) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Tin (Sn) Lead (Pb) Copper (Cu) Mercury (Hg) Silver (Ag) Gold (Au) Least Reactive Making Metals 10 We are investigating the extraction of useful substances from natural materials. Some metals have been known about for a very long time and their date of discovery is described as pre-historic, e.g. gold was used in ancient Egyptian times and before. This is because some metals are found un-combined in the Earth s crust. These metals include gold, silver, copper and mercury. Most other metals are found combined to other elements. Some of these metal compounds, called ores, can release the metal inside them by heating with carbon, e.g. iron, lead, tin, copper and zinc. For example, copper can be extracted from copper carbonate by firstly heating it to give us copper oxide then heating it again, but this time with carbon, to give us copper. The following word equation describes the process fully: 1. copper carbonate copper oxide + carbon dioxide 2. copper oxide + carbon copper + carbon dioxide

10 Electrolysis 11 We are investigating the extraction of useful substances from natural materials. Some metals cannot be separated by heating their ores with carbon. Reactive metals like aluminium require more energy to turn the metal ore compound back to the pure metal again. This process is called electrolysis and the energy needed is supplied by passing an electrical current through the ore. Aluminium, magnesium, sodium and potassium are made this way. Copper can be extracted from a solution of copper chloride by passing an electrical current through it as shown below.