Elements,compounds and mixtures

class 8

1. Elements, compounds and mixtures Done by - Debjani Purkayastha

2. Lesson Objective Elements Compounds Mixtures

3. An Overview MATTER PURE SUBSTANCES COMPOUNDS HOMOGENEOUS ELEMENTS HETEROGENEOUS MIXTURES

4. Introducing Little Miss “Element ” *Chemical process refers to chemical reaction or heat **Electricity refers to electrolysis 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**!

5. 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.

6. 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).

7. 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!!)

8. T h e s e A r e E l e m e n t s Atoms of same element Helium Copper Sodium Molecules of same element Hydrogen gas element Ozone He Cu Na H H O O O

9. Atoms Elements An element is made of tiny particles called atoms. The atoms of an element is different from that of another element. Consists of only one kind of atom

10. Molecules Very few elements exists as atoms besides elements such as helium and neon. Most elements exist as molecules. For example, hydrogen is H2, Ozone is O3. Molecules consisting of a few atoms are called polyatomic molecules. For example Hydrogen (H2) is a diatomic molecule. Ozone (O3) is a triatomic molecule.

11. Chemical Symbols of Elements Chemists use symbols to represent elements. For example, O represents oxygen while Fe represents iron. Element Symbol Calcium Ca Hydrogen H Iron Fe Carbon C Mercury Hg Neon Ne Sodium Na

12. 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. 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.

13. P r o p e r t i e s Metals Non -metals Shiny appearance Dull appearance Solids at r.t.p (except mercury) Gases, liquids or solids at room temp & pressure High melting and boiling points Low melting and boiling points Malleable, Ductile, Sonorous Brittle if solid (general) Good conductors of heat Poor conductors of heat Good conductors of electricity Poor conductors of electricity (expect carbon and graphite)

14. Metals Non – metals Metalloids The metals which exhibit the highest degree of metallic behaviour is known as metals Non-metals are such elements which do not possess any metallic behaviour . Metalloids are such elements, which possess some of the properties like metal, while some like non-metal. Metals are placed on the left side of the periodic table. Non-metals are placed on the right side of the periodic table Metalloids are placed in the middle of the periodic table. Metals have a shiny appearance. Non-metals have a dull appearance. Metalloids have a shiny and dull appearance. Thermal and electrical conductivity is high in metals. It is very low in non-metals. Thermal and electrical conductivity is good though it is less than metals. Metals have low electronegativity . Non-Metals have high electronegativity . Metalloids neither possess a too high or too low value of electronegativity . Metals show ductility and malleability. Non-metals do not show ductility and malleability. Metalloids also do not show this property. Lithium, Sodium,Calcium , Magnesium, Barium, Lead, Indium, Bismuth, Iron, Copper, Zinc, Nickel, etc. Iodine, Bromine, Helium, Neon, Argon, Krypton, Sulfur, Phosphorous, etc. Arsenic, Tellurium, Antimony, Polonium, Tennessine , etc.

15. Introducing Little Mr “Compounds” I am also a PURE SUBSTANCE I am made up of a fixed number of two or more elements chemically combined .

16. Compound 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.

17. What is a compound ? A compound is a substance which is made up of two or more elements chemically combined together. Water Ammonia Consists of two or more elements And They are chemically combined together! H O H H N H H

18. Little Mr “Compound” Property I am formed by atoms of different elements. However, I do not have the properties as them. Examples • Na + Cl2  NaCl (s) (g) (s) • H2 + O2  H2O (g) (g) (l)

19. Fixed Composition of Compounds 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. A compound is made up of different elements chemically combined in a fixed ratio.

20. Various types of separation processes are:  Using a separating funnel: A separating funnel is used for the separation of components of a mixture between two immiscible liquid phases. One phase is the aqueous phase and the other phase is an organic solvent. This separation is based on the differences in the densities of the liquids. The liquid having more density forms the lower layer and the liquid having less density forms the upper layer. Applications:   To separate a mixture of oil and water. To separate a mixture of kerosene oil and water.

21. Simple distillation:- Simple distillation is a method used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.  Applications:   Separation of acetone and water. Distillation of alcohol.

22. Decantation Decantation  is a process to separate mixtures by removing a liquid layer that is free of a precipitate, or the solids deposited from a solution. The purpose may be to obtain a decant (liquid free from particulates) or to recover the precipitate.

23. Sublimation Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state.

24. Evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other based on how they collide with each other. 

25. Magnetic separation Magnetic separation  is the process of  separating  components of mixtures by using  magnets  to attract  magnetic  materials. The process that is used for  magnetic separation  detaches non- magnetic  material with those who are  magnetic .

26. Filtration Filtration is a physical, biological or chemical operation that separates solid matter and fluid from a mixture with a filter medium that has a complex structure through which only the fluid can pass.

27. Gravity separation Sand and sawdust  can be  separated  by  gravity  method. ... Mix  sand and saw dust  in water  saw dust  being lighter will float on water, and  sand  being heavier gets settled at bottom due to  gravitational  force of attraction.

28. Hand Picking The method in which substances in a mixture can be separated by just  picking  them out with the help of  hand  from the mixture is known as  handpicking  method. It is one of the various methods which are carried out in dry conditions.

29. Molecules 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. N2, O2, S8 It can be molecule of a compound. H2O, CO2, NH3

30. Introducing Little Mr. “Mixture” I am formed when two or more substances joined together physically ( without chemical bonds) I have the same properties as all the substances

31. 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. 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. Examples of mixtures include muddy water and air. Air is made up of gases such as nitrogen and oxygen mixed together.

32. Little Mr “Mixture” I do not have a fixed composition of the substances. A Mixture can be: • element + element • element + compound • compound + compound. He can be separated to its substances by physical methods

33. Thank you This is the end of the slide.