Elements, Compounds, Mixtures
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Elements, Compounds, Mixtures

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    Elements, Compounds, Mixtures Elements, Compounds, Mixtures Presentation Transcript

    • Classification of Matter Elements, Compounds, Mixtures
    • Lesson Objective
      • Physical and Chemical Changes.
      • Elements
      • Compounds
      • Mixtures
    • Physical and Chemical Changes
      • All reaction in Chemistry can be divided into two types of changes: Physical or Chemical .
      • Physical Change :
      • NO new substance is formed.
      • These changes are easily reversible or temporary.
      • An example is dissolving salt in water.
      • Other examples of physical change include: melting, boiling, mixing 2 solids or liquids .
      • Chemical Change :
      • A NEW substance is formed.
      • These changes are irreversible or permanent .
      • The new substance formed will have different properties compared to its original elements. (E.g. different melting and different chemical reactions from the original substance.)
      Physical and Chemical Changes
      • One can recognize a chemical change from 2 observations :
      • The new substance has a different appearance , such as different color or different physical state.
      • An example is the electrolysis of water.
      • Reason: Electrolysis of water produces two new substances, Hydrogen gas and oxygen gas. Hydrogen and oxygen are both gases but water is a liquid.
      • A lot of heat is given out in a chemical changes.
      • Chemical changes are called chemical reactions.
      Physical and Chemical Changes
    • Illustration of chemical changes
    • An Overview
    • Elements, Compounds and Mixtures “ single, attached, play play…”
    • Introducing Little Miss “Element” Hi! I am Little Miss “Element” I am PURE SUBSTANCE I cannot be broken down into any simpler substance by means of a chemical reaction* or electricity**! *Chemical process refers to chemical reaction or heat **Electricity refers to electrolysis
    • Elements
      • Definition of an element:
      • An element is a pure substance which cannot be split up into two or more simpler substances by chemical means.
      Sugar is not an element as it can be broken down into carbon and water.
      • Note that an element:
      • Consists of only one kind of atom,
      • Cannot be broken down into a simpler type of matter by either physical or chemical means
      • Can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).
      Elements
    • Examples of elements
      • Elements are made up of tiny particles
      • Elements can be further classified into two groups:
      Atoms Molecules Is the smallest particle of an element and has the same chemical properties of the element Is made up of two or more atoms that are chemically bonded together (note: these atoms are of the SAME element!!) Hi, I am from the “Noble gas” family and I work alone We same same!!
    • These are elements! Atoms of same element copper element sodium element helium element Molecules of same element Hydrogen gas element ozone Cu Na He H O H O O
    • Atoms An element is made of tiny particles called atoms . The atoms of an element is different from that of another element.
    • Elements- Atoms
      • Microscopic view of the atoms of the element argon (gas phase).
      Consists of only one kind of atom
    • What is an atom? Examples of models of atoms: Hydrogen atom Sodium atom Chlorine atom H Na Cl
    • Molecules Very few elements exists as atoms besides elements such as helium and neon. Most elements exist as molecules. For example, hydrogen is H 2 . Ozone is O 3 .
    • Molecules consisting of a few atoms are called polyatomic molecules . Hydrogen (H 2 ) is a diatomic molecule. Ozone (O 3 ) is a triatomic molecule.
    • Elements-Molecules Microscopic view of the molecules of the element nitrogen (gas phase). Consists of only one kind of atom
    • Examples of molecules (elements) N N S S S S S S S S H H O O O O O
    • Allotropes of Carbon molecule (element)
      • Carbon is an element but made up of a very large molecule (also known as MACROMOLECULE)
      • There are 3 types of carbon molecular structures
        • C 60
        • Diamond
        • Graphite
    • Chemical Symbols of Elements Chemists use symbols to represent elements. For example, O represents oxygen while Fe represents iron . Element Symbol Element Symbol Calcium Ca Mercury Hg Carbon C Neon Ne Hydrogen H Silicon Si Iron Fe Sodium Na
    • Classification of Elements – Metals and Non-metals There are two major groups of elements – metals and non-metals . Iron is a metal. Oxygen is a non-metal. There are some elements called metalloids which behave like both metals and non-metals. Metals and non-metals are grouped separately on the Periodic Table .
    • What is an element?
      • An element is a substance that cannot be broken down into two or more simpler substances by any chemical means.
      - They are arranged in the Periodic Table, classified as metals and non-metals. - They may consist of atoms of same element or molecules of the same element. Metals (excluding hydrogen) Non-metals (including hydrogen)
    • Physical Properties metals and non-metals Metals Non-metals Shiny appearance Dull appearance Solids at r.t.p (except mercury) Gases, liquids or solids at r.t.p (room temp & pressure) Malleable, Ductile , Sonorous Brittle if solid (general) High melting and boiling points Low melting and boiling points Good conductors of heat Poor conductors of heat Good conductors of electricity Poor conductors of electricity (expect carbon and graphite)
    • Summarising Elements Metals Non Metals Atoms Atoms Molecules
    • Introducing Little Miss “Compounds” Harlow! Hehee!!! *giggles* I am also a PURE SUBSTANCE I am made up of a fixed number of two or more elements chemically combined .
    • Compounds
      • Note that a compound:
      • can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means),
      • has properties that are different from its component elements, and
      • always contains the same ratio of its component atoms.
      • A compound is a substance which is made up of two or more elements chemically combined together.
      What is a compound?
      • Chemical reactions taking place.
      Qn: Is this a compound? It only contains one type of element. Qn: Is this a compound? It only contains one type of element. H O H O O Qn: Is this a compound? It is not chemically combined.
    • So, what is a compound then? Water Ammonia gas Consists of two or more elements And They are chemically combined together! H
    • Compounds Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white.
    • Making compounds from their elements ELEMENTS COMPOUND hydrogen (colourless gas) oxygen (colourless gas) lighted splint heat, light and explosion water (colourless liquid) Example: Making water (picture) Water molecule Oxygen molecule Hydrogen molecule mixture of hydrogen and oxygen water Example: Making water (models) heat, light and explosion
    • Making compounds from their elements Example: Making iron sulphide compound Iron + sulphur  iron sulphide elements compound + yellow grey  heat heat black
    • Little Miss “Compound” Property #1 I can be represented as a “ chemical formula ” The different elements present in a compound are combined in a fixed ratio
      • General Rules:
      • - Only write the name of the metallic element
      • first
      • - Write the number of atoms of any element
      • in the compound in subscript
      • (applies to only 2 or more atoms)
      • - “ ide” will always be written at the
      • end of the non metal element
      • Special Rules:
        • Does not apply to organic compounds
        • (chapter 18 onwards)
    • Little Miss “Compound” Property #2 I am formed by atoms of different elements . However, I do not have the properties as them.
      • Examples
      • Na + Cl 2  NaCl
      • (s) (g) (s)
      • H 2 + O 2  H 2 O
      • (g) (g) (l)
    • Little Miss “Compound” Property #3 Because of my chemical bonds , I cannot be broken down by physical means. I can only be broken down by chemical reaction or electricity. Electrolysis (breaking down of compound by electricity) 2MgCl(s)  Mg(s) +Cl 2 (g) Thermal Decomposition (breaking down of compound by heat) HgO(s)  Hg(s) + O 2 (g)
    • How do we name compounds? Rule 1 A compound made up of two elements has a name that ends in -ide . • Sodium chlor ide — made up of the elements sodium and chlorine • Zinc ox ide — made up of the elements zinc and oxygen • Carbon diox ide — made up of the elements carbon and oxygen
    • How do we name compounds? Rule 2 A compound that contains hydroxide ions , OH – (a negatively charged ion made up of oxygen and hydrogen) is named a hydroxide. • Potassium hydroxide — contains potassium ions and hydroxide ions
    • How do we name compounds? Rule 3 A compound that contains a negatively charged polyatomic ion containing oxygen usually has a name ending in –ate . • Copper(II) sulph ate — contains oxygen atoms in the sulphate ion • Sodium nitr ate — contains oxygen atoms in the nitrate ion
    • Fixed Composition of Compounds For example, water ( H 2 O ) is a compound made only by joining together two atoms of hydrogen to one atom of oxygen. That is, the ratio of hydrogen atoms to oxygen atoms in water is always 2 : 1 . A compound is made up of different elements chemically combined in a fixed ratio .
    • Chemical Formula of a Compound Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. A compound can be represented by a chemical formula . The chemical formula states • the types of atoms (i.e. elements) in the compound, • the ratio of the different atoms in the compound. Types of atoms: hydrogen, oxygen Ratio of H to O = 2:1
    • How do we write chemical formula? Rule 1 For many compounds that contain both metallic and non-metallic elements, the symbol of the metallic element is written first . • calcium oxide ( Ca O) • sodium chloride ( Na Cl) • magnesium carbonate ( Mg CO 3 )
    • How do we write chemical formula? Rule 2 The number of atoms is written as a subscript, to the right of the atom’s symbol. • water ( H 2 O , not H2O or 2HO) • magnesium carbonate ( MgCO 3 , not MgCO 3 or MgC 3 O)
    • How do we write chemical formula? Rule 3 It is not necessary to write the subscript ‘1’. • water ( H 2 O , not H 2 O 1 ) • calcium oxide ( CaO , not Ca 1 O 1 )
    • How do we write chemical formula? Rule 4 The oxygen atom is usually written at the end of the formula. • water ( H 2 O , not OH 2 ) • carbon dioxide ( CO 2 , not O 2 C) • nitric acid ( HNO 3 , not O 3 NH)
    • How do we calculate the number of atoms in a formula? Pb(NO 3 ) 2 Number of nitrogen (N) atoms = 1 x 2 = 2 Number of lead (Pb) atoms = 1 Number of oxygen (O) atoms = 3 x 2 = 6
    • Compounds can be Decomposed Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition . Mercury(II) oxide Oxygen
    • Summarizing
      • A compound is made up of two or more elements chemically joined together
      • A compound has a fixed composition
      • Every compound has a unique chemical formula
      • A compound has a completely different properties from its elements
      • A chemical reaction (decomposition or electrolysis) is needed to separate the elements in the compound
    • Molecules- Elements or compounds?
      • A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together.
      • It can be a molecule of an element
      • E.g. N 2 , O 2 , S 8
      • It can be molecule of a compound.
      • H 2 O, CO 2 , NH 3
      N N O O S S S S S S S S O H H O O C N H H H
    • Think about this… ROJAK!!
    • Introducing Little Mr. “Mixture” Burp!!!! I am messy! I am formed when two or more substances joined together physically ( without chemical bonds ) I have the same properties as all the substances I am his best friend! AIR
    • Mixtures
      • Definition of a mixture:
      • A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.
    • Mixtures
      • Note that a mixture:
      • consists of two or more different elements and/or compounds NOT chemically combined .
      • Can be homogeneous or non-homogeneous
      • can be separated into its components by physical means , and
      • often retains many of the properties of its components .
      • Microscopic view of a gaseous mixture containing two elements (argon and nitrogen) and a compound (water).
      Mixtures
    • Mixtures
      • Examples of mixtures include muddy water and air. Air is made up of gases such as nitrogen and oxygen mixed together.
    • Little Mr “Mixture” I do not have a fixed composition of the substances.
      • A Mixture can be:
      • element + element
      • element + compound
      • compound + compound
      • (Refer to page 59, Fig 4.7)
      He is a “boo-boo!” He can be separated to its substances by physical methods
    • A mixture of 2 elements A mixture of two elements, e.g. neon (Ne) and hydrogen (H 2 )
    • A mixture of 1 element and 1 compound A mixture of one element and one compound, e.g. hydrogen (H 2 ) and ammonia (NH 3 )
    • A mixture of 2 compounds A mixture of two compounds, e.g. water vapour (H 2 O) and carbon dioxide (CO 2 )
    • Alloy: What is it??
      • It is a mixture of metals with other elements
      • Alloy metals are generally stronger and better in physical properties
      • Examples
        • Steel (Iron + Carbon)
        • Stainless Steel (Nickel + Iron + Chromium + carbon)
        • Brass (Copper + Zinc)
      Yup! That’s ME! Mr Alloy
    • Can you differentiate? Compound Mixture of element & compound Mixture of 2 elements-Alloy Molecules of an element Mixture of 2 elements
    • Conclusion
      • An element is a pure substance which cannot be split up into two or more simpler substances by chemical means.
      • A compound consist of a fixed number of different kinds of atoms chemically combined together.
      • A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.
    • Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Separation Cannot be separated into its constituents by physical methods . Separation can only be done by chemical methods or by electricity. e.g. Water can only be separated into Hydrogen and Oxygen by Electrolysis. Can be easily separated into its constituents by physical methods . e.g. Salt can be obtained from its solution by evaporation. Water can be obtained by simple distillation.
    • Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Composition The composition is fixed. The constituents (elements) in the compound are combined in definite amount. e.g. To form one molecule of water, two atoms of Hydrogen and one atom of Oxygen is needed. Has no fixed composition. The amount of constituents in a mixture can vary. e.g. The amount of salt added into the water to make salt solution can vary and vice versa.
    • Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Properties The physical and chemical properties of the compound is different from the properties of its constituents. e.g. Hydrogen and Oxygen are gases while water is a liquid at room temperature and pressure. e.g. Water has a fixed melting and boiling point. The mixture does not have its own properties. It has the average physical and chemical properties of the constituents that made it up. (Each constituents still retain its own properties) e.g. The salt solution still retains its salt taste. e.g. Salt solution does not have a fixed melting or boiling point, but rather over a range of temperature.
    • Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Energy Change Energy is usually given out or occasionally taken in when a compound is formed. Normally little or no energy is given out or taken in when a mixture is formed.
    • Differences between mixtures and compounds *giggles* HeE stupid… Laugh what? I know I am a little “bushy and hairy” than you… Little Miss Compound Mr Messy VS
    • Comparison between mixtures and compounds Fixed Variable Mp / Bp Has a fixed composition Does not have a fixed composition Composition A chemical reaction takes place when a compound is formed No chemical change takes place when a mixture in formed Energy Change Properties are unique and different from its elements Same properties as its components Properties (chemical / physical) Elements in a compound Cannot be separated by physical methods Components can be separated by physical methods Separation /breakdown Compound Mixture
    • Challenge Time
      • Is mineral water an element, mixture or compound?
    • Challenge Time
      • Are YOU an element, mixture or compound?
    • EXTRA!
      • Human body is made up of 28 elements?
      • About 99% our mass is made up of the 6 main elements
        • Oxygen (65%)
        • Carbon (18%)
        • Hydrogen (10%)
        • Nitrogen (3%)
        • Calcium (1.5%)
        • Phosphorus (1.5%)
    • The End……