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Definition: An element is a substance which cannot be broken down into two or more simpler substances by chemical reactions or electricity.5.1 Building Blocks of Matter?: 5.1 Building Blocks of Matter? Water can be separated into its constituents – hydrogen and oxygen – by passing electricity through. However, hydrogen and oxygen cannot be separated into simpler substances this way. Hence, oxygen and hydrogen are elements . oxygen hydrogen water containing a little sulphuric acid carbon electrodes battery (6 V)5.1 Building Blocks of Matter?: 5.1 Building Blocks of Matter? The element nitrogen makes up 78% of air, while oxygen makes up 21 %. The rest is argon , carbon dioxide, water vapour , etc.Earth’s Crust: Earth’s CrustEarth’s Crust: Earth’s Crust Oxygen makes up about 47% of the Earth’s crust, Followed by silicon (28%) And then aluminium (8%)5.1 Building Blocks of Matter?: Oxygen is part of the clouds in the sky. 5.1 Building Blocks of Matter? Oxygen is present as a gas in the air. Oxygen is combined with the element hydrogen, to form water. Oxygen is combined with the element silicon to form sand. Oxygen is used by plants to make food.Try this:: Try this: You put sugar into a crucible and heat it for some time. You observe that the sugar first melts into brown caramel, and eventually become black charcoal, while there are also colourless liquid droplets condensed on the lid of the crucible. Explain why sugar is not an element.Slide 10: Sugar is not an element because it can be broken down into simpler substances, i.e. charcoal/carbon and water.Try this: Try this Table salt is sodium chloride. It becomes a molten liquid at about 800 °C, and when electricity is passed through the liquid, a yellowish green gas and a silvery liquid result. Explain why table salt is not an element, and state what you think the gas and the silvery liquid may be.5.3 Periodic Table: 5.3 Periodic Table In order to study the properties of elements systematically, scientists have organised the elements into a table called the Periodic Table .5.3 Periodic Table: 5.3 Periodic Table The names of elements are represented by chemical symbols . For example, carbon is represented by ‘C’, whereas chlorine is represented by ‘Cl’. carbon chlorine5.3 Periodic Table: 5.3 Periodic Table Elements that are arranged in the same vertical column belong to the same group . Elements in the same group have the same chemical properties. group5.3 Periodic Table: 5.3 Periodic Table Elements that are arranged in the same horizontal row belong to the same period . As we move from the left to right along one period, the properties of elements slowly change from those of metals to those of non-metals. period5.3 Periodic Table: 5.3 Periodic Table The Periodic Table organises elements broadly into metals and non-metals. metallic non-metallic5.3 Periodic Table: 5.3 Periodic Table The elements on the left side of the zigzag line (in red) are grouped as metals, while those on the right are grouped as non-metals. The elements near this zigzag line are called metalloids . These elements have properties of both metals and non-metals. zigzag line5.2 Classifying Elements: 5.2 Classifying Elements By default, we always discuss the state of matter as at r.t.p . meaning at room temperature (25 o C ) and pressure (1 atm ). Most elements exist as solids at r.t.p ., for example, all metals except mercury; carbon , silicon, iodine, etc. A few elements exist as gases at r.t.p , for example, oxygen, nitrogen, fluorine , chlorine, neon, and so on. Only 2 elements exist as liquids at r.t.p ., they are mercury and bromine.5.2 Classifying Elements: 5.2 Classifying Elements Elements can be classified into two general categories: metals and non-metals .Slide 22: Position in the Periodic Table Type of element State of matter at r.t.p. Examples Left side of the line metals solid Right side of the line non-metals liquid and gas5.2 Classifying Elements: 5.2 Classifying Elements Elements can be classified into two general categories: metals and non-metals . General properties Metals Non-metals Appearance Shiny when polished Usually dull State of matter at room temperature Solid state (except mercury which is in liquid state.) Most are in gaseous state; a few exists as solids; bromine exists as a liquid.5.2 Classifying Elements: 5.2 Classifying Elements General properties Metals Non-metals Ability to withstand stress Malleable – can be beaten into sheets Ductile – can be drawn into wires without breaking Brittle (for solids) – can snap or break easily Non-ductile Density High Low Melting and boiling points High Low5.2 Classifying Elements: 5.2 Classifying Elements General properties Metals Non-metals Ability to conduct electricity Good Poor Ability to conduct heat Good Poor The properties of elements have helped scientists and researchers to use metals and non-metals for various purposes.Properties and uses of metal elements: Properties and uses of metal elements Copper Reddish brown solid Good conductor of electricity Ductile (easily drawn into wires) Corrosion resistant Strong Copper wires Copper is often used to make pipes.Properties and uses of metal elements: Properties and uses of metal elements Zinc Grey solid Prevents rusting of iron Good conductor of electricity Strong Corrosion resistant Zinc is used inside batteries to help produce electricity. Many coins are zinc-plated.Properties and uses of metal elements: Properties and uses of metal elements Aluminium Silvery shiny solid Low density Strong and light Malleable (can be shaped easily) Corrosion resistant Aluminium is used to make aircraft bodies. Most drink cans are made of aluminium. Aluminium is used to make cooking foil.Properties and uses of metal elements: Properties and uses of metal elements Mercury Silvery liquid Does not react easily with other chemicals Mercury vapour is fluorescent (gives off light) Good conductor of heat Expands evenly on heating Mercury is used in thermometers to measure temperature. Mercury can also be used to measure pressure.Properties and uses of metal elements: Properties and uses of metal elements Magnesium Grey solid Burns with dazzling white light Forms base to neutralise excess acid in stomach Magnesium is used to make milk of magnesia, which is used to relieve acid indigestion.Properties and uses of metal elements: Properties and uses of metal elements Iron Grey solid Good conductor of heat and electricity Ductile Strong Magnetic Iron is often used to make cutlery.Properties and uses of non-metal elements: Properties and uses of non-metal elements Iodine Black crystals Poisonous Antiseptic (prevents wound infection) Iodine is used as an antiseptic in medicines.Properties and uses of non-metal elements: Properties and uses of non-metal elements Chlorine Greenish-yellow gas Bleaches dyes Poisonous Chlorine is used in bleaches for our clothes.Properties and uses of non-metal elements: Properties and uses of non-metal elements Diamond (Carbon) Hardest substance known to man Can be polished to form a shiny, reflecting, transparent solid Diamond drills like this can help to cut through very hard metals.Properties and uses of non-metal elements: Properties and uses of non-metal elements Hydrogen Colourless gas Gas with lowest density Explosive Hydrogen is used to fill weather balloons and blimps.Properties and uses of non-metal elements: Properties and uses of non-metal elements Carbon (Graphite) Black solid Smooth Lightweight Good conductor of electricity Carbon is used to make rackets.Properties and uses of non-metal elements: Properties and uses of non-metal elements Nitrogen Colourless gas Unreactive, does not burn or support combustion Low boiling point Nitrogen is used to make fertilisers for farms.Properties and uses of non-metal elements: Properties and uses of non-metal elements Oxygen Colourless gas Essential for life Does not burn but supports combustion Oxygen gas in the tank allows scuba divers to breathe in water. Oxygen is used in the flame for welding.COMPOUNDS: COMPOUNDS5.4 What are Compounds?: 5.4 What are Compounds? A compound is a substance which is made up of two or more different elements chemically combined together. Glass Water Elements in the compound: Silicon, oxygen Elements in the compound: Hydrogen, oxygen Table salt Elements in the compound: Sodium, chlorine Sugar Elements in the compound: Carbon, hydrogen and oxygen Chalk Elements in the compound: Calcium, carbon and oxygenCharacteristics of compounds: Characteristics of compounds The properties of a compound is different from its constituent elements. For example, the compound sodium chloride can be eaten. However, its constituent elements – sodium and chlorine – are not safe for consumption.Characteristics of compounds: Characteristics of compounds Sodium chloride + = sodium chlorine sodium chloride Sodium is a highly reactive solid at room temperature. It burns vigorously when in contact with water. Chlorine is a greenish-yellow poisonous gas at room temperature. Sodium chloride, or table salt, is used in foods to improve their taste and in preservatives.Characteristics of compounds: Characteristics of compounds The constituent elements of a compound are always combined in a fixed ratio by mass OR by number of atoms . For example, to form water, the mass ratio of hydrogen and oxygen that combine chemically is always 1 : 8, and the ratio of number of hydrogen atoms vs. oxygen atoms is always 2:1.How are compounds formed?: How are compounds formed? Combination DEFINITION: A general category of a chemical reaction in which two or more reactants are chemically bonded together to form a single product . r eactant 1 + reactant 2 (+ …) PRODUCTHow are compounds formed?: How are compounds formed? Combination Combustion reactions are often combination reactions. It occurs when elements or compounds burn and combine with oxygen to form one or more new compounds.How are compounds formed?: How are compounds formed? Combination An example of combustion: carbon + oxygen carbon dioxide element element compoundExamples of combustion: Examples of combustion complete combustion carbon + oxygen carbon dioxide incomplete combustion: carbon + oxygen carbon monoxide + carbon magnesium + oxygen magnesium oxide methane + oxygen carbon dioxide + water ethanol + oxygen carbon dioxide + waterHow are compounds formed?: How are compounds formed? Combination In other methods of combination, certain elements and/or compounds can combine to form new compounds when they come into contact with one another .Examples of combustion: Examples of combustion sodium + chlorine sodium chloride sodium + oxygen sodium oxide aluminium + bromine aluminium bromide sodium + water sodium hydroxide + hydrogenHow are compounds formed?: How are compounds formed? Decomposition Decomposition happens when a more complex compound is broken down into simpler substances. For example: sugar water vapour + carbon compound compound elementHow can compounds be broken down?: How can compounds be broken down? Heating and passing and electric current can break down a compound into simpler substances. Some compounds can also be broken down into simpler substances when exposed to light. For example, CFC (chlorofluorocarbon) compound in styrofoam is broken by sunlight into a harmful substance that depletes the ozone layer.5.5 What are Mixtures?: 5.5 What are Mixtures? A mixture consists of two or more different substances that are mixed but not chemically combined together. The substances that make up a mixture may be elements, compounds or both elements and compounds.5.5 What are Mixtures?: Milk is a mixture of compounds such as proteins and fats. Air is a mixture of elements, such as nitrogen and oxygen, and compounds such as carbon dioxide and water vapour. 5.5 What are Mixtures? Examples of mixtures:Properties of mixtures: Properties of mixtures Properties of mixtures Properties of air When a mixture is formed, no chemical reaction occurs. Air is formed by simply mixing its component gases – nitrogen, oxygen, carbon dioxide, noble gases and water vapour. No reaction occurs between the components. A mixture has the properties of its constituent substances. Air has the properties of its components – nitrogen, oxygen, carbon dioxide, noble gases and water vapour . Air supports combustion because the oxygen gas in it supports combustion.Properties of mixtures: Properties of mixtures Properties of mixtures Properties of air A mixture can be separated easily by physical methods (i.e. without involving chemical reaction). Air can be separated into its components by fractional distillation. The components in mixtures are not mixed in any fixed proportion. The proportions of the constituent gases in air may vary with place and time. For example, we can find a higher amount of carbon dioxide in the city than the seaside.Different types of mixtures: Different types of mixtures Solid-solid mixtures Alloys are mixtures of a metal element with other metals or non-metals. An example is duraluminium which is a mixture of aluminium and copper. It is strong and durable and often used in building ships and aircraft engines.Different types of mixtures: Different types of mixtures Alloys An alloy is a mixture of a metal and one or more other elements. It has properties that are better than those of its constituents. Examples of alloys: Steel – an alloy mainly composed of iron with a small percentage of carbon Brass – copper-based alloy containing zinc Bronze – copper-based alloy containing tinDifferent types of mixtures: Different types of mixtures Solid-solid mixtures Concrete is a mixture of cement and gravel. It is used in pavements, architectural structures, bridges, etc.Different types of mixtures: Different types of mixtures Solid-liquid mixtures Calamine lotion is used for treating skin rashes. It is made up of solid zinc oxide, solid calcium hydroxide, liquid glycerine and water.Different types of mixtures: Different types of mixtures Solid-liquid mixtures Chendol is one of the many types of drinks that contain both solids and liquids.Different types of mixtures: Different types of mixtures Liquid-liquid mixtures Alcoholic drinks consist of ethanol and other flavourings dissolved in water. Vinegar is made up of a solution of ethanoic acid and water. wine vinegarDifferent types of mixtures: Different types of mixtures Liquid-gas mixtures Most forms of foam that you see (e.g. in a cup of cappucino or from a bubble bath ) are made up of air bubbles in a liquid.Different types of mixtures: Different types of mixtures Liquid-gas mixtures Soda drinks contain carbon dioxide dissolved in a flavoured drink.Different types of mixtures: Different types of mixtures Gas-gas mixtures The air around us is also a mixture of gases. The properties of air show some common properties of mixtures.Miscellaneous: Miscellaneous http://en.wikipedia.org/wiki/Metals http://en.wikipedia.org/wiki/Non-metals http://periodic.lanl.gov/default.htm http://www.teachnet.ie/macalvey/compound.htm You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.