Grade 9 Revision Chemistry PDF

CHEMISTRY GRADE 9 REVISION 05/11/2024 C. LUCERO  What is Chemistry? Chemistry is the study of the composition, structure, properties and changes of matter. Matter is anything that has mass and occupies a volume. Matter exists in three states - solid - liquid -...

CHEMISTRY GRADE 9 REVISION 05/11/2024 C. LUCERO  What is Chemistry? Chemistry is the study of the composition, structure, properties and changes of matter. Matter is anything that has mass and occupies a volume. Matter exists in three states - solid - liquid - gas What are some examples of matter? What is matter made up of? 05/11/2024 C. LUCERO Organisation of Matter 05/11/2024 C. LUCERO DEFINITIONS An atom is the smallest particle of an element that can exist and still show properties of the element. 05/11/2024 C. LUCERO An element is a pure substance that cannot be broken down into simpler substances by using any ordinary physical or chemical processes. 05/11/2024 C. LUCERO A compound is a pure substance that is formed from two or more different types of elements which are chemically bonded together in fixed proportions and in a way that their properties have changed 05/11/2024 C. LUCERO  Molecules are groups of two or more atoms bonded together which can exist on their own. Molecules maybe made up of atoms of the same kind e.g. Hydrogen gas or of different kinds of atoms e.g. carbon dioxide gas, water A formula unit is the chemical formula of an ionic compound that lists the ions in the lowest ratio that equals a neutral electric charge 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO Atomic Structure 05/11/2024 C. LUCERO  Atomic Number and Mass Number Atomic Number – Z  Mass Number – A (nucleon number) The atomic number of an element is The mass number of an element is the number of protons present in the the sum of the number of protons nucleus of the atom of an element. All and neutrons present in the atoms of an element have the same nucleus of an atom of the element. atomic number. H – 1 proton its Z is 1 C – A = 12 ( 6 protons + 6 neutrons) He – 2 protons its Z is 2 Al – A = 27 ( 13 protons + 14 neutrons) Li – 3 protons its Z is 3 The mass of an atom is mainly the mass of the protons and neutrons in the nucleus of the atom. 05/11/2024 C. LUCERO Chemical Notation 05/11/2024 C. LUCERO  What can we do with this information? If an atom has 10 protons and 10 neutrons, we can say it has - Mass number = 20 - Atomic number = 10 - Number of electrons = 10 If an atom has a mass number of 23 and proton number 11, how many neutrons and electrons are in this atom? 05/11/2024 C. LUCERO  Isotopes Isotopes are atoms of the same element which have the same number of protons and electrons but different number of neutrons. 05/11/2024 C. LUCERO Isotopes of hydrogen 05/11/2024 C. LUCERO MATTER AND ITS STATES Matter is anything that has a) a mass, and b) occupies a space a) mass = a measure of the amount of material the object contains b) Volume = a measure of the space occupied by the object Matter exists in four states: - Solid - Liquid - Gas - Plasma 05/11/2024 C. LUCERO PROPERTIES SOLID LIQUID GAS ARRANGEMENT OF PARTICLES SHAPE Has a definite shape No definite shape, takes the No definite shape shape of the container VOLUME Has a definite volume Has a definite volume No definite volume KINETIC ENERGY Has low kinetic energy The molecules have The molecules possess high intermediate kinetic energy kinetic energy COMPRESSIBILITY Can be compressed Can be easily compressed Can be easily compressed to an appreciably extent INTERMOLECULAR Strong intermolecular forces Intermediate intermolecular Weak intermolecular forces of FORCES of attraction forces of attraction attraction 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO Boiling point & melting point The boiling point of a substance is the constant temperature at which the vapour pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapour. The melting point of a substance is the constant temperature at which it changes form solid to liquid. 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO The Particle Theory (also known as The Kinetic Theory of Matter) The particle theory of matter is a theory that describes matter. It explains the behaviour of solids, liquids and gases. The theory has various assumptions: 1) All matter is made of particles 2) All particles of one substance are identical 3) The particles of matter are in constant motion 4) There are spaces between the particles 5) The particles have forces of attraction between them 6) Temperature affects the speed at which the particles moves. 05/11/2024 C. LUCERO Diffusion & Osmosis Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in concentration. Osmosis is the net movement of water molecules from a region of high concentration to a region of lower concentration through a semi- permeable membrane. 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO More experiments with osmosis 05/11/2024 C. LUCERO Periodicity Periodicity is the recurrence of elements with similar properties at regular intervals in the periodic table. 05/11/2024 C. LUCERO The periodic table The periodic table, also known as the periodic table of elements, arranges the chemical elements such as hydrogen, silicon, iron, and uranium according to their recurring properties. The number of each element corresponds to the number of protons in its nucleus (which is the same as the number of electrons orbiting that nucleus). The seven rows of the table, called periods, generally have metals on the left and nonmetals on the right. The columns, called groups, contain elements with similar chemical behaviours. 05/11/2024 C. LUCERO Group I and II Metals The metals in group I are called the Alkali Metals The metals in group II are called the Alkaline Earth Metals 05/11/2024 C. LUCERO Physical Properties of Group II Elements Atomic radius increases down the group II As the number of shells containing electrons increases from Be to Ba, the atomic radius increases. Shielding of valence electrons by the inner electrons contribute to increasing atomic radius down the group. Ionisation energy decreases down the group II Metal atoms ionise by losing their valence electrons to form cations. Ionisation energies reflect the ease of ionisation of metals. The lower the ionisation energy, the more readily the metal ionises. The larger metal atoms lose their valence electrons more easily than the smaller ones because: 1. The valence electrons are further from the nucleus 2. The valence electrons are shielded by the repulsion of electrons in the filled inner shells. 05/11/2024 C. LUCERO Physical Properties of Group II Elements Group II elements have relatively high melting and boiling points. They have giant metallic structures. There is a general increase in density from Ca to Ba. The masses of the atoms gets bigger as we go down the group. Electronegativity values are generally low and show a slight decrease down the group 05/11/2024 C. LUCERO Chemical Properties Reaction Magnesium Calcium Barium With Oxygen or Air Reacts but only if heated Reacts but only if heated Reacts rapidly at room in air temperature With water A slow reaction, hydrogen Brisk reaction hydrogen is Very rapid reaction; has is evolved and evolved, sparingly soluble hydrogen is evolved; insoluble magnesium calcium hydroxide is soluble barium hydroxide hydroxide is formed. formed is formed With dilute acids e.g. HCl Rapid reaction hydrogen Very rapid reaction, Violent reaction hydrogen – hydrochloric acid is evolved and a salt hydrogen is evolved and a is evolved a salt is formed. (magnesium chloride) is salt is formed. formed What comparisons can you make? 05/11/2024 C. LUCERO Physical Properties of GROUP VII - Halogens Halogens are non-metals Have low melting and boiling points Are more soluble in non-polar solvents than in water(a polar solvent) Are non-electrolytes exist as gases, volatile liquids or soft solids at room temperature, depending on the relative strengths of the intermolecular forces. Element Colour State Chlorine, Cl2 Pale green Gas Bromine, Br2 Brown Liquid Iodine, I2 05/11/2024 Purple-black C. LUCERO Solid Trends Physical Properties Atomic radii increases down the group The number of shells occupied by electrons increases, Electronegativity decreases down the group As atoms get larger the ability to attract electrons decreases Melting and boiling points increase down the group As the size of the halogen molecules increase the strength of the intermolecular forces also increases. Physical state changes from gas to liquid to solid As the intermolecular forces increase, molecules are pulled closer together 05/11/2024 C. LUCERO What is a chemical bond? A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds (force that holds atoms or ions together as a unit). During a chemical reaction, it is the valence electrons that actively take part in bonding. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. 05/11/2024 C. LUCERO BONDING Ionic bonding – electrons are transferred because one is more electronegative and ions are formed. If an electron is lost a cation is formed, if an electron is gained an anion is formed Covalent bonding – electrons are shared among the atoms Metallic bonding – electrons are donated to the sea of delocalized electrons and the pull of the protons in the nucleus and the delocalized electrons holds the bonds together. 05/11/2024 C. LUCERO  To better understand bonding we must know Valence Octet electrons Rule Lewis Dot Diagram 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO So how do we derive the chemical formula of a substance? The method used depends upon the type of compound. Ionic compounds: - corresponding charge transfer Covalent compounds: - valency method - oxidation states/numbers 05/11/2024 C. LUCERO  Ionic compounds In deriving the chemical formula of sodium chloride we identify the valence electrons of each atom. This will tell us whether the atom will gain or lose an electron to form a bond. Depending on how many electrons are lost or gained we can determine the charge the resulting ion will have. Remember any compound formed from a metal and non-metal is an ionic compound and due to the transfer of electron/s ions are formed which are charged forms of the atom. The atom that loses an electron gains a + charge and is 1. Why does the sodium atom become positively called a cation. The atom that gains an charged after losing an electron? electron will have a – charge and is called 2. Why does the chlorine atom become an anion. negatively charged after gaining an electron? 05/11/2024 C. LUCERO Covalent Compounds- valency method- THE VALENCY OF AN ATOM DEPENDS ON HOW MANY ELECTRONS ARE INVOLVED IN BONDING GROUP NUMBER OF BONDS Phosphorus chloride (also called 1 1 phosphorus trichloride) Phosphorus is in Group V 2 2 of the periodic table and has 5 valence electrons. 3 3 Phosphorus will form 3 4 4 bonds with 3 Cl atoms 5 3 using one electron from each atom to pair with 6 2 the lone electrons in 7 1 phosphorus. REMEMBER how covalent bonds are formed? 05/11/2024 C. LUCERO  Oxidation number, also Oxidation number called oxidation state, refers to the total number of electrons that an atom I am sure in your studies you would have either gains or loses in order to form a chemical bond seen compounds written with roman with another atom. numerals after a part of the name in the compound. This roman numeral is used in the name to identify the oxidation state of a particular element in the compound that In a compound the SUM of exhibits variable oxidation states. You the oxidation numbers is always equal to ZERO must keep in mind that some elements have variable oxidation states e.g Manganese has oxidation ranging from +2 to +7 depending on the compound it is a part of. Lead exits as +2 and +4, hence Lead(II) nitrate and Lead(IV) oxide 05/11/2024 C. LUCERO  Structure and Properties of Ionic and Covalent Compounds Prepared by Lucero 05/11/2024 C. LUCERO Introduction The Structure of a solid specifies the arrangement of the particles and the types of bonds which keep the particles in fixed positions within the solid. The properties of elements and compounds depend on the type of particle formed in bonding and the forces between the particles. 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO Properties of Ionic Compounds Solids at room temperature, they are hard, Heat of fusion is the amount brittle and crystalline of energy which must be absorbed per unit mass of the Very high melting points and heat of fusion sample to melt the sample without a change in They conduct electricity well when molten temperature. or when dissolved in water. THEY DO NOT CONDUCT ELECTRICITY IN THE SOLID STATE. Many are highly soluble in water. Solutions of ionic compounds are called electrolytes. They react readily with each other in solution. 05/11/2024 C. LUCERO  Structure of Ionic Compounds A lattice is a regular arrangement of points in two or three dimensions. It is a regular grid-like arrangement of atoms in a material. A crystal lattice is the arrangement of points on which atoms molecules or ions are centred in a crystal. Ionic solids are formed by ionic bonding (electrostatic forces). The particles in the solids are ions. These solids are crystals because of their structure. Ionic Structures are said to be giant structures of ions. 05/11/2024 C. LUCERO Sodium Chloride 05/11/2024 C. LUCERO Properties of Ionic Compounds and Its relation to their Structure. Properties of Ionic Compounds Comment Crystalline solid Due to regular arrangement of ions, resulting from strong attractions between opposite charges. Conduct Electricity when molten On Melting, ions are set free: these ions move to an oppositely charged electrode when a voltage is applied High melting points, high boiling These high values indicate that the ions are held together points, high heats of fusion, high strongly-therefore lots of energy is needed to separate the heats of vaporisation ions 05/11/2024 C. LUCERO Properties of Simple Covalent Compounds Properties of molecular substances Comment Some are liquids or gases at room They consist of small molecules with weak attractive forces temperature between them Low melting and boiling temperatures, Again due to weak intermolecular forces low heats of fusion and vaporisation Some are soluble in water, while some The non-polar molecular substances dissolve in non-polar solvents; are also soluble in non-polar organic substances dissolve in both types of solvents. solvents such as methylbenzene Do not conduct electricity when molten This is due to the absence of ions (NOTE: a few react with water to produce ions and the resulting solution conducts electricity 05/11/2024 C. LUCERO Intermolecular Forces Intermolecular forces are forces between individual molecules and they are said to be weak forces. There are two types of intermolecular forces: 1) van der Waals Forces 2) Hydrogen bonds 05/11/2024 C. LUCERO Van der Waals forces All covalent molecules, whether polar or non-polar, develop temporary or instantaneous dipoles. This results from the uneven movement of all the electrons within the molecules. Van der Waals forces are the weak attraction between oppositely charged ends of molecules with temporary dipoles. The uneven distribution of electronic charge leads to positive and negative charges within the molecules. These are called dipoles. 05/11/2024 C. LUCERO  Hydrogen bonds The hydrogen bond is the weak attraction between an electron deficient hydrogen atom in one molecule and an electron rich electronegative atom in another molecule. 05/11/2024 C. LUCERO Structures of Simple Covalent Solids Solids containing discrete covalent molecules generally have lower melting and boiling points than giant ionic solids, because the covalent molecules have weak intermolecular forces. Such solids are referred to as Simple covalent solids. Examples Sulphur, phosphorus, and Iodine, water(ice) and carbon dioxide(dry ice) 05/11/2024 C. LUCERO  Allotropes Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element. The atoms of the element are bonded together in a different manner. For example, the allotropes of sulphur are rhombic sulphur and monoclinic sulphur the allotropes of carbon include diamond (the carbon atoms are bonded together in a tetrahedral lattice arrangement), and graphite (the carbon atoms are bonded together in sheets of a hexagonal lattice), 05/11/2024 C. LUCERO Giant Covalent Solids A few covalent solids have high melting and boiling points as well as high heats of fusion and vaporisation. Like simple covalent solids, these solids are also formed by covalent bonding, but they do not form individual molecules. Instead they exist as macromolecules in which very strong covalent bonds extend in 3-D. Such compounds are referred to as giant covalent solids. They are usually insoluble in both polar and non-polar solvents. Giant covalent solids may contain one type of atom as in diamond or more than one type of atoms as in silicon dioxide 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO 05/11/2024 C. LUCERO