Elements, Compounds, Mixtures

Elements, Compounds, Mixtures

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.

PHYSICAL AND CHEMICAL CHANGES 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. AN OVERVIEW Heterogenous

ELEMENTS, COMPOUNDS AND MIXTURES INTRODUCING ELEMENTS Element PURE SUBSTANCE 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. ELEMENTS 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).

EXAMPLES OF ELEMENTS ELEMENTS ARE MADE UP OF TINY PARTICLES ELEMENTS CAN BE FURTHER CLASSIFIED INTO TWO GROUPS: Atoms Is the smallest particle of an element and has the same chemical properties of the element Gases from the Noble gas family and work alone Molecules Is made up of two or more atoms that are chemically

bonded together (note: these atoms are of the SAME element!!) THESE ARE ELEMENTS! Atoms of same element Cu copper element Na sodium element He

Molecules of same element H helium element H Hydrogen gas element O O ozone O

ATOMS An element is made of tiny particles called atoms. The atoms of an element is different from that of another element. ELEMENTSATOMS Consists of only one kind of atom MICROSCOPIC VIEW OF THE ATOMS OF THE ELEMENT ARGON

(GAS PHASE). WHAT IS AN ATOM? Examples of models of atoms: H Hydrogen atom Na Sodium atom Cl Chlorine atom

MOLECULES Very few elements exists as atoms besides elements such For example, hydrogen is H2. as helium and neon. Most elements exist as molecules. Ozone is O3. Hydrogen (H2) is a diatomic molecule.

Molecules consisting of a few atoms are called polyatomic molecules. Ozone (O3) is a triatomic molecule. ELEMENTSMOLECULES Consists of only one kind of atom Microscopic view of the molecules of the element nitrogen (gas phase).

EXAMPLES OF MOLECULES O (ELEMENTS) H H O O O S O S

S S S N N S S S 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 C60 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 There areNON-METALS two major groups of elements metals and non-metals. Iron is a metal. Oxygen is a non-metal. Metals and non-metals are grouped separately on the Periodic Table. There are some elements called metalloids which behave like both metals and non-metals. 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 Non-metals (including the same element. Metals (excluding hydrogen) 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 Good conductors of heat Low melting and boiling points Good conductors of electricity

Poor conductors of electricity (expect carbon and graphite) Poor conductors of heat SUMMARIZING Elements Non Metals Metals Atoms Atoms

Molecules INTRODUCING COMPOUNDS PURE SUBSTANCE 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. WHAT IS A COMPOUND? A COMPOUND IS A SUBSTANCE WHICH IS MADE UP OF TWO OR MORE ELEMENTS CHEMICALLY COMBINED TOGETHER. - Chemical reactions taking place. Qn: Is this a compound? It only contains one type Cu of element. Qn: Is this a compound? Qn: Is this a compound?

H H It only contains one type of element. O O It is not chemically H combined. H O SO, WHAT IS A COMPOUND THEN? H

H H O H Water N H Ammonia gas

Consists of two or more elements And They are chemically combined together! 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 Example: Making water (picture) lighted

splint ELEMENTS hydrogen oxygen (colourless (colourless gas) gas) COMPOUND heat, light and explosion water

(colourless liquid) Example: Making water (models) mixture of heat, hydrogen and light oxygen and water explosio n

Hydrogen molecule Oxygen molecul e Water molecul e MAKING COMPOUNDS FROM THEIR ELEMENTS Example: Making iron sulphide compound compound elements

Iron + heat sulphur iron sulphide heat + yellow

grey black COMPOUNDS PROPERTY #1 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) COMPOUNDS PROPERTY #2 Formed by atoms of different elements. However, does not have the properties as them.

Examples Na + Cl2 NaCl (s) (g) (s) H2 + O2 H2O (g) (g) (l) COMPOUNDS PROPERTY #3 Electrolysis (breaking down of compound by electricity) 2MgCl(s) Mg(s) +Cl2(g) Thermal Decomposition (breaking down of compound by heat) HgO(s) Hg(s) + O2(g)

Because of my chemical bonds, they cannot be broken down by physical means. They can only be broken down by chemical reaction or electricity. HOW DO WE NAME COMPOUNDS? 1 elements A compound madeRULE up of two has a name that ends in -ide. Sodium chloride made up of the elements sodium and chlorine Zinc oxide made up of the elements zinc and oxygen

Carbon dioxide 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) sulphate contains oxygen atoms in the sulphate ion Sodium nitrate contains oxygen atoms in the nitrate ion FIXED COMPOSITION OF COMPOUNDS A compound is made up of different elements chemically combined in a fixed ratio. For example, water (H2O) 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.

CHEMICAL FORMULA OF A COMPOUND 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 (CaO) sodium chloride (NaCl) magnesium carbonate (MgCO3) HOW DO WE WRITE CHEMICAL FORMULA? RULE 2 The number of atoms is written as a subscript, to the right of the atoms symbol. water (H2O, not H2O or 2HO) magnesium carbonate

(MgCO3, not MgCO3 or MgC3O) HOW DO WE WRITE CHEMICAL FORMULA? RULE 3 It is not necessary to write the subscript 1. water (H2O, not H2O1) calcium oxide (CaO, not Ca1O1) HOW DO WE WRITE CHEMICAL FORMULA? RULE 4 The oxygen atom is usually written at the end of the formula.

water (H2O, not OH2) carbon dioxide (CO2, not O2C) nitric acid (HNO3, not O3NH) HOW DO WE CALCULATE THE NUMBER OF ATOMS IN A FORMULA? Number of nitrogen (N) atoms Number of lead (Pb) atoms = 1 =1x2=2 Pb(NO3)2 Number of oxygen (O) atoms

=3x2=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. Oxygen Mercury(II) oxide 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 SS S S N N O O S

IT CAN BE MOLECULE OF A COMPOUND. S SS E.G. N2, O2, S8 H2O, CO2, NH3 H O H O C

H O H N H MIXTURE S 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. 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) CAN YOU DIFFERENTIATE? Mixture of 2

elements-Alloy Compound Mixture of element & compound 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. COMPARISON BETWEEN MIXTURES AND COMPOUNDS Mixture Compound Components can be separated by physical methods

Same properties as its components Elements in a compound Cannot be separated by physical methods Properties are unique and different from its elements Mp / Bp No chemical change takes place when a mixture in formed Variable A chemical reaction takes

place when a compound is formed Fixed Compositio n Does not have a fixed composition Has a fixed composition Separation /breakdown Properties (chemical / physical)

Energy Change

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